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                       LIGHTNING ROD CONFERENCE.


                                 REPORT
                                 OF THE
             DELEGATES FROM THE FOLLOWING SOCIETIES, VIZ.:

                        METEOROLOGICAL SOCIETY.
            C. BROOKE, F.R.S., _Past President_ [THE LATE].
                E. E. DYMOND, F.M.S., _Vice-President_.
                   G. J. SYMONS, F.R.S., _President_.

                 ROYAL INSTITUTE OF BRITISH ARCHITECTS.
                 PROF. LEWIS, F.S.A., _Vice-President_.
                J. WHICHCORD, F.S.A., _Past President_.

          SOCIETY OF TELEGRAPH ENGINEERS AND OF ELECTRICIANS.
            LATIMER CLARK, M. INST. C.E., _Past President_.
         W. H. PREECE, F.R.S., M. INST. C.E., _Past President_.

                           PHYSICAL SOCIETY.
              PROF. W. G. ADAMS, F.R.S., _Past President_.
            PROF. G. CAREY FOSTER, F.R.S., _Past President_.

                           CO-OPTED MEMBERS.
                       PROF. W. E. AYRTON, F.R.S.
                       PROF. D. E. HUGHES, F.R.S.

  _With a Code of Rules for the Erection of Lightning Conductors; and
                          various Appendices._

             EDITED BY THE SECRETARY, G. J. SYMONS, F.R.S.


              LONDON: E. & F. N. SPON, 16, CHARING CROSS.
                     NEW YORK: 446, BROOME STREET.

                                 1882.




              KENNY & CO., PRINTERS, 25, CAMDEN ROAD, N.W.

------------------------------------------------------------------------




                               CONTENTS.


                                                                    PAGE

 PREFACE                                                               v


 REPORT                                                                1

   Section 1.—The purpose which a lightning conductor is intended
     to serve                                                          1

   Section 2.—A statement of those features in the Construction
     and Erection of Lightning Conductors, respecting which there
     has been, or is, a difference of opinion, and the final
     decision of the Conference thereupon                              3

       Points                                                          3

       Material for Conductor                                          5

       Size of Rod                                                     6

       Shape of Rod (Rod, Tube, Tape, Rope, Plait)                     7

       Joints                                                         10

       Protection of Rod                                              10

       Painting                                                       11

       Attachment to Buildings                                        11

       Earth Plates                                                   11

       Space Protected                                                12

       Height of Upper Terminal                                       14

       Testing Conductors                                             14

       Internal Masses of Metal                                       15

       External Masses of Metal                                       16

   Section 3.—Code of Rules for the Erection of Lightning
     Conductors                                                       16


 APPENDICES—

   A.—Circular and Questions issued to Manufacturers, and their
     Replies                                                         (1)

   B.—Analysis of, and remarks upon, the views of the
     Manufacturers                                                  (17)

   C.—Reply from Manufacturers received after the completion of
     Appendix B.                                                    (23)

   D.—Report of the Representatives of the Royal Institute of
     British Architects                                             (27)

   E.—Particulars of Accidents by Lightning, collected 1857–59, by
     Mr. Symons, and Report upon the same                           (43)

   F.—Abstracts of Printed Documents                                (51)

   G.—Catalogue of Works upon Lightning Conductors                 (143)

   H.—Application to, and Replies from, the Local Hon. Secretaries
     of the Society of Telegraph Engineers and other distinguished
     Foreign Authorities                                           (175)

   I.—General Correspondence                                       (183)

   J.—Data respecting the Sectional Area of Metal requisite for
     Lightning Conductors                                          (223)

   K.—Notes respecting Lightning Conductors, collected in Paris in
     May, 1881, by Messrs. Preece and Symons                       (225)

   L.—On the Lightning Conductors at the Paris International
     Electrical Exhibition, by Messrs. Dymond and Symons           (229)

   M.—Miscellaneous                                                (233)

   Index to Appendices                                             (245)




                             ILLUSTRATIONS.


                                                                    PAGE

 Sketch illustrative of terms employed                            face x

 Sketch illustrative of area of protection                            13

 Plans and Elevation of Nottingham Castle                           (25)
                                                                    (26)

 Tower of Church of Week St. Mary, Cornwall                         (32)

 Plan and Elevation of Twyford Moors, Winchester                    (34)

 Plan and Elevation of St. James’ Church, West-End, Hants.          (35)

 Plan and Elevation of houses at Lewisham, Wandsworth, and Forest   (38)
   Hill

 View of Tower of Holborn Union Infirmary, Holloway                 (40)

 Plan and Elevation of Laundry at Gravesend                         (41)

 Regnier’s System of Lightning Conductors                           (54)

 Joints and Earth Terminals recommended in France in 1807           (55)

 Powder Magazine, with oblique as well as vertical rods             (57)

 Mode of attaching Conductor to Upper Terminal                      (59)

 View and Plan of Bruntcliffe Gunpowder Store                       (75)

 View of Board House, at Purfleet                                   (78)

 View and Plan of Heckingham Poorhouse                              (87)
                                                                    (88)

 Diagrams illustrative of space protected                          (135)
                                                                   (136)

 Plan and Elevation of Church of Ste. Croix, at Ixelles            (141)

 Sketch of arrangements for Public Buildings in Denmark            (177)

 Plan and Elevations of Systems for Powder Magazines in Denmark    (178)

 Attachment and Earth Terminal used in Italy                       (180)

 Sections of Rods used by the Trinity Board                        (183)

 Eddystone and Spurn Point Lighthouses                             (184)

 South Foreland High Light                                         (185)

 Eddystone Lighthouse                                              (191)

 Plan and Elevation of house at Trolley Bottom, St. Albans         (197)

 Plan and Elevation of washhouse of Middlesboro’ Fever Hospital    (203)

 Plan and Elevation of Indian Pagoda                               (207)

 Plan and Elevation of Upwood Gorse, Caterham                      (211)

 Sections of Rod at Upwood Gorse, Caterham                         (214)
                                                                   (215)

 Sections of Munson’s Rods                                         (216)

 View and Section of Cutting’s Conductor Coupling                  (217)

 Plan and Elevation of Christ Church, Carmarthen                   (218)

 Plan and View of house, and of Bootham Bar, York                  (220)
                                                                   (221)




                                PREFACE.


Although France and other nations have taken active steps to give
official sanction to the best known means of protection from the ill
effects of atmospheric electricity, nothing in this way has ever been
done in England for the public generally.

The enquiries by householders and public bodies for advice and
instruction were so numerous, the absence of authorized or well-matured
directions was so marked, the practice in vogue so varied and anomalous,
that it occurred to the Meteorological Society to take some action in
the matter.

Accordingly, at a Meeting of the Council of the Meteorological Society,
held on 15th of May, 1878, it was resolved—

  ‘That the House Committee be instructed to address the following
    Societies:—

                 THE ROYAL INSTITUTE OF BRITISH ARCHITECTS,
                 THE PHYSICAL SOCIETY,
                 THE SOCIETY OF TELEGRAPH ENGINEERS,

    asking them to name delegates to co-operate in considering the
    desirability or otherwise of issuing a code of rules for the
    erection of lightning conductors, and to proceed in preparing a code
    if it is thought desirable.’

In accordance with this resolution the following letter was addressed to
the Secretaries of the above Societies:—

                                     THE METEOROLOGICAL SOCIETY,
                                 30, GREAT GEORGE STREET, WESTMINSTER,
                                               _June 14, 1878_.

  SIR,

  The Council of the Meteorological Society have had under their
  consideration for some time the possibility of formulating the
  existing knowledge on the subject of the protection of property from
  damage by electricity, and the advisability of preparing and issuing
  a general code of rules for the erection of lightning conductors.

  They are of opinion that this would best be done by a joint
  committee of representative members of those Societies before which
  such subjects most naturally come; and they have, therefore, decided
  upon inviting the co-operation of your Society by the nomination of
  one or more delegates to join a Committee by whom the whole question
  should be considered, and to whom also any written communications
  would be submitted.

  The Council trust that your Society may be represented by delegates;
  but if that course be impossible, they invite any written
  suggestions which you may have to offer.

  A meeting of the delegates will be called for an early date after
  the receipt from the Societies consulted, of the names of the
  gentlemen nominated by each.

                               We are, Sir,

                                 Your obedient servants,

                                   G. J. SYMONS, }
                                   JOHN W. TRIPE,} _Hon. Secretaries_.

In reply to this circular all the societies invited nominated delegates,
and the Conference was constituted as follows:—

 Meteorological Society.            │C. BROOKE, F.R.S., _Past
                                    │  President_.

                                    │E.  E. DYMOND, F.M.S.

                                    │G. J. SYMONS, F.R.S., _Secretary_.

 Royal Institute of British         │PROF. LEWIS, F.S.A.
   Architects.                      │

                                    │J. WHICHCORD, F.S.A., _Vice
                                    │  President_.

 Society of Telegraph Engineers and │LATIMER CLARK, M. Inst. C.E., _Past
   of Electricians.                 │  President_.

                                    │W. H. PREECE, F.R.S., M. Inst.
                                    │  C.E., _Vice President_.

 Physical Society.                  │PROF. W. G. ADAMS, F.R.S.,
                                    │  _President_.

                                    │PROF. G. CAREY FOSTER, F.R.S.,
                                    │  _Past President_.

The steps taken by the delegates will be best explained by a short
narrative chiefly formed of extracts from the minute book of the
Conference.

The first meeting was held at the rooms of the Meteorological Society,
on November 14th, 1878, when all the delegates were present. Mr. C.
Brooke, F.R.S., was appointed _President_ of the Conference, and Mr. G.
J. Symons, F.R.S., _Secretary_.

Professor W. E. Ayrton was elected a member.

A circular, which will be found in Appendix A, was drafted for issue to
manufacturers of lightning conductors. This was sent to sixty-five
firms, but only eight replied, and their answers are printed verbatim in
the same Appendix. An analysis of the replies forms Appendix B. Appendix
C is a reply received too late for insertion in Appendix A, and after
Mr. Preece had compiled Appendix B. Another reply from an American firm
will be found in Appendix I, p. (192), making ten in all.

At a subsequent meeting, the delegates from the Royal Institute of
British Architects were requested to ask the Council of that body to
issue a circular to their members inviting them to furnish information
respecting buildings injured by lightning. This circular, together with
abstracts of the replies, and a brief Introductory Summary, by Messrs.
Lewis and Whichcord, will be found in Appendix D.

Mr. Symons submitted to the meeting a mass of statistics respecting
accidents by lightning which he had collected in the years 1857–59; they
were referred to Professor Ayrton, and his note upon them constitutes
Appendix E.

At the meeting on August 5th, 1879, the Secretary announced the death of
the President of the Conference, Mr. C. Brooke, F.R.S., a vote of
condolence was passed unanimously, and ordered to be forwarded to Mrs.
Brooke. The Conference then proceeded to elect a new Chairman, and it
was unanimously resolved that Professor W. G. Adams, F.R.S., be
requested to accept the office.

The following circular was approved and ordered to be forwarded to a
large number of the most important newspapers and periodicals throughout
the United Kingdom.

                         LIGHTNING CONDUCTORS.

      _To the Editor of_ ——

  SIR,—

  In the summer of 1878 delegates were nominated by the following
  Societies, viz., the Royal Institute of British Architects, the
  Society of Telegraph Engineers, the Physical Society, and the
  Meteorological Society, for the following purpose:—

    “To consider the possibility of formulating the existing knowledge
      on the subject of the protection of property from damage by
      electricity, and the advisability of preparing and issuing a
      general code of rules for the erection of Lightning Conductors.”

  The delegates have held several meetings, and have already
  collected, firstly, from the manufacturers of Lightning Conductors,
  and secondly, from the Members of the Royal Institute of British
  Architects, a large amount of thoroughly practical information.
  Several of their number are also engaged in forming abstracts of the
  salient features of the literature of the subject.

  The Members of the Conference are, however, most anxious that their
  Report should be as trustworthy and as exhaustive as possible, and
  they have, therefore, instructed me to ask you to assist them by
  publishing this epitome of their proceedings, and allowing them to
  invite correspondence upon the points mentioned below.

                                I am, Sir,
                                    Your obedient servant,
                                      G. J. SYMONS, F.R.S.,
                                        _Secretary to the Conference_.

  LIGHTNING ROD CONFERENCE,
      30, GREAT GEORGE STREET, S.W.


                     CLASS OF FACTS MOST REQUIRED.

  Full details of accidents by lightning, stating especially whether
  the building struck had a conductor or not. If there was a
  conductor, state its dimensions—construction—mode of attachment to
  building—whether its top was pointed—distance of its upper terminal
  from the place struck—nature and extent of the connection between
  the conductor and the earth, and whether the earth was dry or
  moist—whether the conductor was itself injured—and whether the
  conductor or the point struck was the most salient object in the
  vicinity. Information is also desired, either verbally or by
  sketches, as to the position of metal spouting and lead roofing
  relatively to the point struck, and to the conductor.

  Details of the thickest piece of metal melted by a flash of
  lightning are much needed.

  Unimpeachable evidence of the failure of conductors is much desired,
  as such failures would be extremely instructive.

The replies were by no means as numerous as was expected: the most
important will be found in Appendix I.

At the meeting, October 27th, 1879, it was resolved “That the members of
the Conference will undertake to prepare abstracts of the principal
English and Foreign books upon Lightning Conductors.” This work became
extremely heavy, and occupied much time, as will be seen from Appendix
F, which contains abstracts of sixty separate treatises, of which 26 are
from English, 17 from French, 6 from Belgian, 5 from American, and 5
from German authors, and one is from the Norwegian.

In order to guard against omitting important works, it was resolved
“That application be made to the Society of Telegraph Engineers for
advance sheets of the Ronalds Catalogue.” From it, supplemented by Mr.
Latimer Clark’s and other lists, the Secretary compiled Appendix G.,
which contains the full titles of no fewer than 704 separate works upon
lightning conductors, or on subjects intimately connected therewith.

At the same meeting it was resolved that efforts be made to obtain a set
of the official instructions issued in all foreign countries. The
circular issued, and an abstract of the information collected, including
replies from America, Belgium, Denmark, Germany, Holland, India, Italy,
and Norway, will be found in Appendix H. Full details respecting the
practice in France will be found in Appendices F, K, and L, and a notice
of Zenger’s Austrian system, on p. (104).

At the meeting, Nov. 20th, 1879, the Secretary was unanimously requested
to act as Editor of the Report.

At the meeting, Jan. 22nd, 1880, a letter was received from Mr. R. H.
Scott, F.R.S., _Secretary to the Meteorological Council_, enclosing a
report respecting the injury to the “Southern Queen,” it was resolved,
“That some of the delegates visit the ship.” The report and a note of
the results of the visit will be found in Appendix I page (205).

At the meeting, April 15th, 1880, Prof. D. E. Hughes was unanimously
elected member of the Conference.

At the meeting, July 6th, 1880, the Secretary handed in a sketch of a
house with various parts of the lightning conductor marked upon it, and
obtained from the delegates definite names for each portion, in order
that in framing the report there might be no uncertainty as to what was
meant by any special term, great confusion in this respect having
previously existed.

The terms adopted have been: _Conductor._—The whole arrangement for the
protection of a building. _Point._—The upper termination of the
conductor, whether blunt or sharp, single or bifurcated. _Upper
terminal._—That portion of the conductor which is between the top of the
edifice and the point. _Joint._—Any connection between any two parts of
the conductor. _Rod._—The main portion of the conductor, whether it
consist of rope, tape, tube or solid rod. _Circuit des Faîtes._—A rod
running round the eaves of a house, the battlements of a tower, &c.
_Earth plate._—The termination of the conductor in the ground, the
pattern being indicated by special terms.

The accompanying lithograph will, it is hoped, supply all additional
necessary particulars.

It is desirable to state that the illustrations in this Report have been
prepared by Mr. E. White Wallis, F.M.S., so as to bring out the various
features distinctly, and as nearly as possible in true proportion, but
without any attempt at artistic finish.

The meetings during the latter part of 1880, and the early part of 1881,
were devoted chiefly to the discussion of various questions as bases for
the report. Much time was also occupied in perfecting the various
appendices, and in compiling an exhaustive index to them.

In May, 1881, Messrs. Preece and Symons, being in Paris, made careful
enquiries as to the existing practice in France respecting lightning
conductors. Their notes form Appendix K.

At the meeting held on May 27th, 1881, the Secretary was instructed to
draw up a draft report, and this having been put in type was sent to all
the delegates; carefully considered, revised, and amended at various
subsequent meetings, and finally adopted.

[Illustration:

  INDEX SKETCH OF LIGHTNING CONDUCTOR, ILLUSTRATING THE TERMS EMPLOYED
    IN THE REPORT.
]

                      TERMS APPLIED TO THE VARIOUS
                         PARTS OF A CONDUCTOR.

                      _Ⴤ_ _Crutch_
                      ⊞⬜⊞ _Strap_
                       ⋂  _Staple_
                       ⚲  _Wall Eye_
                       A  _Point_
                       B  _Upper Terminal_
                       c  _Joint_
                       D  _Rod_
                       E  _Ridge Rod_
                       F  _Circuit des faîtes_
                       G  _Earth Plates_
                      G^1 _Earth Plates Sanderson_
                      G^2 _Earth Plates Borrel_
                      G^3 _Earth Plates Spang_




                                REPORT.


The Delegates are of opinion that it will conduce to clearness of
statement if their Report be divided into three sections—

  (1) The purpose which a lightning conductor is intended to serve.

  (2) A statement of those features in the construction and erection of
        lightning conductors respecting which there has been, or is, a
        difference of opinion, and the final decision of the Conference
        thereupon.

  (3) Code of rules for the erection of lightning conductors.


   SECTION I.—_The purpose which a Lightning Conductor is intended to
                                serve._

A flash of lightning is the passage of an electric spark between two
bodies oppositely or unequally electrified, and between which the
difference of electric pressure or potential is sufficiently strong to
break across the air space which separates them, and to produce what is
known as a disruptive discharge. A flash may pass either between one
cloud and another, or between a cloud and the earth. In the former case
damage is not likely to be done, in the latter damage is or is not done,
according to the point at or from which the lightning strikes. The more
any object projects above the general level, the less is the distance
between it and the cloud, and as the less the distance the less the
resistance offered to the discharge, high objects are, _cœteris
paribus_, most frequently struck. Some substances, such as copper or
iron, can conduct a large quantity of electricity with facility, and are
called good conductors. Other substances, such as living vegetable or
animal matter, offer much obstruction, and form only partial conductors;
while dry earth, stone, and wood almost entirely prevent the passage of
electricity, and are very bad conductors—in fact, insulators.

For instance, a man may with perfect impunity clasp a copper rod an inch
in diameter, the bottom of which is well connected with moist earth,
while the top of it receives a violent flash of lightning. But if the
electricity does not find a path prepared for it, it will utilise such
partial conductors as may be reasonably near, for example—the heated air
from a kitchen chimney, the soot inside, and then the metal range at the
bottom; here, however, stone or dry material is generally found, which
will not conduct it, and then it dashes across the kitchen at some gas
or water pipe, or some pump or drain leading to damp earth, doing
serious damage on the way: or it may meet some tree in its course and
rend it from top to bottom, and if the human body intervene life may be
destroyed. Mechanical injury is inflicted only where the conduction for
the discharge is imperfect.

A lightning conductor fulfils two functions: it facilitates the
discharge of the electricity to the earth, so as to carry it off
harmlessly, and it tends to prevent disruptive discharge by silently
neutralising the conditions which determine such discharge in the
neighbourhood of the conductor.

To effect the first object a lightning conductor should offer a line of
discharge more nearly perfect, and more accessible, than any other
offered by the materials or contents of the edifice we wish to protect.
To effect the second object the conductor should be surmounted by a
point or points. Fine points and flames have the property of slowly and
silently dissipating the electrical charges; they, in fact, act as
safety valves.

If all these conditions be fulfilled; if the points be high enough to be
the most salient features of the building no matter from what direction
the storm cloud may come, be of ample dimensions and in thoroughly
perfect electrical connection with the earth, the edifice with all that
it contains will be safe, and the conductor might even be surrounded by
gunpowder in the heaviest storm without risk or danger.

All accidents may be said to be due to a neglect of these simple
elementary principles. The most frequent sources of failure are
conductors deficient either in number, height, or conductivity, bad
joints, or bad earth connections. There is no authentic case on record
where a properly-constructed conductor failed to do its duty.


   SECTION II.—_A Statement of those features in the construction and
 erection of Lightning Conductors, respecting which there has been, or
 is, a difference of opinion, and the final decision of the Conference
                              thereupon._

                  Points.
                  Material for Conductor.
                  Size of Rod.
                  Shape of Rod.
                    (Rods, Tubes, Tape, Rope, Plait.)
                  Joints.
                  Protection of Rod.
                  Attachment to Building.
                  Earth Plates.
                  Space Protected.
                  Height of Upper Terminal.
                  Testing Conductors.
                  Internal Masses of Metal.
                  External Masses of Metal.


=POINTS.=—Starting with the extreme top, we have first to deal with the
question of points. The utility of points was hotly contested rather
more than a century since, and an abstract of the discussion will be
found in Appendix F, page (79), and difference of opinion still exists
as to their precise functions and value. The decision as to the best
form of points is complicated by two opposing requirements (1), the
sharper the point the more rapid the silent discharge of electricity,
and, therefore, the more effective the conductor; but (2) the sharper
the point the more easily is it destroyed by oxidation, or fused, should
a heavy disruptive discharge fall upon it.

Attempts have been made by the use of gold, silver, and platinum, to
obtain a sharp point which should not only be durable, but, owing to its
high melting point, resist fusion by a disruptive discharge. But such
metals are very expensive, and the statements in Appendix F, pages (67,
69, 73, 103, 123, 128, and 139) prove that even platinum points are
often damaged. Copper points whose sectional area is less than ·05 of a
square inch are very liable to be melted. Lightning has even fused a
copper rod ·10 sq. in. in sectional area, _i.e._, 0·35 in. in diameter,
and there are many rods still standing of which the extremity has been
melted into a button or knob.

For these reasons it seems best to separate the double functions of the
point, prolonging the upper terminal to the very summit, and merely
bevelling it off, so that, if a disruptive discharge does take place,
the full conducting power of the rod may be ready to receive it, and,
therefore, that there may be no risk of melted particles of metal
setting fire to the building, as has occurred. [Appendix F, p. (93).]

At the same time, having regard to the importance of silent discharge
from sharp points, we suggest that at one foot below the extreme top of
the upper terminal there be firmly attached, by screws and solder, a
copper ring, bearing three or four copper needles, each 6 inches long
and tapering from ¼ inch diameter to as fine a point as can be made; and
with the object of rendering the sharpness as permanent as possible, we
advise that they be platinized, gilded, or nickel plated.

Vanes, finials, and ornamental ironwork so frequently form the upper
portion of edifices, that it is essential to consider their relation to
the conductor. They should always be in perfect metallic connection with
the conductor. The possibility of such metal work inducing the charge to
desert the conductor for some other path is sometimes suggested, but it
could not happen unless the conductor were out of order, _e.g._, of
inadequate conducting power, or had an imperfect earth-contact.

With respect to factory chimneys, a different practice prevails in
England from that which is nearly universal on the Continent. In this
country one straight rod is usually carried up on one side of the
chimney to a height above the top about equal to the diameter of the
chimney. On the Continent two arches of iron are put crosswise over the
aperture of the chimney, and a vertical rod is carried up from the
intersection. In both systems the upper terminal suffers from the
corroding effect of the fumes from the chimney. Dr. Mann thought,
Appendix F, p. (132), that considering the ready path for lightning
afforded by the heated smoke discharged from chimneys, a coronal
conductor should be placed upon them, as well as a multiple point.
Messrs. Gray say, p. (9): “For high chimney shafts we fit a copper band
round the top, and four points thereon connected to main down rod.” The
Edinburgh Gas Works chimney, 341 feet high and 14 feet across at the
top, was fitted with a conductor under the advice of Faraday, Appendix
F, p. (89). It had an iron plate on the top; Faraday directed that the
rod should be connected with this plate, and the upper terminal should
rise vertically 6 feet above it.

We are of opinion that a coronal or copper band, with stout copper
points, each about 1 ft. long, at intervals of 2 or 3 ft. throughout the
circumference, will make the most durable and generally useful protector
for a factory chimney, but these points should be gilded or otherwise
protected against corrosion.


=MATERIAL FOR CONDUCTOR.=—Iron and copper are practically the only two
metals which need consideration; brass, which has sometimes been used is
so perishable that its employment is a self-evident error. We will
assume the conductivity of equal lengths and weights of iron to be, in
the case of steady currents of electricity, ⅙th that of copper, and the
cost of iron to be ⅑th that of copper, this would make the cost of
copper for equal conducting power ^9⁄_{6}ths, or 50 per cent. dearer
than iron. But there are other matters to be considered: (1) the great
weight and bulk of iron rods; (2) their deterioration by rust; (3) the
serious obstruction offered by a rusty joint; (4) the suddenness of
lightning discharge which modifies the conductivity; and lastly, that
iron is so much more rigid than copper that (except in the form of iron
wire rope, of which we shall speak hereafter) it can rarely be used in
greater lengths than 20 feet, and thus numerous joints become necessary,
whereas every needless joint should be avoided.

As regards galvanizing, we think it scarcely judicious to trust entirely
to it for protection against oxidation, for many instances of imperfect
galvanizing have come to our knowledge.

On the other hand copper becomes brittle, not only when exposed to the
air, but also by the passage through it of powerful charges of
atmospheric electricity. Franklin used iron, and it is employed in
America and on the Continent much more generally than copper, and it is
less tempting to the thief.

Nevertheless, as the cost of erection bears a considerable ratio to the
cost of the rod itself, and as iron possesses the disadvantages above
stated, we think that in all ordinary cases a copper rod will in the end
prove the cheapest, as it will certainly be the most durable.


=SIZE OF ROD.=—This is perhaps the most difficult subject which has to
be determined. We greatly regret the shortness of Table I. in Appendix
K; but we think that it must be assumed from it that lightning has fused
a copper rod ·10 in. (⅒th) in area, _i.e._, weighing 6 ounces to the
foot. We have also the Caterham case, Appendix I, p. (214), where a
copper tube weighing 5¾ ounces per foot was heated to redness.

The saving of cost which might be effected by using, for very low
buildings, rather slighter rods than for ordinary edifices is not worth
considering. In a 30 feet rod it could hardly amount to 10s. We
therefore recommend as the _minimum_ to be used:—

 Material. Pattern.  Diameter. Sectional Area of Metal. Weight per foot.
                        in.            sq. in.
 Copper    Rope          ½                          ·10           6  oz.
 Copper    Round Rod     ⅜                          ·11           7  oz.
 Copper    Tape        ¾ × ⅛                        ·09           6  oz.
 Iron      Round Rod   9/10                         ·64          35  oz.


=SHAPE OF ROD.=—This depends upon a subject which until lately was
warmly discussed, viz., upon the relative importance of the sectional
area, and of the superficial area of a conductor; a matter which has
been the subject of active discussion among electrical authorities.
Faraday and Sir W. Snow Harris, for example, held diametrically opposite
views respecting it. [Appendix F, p. (89), and I, p. (195).]

There is abundant and conclusive evidence that in the case of steady
electric currents, conductivity depends upon sectional area alone, and
not at all upon extent of surface, and experiments by Mr. Preece and Dr.
Warren De la Rue tend to show that, in the case of sudden discharges
from condensers, to which lightning discharges are probably analogous,
the influence of form is not considerable. On the other hand, there is
equally conclusive evidence that the facility with which currents of
short duration pass through conductors is affected by the form and
arrangement, as well as by the sectional area of the conductors. Upon
the whole we agree with the opinion quoted below, from a writer
recognized in the United States as a high authority on lightning
conductors, who, after describing and engraving more than fifty patterns
of rods, says[1]:—

Footnote 1:

  Spang, “A Practical Treatise on Lightning Protection,” p. 121.

  “The alleged improvements in the said conductors are, in nearly all
  cases, worthless, or of a trifling and unimportant character. The
  fact is, the said conductors are quite inferior, and contain no
  essential improvement upon the ordinary round iron rod used during
  the days of Franklin.”

In Europe the only forms at all generally employed are:—

Rods (round or square); Tubes; Tape; Ropes (wire, or wire with hemp
centres); Plait.

=Rods= (round or square).—The advantages and disadvantages of rods are
easily stated. The advantages are their durability and their rigidity,
the latter being of importance for long upper terminals. The
disadvantages are the necessity for numerous joints, and the difficulty
of avoiding serious disfigurement to the building to which they are
attached.

=Tubes= have much the same merits and demerits, with the additional
objection that they are necessarily of larger diameter than solid rods,
and therefore more conspicuous. They have also an additional
disadvantage in that they are generally joined together by screw
collars. The cutting of the thread in the tube seriously diminishes the
sectional area, and the joint so made is electrically defective. If
tubes are used, the joints should be made as directed in the code of
rules under the head of joints.

=Tape= is a form of rod which is of comparatively recent introduction,
and possesses many advantages. Foremost among these is the length which
can be supplied in a single piece. Where, as at the junction with an
upper terminal, a joint is needed, it is easily made by clamping or
rivetting the two surfaces together and then imbedding the whole in a
mass of solder. No kind of coupling known to us is, in our opinion,
equal to this very simple one. Owing to the flexibility of the tape it
can be made to follow closely the outlines of a building, or may be
countersunk in it, and painted over, but, as stated further on, abrupt
bends should be avoided, and the precautions and instruction set forth
on page 18 should be followed. The objections to tape, Appendix A, pages
(5) and (16) will be found to be objections, not to tape _per se_, but
to bad practice on the part of some persons who have fitted it up and
availed themselves unduly of its flexibility.

=Ropes.=—For many years past rope constructed of twisted strands of
copper or of iron wires has been largely employed for lightning rods.
There is on record a very remarkable case of the complete destruction of
a brass wire rope, an event which, if it had been repeated, might justly
have been regarded as a serious objection to the use of ropes. This case
is fully reported in Appendix F, pages (62–63); and from it some French
electricians have concluded that lightning may single out some wires
from a rope and travel along them in preference to the rest, even when
the whole of them are hardly sufficient to give it a free passage.
Whatever may have been the explanation, this accident seems to be
unique, and even if we accept the explanation given, the only extra
precaution which it calls for, is the soldering of each extremity of the
several wires forming the rod, and at every joint, into a single mass.

We agree with M. Borrel in thinking that serious evil arises from using
wire of too small diameter, which involves an additional number of
interstices for the lodgement of dirt, smoke, and water, and at the same
time renders the wires too thin effectually to resist oxidation. We have
had before us rope ⅜ in. in diameter, composed of 49 strands of a copper
wire about No. 19 B.W.G., say 0·04 in. in diameter. On the contrary, one
firm speaks of employing No. 10 B.W.G., _i.e._ 0·14 in. diameter, and in
special cases Nos. 8 and even 7, which would be about 0·17 in. and 0·19
in. diameter respectively: these would not be open to the objection we
have raised.

The objection to thin wires is necessarily greater with iron ropes, even
if galvanized, than with copper, for irrespective of the doubt as to the
perfect galvanizing of every part, there is the greater brittleness, and
consequent risk of damage from defective continuity.

=Ropes with Hemp Centres.=—One English firm sent us a specimen of
6–strand copper rope with a hemp core, and we understand that the same
pattern is occasionally used both in iron and copper in France. We do
not know the precise object aimed at—probably flexibility—but
considering the perishableness of such a core, its variation in length
with the hygrometric state of the air, and its invariability when the
copper is varying with temperature, we cannot regard it as a wise
construction.

=Plait.=—This form of rod was probably designed in the belief that the
essential element in a lightning rod was plenty of surface. It is made
in two sizes, with copper wire, about No. 16 B.W.G., plaited into a sort
of ribbon. It invites oxidation as much as is possible, and is in our
opinion neither durable nor trustworthy. The original form of this rod
was ridiculously bad; for it consisted of 13 copper wires and 1 zinc
one. Every time that it became wet, feeble electric action was set up,
and the zinc wire was gradually destroyed, without the slightest benefit
to anybody.


=JOINTS.=—The most fruitful sources of danger in rods are _bad joints_,
not necessarily those that are mechanically bad, but those that are so
electrically. A joint is said to be electrically bad when it offers
resistance to the passage of electricity through it. _There should be no
resistance whatever._ A careful inspection by Capt. Bucknill, R.E.
(Appendix M, p. 243), has proved that bad joints in lightning rods are
very abundant, though they appear perfectly sound; and everyone who has
measured the electrical condition of conductors confirms this fact. Bad
joints have the same effect as lengthening the conductor; and, in one
case, one bad joint was found to have the same effect on a discharge of
electricity as a conductor 1,900 miles long. It is evident that such
rods may be worse than useless, for other parts of the building may
offer easier paths for the discharge to the earth. If the joint be
imperfect, and the rod convey a charge to earth, heat will be generated
at the joint, the rod may be fused, and the discharge be diverted to the
building.

Screwed, scarfed, and rivetted joints, however well they may be made
mechanically, are certain to rust and corrode in time, owing to the
expansions and contractions due to changes of temperature admitting
moisture, and thus causing corrosion and resistance. No joint can
possibly be electrically perfect that is not _metallically continuous_,
and careful soldering, in addition to screwing, scarfing, or rivetting,
is the only certain mode of securing this. Soldering is a method that
has borne the test of experience, and its success as a means of securing
perfect joints leaves no excuse for its omission. The fewer joints the
better, but where there are joints they can only be made electrically
secure by careful soldering.


=PROTECTION OF ROD.=—The lower part of copper rods is sometimes stolen
for the sake of the metal. This can be guarded against by putting it
inside a length of iron gas-barrel, extending from some distance below
ground to 10 ft. above it.


=PAINTING.=—Iron conductors, even if they are galvanized, should be
painted throughout, except at the points, which should be gilded or
nickel-plated.

In France and Belgium painting is resorted to to a considerable extent,
and the practice was recommended by the late Professor Joseph Henry, and
followed very largely in America. [Appendix F, pages (99) and (113).]


=ATTACHMENT TO BUILDINGS.=—The evidence against the use of glass or
other material in order to insulate the conductor, is overwhelming, and
insulation may be regarded as unnecessary and mischievous. The
essentials are (1) that the rod be attached to the building by
fastenings of the same metal as itself, (2) that the fastenings be of
adequate strength, (3) that they be of such form as not to compress or
distort the rod, (4) that they allow play for its expansion and
contraction, (5) that they hold it firmly enough to prevent all the
weight falling on any one bearing.

Where practicable it is well to take the rod down that face of the house
which is most exposed to rain.


=EARTH PLATES.=—This portion of the lightning conductor is of the utmost
importance, but has hitherto been the most neglected. The majority of
cases in which lightning has caused injury very near to or upon
conductors are traceable to those conductors having imperfect earth
terminals. We know of many cases in which the earth terminals have been
miserably imperfect, or entirely neglected, when the above-ground
portion has been perfectly satisfactory. In fact, though it may be
admitted that the case found by Dr. Mann,[2] of the lightning rod of a
church tower, the lower end of which was thrust into an empty glass
bottle, is an exceptionally bad one; yet there are sadly too many, of
which the Middlesboro’ case, Appendix I, page (217) is a perfectly fair
type.

Footnote 2:

  Quarterly Journ. Met. Soc., Vol. II., p. 420.

A convenient earth connection is often afforded in towns by the iron
mains for gas and water—arguments both for and against the utilisation
of both water and gas mains will be found in the Appendix—we, therefore,
need only state our opinion in favour of connection with both. But no
connection should ever be made with soft metal pipes, because of the
risk of their fusion; and the conductor should be kept as far as
possible from internal gas pipes on account of the risk of lighting the
gas at an imperfect joint.

As a general rule we advise the soldering of a plate of metal, copper to
copper, iron to iron, to the lower end of the conductor. The earth plate
should always be of the same metal as the rod, otherwise destructive
galvanic action sets in. This plate, which may be flat or cylindrical,
must not have less surface than 18 square feet, _i.e._, 9 square feet on
each face; there is no advantage in notching or pointing it. A hole must
be dug, or well sunk, to receive this plate, and the hole must be so
deep that the earth surrounding the plate shall _never_ be dry. Any
available drain or other water should be allowed to soak into the earth,
over the site of the plate. After the hole has been dug, and the plate
lowered into position, it should be filled with cinders, or coke. In
extremely dry rocky localities, it is sometimes impossible to fulfil
these conditions: then the best thing to do is to bury three or four
hundredweight of iron at the foot of the conductor, still using the
earth plate and the coke, and taking especial care that the rain-water
and sink pipes discharge over it.

All drains, water-courses, in fact, everything which will assist in
distributing the charge over a large extent of moist earth should be
utilized by leading branches from the earth plate to them, or a long
length of the rod may be laid in a drain if it be one which will be
constantly wet.


=SPACE PROTECTED.=—The question as to the extent of the space which will
probably be protected by a lightning rod is one which is of very great
practical importance, because it governs the number and height of the
upper terminals which are required for the protection of any given
building. The index to the Appendix shows that “Protection, Area of,” is
discussed upon twenty-nine pages in different parts of the Appendix. It
has been laid down that the space protected was a cone, having the point
for its apex, and a base whose radius was equal to twice the height of
the point, while the latest French official instructions, Appendix F, p.
(67), state that a point will “effectively protect a cone having the
point for its apex, and a base whose radius is 1·75 of its height.” The
English War Department instructions considerably reduce this space by
asserting, Appendix F, p. (71), that “no precise limit can be fixed to
the protecting power of conductors. In England the base of the protected
cone is usually assumed to have a radius equal to the height from the
ground; but though this may be sufficiently correct for practical
purposes, it cannot always be relied upon.”[3]

Footnote 3:

  On page (96) two instances are recorded in which, if the evidence can
  be trusted, the stroke fell within a radius equal to the height, but
  it is only right to say that the facts are not very clearly recorded.

[Illustration: Sketch illustrative of area of protection]

According to this rule, the church of Ste. Croix (see Appendix F, p.
(141)), would require four upper terminals, one on steeple, one on
chancel, and one in the middle of each half of the transept.

From theoretical considerations stated by Mr. Preece, Appendix F, p.
(137), he arrives at the conclusion that “A lightning rod protects a
conic space whose height is the length of the rod, whose base is a
circle having its radius equal to the height of the rod, and whose side
is the quadrant of a circle, whose radius is equal to the height of the
rod.”

At present we have not sufficient data to enable us theoretically to
calculate the space protected by a lightning rod, and therefore we are
compelled to draw up our rules upon the question entirely from
experience, and here we find, that with the doubtful exceptions already
mentioned, there is no recorded instance of a building being struck by
lightning within a conical space, the radius of whose base was equal to
its height, and we think that the adoption of this rule may reasonably
be expected to yield that security in the future, which as far as we
know, it has done in the past.


=HEIGHT OF UPPER TERMINAL.=—This matter is one which may be left
entirely to the option of individual architects and engineers, subject,
of course, to the opinions expressed under the heading “Space
Protected.” In France extremely long _tiges_, or upper terminals,
generally 33 feet long, are used; but it is obvious that they are
necessarily very strong and heavy, and both by their weight and by the
great leverage which they exert when there is any wind, they must
produce serious vibrations in the roof. In England hitherto the opposite
error is almost universal, and we seldom see a conductor carried high
enough to protect all the building to which it is attached. The question
of appearance comes in here, but concerning it we need only remark that
while in England care seems generally taken to conceal the conductors,
in France they are, to a certain extent, made features of the edifice.
With a proper exercise of taste, the terminals of the lightning
conductors can be made to assist the ornamentation of the building, as
has been done in many cases.


=TESTING CONDUCTORS.=—Periodical examination and careful testing of the
lightning conductor are requisite to maintain the system in efficient
order. Points will corrode from oxidation and fusion; joints will get
loose and bad through the action of weather and workmen; connections
will decay both above and below ground; imperfections will develope
themselves; alterations will be made by landlords and tenants; and, in
spite of every precaution during erection, the conductor will thus lose
its efficiency if it be not _maintained_ in thorough order. For this
purpose inspection should be both visual and electrical. In order to
facilitate the electrical examination of the conductor, some firms have
erected a double rod, connected with one upper terminal, one on each
side of a chimney or shaft; this is a very efficient arrangement, for it
provides a means for testing from the ground. It has also been proposed
to carry an insulated wire alongside or even within the rod, connected
to the terminal at the top, and to the testing apparatus at the bottom.

A testing apparatus has been devised by Mr. Anderson (_Lightning
Conductors_, p. 60). M. Borrell, Appendix K, p. (226), Captain Bucknill,
R.E., Appendix M, p. (244), and Mr. Vyle, Appendix M, p. (244), have
also introduced apparatus for the purpose. The system in use in Paris,
Appendix K, p. (225), and M, p. (245), is perhaps the simplest and
cheapest, and is effective as regards testing the efficiency of the
conductor, but not that of the earth connection.

The efficiency both of the conductor and of its earth terminal should be
annually tested. As this testing involves some skill and familiarity
with electrical apparatus it would be advantageous if some competent
person were officially appointed, either by the government or by some
recognised authority, to perform this duty.


=INTERNAL MASSES OF METAL.=—All large and long masses of metal, such as
beams, girders, pipes, hot water systems, and large ventilators fixed in
the interior of buildings, should be electrically connected with the
earth, or with the conductor; but the soft metal gas pipes should never
be used as conductors. The inlet and outlet pipes of large meters should
always be, independently of the meter, electrically connected with each
other, for two remarkable cases of the explosion of a meter have
occurred through the presence of a joint in the pipe electrically bad
owing to the use of India-rubber packing. Appendix M, p. (239).


=EXTERNAL MASSES OF METAL.=—Large constructive and decorative ironwork,
such as guttering, flashings, railings, finials, vanes, &c., and all
masses of metals used in building, should be connected to each other,
and to the earth direct, or to the conductor. In fact, the gutters and
water pipes are already frequently utilized as a partially protective
system. The ventilators of soil pipes may also be employed in this way,
and even made sightly by the addition of an ornamental finial fitted
with points, but care must be taken that the joints are metallic and not
made with red lead or putty; and it must not be forgotten that the
conductivity of lead is very small, so that undue reliance must not be
placed upon pipes made of that metal.


 SECTION III.—_Code of Rules for the Erection of Lightning Conductors._

The following Code of Rules should be carefully attended to in drawing
out a specification for a Lightning Conductor, the reasons for each
being given in the previous Sections and in the Appendix:—

  =Points.=—The point of the upper terminal should not be sharp, not
      sharper than a cone of which the height is equal to the radius of
      its base. But a foot lower down a copper ring should be screwed
      and soldered on to the upper terminal, in which ring should be
      fixed three or four sharp copper points, each about 6 in. long. It
      is desirable that these points be so platinized, gilded, or nickel
      plated as to resist oxidation.

  =Upper Terminals.=—The number of conductors or points to be specified
      will depend upon the size of the building, the material of which
      it is constructed, and the comparative height of the several
      parts. No general rule can be given for this; but the architect
      must be guided by the directions given at pp. 12 to 14. He must,
      however, bear in mind that even ordinary chimney stacks, when
      exposed, should be protected by short terminals connected to the
      nearest rod, inasmuch as accidents often occur owing to the good
      conducting power of the heated air and soot in a chimney (p. 2).

  =Insulators.=—The rod is not to be kept from the building by glass or
      other insulators, but attached to it by metal fastenings. (See p.
      11.)

  =Fixing.=—Rods should preferentially be taken down the side of the
      building which is most exposed to rain. They should be held
      firmly, but the holdfasts should not be driven in so tightly as to
      pinch the rod, or prevent the contraction and expansion produced
      by changes of temperature.

  =Factory Chimneys.=—These should have a copper band round the top, and
      stout, sharp, copper points, each about 1 ft. long, at intervals
      of two or three feet throughout the circumference, and the rod
      should be connected with all bands and metallic masses in or near
      the chimney. (See p. 5.) Oxidation of the points must be carefully
      guarded against.

  =Ornamental Ironwork.=—All vanes, finials, ridge ironwork, &c., should
      be connected with the conductor, and it is not absolutely
      necessary to use any other point than that afforded by such
      ornamental ironwork, provided the connection be perfect and the
      mass of ironwork considerable. As, however, there is risk of
      derangement through repairs, it is safer to have an independent
      upper terminal. (See p. 4.)

  =Material for Rod.=—Copper, weighing not less than 6 oz. per foot run,
      and the conductivity of which is not less than 90 per cent. of
      that of pure copper, either in the form of tape or rope of stout
      wires—no individual wire being less than No. 12 B. W. G. Iron may
      be used, but should not weigh less than 2¼ lbs. per foot run. (See
      pp. 5 to 10.)

  =Joints.=—Although electricity of high tension will jump across bad
      joints, they diminish the efficacy of the conductor; therefore
      every joint, besides being well cleaned, screwed, scarfed, or
      rivetted, should be thoroughly soldered. (See p. 10.)

  =Protection.=—Copper rods to the height of 10 feet above the ground
      should be protected from injury and theft, by being enclosed in an
      iron pipe reaching some distance into the ground.

  =Painting.=—Iron rods, whether galvanized or not, should be painted;
      copper ones may be painted or not according to architectural
      requirements.

  =Curvature.=—The rod should not be bent abruptly round sharp corners.
      In no case should the length of the rod between two points be more
      than half as long again as the straight line joining them. Where a
      string course or other projecting stone work will admit of it, the
      rod may be carried straight through, instead of round the
      projection. In such a case the hole should be large enough to
      allow the conductor to pass freely, and allow for expansion, &c.

  =Extensive Masses of Metal.=—As far as practicable it is desirable
      that the conductor be connected to extensive masses of metal, such
      as hot-water pipes, &c., both internal and external; but it should
      be kept away from all soft metal pipes, and from internal
      gas-pipes of every kind, respecting which see page 15. Church
      Bells inside well protected spires need not be connected.

  =Earth Connection.=—It is essential that the lower extremity of the
      conductor be buried in permanently damp soil; hence proximity to
      rain-water pipes, and to drains, is desirable. It is a very good
      plan to make the conductor bifurcate close below the surface of
      the ground, and adopt two of the following methods for securing
      the escape of the lightning into the earth. A strip of copper tape
      may be led from the bottom of the rod to the nearest gas or water
      _main_—not merely to a lead pipe—and be soldered to it; or a tape
      may be soldered to a sheet of copper 3 ft. × 3 ft. and 1/16 in.
      thick, buried in permanently wet earth, and surrounded by cinders
      or coke; or many yards of the tape may be laid in a trench filled
      with coke, taking care that the surfaces of copper are, as in the
      previous cases, not less than 18 square feet. Where iron is used
      for the rod, a galvanized iron plate of similar dimensions should
      be employed.

  =Inspection.=—Before giving his final certificate, the architect
      should have the conductor satisfactorily examined and tested by a
      qualified person, as injury to it often occurs up to the latest
      period of the works from accidental causes, and often from the
      carelessness of workmen. (See p. 14.)

  =Collieries.=—Undoubted evidence exists of the explosion of firedamp
      in collieries through sparks from atmospheric electricity being
      led into the mine by the wire ropes of the shaft and the iron
      rails of the galleries. Hence the headgear of all shafts should be
      protected by proper lightning conductors.

                                                    (Signed)

                                                        W. GRYLLS ADAMS.
                                                        W. E. AYRTON.
                                                        LATIMER CLARK.
                                                        E. E. DYMOND.
                                                        G. CAREY FOSTER.
                                                        D. E. HUGHES.
                                                        T. HAYTER LEWIS.
                                                        W. H. PREECE.
                                                        G. J. SYMONS.
                                                        JOHN WHICHCORD.

  _December 14th, 1881._




                              APPENDIX A.

                         CIRCULAR AND QUESTIONS
                               ISSUED TO
                 Manufacturers of Lightning Conductors,
                                  AND
                         THEIR REPLIES THERETO.


  NOTE.—There are only two points requiring mention respecting the
      following replies. First, that in order to avoid useless
      repetition of the questions, the answers are numbered, and the
      corresponding question will be found in the following circular.
      Secondly, that the replies are verbatim, as received from the
      manufacturers, except that frequent entries will be found in
      square brackets, _e.g._ [A 0·11 in.] These represent approximately
      the sectional area of the conductors, and are given to facilitate
      the comparison of the conducting capacities of the very various
      patterns submitted to the Conference.


                               CIRCULAR.

                       LIGHTNING ROD CONFERENCE.

                            30, GREAT GEORGE STREET, WESTMINSTER, S.W.
                                            _November 14th, 1878._

  At the invitation of the Meteorological Society delegates have been
  nominated by the following Societies:

                 Royal Institute of British Architects,
                 Society of Telegraph Engineers,
                 Physical Society,
                 Meteorological Society,

  to consider the present modes of erecting Lightning conductors, and
  improvements therein.

  At a largely attended meeting held this day I was instructed to
  forward to you the questions stated below, and to request you to
  forward with your replies any remarks which you may wish to lay
  before the Conference.

  If you desire any specimens to accompany your remarks, I shall be
  glad if, whenever possible, they do not exceed five inches in
  length.

                        I am,
                            Your obedient Servant,
                                              G. J. SYMONS,
                                        _Secretary to the Conference_.


                               QUESTIONS.

 (_It is requested that the replies be written on foolscap paper, on one
 side only, and that they be numbered in accordance with the questions._)

  1. Form, dimensions, and material usually adopted by you for upper
        terminals.

  2. Material and dimensions of conductor.

  3. Is any definite proportion between the length and sectional area of
        the conductor observed, and if any, what?

  4. Joints, how made.

  5. Attachment to building, how made.

  6. Ground connection, how formed, and of what extent.

  7. Extent of area supposed to be protected.

  8. If there is more than one terminal, is the size of the conductor
        increased?


                                REPLIES.

                                                 39, WAPPING, LONDON, E.

1. The upper terminals are made of a copper tube ⅝ inches in diameter
and 1/16 inches thick [A. 0·11 in.] In the upper end of the tube is
fitted 15 inches of copper rod tapered to a point at the top, into which
is fixed 3 or more smaller rods about ¼ inch in diameter [A. 0·05 in.]
each tapered to a point, and brought into the parent rod in a curve (not
at an angle). The next part of the tube, down to about 9 inches from the
bottom, is filled with a stiff iron rod to strengthen it, the lower end
of the tube being left open to receive the rope. This constitutes what
is called “the point.” These points vary in length from 2 or 3 to 8 or
10 feet when used for buildings. A square-topped tower would require a
much higher point than would be necessary for the top of a spire.

Sometimes the points are tipped with platinum, which we consider to be
altogether superfluous.

2. The conductor is simply a wire rope, varying in size, and mostly
either ⅜, ½, or ⅝ inches in diameter [A. 0·11, 0·20, or 0·31 in.] These
ropes are made in two different forms: the one ⅜ inch diameter [A. 0·11
in.], most suitable for ships’ use, is composed of 49 No. 18 guage
copper wires, each wire having a circumferencial measurement of ·157
inches [A. 0·002 in.]; the circumferencial or surface measurement of the
whole of the 49 wires is equal to 5·693 inches [A. 0·11 in.], or say,
equal to the surface of a copper band 2·846 inches wide—_i.e._,
measuring both sides of the band.

The other make, say ½ inch diameter [A. 0·20 in.], much used for lofty
buildings, is composed of 7 No. 7 guage copper wires, each wire having a
circumferencial measurement of ·581 inches [A. 0·027 in.]; the
circumferencial or surface measurement of the 7 wires is equal to 4·067
inches [A. 0·19 in.], or say equal to the surface of a copper band 2·033
inches wide.

3. There is no definite proportion observed between the length and
sectional area of the conductor. We take it that the sectional area
should be the same, irrespective of length, as we do not trace that
lightning varies in intensity while passing through a conductor of
greater or less length. The rather prevalent idea that a smaller
conductor is sufficient for a low building is, we think, erroneous, as
we do not find any data to show that lightning in its descent loses any
portion of its force until it actually enters the earth.

4. The copper rope is joined to the upper terminal by passing the end of
the rope into the tube at the lower end of the terminal for the space of
about 9 inches, and fixing it with 3 copper rivets. There is no other
join in the conductor whatever—a feature of much greater importance than
is sometimes admitted.

5. The upper terminal is passed through two strong earthenware
insulators which are usually fixed to the building by two strong
galvanized iron staples. Other modes of fixing the terminal must
sometimes be resorted to, as some factory chimneys are capped with iron,
and buildings of varied forms must be treated with according to
circumstances. Having fixed the terminal, the rope may then be led down
the building on the most convenient side for the purpose, and fixed at
intervals of 6 or 8 ft., according to circumstances, with glass
insulators supported by copper brackets. The rope should be given the
straightest course practicable from the upper point down to the earth,
carefully avoiding all angles, specially an acute angle, as much as
possible, and in its passage it should be kept clear from any other
metal in the building.

There are three matters to which we would call special attention, viz.:


          _Insulators, Angles and Joints, Metal in Building._

_Insulators._—When copper rope lightning conductors were first
introduced, about the year 1837, a circumstance occurred which at once
proved the efficiency of the conductor, and suggested the use of
insulators. The late Mr. Andrew Smith, C.E., had fitted a factory
chimney in the East of London with a rope conductor, which was fixed to
the chimney by iron staples. In a violent storm which occurred soon
afterwards, the lightning was seen to pass down the conductor, which
remained unaltered in any way; but on examining the chimney it was found
that the brickwork had received a concussion at most, if not all, of the
staples, showing that the lightning in passing had expended part of its
force on the iron staples. It is probable that, if the staples had been
made of thicker iron, and had been so placed as to lead off from the
conductor with easy curves inwards, instead of being driven into the
wall at right angles with the conductor, the concussions would have been
much more violent than was the case.

_Angles and Joints._—It must be obvious to any one that lightning, as
well as any other matter or thing which travels at high speed, would be
greatly obstructed in having to turn corners. It must also be borne in
mind that lightning is of intense heat, and while passing in a straight
line the effect of its heat is lost in the velocity of its motion; but
in passing an angle its momentary pause (much too brief to be
calculated) is sometimes enough to create sufficient heat to fuse the
conductor at the angle. For this reason all angles must be avoided, and
easy curves having a downward tendency substituted.

The angles in copper tube conductors are doubly objectionable, for,
having joins as well as angles, they are liable, by the effect of heat,
to become disjointed. It would be difficult, if not impossible, to fit a
tubular conductor, except in a straight line from end to end, without
this double objection. Similar objections apply also, in a greater or
less extent, to the copper band conductors, as they are made with joins,
and, when fixed up, are usually carried into and over as many angles as
come in their way. They do not so readily follow all the sinuosities of
a building as a rope does on the curve principle.

The flat band conductors, which are composed of a number of galvanized
iron and copper wires combined, are simply a frivolity.

_Metal in Buildings._—Taking the conductivity of copper as from 7 to 10
times greater than that of iron, it would probably follow, that if two
rods, the one of copper the other of iron, in these proportionate sizes,
were brought together in one common terminal or point, and led by the
same course to the earth, as much of the fluid would possibly pass down
the one as the other. On this principle, we avoid contiguity with any
metal in a building, especially if in large masses, such as machinery,
&c.

_Ships’ Conductors._—In fitting the rope conductor to a ship’s rigging
it is only necessary to pass it through a hole in the truck, so that the
end may stand about 6 inches above the truck. It may be held up by a pin
or key passed through the rope close over the truck, and then carried
down the topgallant backstay (to which it should be tied at intervals
with yarn) to the gunwale, where a sufficient length of the conductor
should be kept in a coil to reach well down into the sea in any position
of the ship. In stormy weather the coil may be untied, and by its own
weight the end will drop down into the sea as required. Sometimes the
rope is shackled at the gunwale to a strip of sheet copper about 3
inches wide, which is nailed down the ship’s side till it meets the
sheathing at the bottom. The strip of copper should _overlay_ the
sheathing for a few inches. It may be noticed that this kind of
conductor, fitted with a coil at the gunwale, is without any join
whatever, and that it takes almost a straight course direct from the
truck into the water.

The copper band conductors let into the mast and carried through the
hull of the ship are objectionable and unsafe, as, in passing from each
portion of the mast, they require moveable joints, so as to admit the
several parts of the mast being run up or down as required. These joints
present angular interruptions which may become out of order, and, in
passing through the hull, any rupture of the band in that part, or the
contiguity of other metals, may cause serious consequences. Certainly,
there can be no necessity for carrying the lightning through the ship
when, by a safer and much more simple method, it may be kept altogether
outside.

In the smaller vessels, where the mainmast is well above the other
masts, it may be sufficient for that mast only to be fitted with a
conductor, but in larger ships, particularly long steam-ships, where the
masts are a considerable distance apart, each mast should have a
conductor.

We do not, either in theory or in practice, know any necessity for
protecting the yards with conductors, though it is not altogether
improbable that, in the absence of conductors on the masts, the yards
might get damaged while the masts remain uninjured.

6. The end of the rope should be buried in moist earth, and carried in a
curve to 5 or 6 feet from the foundation. In clay ground and on the
shady side of a building about 3 feet below the surface would be deep
enough; but in lighter ground, and particularly on the sunny side, it
should be buried 6 or 7 feet deep, to ensure sufficient moisture at all
times of the year.

7. As the course by which lightning approaches the earth is very
devious, it would be difficult to determine with certainty the extent of
area protected; but, viewing the absence of damage to the most remote
parts of the roofs of buildings which have been properly fitted with
conductors within the last 40 years, we should think the area protected
may be taken as equal to from 3 to 5 or 6 times the height of the
conductor.

8. When two or more terminals are used, the main rope should be somewhat
enlarged; otherwise, the collective quantity of fluid received on the
several points may be too great for the common channel.

                                                    WILKINS & WEATHERBY.

                  *       *       *       *       *

                                              DORA STREET, LIMEHOUSE, E.

We have to own receipt of your valued communication of the 14th ult.,
and with great pleasure to submit for the consideration of the
Conference the following replies to their questions. We have endeavoured
to make them as explicit as possible, but it is difficult adequately to
describe our system on paper, and we suggest for the consideration of
the Conference the advisability of showing any Committee they may
appoint one or two of the numerous public buildings fitted by us.

Any further particulars or drawings you may require we shall be glad to
send you; and it is with great pleasure that we add that any services we
can render you in your valuable investigations are at your disposal.

1. A five-pointed copper spindle, the sharp points of which are
silvered, and single points on high chimney shafts to the number of four
or five.

2. Copper solid bands, or tubes, “as samples sent,” being simple,
durable, cheap, and the most capacious form for the safe conduction of a
heavy stroke of lightning, the bands being from 1 inch to 3 inches in
width and ⅛ inch thick [A. 0·12 to 0·37 in.], and the tubes from ¾ to 1½
inches in diameter and ⅛ inch thick [A. 0·24 to 0·54 in.].

3. Yes; experience has proved that nothing less than 1½ inch bands [A.
0·18 in.] should be used for the main conductor to ordinary houses, with
¾ [A. 0·09 in.] to 1 inch [A. 0·12 in.] bands for branches, and from 2
to 3 inches [A. 0·24 to 0·37 in.] bands as main conductor to buildings
of large area, with 1 to 1½ inch [A. 0·12 to 0·18 in.] for branches; or,
in the case of chimney shafts, ¾ inch to 1½ inch tube [A. 0·24 to O·54
in.] for main conductor, and 2 to 3 inches flat band [A. 0·24 to 0·37
in.] for tops of same.

4. The bands are in long lengths, are lapped, closely rivetted and
soldered, to form a continuous band; while the tubes have patent
insertion joints, the upper end being turned and fitted into the lower
end, which is bored, and the tube then forms a continuous line
externally and internally.

5. Copper holdfasts to suit shape and size of conductor.

6. Not less than 30 feet of 1½ inch to 2 inch copper bands [A. O·18 to
0·24 in.] in two or three branches, with forks at end of each band, and,
if water is not near, the trenches half filled with carbonaceous
materials and well watered, as this material will readily absorb the
least moisture and retain it, while being in itself the best conductor.
But much will depend upon the nature of the ground; for if chalk or rock
foundation and water cannot be got at, the ground branches must be at
least doubled, and the trenches deeper and made up of carbonaceous
materials and earth.

7. Our experience is that no appreciable extent is protected by a single
rod conductor in the presence of other influences. The chimney-stacks,
lined with carbon in the shape of soot, with the heated gases, cause a
rarefaction in the atmosphere, and form an easier passage for the
electric fluid. Roofs and buildings having large masses of metals will
be more likely to influence lightning than the single line of copper rod
generally fitted. Many cases have occurred of chimney-stacks 4 feet to 9
feet across being struck opposite the conductor, and lead roofs,
gutters, lead ridges, &c., from 10 feet to 20 feet from the rod
conductor.

8. No; the system of conduction used by us does away with this, the
lines of conduction being ample.


                                REMARKS.

From our close connection with the late Sir William Snow Harris, adviser
to the Crown for upwards of twenty-five years in regard to lightning
conductors for the navy, and having made lightning conductors our
especial practical study for thirty-five years, we may be pardoned for
making a few remarks on the protection of buildings from lightning.

We would, firstly, say that the system of conductors now fitted by us is
based upon these past years of experience, and upon facts collected
during this period, of accidents to buildings having the ordinary single
line of conduction, as also from the practical success of the conductors
in the navy.

The form of conductors used by us has been adopted after considerable
experience, as being the most simple, solid, durable, and capacious form
of conductor for the safe conduction of heavy strokes of lightning.

In place of insulators as fastenings, we use copper holdfasts, as we
found the former dangerous and useless, as the glass, being
non-conductive, the expansion and heat of the electric fluid, being
confined, broke them, and caused an unsafe concussion; and it is also a
disadvantage for a conductor to be away from the building, as nearly
every material in nature assists, without detracting from, the safe
discharge of the electric fluid through a good copper conductor. We find
that the copper wire rope conductor, usually applied, is seldom more
than ⅜th of an inch in diameter; but we did once remove, from the tower
of St. Mary’s Church, Taunton, a copper wire rope conductor of ⅞th of an
inch in diameter [A. 0·60 in.], said to be especially made to
order—certainly the largest we ever came across; but it failed to give
the necessary protection in a lightning storm, which did much damage to
the tower and roof of the church. As capacity or weight of copper is the
most important for safe conduction, copper wire rope is very deceptive
in this respect, as will be seen by the following comparisons, viz.:—A
copper wire rope conductor of ⅜ inch diameter [A. 0·11 in.] weighs 2¾
ounces per foot, not equal to a plain solid band ⅜ inch wide and ⅛ inch
thick [A. 0·046 in.], which weighs 2·907 ounces per foot. A copper wire
rope conductor of ½ inch diameter [A. 0·20 in.] weighs 5 ounces per
foot, not equal to a solid band of ¾ inch wide and ⅛ inch thick [A.
0·092 in.], which weighs 5·814 ounces per foot. A copper wire rope
conductor of ⅝ inch [A. 0·31 in.] weighs 9½ ounces per foot, not equal
to a solid band of 1¼ inch and ⅛ inch thick [A. 0·153 in.], which weighs
9·690 ounces per foot. This is the largest size of wire rope conductor
made or used.

From the above will be seen what protection can be given by conductors
of such small capacities; and we may add that solid band conductors of
the same weight, and superior in every way, can be fixed at less than
half the cost of the wire rope, _foot_ for _foot_.

Copper chains and copper wire bands, as conductors, answer in so
uncertain a manner with the galvanometer, that they should never be
used.

Iron in any form should be avoided, from its lower conducting power, and
its utter uselessness when in a rusty and decayed state.

With regard to testing with the galvanometer, the mere testing of the
conductors is no proof of the security of the building itself. We not
only test the conductors, but also the building, to prove that it is
under safe conduction in lightning storms.

In conclusion, we beg to state that our patent system of protection is
the application of one or more main down and ground copper conductors
and sizes, according to the height and area of the building, the fitting
of the copper bands to each chimney-stack, and connecting the same, and
the connecting of all the metals on the roofs thereto and to the main
conductor, so that there shall be no circuit by which the lightning
fluid would be likely to attack without having its exit to the main
conductor.

For high working chimney-shafts we fit a copper band round the top, and
four points thereon connected to main down conductor.

For further information, we earnestly solicit the careful perusal of our
pamphlet and papers herewith.

                                                       J. W. GRAY & SON.

                  *       *       *       *       *

                                          CHIPPENDALE MEWS, HARROW ROAD.

1. Upper terminals pointed with one or more points, according to the
nature of the building to be protected. Dimensions vary in like manner.
Material—copper or brass, with electro-gilded points.

2. Conductor composed of copper or galvanized rope, according to height,
&c., of building, &c., dimensions varying with resistance of the
circuit.

3. The sectional area varies with the length.

4. Joints made, as far as possible metallically; where solder cannot be
used, screw joints are made use of.

5. Attachment to building direct by metallic ties of requisite form.

6. Ground connection—When practicable, the end of conductor is
metallically connected with gas or water _main_, otherwise a hole is dug
deep enough to meet always moist earth. The end of conductor is either
attached to an earth plate, or coiled up in a bundle and surrounded by
coke.

7. The area protected is supposed to be a radius equal to the height of
conductor.

8. If more than one terminal is attached to one conductor, the size of
the latter is increased, except under certain conditions.

                                                        F. RUSSELL & CO.

                  *       *       *       *       *

                                       137, PRINCESS STREET, MANCHESTER.

1. A copper tube 1¼ inch diameter or 1 inch diameter, finished at the
upper end, with a forged copper point or cone, connected with the tube
by a cast copper (or gun-metal) coupling, into which coupling are also
screwed three or more smaller points round the larger central one. At
the lower end the tube is screwed into a somewhat similar coupling, to
receive also the brazed and screwed end of the conductor. Or a solid
copper rod ½ inch diameter [A. 0·20 in.], or _wrought_ iron rod 1 inch
diameter [A. 0·79 in.] (where iron conductors are used) the rod in
either case forged to a blunt point, and screwed at the lower end, like
the tube first described, to fit the coupling.

2. (_a_). Copper wire rope of 7 strands each, No. 10 Birmingham wire
gauge, or in specified cases of No. 8 or 7 wire gauge, making, when
spun, a rope with a sectional area varying from 7/16 to 11/16.

  (_b_). Solid copper rods ½ inch diameter [A. 0·20 in.].

  Solid iron rods 1 inch diameter [A. 0·79 in.].

  (_c_). Copper band or “tape” of sizes from ¾ × ⅛ to 2 or 3 × 3/16
        inches [A. 0·09 to 0·38 or 0·56 in.].

  (_d_). Copper tube ⅝ inch diameter outside, and ⅛ inch thick [A. 0·20
        in.]

3. Although no definite rule exists for the proportional sizes of the
conductor, it is usual and prudent in a large building to employ for the
main conductors, which should come from the highest and most exposed
points to the earth in the most direct way, a larger conductor than
would be required for a small building, and the branches or connections
to this main conductor may be smaller in sectional area than the
principal one. Thus, a church tower with four angle pinnacles may be
protected by four finials or points, one to each pinnacle, and these
four parts fitted to rope of 7 wires No. 10 gauge [A. 0·10 in.], to be
united to a continuous band round the parapet, from whence a rope of 7
wires No. 8 gauge [A. 0·15 in.] should descend into the earth; or an
infirmary or workhouse built with wings would have, perhaps, three
direct rod conductors, one to each chimney stack, and connections with
the water spouts, or lead flashing made of small copper tape ¾ × ⅛ [A.
0·09 in.] _soldered_ to the lead and worked round the rods.

4. The fewer joints the safer, and for this reason—the copper _rope_ or
_tape_ is better than the rod or tube, as the former is made
conveniently any required length, and the danger of a fault or break in
the continuity is avoided. Of the necessary joints the rope requires one
at its junction with the top rod or tube; this is made by brazing a
small ring of brass (or copper) round the rope; the solid end thus
formed being chased with a deep male thread, which fits the prepared
base of the rod. The branch conductors or connections, with adjacent
constructive or decorative iron work—as beams, girders; cresting, vanes,
&c., are made by threading a bead with a similar ring to receive the
branch, as that already described. Where the branch reaches its object a
ring or solid coupling should be “tapped” into the girder or cresting,
to ensure thorough metallic connection, if the destination of the branch
be the lead flashing, the seven wires must be opened like a fan, and
_each wire_ strongly soldered with common plumbers’ solder to the lead—

  (_b_). Copper or iron rods are made continuous by couplings of either
        metal, as the case may be, which should exceed the diameter of
        the rods by enough metal to allow of a good thread. These
        couplings should be hexagonal or octagonal in plan, to allow the
        workman a certain grip; and the thread should be of the kind
        called right and left, so that while screwing one length he may
        not unscrew the other. These conductors require very careful,
        steady workmen, as a great element of danger exists in these
        numerous joints.

5. The various natures of the buildings provided with conductors require
separate, and often different treatment: but the principle in all cases
is the same, viz., to attach the conductor closely to the fabric, and
the more the conductor is made an integral part, as it were, the more
efficacious it will be. Any attempts at so called isolation are opposed
to the theory of protection by conductors. The mechanical means of
fixing are best illustrated by diagrams, the chief objects to be
considered are—

  (_e_). Permanence or strength and durability.

  (_f_). Room for expansion of the conductor.

  (_g_). Facility in fixing without cutting or breaking the conductor.

  (_h_). Neatness in appearance.

These objects are gained by a careful consideration of the materials to
which the conductors are fixed by “holdfasts,” for stone, slate or
tiles, wood, and iron. It is important that _sharp_ bends be avoided. A
string course, for instance, should be drilled, and the rod or rope
passed straight through. Also, that any metal bodies in the line of the
conductor should be connected with it by staples screwed into such
bodies. It is most necessary that the ends of vane bolts or rods should
be joined to the conductor, or, where this is impossible, should be
fitted with an independent wire or rod to the earth.

6. The connection with the ground is of special importance, as the
object of the conductor is to provide a free passage between the two
currents, and if this be not done, a lateral discharge is pretty sure to
result. A building provided with suitable conductors, properly fixed,
should at all conditions of the atmosphere, allow a free course to the
electricity, and be in all its parts electrically equivalent, and with
this intention the several parts (as mentioned in answer to question 3)
are brought into connection with each other or with the ground. The
actual length of the ground conductor is fixed by the nature of the
subsoil, as it is obvious that dry sandy soil is unsuitable for a
termination. We therefore continue the rope or tape until a good damp
earth is reached, if possible, a spring or open water—generally
speaking, about 5 to 10 yards will be sufficient in most localities. The
conductor is then buried 5 to 10 feet, or upwards, in the damp earth or
water. If a rope, the several strands are unravelled and opened out: if
a rod or tape, a discharging fork is usually attached to the end to
promote the easy discharge, for which purpose it is also usual to fill
the trench with charcoal. The trench must be dug with a slight fall from
the building downward.

7. The extent of area supposed to be protected by the conductor is
estimated by many as included in a radius of double the height of the
conductor from the base line; but the immunity from accident enjoyed by
many buildings situated at a greater distance from a number of tall
factory chimneys; or to take an opposite example, in a city where there
are many lofty spires or towers, would go to show that a number of
conductors attached to tail objects, serve to obviate the dangers
arising from lightning by providing, at many different points, a direct
communication between the positive and negative currents which exist in
the clouds and earth. We have never known a church spire, when the
conductor was fixed in accordance with ordinary skill, injured by
lightning; and the tall factory chimneys of our manufacturing towns
afford strong corroborative evidence of the value of conductors, and
this in two ways—first, because those to which conductors are fixed, do
not get struck; and, second, because those unprovided with conductors,
_do_ get destroyed from time to time.

8. A reference to the answer to No. 3 question, will show that we
consider that when several terminals are used, an increased diameter is
advisable in the main or principal conductor; but it must be remembered
that either of the conductors referred to in the answer to question 2,
is greatly in excess of what many eminent electricians consider
necessary. A single wire being thought sufficient of 3/32 inch diameter
(A. 0·06 in.) for any ordinary current of electricity. But both the
English and French Governments have thought it prudent to specify a
copper body, with a sectional area of ½ inch in English, or 1 centimetre
in French (0·40 in.)—partly to provide against corrosion, which would
rapidly deteriorate a thin wire, and partly to obviate the danger of the
melting of the smaller conductor under the continued force of an
unusually strong shock of lightning. We, therefore, respectfully follow
the decision of such experts as have, by careful experiment and
considerable diligence, acquired the knowledge they possess—both as to
the substance, the form, and the treatment of this subject; and have
only to add the fact, that any small experience we have practically had,
goes to support the conclusions already arrived at by these authorities.

                                                      FREEMAN & COLLIER.

                  *       *       *       *       *

                                      24 & 26, LEVER STREET, MANCHESTER.

1. Our upper terminals are made of copper or brass, plain spike or ball
with spike at top, and three radiating from it, or four or five spikes
radiating from the ball. Attached to the ball (screwed into it) is a
solid rod of copper, to which the conductor is fastened, as explained
below.

2. Conductor is made of good quality copper wire strand 7 ply: ⅜ inch
[A. 0·11 in.] to 7/16 inch [A. 0·15 in.] diameter.

4. Joints of the strand not usually permitted, as we spin it any
reasonable length.

The end of the conductor is knotted and drawn through a cup-shaped ring
of metal one end, the top of which is screwed into the bottom of the
solid rod of the terminal. This makes a good connection.

5. Copper holdfasts fasten the rod to the building.

6. Ground end is coiled loosely in damp earth or a well.

                                     RICHARD JOHNSON, CLAPHAM, & MORRIS.

                  *       *       *       *       *

                                                180, ROTTEMORE, GLASGOW.

We beg to reply to your queries on the material, system, and fitting of
lightning conductors, as practiced by us for over 25 years, during which
time we have never had a building injured in which we have been engaged,
and have fitted from 15,000 to 20,000 feet a year, without
advertisement.

1. Uniformly solid copper, consisting of 1 centre concave point, about
14 inches long, presenting 8 sharp angles = 3½ inch surface; this is
surrounded by 4 smaller points of same construction. These all terminate
or spring out of a hollow copper ball, which is screwed on a copper tube
¾ inch diameter inside, and from 4 inches to 5 inches long, according to
requirement. The copper cable is passed through this tube, is knotted
inside of the ball, and the points are all screwed against it, which
forms the point of contact, and thoroughly fixes the cable at the top;
but the fixing of the top or terminal rod is fashioned in accordance
with the requirements of the building or material to be fixed to.

2. Uniformly copper cable constructed of 49 strands, _hard drawn square_
copper wire Nos. 17, 18, or 19 w.g.

3. We never use less than 6–inch surface, _i.e._, measuring the
circumference of each wire, we contending that surface is the only power
of the conductor. Up to 150 ft. we use No. 19 (= ½ inch diam.) [A. 0·20
in.], ¾ inch for a longer length of cable (_i.e._, 17 or 18) [A. 0·44
in.].

4. Usually with a gun-metal screwed coupler.

5. With brass holdfasts, lined with porcelain, glass, or guttapercha.

6. Spread out end of strands of cable like a fan, and bury it in the
moist earth a few feet deep, in an oblique way tending from building.

7. 30 to 40 yards.

8. We invariably run one cable from each terminal or top rod: but in
spires we commonly take a connection from the _bottom_ of the vane rod,
and connect it to the main conductor, which goes to the highest point of
vane or final: if the former, we fix a copper bush or disc to the vane
rod at foot of vane, which is fast to cable, and a corresponding one on
vane, with cable at highest point, when the cable is fringed out,
presenting its 49 points, and by these discs the vane revolves with that
portion of the conductor attached, and the point of contact is given by
the discs.

                                                   C. H. PENNYCOOK & CO.

                  *       *       *       *       *

                                               ALL SAINTS’ WORKS, DERBY.

1. Form for upper terminals:—A straight copper tube, ¾ inch diameter;
thickness of metal, 15 B.W.G. [A. 0·15 in.], with solid copper point (no
branches); the point is soldered and rivetted into the tube; or a solid
copper rod, ½ inch diameter [A. 0·20 in.], tapering towards the top.

2. Material and dimensions of conductor:—Either a copper band of 2½
inches wide and No. 16 B.W.G. thickness [A. 0·16 in.]; or a copper wire
rope, ½ inch diameter, of 6 strands, each strand containing 6 wires [A.
0·20 in.].

3. Proportion between length and sectional area of conductor:—The ½ inch
copper rope [A. 0·20 in.], or 2½ × 16 B.W.G. band [A. 0·16 in.], is used
for heights not over 120 feet; for higher buildings, a ¾ inch rope [A.
0·44 in.] or band, 2½ × 12 B.W.G. [A. 0·27 in.] should be used.

4. Joint, how made:—Joint is made between band and copper rod with a
brass screwed socket, the rod is soldered and rivetted into socket, and
the band is soldered round socket, then soldered and rivetted. When the
copper rope is used, a hole is drilled into socket, same diameter as
rope, at the lower end, and turned out conical shape; the rope is then
passed through the socket, the ends spread out, and the spaces filled up
with solder.

5. Attachment to building:—The conductor is fixed close to building
_without_ insulators, and is brought into close contact with the
spouting; is closely attached to chimney and walls by means of copper
straps and copper nails driven into the masonry.

6. Ground connection:—Should a good, permanent drain be near, the
conductor is brought to it and bound round and firmly fixed.

If there should be an open drain or brook, the conductor is brought
under it at _sufficient_ depth that if the stream be dry at any time
there will be sufficient moisture to carry away the charge without
disruption. Should there be neither drain pipes nor brook sufficiently
near, the conductor is taken from 12 to 20 feet below the surface to the
clay, where it is certain to be always damp, even in seasons of the
greatest drought ever known.

In no case should the earth connection be taken into a closed tank or
well.

If a band be used, it should be cut into strips about 18 inches long and
laid in different directions; rope should be unwrapped and spread in a
similar manner.

7. Supposed area protected:—It is impossible to determine exactly the
area the conductor protects. It is erroneously supposed that the rod
will protect buildings within its radius, but experience will not bear
out this axiom. Many instances may be related of buildings being struck
much within the radius of well-protected churches or chimneys.

The protection a conductor affords depends to a great extent on the
relative positions of the electric discharge and the objects that it may
meet in its course. As a general rule, a church with a high spire with a
proper conductor may be considered to protect the remainder of the
edifice; but a low, straggling building should have several conductors
at the _outside_ highest points.

8. If there is more than one terminal is the size of conductor
increased?—No; as sufficient material should always be used to carry off
without disruption the heaviest known charge, it is unnecessary to
increase the size of conductor. Should two or more upper terminals be
connected with the main conductor, the size of material need not be
increased; for if two or more terminals receive the charge
simultaneously it necessarily follows that it is sub-divided; therefore
the conductor will have no more work than if one point only had been
struck.

_Note._—We quite agree with Snow Harris regarding insulators, that if
there be anything in insulators they are a disadvantage, for if the
building be struck in any other part than the conductor, the current
cannot easily find its way to the conductor. The current will take the
line of least resistance; therefore it is reasonable to assume that the
building is more certain to escape the disruptive force of lighting when
the conductor is in close proximity with the building.

                                                       JOHN DAVIS & SON.

                  *       *       *       *       *

                                         BIGG MARKET, NEWCASTLE-ON-TYNE.

1. For upper terminals I generally use ½ inch diameter solid copper rod
[A. 0·20 in.], or ¾ inch diameter tube [A. 0·24] with four points, and I
fix them 4 or 6 feet above the building they are intended to protect. I
always endeavour to get the upper terminal as near the size of the
conductor as is consistent with strength. I make my points of the best
copper tipped with platinum.

2. For the conductor I use ½ inch diameter copper wire rope [A. 0·20
in.], which is (in my opinion) the best and most applicable conductor
used, as it appears to be an open question, at present, whether it is
surface or mass which conducts. If it is mass, then a tube conductor is
insufficient. If it is surface, then a solid rod is superfluous. The
copper tape conductor I consider the worst form of any, as it bends too
easily round sharp corners, projections, &c., of buildings, which is a
thing to be avoided as much as possible. A conductor should be brought
to earth as direct as possible, and with no bends if they can be
avoided. The copper wire rope conductor has both surface and mass
conduction, and can be led about roofs and other difficult places better
than any other form of conductor that I know of.

3. None; I imagine it is not necessary.

4. I avoid joints as much as possible; but, when they must be made, I
scrape the ends of my wire bright, and then splice or interlace them
together, covering the whole with thin sheet lead—I object to solder, as
I think it must interfere with surface conduction; the wire is fastened
to the upper terminal, with a Matthew Walker knot let into a hollow cup,
and the terminal screwed down on it.

5. I attach my wire to the building with a brass or gun-metal holdfast 4
inches long, having a ⅝ hole, the inner edge being flush with the wall
of the building, so as to allow the conductor to touch the wall of the
building all the way up, and still allow plenty of room for the free
passage of the electric fluid. I do not approve of insulators, nor yet
of that kind of holdfast that is driven in tight on to the wire, for I
think that must interfere with the clear passage of the electric fluid.

6. I cut a trench some 15 or 20 feet long, gradually deepening from 1
foot at the commencement to 4 ft. at the termination, which I fill with
pounded charcoal and bury the wire in it. Earth-plates are not necessary
when this is done.

7. It is calculated that a conductor will protect a surface in the shape
of a cone, the diameter of the base of which is equal to the height of
the conductor. Thus, if a conductor were 100 feet high, the space
protected would be represented by a straight line drawn from a radius of
50 feet from the base of conductor, to a radius of 8 or 10 feet from its
highest point.

8. I consider, if there are two terminals, there should also be two
wires, or the wire should be of sufficient capacity to carry off a
double charge, in case both terminals should be struck at one time. I
think the conductors should certainly be of sufficient capacity to carry
off any charge that might be received by the terminals, be they few or
many.

                                                          T. MASSINGHAM.




                              APPENDIX B.

                     ANALYSIS OF, AND REMARKS UPON,
                      THE VIEWS OF MANUFACTURERS.


On Nov. 14th, 1878, a circular was issued to the principal lightning-rod
manufacturers in this country, inviting their replies to various
questions that were submitted to them, and also any remarks that they
might wish to lay before the Conference.

Replies have been received from—

           Messrs. WILKINS & WEATHERBY, of London.
           Messrs. GRAY & SON, of London.
           Messrs. F. RUSSELL & CO., of London.
           Messrs. JOHNSON, CLAPHAM, & MORRIS, of Manchester.
           Messrs. FREEMAN & COLLIER, of Manchester.
           Messrs. PENNYCOOK & CO., of Glasgow.
           Messrs. DAVIS & SON, of Derby.
           Messrs. MASSINGHAM, of Newcastle-on-Tyne.

All well-known firms, who have written fully and freely, and whose
experience is very extensive.

It is impossible to read these replies without feeling the absolute need
of such a Conference as that which has been formed, to collect facts, to
digest opinions, and to endeavour to formulate some guiding principles
for uniformity in practice—for here we have the most diverse modes of
execution detailed, the most opposite views expressed, and the most
varied experience narrated. In fact, some ideas enunciated are quite
opposed to the teachings of science. Where practice is so opposite,
error must abound: and, therefore, there must be great need for an
effort to reduce the system of constructing lightning conductors in this
country to some uniform basis. On no one single point, except in the use
of copper and the necessity for reaching damp earth, do any two
manufacturers agree in adopting similar measures.

I will take each question submitted _seriatim_.


1. _Form, dimensions, and material usually adopted for upper terminals._

There are single points and branching points, fine points and blunt
points, cones, spikes, balls with spikes on top, and balls with
radiating spikes.

The dimensions vary with each form, and they are made of solid copper
and copper tube, of brass, of iron, and of gun-metal. The ends are
sometimes silvered, sometimes gilt, and sometimes tipped with platinum.
But there is no rule or uniformity; and one manufacturer acknowledges
that, while he sometimes tips the points with platinum, he considers the
practice to be altogether superfluous.

Now it is clear that if there be any electrical efficacy in points _as
points_, they should be made in such a form, and of such a material, as
to maintain their efficiency permanently. The writer is very strongly of
opinion that the efficiency of lightning conductors is due principally
to the peculiar electrical action of their points. He sees no advantage
whatever in multiplying these points. In his opinion each conductor
should end in one fine platinum point. It would thus act as a dissipator
of the electric charge in its immediate neighbourhood, and would then
_prevent_, and not favour discharge. Moreover, points demand frequent
inspection, attention, and renewal. He thinks that one function of the
Conference should be to examine some of these points _in situ_, if
possible. At present they are erected and left to their fate.


2. _The Material and Dimensions of the Conductor._

The use of copper is almost universal, but two manufacturers
occasionally use iron. The form varies. The majority use wire rope, but
some use rods, others bands or tapes, others tubes. One firm uses a
cable “constructed of 49 strands of hard-drawn _square_ copper wire.”
Another firm uses a wire rope, simply because “it appears to be an open
question, at present, whether it is surface or mass which conducts.” The
dimensions are as varied as the form, from a wire rope ⅜th of an inch in
diameter to a copper band 3 inches wide and ⅛th thick.

The only point worthy of note is, that no one uses a smaller conductor
than a copper rope ⅜th in diameter (_i.e._ 4 oz. of copper per foot
run).

Leaving the dimensions as a question for future investigation, the
points submitted for the consideration of the Conference under this head
are—

  1. Is conduction a question of surface or of mass?

  2. Is copper alone to be used?

  3. Is the conductor to be in the form of a rope, a rod, a tube, or a
        band?

Now, on the first point the writer entertains no doubt whatever that the
conduction of atmospheric electricity is simply a question of mass, and
that the lightning protector acts simply as a conductor obeying the laws
of Ohm.

On the second point he sees no objection whatever to the use of iron,
when properly galvanized, in situations free from chemical impurities.
The reasons urged against its adoption are extremely weak. First, it is
said to decay rapidly; and, secondly, it is said to be a very much worse
conductor than copper.

The rusting of iron is almost entirely checked, in pure air, by
galvanising or coating with zinc. It is used for nearly every other
purpose in connection with building, and it is difficult to understand
why it should be discarded on account of its liability to decay for this
particular purpose, where it is always under supervision.

Again, pure copper conducts about six times better than pure iron: but
we never get pure copper in lightning conductors. Moreover, the
manufacture of iron wire for telegraphic purposes has increased so
enormously during the last two or three years, that the wire now
supplied conducts 50 per cent. better than it used to. Hence the
difference between the two in this respect is not so great as theory
indicates; and it would be well for the Conference to satisfy itself on
this point by having similar sized wires made of the two materials, and
having them measured electrically for their resistance.

But it has been pointed out by the late Mr. Brough (_Phil. Mag._, May,
1879), that by regarding (1) the influence of the rise of temperature,
(2) the difference between the specific heats, and (3) the relative
dimensions, iron conductors can be made much smaller than was formerly
supposed: and, that as iron is so much cheaper, iron rods can be made
equally efficient for a much less sum than copper. Moreover, the use of
iron enables the architect to use one kind of metal throughout his
structure, and thus avoid anywhere the contact of dissimilar metals,
which always results in decay.

On the third point, the writer is clearly of opinion that a galvanized
iron _rope_ is amply sufficient for country residences and buildings
free from chemical actions. In such places, and in towns, copper should
be used. A rope, whether of iron or copper, is easily handled, it can be
made of any size, it can be led in any direction without bends or
angles, it is neat and easily jointed, diverted, or lengthened.

The writer refrains from expressing any opinion on its dimensions here,
for this is a point that will require most careful examination by the
Conference.


3. _Is there any definite proportion between the length and sectional
area of the conductor?_

The majority of the manufacturers increase the size of the conductors
for high buildings—one making the limit 120 feet, another 150 feet,
while a third “varies the sectional area with the length.” One firm does
not consider any difference necessary, while another takes it that the
sectional area should be the same irrespective of length, for “lightning
does not vary in intensity while passing through a conductor of greater
or less length.”

Now, the laws of electricity clearly show that to maintain equal
efficiency we must vary the sectional area as we increase the length of
the conductor; but it is a question for the Conference to decide whether
we should not recommend a rope of uniform dimensions that would be
equally applicable for high and low buildings. Within ordinary limits
the necessity for increased thickness for increased height is scarcely
evident, but the remedy of an increased sectional area, with the number
of separate points erected, is very clear. Indeed, each point should be
the terminal of a conductor, whose sectional area should be uniform to
the earth. For if it be not so, and each conductor be fully charged with
electricity, then when the sectional area diminishes there will be
congestion, resulting in heat and discharge to the building. Hence the
thickness of the main conductor must increase with the number of
separate points erected.


4. _Joints, how made._

Some are rivetted, others are screwed, others are coupled by right and
left-handed screws. Tubes are socketed into each other. In one case “the
end of the conductor is knotted and drawn through a cup-shaped ring of
metal.”

There can be no doubt that joints are the greatest source of danger in
lightning conductors. If a joint be imperfect, and the conductor be
conveying a charge to earth, heat will be generated there, the conductor
may be fused and rendered useless, and the discharge will be diverted to
the building. Or the joint may be so bad—that is, its resistance may be
so great—that it renders the conductor practically useless, for other
parts of the building will offer easier paths to the earth. Though the
use of solder is pretty general, it is not universal. Indeed, one
manufacturer objects to it because “it must interfere with surface
conduction!” It certainly should be imperatively used. No joint can
possibly be perfect that is not metallically continuous. Careful
soldering is the only certain mode of securing this, and that this is
practicable is evident from the millions of perfect joints in telegraph
wires. To scrape the ends of wire bright, and cover the whole with thin
sheet lead, as is done by one firm, is simply to court danger. The
absence of joints in wire rope is one great element in its favour.


5. _Attachment to building, how made._

Some attach the conductor to the building by copper straps and nails;
some use holdfasts, either of copper wire or gun metal; others use
staples; one uses metallic ties. Several pass the conductor through
insulators of glass, porcelain, or earthenware. But the majority discard
insulators as useless.

In the opinion of the writer they are quite right, for it is difficult
to understand what useful function the insulator performs. One fact that
occurred in 1837 is given as a reason for their use, but the fact
militates against the efficiency of the conductor rather than the
absence of insulators. If the conductor were perfect there could have
been no concussion at the point of attachment. If it were imperfect
there may have been, for the discharge would seek other paths to earth.
Some manufacturers use holdfasts of a different metal to that of the
conductor. This is wrong, for where different metals are used galvanic
action sets in, tending to decay and rupture. The attachments for this
reason should always be of the same metal as the conductor.


6. _Ground connection, how formed, and of what extent._

The necessity for reaching moist ground is generally recognised, but
various curious ways for making earth connection are suggested. One firm
considers that a band cut into strips 18 inches long would suffice,
while another says that not less than 30 feet, in two or three branches,
with fork at the end of each band, should be used. One firm is very
brief: “Ground end is coiled loosely in damp earth or a well.” The use
of coke, powdered charcoal, or carbonaceous materials, is insisted upon
by others.

It is questionable whether the difficulty of fitting a good connection
with the earth is fully realized. None but telegraphists know the great
difficulty there is in doing this. The first object to be secured is a
good damp soil, and the next as large a conducting surface as possible.
Metal pumps, iron, gas, or water pipes, wells in which plates of metal 2
or 3 feet square are placed, or similar plates may be buried in
perpetually damp ground, or in holes well filled with powdered coke.
Moisture in some form is essential, and without it a lightning protector
is of small service.


7. _Extent of area supposed to be protected._

The majority of the firms consider that the area protected has a radius
equal to the height of the conductor; but one firm considers that this
should be multiplied by five or six times; while another asserts, “that
no appreciable extent is protected by a single rod conductor;” and
another, that “many instances may be related of buildings being struck
much within the radius of well protected churches or chimneys.”

We have no experience at present to enable us to form a definite opinion
on this point. The Committee of the French Academy, gave the radius as
equal to twice the height of the conductor from the ground, but
buildings have undoubtedly been injured within this limit. The writer
does not think that a greater radius than the height should be taken:
but thinks that this is one of the most important questions that the
Conference could determine. Calculation might, to a certain extent,
settle the point: but it is more a case for experience.


8. _If there is more than one terminal, is the size of the conductor
increased?_

This question has been partially considered. (See No. 3.)

                  *       *       *       *       *

Some firms do not consider any increase necessary: others think that
when two or more terminals are used, the main rope should be somewhat
enlarged; while others run one cable from each terminal, or make the
conductor of sufficient capacity to carry off the double charge.

The writer considers that every conductor should be complete in itself:
or, if this is inconvenient, then the size of the main conductor should
be enlarged in proportion. It does not at all follow, as one firm
implies, that if two or more terminals receive the charge
simultaneously, it is necessarily sub-divided. Each charge may be full
and complete in itself, and be sufficient to fill the wire; and,
therefore, if the main conductor be not increased, accident may result.

                  *       *       *       *       *

There is no doubt whatever that great consideration should always be
given to the lessons of experience, and the opinions of those who have
made the erection of lightning conductors for 35 years their especial
practical study, are much entitled to weight; but such practice may have
originally been based on error, and the teachings may not have been
guided by science. Where such variety of practice abounds, there must be
fallacy somewhere, and, therefore, danger; and not the least of the
beneficial labours of the Conference will be to point out to these
different practical men, where their faults and their departures from
truth exist.

                                                           W. H. PREECE.

_August 8th, 1879._




                              APPENDIX C.

REPLY FROM MANUFACTURERS, RECEIVED AFTER THE COMPLETION OF THE ANALYSIS
                        WHICH FORMS APPENDIX B.


                               FARADAY STEAM WORKS,
                                        ST. JOHN’S ROAD, HUDDERSFIELD.
                                               _11th November, 1879._

  SIR,

  Enclosed we have pleasure in handing you our replies to the eight
  questions which you ask lightning rod manufacturers and erectors,
  together with three tracings, showing our system of protection under
  different conditions. In the case of Nottingham Castle we considered
  it necessary, on account of the rock on which the castle was built,
  to adopt an extensive system of lateral points in earth termination,
  by running all the main conductors from the building down the
  shrubbery into the moat, where we formed the flat copper band into
  the form of gridirons, in which several hundred feet of the copper
  band has been used, and the termini of the ribs pointed, and the
  whole being sunk eight feet, and two cart-loads of gas carbon laid
  over each grid.

                                               Yours obediently,
                                                       SANDERSON & CO.


       REPLIES TO THE QUESTIONS OF THE LIGHTNING-ROD CONFERENCE.

I.—Usually a length of copper tube 5 feet long 1 inch diameter × No. 8
B.W.G., which is termed the elevation rod, surmounted by a solid copper
point, forged from ⅞th of an inch round bar, wrought three parts of its
length to a square tapering point, the said elevation rod and point are
screwed together by a copper ball-shaped union, into which are screwed
four smaller points at an angle of 45 degrees. When fixing lightning
conductors on church spires and turrets we usually run the copper tape a
few inches above the vane or finial, having previously prepared and
pointed the tape; by this system all joints are avoided.

II.—We, the sole inventors, manufacture the solid copper tape lightning
conductors of the following sizes:—

  Nos.  │   1   │   2   │   3   │   4   │   5   │  21   │  22   │  23
        │  in.  │  in.  │  in.  │  in.  │  in.  │  in.  │  in.  │  in.
        │⅝×1/12 │  ¾×⅛  │  1×⅛  │ 1½×⅛  │  2×⅛  │1×1/16 │1½×1/16│2×1/16
   [A   │  ·05  │  ·09  │  ·13  │  ·19  │  ·25  │  ·06  │  ·09  │ ·13]

and in continuous lengths up to 500 and 600 feet.

III.—Yes. For heights of say 50 feet we recommend our No. 2 (¾ in. × ⅛
in.) size; for 100 feet our No. 3 (1 in. × ⅛ in.) size; and for 200 feet
or over, our No. 4 (1½ in. × ⅛ in.) size; or our Nos. 21 (1 in. × 1/16
in.), 22 (1½ in. × 1/16 in.), or 23 (2 in. × 1/16 in.) according to
position and circumstances.

IV.—In the case of church spire or turret conductors we have no joints
whatever, as described in Answer I., but where elevation rods and points
are used we make a copper coupling, screwed at one end to receive the
elevation rod, and at the other end to receive the copper tape, which is
firmly rivetted into the coupling, and thence soldered or brazed. But
when a complete system is employed with branches or tributaries, running
from several points on to the main conductors, we make the joint by
means of copper rivets, and then solder.

V.—By means of gun metal clips, or holdfasts, let into the building,
which secures the copper tape in close contact with the face of the
building. Under no circumstances do we use glass, ebonite, or other
insulators.

VI.—In good moist earth 5 feet or 6 feet deep we simply run the copper
tape out from the building some 20 feet, and then rivet a copper earth
plate on to same, or sometimes employ a large gridiron made of copper
tape, using as much as 200 lineal feet in its construction. Wherever we
make earth terminations in rocky, dry, or gravelly soil, we always fill
in with a load of small coke, charcoal, or other carbonaceous matter,
and also divert the rain fall-pipe system over the termination so
formed; also, wherever possible, we connect the conductor with the gas
and water systems outside the building. In all cases of earth
terminations, the size of earth-plate is in proportion to the size of
conductor employed, and other circumstances.

VII.—We are unable to come to any conclusion as to any definite area
which one lightning conductor will effectively protect, and no two
writers appear to agree on the subject; but from actual practical
experience of 30 years, combined with the closest observance and
research, we are in the position to say, emphatically, that a conductor
on one prominent elevation—for example, a turret will not protect a
similar elevation, be it only 1 yard, or 50 yards distant; but that
providing that two prominent features be provided with a conductor point
on each, then on the same foundation, we say that both of them would be
effectively protected. But for the purpose of simplifying and
practically illustrating our views on this subject, we enclose you
tracings and particulars of several buildings for which we have designed
the system of lightning conductors, and which we believe to be perfect.

VIII.—Yes,—always, and in proportion to the number of extra terminals
adopted.

                                                         SANDERSON & CO.


     DETAILS OF LIGHTNING CONDUCTORS APPLIED TO NOTTINGHAM CASTLE.

The following three engravings render very few verbal details necessary.
Fig. 1 gives the east elevation of the castle, it shows part of a
flag-staff 115 feet high, which has a conductor, also three of the
principal terminals, and twenty-six minor points upon the building, and
by two dotted lines the position of two of the main conductors to earth.
The principal terminals are tapered iron tubes, 13 feet long, carrying
copper tapes 1 inch × 1/16th and terminating with copper points tipped
with platinum; the minor points are of solid copper 9 inches long. The
main conductors to earth are copper tapes 2½ in. × 1/16th.

[Illustration:

  FIG. 1.
]

Fig. 2 give a plan of the roof, much of which is of glass with wooden
rafters. The twelve principal terminals are shown by small rings, the
ninety-four minor points by round dots, the horizontal copper tape (2
inches × 1/16th), uniting all the upper terminals, by a pecked line, and
the position of the main conductors to earth by dotted crosses. All the
gutters are metallically connected with the conductors.

[Illustration:

  FIG. 2.
]

Fig. 3 gives a general plan (for which we are indebted to the
architects, Messrs. T. C. Hine & Sons) of the castle and grounds, and
also a little section indicative of the precipitous eminence on which
the castle stands. From these it will be seen that two of the main
conductors to earth are carried underground at a depth of about 4 feet,
under the terrace and down the slope and terminate in trellis-work,
about 14 feet square, of 2½ inches × 1/16th copper tape rivetted at
every intersection. The other earth contact is obtained by bolting the
terminal on to the town water-main. The total length of tape used in the
earth connections was about 500 feet.

                                                         SANDERSON & CO.

[Illustration:

  FIG. 3.
]




                              APPENDIX D.

                     REPORT OF THE REPRESENTATIVES
                                 OF THE
                 ROYAL INSTITUTE OF BRITISH ARCHITECTS
                                 TO THE
                       LIGHTNING ROD CONFERENCE.


The Council of the Royal Institute of British Architects sent out
upwards of 600 circulars (a copy of which follows this Report) to their
Architectural Members requesting information as to injury by lightning
to any buildings known to them.

The Council also requested the same information from their Honorary
Associates (upwards of 100 in number), who are chiefly men eminent in
the Scientific, Literary, and Artistic world.

The Council have received up to this date only 35 answers from
Architects, and 1 from the Honorary Associates.

Of these answers many are to the effect that no case of injury has
arisen to works under their direction. The remainder give 33 instances
of damage, and enter, in many cases, very fully into the details of
them.

The instances given may be roughly classified thus:—

There are 26 of buildings injured where there were no conductors.

In 9 of these the lightning did some injury to the chimneys and other
exposed parts, and was then conducted safely to the ground through the
metal gutters and rain water pipes.

In three other instances the lightning appears, from the statement of
persons in the building struck, to have dispersed and passed out by open
doors, &c.

We give no opinion as to this, but the facts are distinctly stated. In
several other cases the lightning passed off in several distinct
directions and currents.

There are 6 cases of buildings being injured although protected by
lightning conductors. In one of them (No. 14) the failure is clearly
explained by the fact that the lower part of the conductor had been
stolen, leaving only two or three feet of it in the ground. The
lightning in this case broke through a wall 4 feet 6 inches thick, at a
height of 6 feet from the floor to a gas pipe.

In another case (No. 3) a gable was struck, although close to a spire
and turret which had a lightning conductor.

In another (No. 7) the part struck (a chimney) was 64 feet away from a
tower, in the same building having a lightning conductor.

In No. 24 the conductor was sufficient protection until it passed at a
sharp bend round some mouldings; these it injured, but did no further
damage.

In two cases (Nos. 21 and 23) the discharge injured some gas tubing near
it, and set fire to the gas, and by its means to the building.

We beg finally to call attention to the drawings attached to No. 7 (Mr.
Colson, of Winchester), showing the injury to trees 130 feet away in a
direct line from a spire which was destroyed, it having no conductor.

                                                   T. HAYTER LEWIS, V.P.
                                                   JOHN WHICHCORD, V.P.


                               CIRCULAR.


                       LIGHTNING ROD CONFERENCE.

  SIR,

  I beg leave to inform you that the Council have appointed two of
  their members to meet delegates from several scientific societies in
  order to confer as to the best methods of protecting buildings from
  lightning; and in accordance with a resolution of that conference I
  have the honour to forward to you, by the desire of the Council, the
  questions appended below.

  I shall be much obliged if you will return me this paper, with any
  answer you may be in a position to make to the questions, on or
  before Monday the 20th of January, 1879; and

                                           I remain, Sir,
                                               Your faithful servant,
                                                     WILLIAM H. WHITE,
                                                         _Secretary_.

  9, CONDUIT STREET, HANOVER STREET, W.
          _19th December, 1878._


                               QUESTIONS.

1. Have any buildings, in the construction of which you have been
professionally engaged, or which are otherwise well known to you, been
struck by lightning?

2. If so, state briefly the damage done to them, describing their
general plan and construction by sketches or otherwise, particularly
noting the position of any metal work to roofs, pipes, &c.

3. Were the buildings furnished with lightning conductors? If so,
describe them in relation to the following heads:—

(_a_). Their materials and dimensions.

(_b_). Their attachment to building.

(_c_). Their connection with the ground.

(_d_). Their upper terminals.

(_e_). The height of conductor above chimney or other adjacent part of
the building.

(_f_). If there existed more than one conductor state the distance from
one another.

4. What was the distance of the point struck, horizontally and
vertically from the conductor?

5. Was any damage done, and if so how much, to the conductor, and in
what manner?

6. Give particulars as to any trees within a short distance of the
building struck.

                  *       *       *       *       *

  The replies received to this Circular are too long to be printed in
  full, they have therefore had to be epitomised in the following
  list, and consequently cannot be given as separate answers to each
  question.

  The replies were all numbered consecutively, so that the numbers
  omitted in the list refer to circulars returned by members who had
  no information to give on the subject.


                          REPLIES TO CIRCULAR.

2. _St. Aubyn, J. P. Week St. Mary, North Cornwall._—The tower of this
church stands on very elevated ground, and has lofty pinnacles, three of
which have been struck at different times, on each occasion one of these
pinnacles was shattered, and had to be taken down and rebuilt. Some of
the stones are held by iron cramps, but no iron or other metal spindles.
The roof of the tower, as well as that of the church, is slate, without
spouts, and there are no lightning conductors to the building. There is
open country all round the church, and no tree of any size within a mile
of the tower.

The following detailed report was received direct from the Rev. G. H.
Hopkins, the rector of the parish:—

  _An Account of the position of the Church of Week St. Mary, in the
    County of Cornwall, and the effect of Lightning upon the Pinnacle
    and Tower when struck for the fourth time this century on November
    8th, 1878._

  _Situation of the building._—The situation of the church is at the
  northern angle of an extensive triangular plateau, which towards the
  south is much broken by small valleys and low hills, while the high
  land is for the most part moor, broken in places by cultivated
  ground and small plantations. Within a quarter of a mile from the
  church, on three sides, the ground commences to fall very rapidly to
  a depth of 200 or 250 feet; it is three miles from, and nearly 500
  feet above, the sea; to the N.W. lies Widemouth Bay, one of the very
  few breaks in the cliff along the coast of North Cornwall; the
  entire extent of this break is quite a mile-and-a-half; between the
  Bay and the extremity of the plateau, at which the church is built,
  the surface is broken by low hills, only one of which exceeds 250
  feet above the sea level, and this exception is separated by one
  valley from the church hill; half a mile south of the church is the
  highest ground in the parish, but neither this nor any hill for
  several miles exceeds in height the pinnacles of the tower. The
  elevation of the building above the surrounding country can be
  better understood from a local rumour that 28 churches are visible
  from the battlements of the tower, and the average size of a parish
  attached to each church is 6000 acres. The highest point of the
  pinnacle is 90 feet above the ground.

  _No mines or spring of water beneath it._—There is no evidence of
  the existence of any metalliferous lode in the parish, and certainly
  no such attractor of electricity lies beneath the church, nor is
  there any spring of water near the foundations; but as the surface
  soil is clay, the rain water has no means of flowing away, except
  over the surface, and a few hours of moist weather make the soil
  like a wet sponge.

  _Circumstances._—The tower was struck at 6.45 a.m. on November 8th,
  1878, the weather having previously been gusty, with sudden storms
  of hail and rain as each heavy cloud came up from the sea: many
  times during the night the downfall of hail was very violent, and it
  was during one of these storms that the single electrical discharge
  took place; the hailstones were considerable, both in number and
  size, when the flash occurred, and they certainly commenced falling
  before the shock took place.

  _Brightness of the flash._—The brightness of the lightning was
  intense, and I have been at some trouble to inquire into the effect
  which it had upon those who saw it. I was awake, and the lightning
  illuminated the room through double chintz curtains and dark-green
  blinds, the windows looking away from the church, and being more
  than a quarter of a mile from it; during the storm a farmer took
  refuge in a closed cattle shed, 200 yards from the church, and he
  spoke afterwards of his impression that he was surrounded by fire;
  two farmers going to Camelford fair, were at the time waiting on the
  road, a mile-and-a-half from the church, and their impression was
  that they were enveloped in flame, and the flame came between them;
  these experiences were given to me at different times, and were
  independent evidences of individual opinion. At Holsworthy, eight
  miles away, in a direct line, two ladies were attending their sick
  mother, and the vividness of the lightning obscured the brightness
  of the light of two candles and a paraffin lamp.

  _The loudness of the thunder._—The loudness of the clap of thunder
  was very great; of course it shook my house; and a neighbouring
  rector, who lives three miles away, in an adjoining parish, felt the
  effect of the clap to an extent which was very unusual; at
  Camelford, lying W.S.W., and distant about twelve miles, with a
  considerable range of hills between, the thunder was not heard; but
  two miles nearer, and in the same line, it was just heard: this
  latter station being on the summit of the range; at Holsworthy,
  lying E.N.E., it was heard as an awful peal; at Kilkhampton, which
  lies directly N., and separated by a broad broken valley, the
  thunder was blamed with causing colts to break through a fence from
  terror, and the distance is ten miles. I am unable to give any
  further account either of the distance the thunder was heard, or of
  the intensity of the light of the flash. As the wind was blowing
  from the west, with a slight bearing towards north, the effect of
  the wind upon the sound is evident.

  _Effect upon the pinnacle._—The S.W. pinnacle (A) was struck, and
  apparently the effect of the lightning was not felt upon the two
  uppermost stones, namely a small cross and a truncated cone, which
  supports it at the summit, both of granite. It may be remarked that
  the entire facing of the tower is granite, the interior masonry
  being made up of small stones of different kinds, which exceeds 3
  feet in thickness, while the blocks of granite which face the tower
  vary from 10 to 12 inches in thickness, and in some cases are of
  immense size and weight. As soon as the current could reach that
  part of the pinnacle which is made up of courses of separate stones,
  the mischief commenced, and the effect was to force the stones out
  all round the axis of the pinnacle, so that in the same course many
  of the stones were separated by intervals of from 1 to 5 inches; one
  great block, measuring 2 feet in length, was thrown right out, but
  fortunately fell outside the tower walls, and left a gap in the
  pinnacle opening towards that quarter from which the storm came. The
  entire pinnacle was shattered, and all the courses of stones which
  make it up dislocated, as well as the two courses of stones which
  lie beneath it. The fierce rain storms had long ago washed away all
  the mortar from between the stones which compose the outside of the
  tower, and probably every shower wets the interior of the masonry;
  and this was especially the case at one part where there is a
  considerable leak of drainage from the roof of the tower.

[Illustration: Tower of Church of Week St. Mary, Cornwall]

  _Effect upon the tower._—The course of action of the current was
  from the pinnacle to this leakage, where a stream of water was
  running down the wall and between the granite facing and interior
  masonry; the downward course of the water was arrested by the belfry
  light, and then has to fall to the masonry below the window; just
  above the window a large block of granite C (outside measurement 2
  feet by 14 inches), was thrown out in such a way that it hangs like
  a halfopen door, the projecting edge being that which lies just
  below the leakage, and standing out about 10 inches from the wall;
  across the belfry window runs an horizontal iron bar, and at the
  bottom of the window lies an old iron bar; the stonework beneath
  this bar was much knocked about. From that spot the effect of the
  lightning disappears, until it reached an immense carved granite
  block D, which lies on the south side of the tower, and very near
  its south-east corner; and a few feet below this the leaden gutter E
  (through which part of the roof drainage is poured to the ground),
  runs some feet down the wall towards the earth, but does not reach
  the earth by 12 feet. The immense carved granite block is broken
  into two almost equal parts by a line parallel to its vertical
  edges, and the two parts are separated by quite half an inch; the
  fracture of the stone is not quite straight nor clean, and the parts
  of the stone do not project beyond the surface of the tower. I have
  been unable to trace the course farther; it may have passed along 70
  feet of leaden gutter, between the nave and south aisle (F) to the
  east end of the church, or gone to ground at the base of the tower.
  Three or four days later, during a very high wind, a second stone
  fell from the pinnacle; this same stone had been partially thrust
  out on a previous occasion in 1865. Upon examination the pinnacle
  was found to be in such a precarious condition that a single blow
  with a hammer on one small stone would have endangered the whole.

  _Previous injuries._—On October 19th, 1843, at 10 p.m., the S.E.
  pinnacle (B) was completely torn down, and two courses of stones
  just beneath it were greatly damaged. The line of action of the
  current was to the north-east edge of the tower, towards the leaden
  gutter, between the nave and north aisle, over this it threw out a
  great block of granite; from that point it passed along the leaden
  gutter and across the roof at the north aisle, to a strong iron bar
  running vertically down the third out of the four north windows;
  this window was considerably damaged, and still bears marks of rough
  usage; how it happened that two other windows near the tower, and
  similarly fitted up with iron bars, were passed untouched is a
  mystery; to some extent all the windows in the church were somewhat
  damaged, the framework being of wood they were much shaken, and
  partially separated from the masonry. This was probably caused by
  the effect of the current upon the air in the building: the
  direction of the damage being due to the outward pressure.

  In 1812 the north-east pinnacle was struck, and also some little
  time before 1688, as there is a stone engraved with that date upon
  it, and the date of the tower is the close of the fifteenth century.

  The dates of these misfortunes have been as follows:—

                       About 1688 N.E. pinnacle.
                             1812 N.E. pinnacle.
                             1843 S.E. pinnacle.
                             1865 S.W. pinnacle.
                             1878 S.W. pinnacle.

  The north-west pinnacle appears to have escaped, and it stands just
  over the tower stairs. The south-east pinnacle, which was struck in
  1843, was at that time surmounted by a weathercock.

  _There never has been a lightning conductor to any part of the
  church._

  One word further. I have been the holder of the benefice since the
  autumn of 1876; last summer the specifications for the complete
  restoration of the church, at a cost of £2000, were sent to me by
  the architect; before forwarding the same to the Bishop of the
  Diocese I supplied the omission of a lightning rod in the
  specification.

  _Meteorological Notes._—It is a noteworthy fact that on each
  occasion during this century when a pinnacle has been struck, the
  season has been between November and March, with _one_ electrical
  discharge during the storm. It is also remarkable (an experience
  founded certainly on only two summers, but during that time the rule
  has been invariable) that all round the neighbourhood summer
  thunderstorms may be passing in their usual fitful manner of storm
  and sunshine, but immediately a summer thunderstorm passes over this
  village there is a complete break in the weather for eight or ten
  days.

  _Rainfall._—1877: 49·11 in., 213 wet days; 1878: 48·03 in., 212 wet
  days.

  3. _Baker, A. J. Rosherville Church, near Gravesend._—The west gable
  of the south aisle was struck by lightning, although close to the
  tower and spire which were provided with a lightning conductor, and
  received no injury.

  5. _D. Brandon. St. Ann’s Hotel, Buxton._—In 1875 a chimney-stack
  was shattered by lightning, the concussion in the flue drove fire
  and smoke into the drawing-room, displaced the mantle-piece, and
  broke many panes of glass. The hotel occupies half a crescent, the
  stack being in the middle of the crescent. The building had no
  lightning conductor, and there were no trees nearer than five or six
  hundred feet.

  7. _J. Colson. Twyford Moors, near Winchester._—Struck by lightning
  in June, 1878. This building (of which a plan is given) was provided
  with one lightning conductor fixed to the tower. The upper terminal
  branched into five points, about four feet above tower roof; the
  conductor, which was ⅜-inch copper wire-rope, was attached to the
  upper part of the tower, with glass insulators, and in the middle
  nailed to the wall through lead flashing, then carried down
  rain-water pipe into cesspit. The point of the building struck by
  the lightning was distant about sixty-four feet horizontally and
  sixteen feet vertically from the upper terminal of the conductor.
  Damage done was very slight, tiles and laths being knocked off, but
  no sign of scorching. The conductor was not injured; there are no
  trees near the building.

[Illustration: Plan and Elevation of Twyford Moors, Winchester]

              C Conductor.
              * Point struck.
              P Rain-water pipes attached to iron gutters.

  7_a_. _St. James’ Church, West End, Hants._—Struck by lightning at 5
  p.m., on June 12th, 1875. The church stands on the top of a hill
  with many trees near, it is built of brick with a lead ridge to
  roof, iron and lead gutters, iron rain-water pipes P, and two iron
  chimneys. The spire is of brick, with stone angles fixed by iron
  cramps; the spire was finished by an iron bar at the top, but was
  not provided with a lightning conductor. The damage done to the
  spire was considerable, as shewn in the engraving, making it
  necessary to pull it down, but the tower was not injured. Stones
  from the spire were thrown through the trees at B, which are 126
  feet distant from the church, cutting off some of the boughs. The
  tree at A was untouched.

[Illustration:

  St. James Church, West End, Hants.
]

  12. _T. Hawksley._ Several Steam Chimneys not provided with
  lightning conductors; upper portions knocked down, chimney split or
  often skinned by the lightning, _i.e._, the four and a half inches
  of brickwork taken off; details not given. Now uses Gray’s system of
  lightning conductors for such buildings, which is found successful.

  13. _A. Hill._ In South Africa houses are generally roofed with
  corrugated iron, and protected from lightning by planting a circle
  of high trees round them.

  14. _G. J. Hine. All Saints’ Church, Nottingham._—Struck about
  twelve years ago; tower and spire 150 feet high, with one conductor
  of half-inch copper wire-rope, with platinum terminal, and secured
  by insulated brackets, but earth contact only two feet long at time
  of accident the rest having been stolen. The lightning passed down
  the conductor till within six feet from the ground, where it passed
  through a wall of solid masonry four feet six inches thick,
  displacing some of the stones, to an inch-iron gas pipe inside the
  church. In passing off along the gas pipes under the floor, it so
  far disarranged them as to cause a considerable leakage of gas,
  which was set fire to by a candle some hours after the accident and
  exploded. There were no trees, only a few shrubs near.

  16. _J. Jerman. Alphington Church, near Exeter._—Tower struck about
  March, 1828; the church had no lightning conductor. The tower was
  rent through the masonry vertically, damaging parapet and ungearing
  and injuring bells, which were being rung at the time; one ringer
  was killed, and some of the others had the heel-plates melted off
  their boots. There are few trees of any size near the tower, which
  surmounts all adjacent buildings; it had pinnacles and a weathercock
  on the top, and a lead roof with spouts, no down pipe. Very few
  casualties from lightning occur in Devonshire.

  18. _E. J. Law._—The tower, surmounted by a cast iron vane, of a
  house built under my superintendence, was struck; the slates
  stripped from the roof, and the charge apparently escaped down the
  rain-water pipe; it divided, however, and passed to an adjoining
  ridge, chipped a piece off the iron cresting and hurled it some
  twenty yards from the building. Lightning conductor ordered, but not
  erected; cast iron ridges to all the roofs. Large infirmary within
  two hundred yards and high church tower within three hundred yards,
  and houses nearer, of equal height to the one struck, and with cast
  iron crestings, none of these were injured.

  18_a_. _St. Sepulchre’s Church, Northampton._—Vane on top of spire
  struck by lightning, passed down the rod, then to frame of one of
  the spire windows, and thence to clock face, from clock face it
  passed down the gas pipe, leaving no further trace.

  19. _T. Hayter Lewis. Lewisham, 1872._—Zinc chimney of house struck;
  lightning went down flue A, thence to a gasalier (glass) B, broke it
  to pieces and passed harmlessly to the other end of the house where
  the pipe ended at C, broke through a partition there and the window
  D, and passed down the rain-water pipe E to the earth.

[Illustration:

  SECTION.
]

  19_a_. _Wandsworth, 1875._—Chimney of house struck and damaged as
  shown in sketch, lightning then passed along eaves gutter F, and
  down the iron water-pipe G, doing no further injury.

[Illustration:

  PLAN AND ELEVATION. PLAN.
]

  19_b_. _Addiscombe, 1878._—Chimney struck above H, the lightning
  passed down flue, slightly injured the chimney-pieces, and
  apparently passed through the two open doors to the road, as the
  tenant standing at J distinctly felt a shock.

  19_c_. _Forest Hill._—Chimney (K) struck, lightning followed gutters
  shown by dotted line in sketch, part no doubt escaped by pipe L, but
  some passed along gutter to M doing slight injury to brickwork
  there, the window N was broken, and the gilt bead under cornice in
  rooms K and O was blackened.

[Illustration:

  PLAN AND ELEVATION.
]

  19_d_. _University College, London._—A chimney has been struck on
  two occasions, but little damage done; the lightning passed off by
  gutters and rain pipes which enter the drains; the top of the dome,
  which is of stone, has escaped.

  21. _J. Murgatroyd. St. Mary’s, Crumpsall, near Manchester._—A
  lightning conductor from spire touched the eaves gutter, and a gas
  pipe touched the end of this gutter. The lightning passed from the
  conductor along the gutter to the gas pipe, melted it, and set the
  church on fire by igniting the gas.

  22. _T. Oliver._—Never had a building damaged during thirty years
  practice; uses ½ inch copper rope for lightning conductors, in
  contact with any iron work near, and buried 8 feet in ground in
  ashes.

  23. _Wyatt Papworth._—Tall spire struck. The church stands in an
  open position with no large trees near. It was provided with an iron
  lightning conductor ¾ in. diam., fixed with iron holdfasts, and
  carried down inside the spire and tower into ground; the top of it
  was said to be attached to a bold copper finial on the spire about
  150 feet from the ground, and 50 feet above ridge of roof; the
  lightning is supposed to have first struck the finial, it slightly
  deranged some beds of masonry in upper part of spire, then descended
  by iron rod to belfry, melted a gas tube in the floor, and set fire
  to the belfry by igniting the gas.

  23_a_. House in country road. The lightning struck chimney-pot,
  descended flue to fire-grate and there divided, one part passed to
  fire-grate below and damaged the gasalier, another part destroyed a
  box of clothes near grate, then passed out of door into another
  room, struck the grate and passed into room below doing no further
  damage.

  23_b_. Another house situated at the corner of country road with
  high trees near, lightning followed bell wires, stripping paper, &c.

  23_c_. At a third house, chimney pot struck, shaft and eaves gutters
  damaged.

  24. _J. L. Pearson._—Weathercock of a tall spire in an exposed
  situation struck.—There was a wire rope conductor attached to the
  bar carrying the vane and passing down inside the spire and out at
  the belfry window, the bells being connected with it; it was
  attached to the tower by ordinary metal hooks, and was carried 6 or
  8 feet into the ground, and about 10 feet from the base of the
  tower, the strands being spread out. The conductor was bent about
  very awkwardly under copings, and in some places, at right angles,
  the damage was very slight, and was limited to projections of
  mouldings close to a bend in the conductor about 20 feet above
  ground. The conductor itself was uninjured. Some insignificant trees
  100 yards distant.

  26. _E. C. Robins. St. Matthias’s Church, Brixton._—No conductor,
  although the church had previously been struck. I have now put one
  up, leading its lower end into a cistern of water. The portland
  stone terminal cross was shattered, and the stones of the cornice of
  the two topmost stages were displaced.

  28. _H. S. Snell. The Holborn Union Infirmary, Upper Holloway, in
  course of erection._—Conductor not fixed. Apex of tower roof, 160
  feet from ground, having only roof timbers, some lead-work A at
  apex, and vane (gilded iron) fixed. The damage commenced just below
  lead-work on apex, and three out of four hips were much torn and
  shattered, necessitating taking down and rebuilding; the hips were
  each framed in three sections, bolted together with iron bolts, and
  in nearly every case the bolts seem to have specially attracted the
  fluid causing slight charring. One of the dormer windows B was also
  separated from the spire. The fluid appeared eventually to have been
  attracted by the water-pipes, which rise to top story of building,
  and so passed away. It will be noted as peculiar that the iron vane
  was not touched, and that the damage commenced immediately below it.
  [The damage evidently occurred _only_ where the conducting materials
  were absent, the iron vane and the lead would naturally bear no
  trace of injury.—ED.] No trees nearer than 150 feet, and these much
  below the top of tower.

[Illustration: View of Tower of Holborn Union Infirmary, Holloway]

  32. _J. B. M. Withers._ Detached house, near Sheffield, in course of
  construction.—No conductor; the top of a chimney fifty-two feet six
  inches above the ground was struck and deranged but not thrown down.
  The nearest ironwork was an ordinary cast gutter, twenty feet from
  the top of the chimney. No trees within sixty yards of the building.

  34. _G. Wrottesley (Col. R.E.)._ Chimney shaft of a laundry at the
  Barracks at Gravesend.—No conductor. The chimney shaft, forty feet
  high, was entirely destroyed by a heavy charge of electricity as low
  down as the eaves of the building—at this point iron gutters went
  round the building and outside the chimney shaft, and the charge
  passed harmlessly away to the earth by the rain water pipes P. Not a
  brick was left in place above and not one disturbed below the
  gutter; the shaft appeared as if cut off by a knife at this point.
  No trees within 100 or 150 yards. The disruptive force was so great
  that the bricks were scattered over a radius of 200 feet, and the
  slate roof was riddled like a colander by the brickbats.

[Illustration:

  ELEVATION AND PLAN.
]

  36. _E. N. Clifton. Bethnal Green_—A four-roomed house, one of a
  row, with a V shaped roof, was cut in two by lightning; a fissure
  was made in the front and back walls, and also in the middle plaster
  partition. The fluid entered the house between the front windows and
  passed through the partition and back wall, rather to the side of an
  iron pipe at the back which was the only metal near. No trees in the
  neighbourhood.




                              APPENDIX E.

PARTICULARS OF ACCIDENTS BY LIGHTNING COLLECTED IN THE YEARS 1857, 1858
AND 1859 BY MR. SYMONS, AND REPORT UPON THE SAME BY PROF. W. E. AYRTON.


                         _Selected accidents._


                                   I.

About a quarter past ten p.m. on Aug. 14, 1857, an occurrence took place
at the Brick-lane station of the Chartered Gas Company, St. Luke’s,
which caused some alarm. It appears that the lightning struck one of the
iron columns which supported one side of a gasometer, or gas holder,
situate on the right hand side of the yard. Owing to the column having
been thus struck by lightning, the gas, comprising many hundred thousand
feet, became ignited. Fortunately, the services of the firemen were not
required, for, owing to the admirable directions given by Mr. Upward,
the superintendent of the works, and the exertions of the men under him,
the flames were subdued in a comparatively short period. Fortunately no
person was injured, and no damage was done to any of the surrounding
property.


                                  II.

At half-past eleven on Aug. 14, 1857, there was a terrific discharge of
lightning, by which the south-east pinnacle of St. Michael’s Church,
Stamford, was instantaneously struck down. The Church of St. Michael is
a modern structure, erected in 1832. It is situate in the centre of the
town. The south-east pinnacle, which received the electric fluid, was
composed of a mass of masonry, weighing about fifteen hundred weight;
the iron clamps or ties by which the work was bound together served as
partial conductors. At every break in their arrangement a series of
disruptive discharges of the electric fluid took place in lateral
directions, driving out large masses of the stonework, spreading them
over the roof of the nave and churchyard, doing considerable damage to
the roofing and tombstones. The effect of the fluid when it reached the
base of the pinnacle, from not meeting with a ready conducting medium,
was to uplift the whole mass imparting to it at the same time a kind of
circular motion to the southward, the apex of the pinnacle falling in a
line with its original base; and the base having traversed about the
eighth part of the circle, fell into the roof of the tower. Immediately
at the base of the pinnacle there is a three-inch iron spout or tube
erected to convey the water from the tower roof. This iron tube the
electric fluid entered, and, finding through it an unopposed channel,
passed down the tower, and finally into the earth, without doing more
damage. The iron tube or spouting in this instance, and by mere
accident, acted the part of a lightning conductor, and served to protect
the other parts of the tower from most serious injury, if not entire
destruction.


                                  III.

At Walthamstow, at 7.30 a.m., on June 5th, 1858, the flag staff of the
church was shivered, the gutters were torn up, the robing room and
various parts of the exterior injured, and the gas pipes torn open.


                                  IV.

_Effects of lightning on a chimney stalk 240 feet high._—Facts collected
by Alexander Cruickshank, 28th June, 1859:

During the thunder storm at Aberdeen, between 8 and 9 a.m., 26th June,
1859, the lightning struck Messrs. Richard & Co’s chimney, 240 feet
high, at Rubislaw, Bleachfield, one mile west of the city. At the height
of 120 to 140 feet three patches of surface bricks were torn off. By the
aid of a telescope and knowing the size of the bricks and the thickness
of the mortar between them, the two largest patches of denuded bricks
were 7 feet by 3 feet and 4½ feet by 3 feet—the longest measurements are
vertical. These patches were visible to the naked eye at least two miles
off. The parts denuded were 4½ inches thick, or the breadth of a brick
when placed with its largest surface horizontal and its sides external
and internal. Every fourth layer, however, of the bricks have their ends
placed external and internal with respect to the axis of the chimney,
and these bricks are broken across at the depth of 4½ inches, or midway
between their internal and external ends, the latter being at the
surface of the chimney. Thus three-fourths of the bricks of the denuded
patches were torn off through the lime seam parallel to the surface of
the chimney, while a fourth of the number has been broken across in the
same vertical plane. Another portion of the surface bricks, 10 feet
(vertical) by 3 feet, has not been entirely detached from the side of
the chimney but forms a bulging of 1 foot at its greatest projection,
and is visible in profile half a mile off. The lightning on striking the
chimney appeared like a cricket ball, of the brightness of iron at a
white heat. This instantaneously passed into a bluish flame a little
darker than that of common salt when thrown on the fire. A momentary
flicker and a hard crack were perceived. The lightning seems to have
struck the chimney 20 feet above the uttermost denuded patch at a small
abraded spot occupying a few bricks, and reddish when seen from the
ground. The chimney has no lightning conductor and the damage done has
not affected its stability and draught.

_Additional remarks_, by Alexander D. Milne, chemist, of Rubislaw Works.
6th December, 1859.—Half the lower bulging part, where the force of the
electric fluid seems to have become diffused or spent, fell during the
gale of 3rd and 4th December. The 3rd inst. had been frosty, followed by
thaw, rain, and wind from S.W. The part newly exposed is 10 feet in
vertical height and 2 feet across, and the first mortar joint forms also
the plane of separation, the radial bricks being cut right across. The
lower edge of the patch is 100 feet from the ground, and the four
patches extend upwards in an irregular line for 40 feet, not vertically,
but in a spiral of about one-third round the circumference of the
chimney. The abraded spot through which the fluid seems to have
penetrated is 20 feet farther up in the same oblique direction. It seems
to be about 6 inches in diameter, and the part appears as if broken by a
hammer from the outside, instead of being forced out from within, as in
the denuded parts below. We may form a conception of the immense
disruptive force exercised, thus: 105 bricks are torn off, area of each
14⅞ths square inches; total area, 1562 square inches. Force or dead
weight required to tear asunder: 1 square inch of brick has been found
to be 300 lbs. Total disruptive force 468,600 lbs., or 209 tons, and
this on the bricks cut across alone. In addition we have a mortar joint
three times the above area, which at a moderate estimate of one-third
the strength, or 100 lbs. per square inch, gives 209 tons more, or 418
tons in all, the approximate dead weight required to tear off what has
fallen. Allowing for what is damaged but has not fallen, the electric
fluid must have had a momentary disruptive force of 500 tons.


                                   V.

_Gloucester, July 2nd, 1859._—Two clumps of objects were struck, two elm
trees in the Spa walks and Rycroft Chapel—with the adjoining elm. This
shows the lightning to have been forked, as they were both struck at the
same time, and there was a double explosion of thunder; the extremities
of the fork were 1480 feet from each other. The trees in the Spa
standing close to each other were stripped from a great height, of six
or seven inches width of bark, which, with the branches, was strewed to
the distance of several yards. The elm at California had a large bough
struck off; the lightning then ran along another branch, struck the
stone edging of the roof of the chapel, scorching the end of the bough
and chipping great pieces off the stone; it then ran along the metallic
gutter to the end of the roof near the schoolroom, where it descended
the iron spouting to the ground, bursting the spouting at the joints,
where it was a quarter of an inch thick, and in one place knocked a hole
in the wall ten inches deep, as if some superior conductor had attracted
it inside.


                                  VI.

I delayed answering your note until I could give you a correct
description of the damage done to the chimney by examination from the
scaffolding (which we were erecting at the time of its receipt.)

The chimney is a portion of some additions made to my manure works only
last November. It was struck during a fearful thunderstorm on Tuesday
the 19th of July, about three o’clock in the afternoon. The electric
fluid detached about one-third of the topmost stonework, which fell with
great violence through the roof of the buildings below; it then
displaced and passed through the joints of the remainder of the
stonework to the brick shaft. This octagonal brick shaft it split and
shattered in all directions on three of its sides, for a space of about
twenty-five feet, completely detaching portions of the brickwork several
feet in length, both inside and out; after which it split the remainder
of the shaft asunder in a straight line through a further space of about
fifteen feet to the stone base. This stone base it also displaced
(passing through the joinings,) and through seven feet more solid
brickwork, to an open ventilator placed under the roof of a building at
the foot of the chimney.

Through the ventilator a portion of the electric fluid seems to have
escaped from the chimney into the interior of a large warehouse, some of
the main timbers of the roof of which it has split and shattered very
much. A portion only of the fluid seems to have escaped in this way, as
the chimney is split below the ventilator for a further space of about
ten feet.

Several persons were at work in the warehouse at the time, none of whom
were injured in any way (although they felt benumbed.) Two strong horses
standing in a cart were, however, struck down by the lightning on its
escape from the warehouse.

The greater portion of the chimney must come down; in fact, we are now
taking it down.

                                                         JOHN STERRIKER.

Driffield, _August 8th, 1859_.

P.S.—In the construction of the chimney, hoop iron was imbedded in the
body of the brickwork every five or six courses, to bind it together;
and this, I think, prevented the whole of the upper shaft from being
thrown down, although in many places the iron has been completely fused.
The total height of the chimney was 85 feet.


_Extract from Mr. Symons’s report on Thunderstorms in 1857–58 and 1859._

     [Read at the Oxford Meeting of the British Association, 1860.]

_Lightning Conductors._—No building provided with a conductor is
recorded to have been injured during the three years; in a few cases
bars or pipes of metal acted as such, so far as they extended. The first
instance was at Wibsey School, where the charge, which killed one boy
and injured eight others, had passed safely down an iron pendant from
the roof—in fact, an iron rod of, I believe, small diameter.

In the case of a house in Camden Square, the charge which overturned one
end of a stack of chimneys, passed safely down the iron water-pipe at
the back of the house.

The flash which injured Ryecroft Chapel, Gloucester, first struck an
elm-tree close to the chapel and broke off a large bough, it then darted
to the roof, ran along the metallic gutter to the end of the roof, where
it descended the iron spouting to the ground, bursting the spouting at
the joints, where it was a quarter of an inch thick, and in one place
knocked a hole in the wall ten inches deep, as if some superior
conductor had attracted it inside.

I presume few persons will now oppose the results obtained by the
elaborate investigations of Sir W. Snow Harris, either as to the
_utility_ of conductors, or their best form and distribution. These
points being admitted, it remains to ascertain why they are not more
generally used—why, in short, the accidents I have enumerated (with,
perhaps, as many more of which I have not heard) are allowed to
occur—that they are preventible there is no reasonable doubt. I believe
that the reason that conductors are so comparatively seldom used may be
expressed by one word—expense; a remark made by Professor W. Thomson, at
the Aberdeen meeting, was a strong illustration of this point, “If I
urge our manufacturers to put up lightning conductors they say, ‘It is
cheaper to insure than to put up conductors.’”

But as no insurance nor ought else can compensate for loss of life, it
becomes important to consider if any cheap and effectual substitute for
a regular conductor can be found.

One plan for effecting this, as far as private dwellings are concerned,
is that of connecting the lead gutters of the roof with the rain water
pipe, and with a rod projecting a few feet above the chimneys; it is
obvious that both gutters and pipe would derive additional conducting
power from the water which (at such times as the conductor is required)
is usually flowing along them.

I am not sufficiently acquainted with the laws of electric action to
offer an opinion on this plan; as far as my own limited experience goes,
I think it would be decidedly better than the entire neglect which now
so largely prevails, for it would probably induce the shock to pass down
the outside of the house instead of down the chimney inside, which has
hitherto been its most frequent course.

I much wish that those who have turned their attention to electric
action would express a decided opinion on the matter. In one of the
foregoing cases the iron pipe was perfectly competent and effectual in
conveying the charge; and in the other the damage (limited, be it
remembered, to bursting the joints) doubtless arose from the
intervention of the _lead_ between the two lengths of pipe—considering
the somewhat low conducting power of the lead, such a result might
almost have been anticipated.


_Kind of Trees Struck._—In sixteen cases the class of tree struck has
been mentioned; of these one-third were elms. The next in order of this
unenviable distinction are the oak, ash, and poplar; instances also
occurred of the crab, the lime, and the willow being injured by
lightning.

It is satisfactory to find that as far as so short a series is
competent, it corroborates previous opinions on the subject. I may
perhaps be permitted to quote one of the earliest with which I am
acquainted. In the year 1787 Mr. Hugh Maxwell wrote to the American
Academy that he thought he might state from his own experience that the
elm, chestnut, oak, and pine, are _often_; ash _rarely_; and beech,
birch, and maple _never_ struck.

A communication with which I have been favoured by Mr. Ingram, of
Belvoir Castle, bears closely on this subject, and is, I think, worthy
of consideration. He says, “I filed your letter, resolving to keep a
sharp look out in my rides about the neighbourhood for all the
thunder-blasted trees. It is of course difficult to obtain perfectly
accurate information, because trees are taken away after their
destruction; but I have ascertained that within the area of Croxton
Park, twenty per cent. of the trees (oaks) have been struck by
lightning. The park is situated on high ground; the substratum is rock
(limestone), which has more or less iron in it. The oaks, where the soil
is strongly ferruginous, are useless as timber trees; the wood, when
sawn, splits and rives in every direction, possibly from the quantity of
iron.”

                  *       *       *       *       *

  The accounts given in the notes supplied to me by Mr. Symons are of
  great interest, but as the majority of the buildings struck had no
  lightning rods the details of the destructions do not bear
  immediately on the object of our Conference. There are, however,
  some few facts which may probably be of interest.


1.—_Damp air although not a conductor for ordinary electricity (see the
writings of Sir Wm. Thomson) may be a conductor for lightning_:—

For there are many instances of sheep and horses being killed in open
fields. This may have been due to the sheep collecting together in a
flock, and the air above them becoming moist from the perspiration
arising from the flock.


2.—_Certain coincidences of earthquake waves and atmospheric electrical
storms have been observed._—The following may, perhaps, be one:—

June 5th, 1858.—During thunderstorm at Pegwell Bay the water in the Bay,
the tide being then about two hours past flood, suddenly receded about
200 yards, and returned to its former position within the space of about
twenty minutes.


3.—_Open doors allow lightning to pass through._

August 12th, 1858, Bedford.—The lightning passed through five open doors
in its way from a chimney, which was originally struck, to an open
window, by which it went out, all the doors being on the ground floor.


4.—_Difficulty of making lightning conductors to protect buildings._

August 18th, 1858. Neighbourhood of Norwich—A boy riding on a pony
escaped unhurt, while the pony was killed by lightning.

St. Peter’s Church, Brighton.—The tower was provided with a lightning
conductor, but it was only carried up one of the pinnacles, hence one of
the other pinnacles of the tower was struck—the distance between the
pinnacles being scarcely ten feet.

Sometimes trees are struck in the middle, and not at the top.

New Kent Road.—While a man was sawing wood, the lightning entered by the
window, struck the blade of the saw, burnt the handle, but did not
injure the man.


5. _A small body perfectly insulated from the ground is not safe from
lightning._

October 11th, 1858. Kilham, Yorkshire.—Two sea gulls, while flying, were
killed by lightning.


6. _Advantages of lightning conductors._

During 1857, –58, –59 almost the whole of the buildings reported as
damaged by lightning were unprovided with lightning conductors. Among
those struck but not damaged were buildings on which metal bars or pipes
acted as conductors as far as they went, proved by the lightning having
burst the metallic spouting at the joints.


7. _Expense of Conductors._

Sir W. Snow Harris’ rule:—

             Copper solid  0·5 in. in diameter
                     tube  1·5 in. in diameter ¼ in. thick.
             Iron solid   0·75 in. in diameter
                     tube 2·00 in. in diameter ¼ in. thick.

Minimum cost one shilling per foot, not including cost of carriage and
fixing.

                  *       *       *       *       *

Sir William Thomson, at the meeting of the British Association at
Aberdeen, said “If I urge on Glasgow manufacturers to put up lightning
conductors they say it is cheaper to insure than to do so.”

This shows the importance of economy in the construction of conductors,
and consequently of the determination of the least expensive conductor,
which will be safe for any special building. One of the most important
points to determine, it appears to me, is whether an electric current,
when the electro motive force is very high, passes along the surface or
through the body of a conductor, since on the result of this must depend
whether we give a lightning conductor large surface, or large sectional
area—in fact, whether a tube of large diameter, but with comparatively
thin walls, is better than a solid rod of much smaller diameter.

In the May number for this year of the Philosophical Magazine, there
appeared an interesting article, by the late Mr. Brough, “On the proper
Relative Sectional Areas for Copper and Iron Lightning Rods,” in which
Mr. Brough arrived at the result that the sectional area of an iron rod
conductor should be to the sectional area of a copper rod in the ratio
of 8 to 3; from which he concludes that an iron rod will be the cheaper
conductor. But this result is obtained on the assumption that the
resistance of rods of the same length, and of the same material for
lightning, are inversely as their sectional areas, a result about which
I think there may well be doubt.

                                                           W. E. AYRTON.




                              APPENDIX F.

                    ABSTRACTS OF PRINTED DOCUMENTS.


                     FRENCH OFFICIAL PUBLICATIONS.

                          _Preliminary Note._

In 1784, the attention of the French Government having been directed to
the desirability of protecting the powder magazines of the kingdom from
damage by lightning by the employment of conductors, a system of
construction was proposed by two officers of the Engineers and
Artillery. This system was referred by the Minister of War to the
Academy of Sciences for consideration and report. From time to time
subsequently other proposals of a like nature, and other inventions and
improvements in the construction of lightning rods were considered by
the Academy, and reported upon by various Committees.

At the request of the Conference, I have endeavoured, in the following
pages, to give in as condensed a form as possible an accurate abstract
of their contents, and to avoid, in all cases, the expression of any
opinion, either adverse or concurrent, upon the principles or
suggestions contained in them.

                                                           E. E. DYMOND.


REPORT _made to the_ ACADEMY OF SCIENCES, _by_ FRANKLIN, LEROY, COULOMB,
                       DE LA PLACE, _and_ ROCHON.

                          _24th April, 1784._

Certain proposals for erecting lightning rods for protecting the powder
magazines at Marseilles having been submitted to the Academy for their
opinion, a committee, consisting of the above-named, was appointed to
examine and report.

They begin by enunciating the theory which should regulate the erection
of conductors, and they lay down the following rules:—

1. The extent of the building should first be ascertained to decide
whether one or more conductors should be used. Electrical experiments
had not yet made known anything of the extent to which the action of the
point of the conductor reached. But since buildings had been supplied
with conductors many observations had shown that those parts of them
which were more than 45 feet French (48 English) from the point of the
conductor had been struck by lightning.

2. When there are many points or arrows on the building they should be
connected together and also connected with all parts of the roof which
are covered with lead, and also connected with the weathercocks or
ornamental metal points so as to form one metallic system with the
conducting bars.

3. It is not less important that these bars should be thoroughly joined
together; for a solution of continuity in them produces a resistance to
the passage of the electricity according to the extent of their
separation.

4. It is necessary that the bars should communicate thoroughly with
moist earth or, better still, with water.

As to the height of the points they should be at least 12 or 15 feet (13
to 16 feet English), or even more if the building is a large one. It is
certain that the higher they are the wider the extent of their action.
They should be 2 inches (2·2 English) square at the base and greater in
proportion as their height exceeds 15 feet (16 English). If the
conducting bars are 8 or 10 lines (or, say 1 inch) square, it will be
more than enough. No case had occurred in which iron bars of this size
had been in any way damaged or altered by the passage of lightning.

The reporters then proceed to examine the two proposals for protecting
the powder magazines at Marseilles, sent in by M. Ravel de Puy Contal
and M. Pierron. They were both for the same building which was 31 toises
long and 8 toises wide (about 198 by 51 English feet). The first
provided for the erection of three points on the ridge of the roof, and
of four others, one at each angle of the building; the second had also
three points on the ridge, but the other four were alternated on the two
sides of the roof, and iron bars were carried all along and connected
with all the points. The manner in which the terminals were fastened to
the roof and the conducting bars fastened together and led to the water
was the same in each proposal.

The reporters remark concerning the second that the conducting bars laid
horizontally along the roof would involve a great and unnecessary
expense, but the points should be retained, only instead of placing them
alternately they should be set up so that each of them was half way
between the middle and the end of the roof, and instead of connecting
these points by bars along the length of the roof, they should be
connected with the one connecting the three points on the ridge by bars
joining it perpendicularly.

As to the method proposed for joining the several parts together the
reporters cannot help thinking that in their desire to make thoroughly
good connections MM. Pierron and de Ravel had proposed a plan involving
too much difficulty and superfluous expense [It seems to have been
proposed to screw the bars into each other], and they recommend instead
of this to make at the base of each point, immediately above its
insertion into the roof, a circular flange about 2 inches in diameter
and 2 lines thick, with a hole half an inch in diameter in the middle
and at the ends of each conducting bar to make a similar flange and to
bolt the flanges together with a sheet of lead between them. Crutches
should be fixed on the roof to carry the conducting bars. The points
should be fixed three on the ridge and two on each side of the roof half
way between the point in the middle and that at each end. These four
should be connected with the conducting rods running along the ridge and
should overtop the ridge by at least 6 feet (6 feet 5 inches English).
By this arrangement all parts of the roof would be well protected.

The reporters highly approve of the way in which the conducting bars are
connected with water by being led into the sea, but if at the other end
of the building there is sufficient earth on the surface, and the soil
is not entirely rock the conductor from the point placed at that end
might be led into it. It is recommended that the points of copper should
be screwed to the terminals for convenience of removal when necessary.


  REPORT _made to the_ NATIONAL INSTITUTE, _by_ LEROY, LA PLACE, _and_
COULOMB, _on a Lightning Rod for Powder Magazines proposed by_ REGNIER.

              _6 Nivose, Year 8_ (_23rd December, 1789._)

The reporters think it desirable to make some general observations on
lightning rods, the rather that it appears that some persons have had
fears as to the certainty of their effect.

It is impossible to reject the theory upon which Franklin had proceeded
in providing lightning rods for the purpose of protecting buildings from
damage by lightning. Still, as the theory needed to be confirmed by
facts, it might at first have been doubted whether the lightning rods
were really effectual; but now that observation, and experiment had
proved the truth of the theory there was no longer any room to question
their utility. It may even be remarked that observations had not only
proved that they were effective when well constructed, but that they
conducted the lightning down without accidents, even when they had some
defects, which might have caused one to doubt their efficacy. The
defects alluded to were a blunted point and a break in the continuity of
the conductor. With reference to these two cases observations have
shown—1st. That although the points have been blunted, they still
attract the lightning from the clouds to themselves in preference to the
surrounding objects. 2nd. That although the several parts of the
conductor are not thoroughly joined together, the lightning will still,
if the break be not too considerable, pass along the conductor without
accident.

In support of the first proposition they quote the observations of
Doctor Rittenhouse, of Philadelphia, who had examined several of the
points in that city, and had found them melted, showing clearly that
they had been struck by lightning, and probably more than once, as it
had been shown by many observations that where, from local circumstances
(not then fully ascertained,) lightning had struck in certain places or
on certain buildings, it was not uncommon to see it strike again; and a
number of observations of a different sort had shown that lightning was
attracted by metals on buildings even when they were but slightly
pointed, such as tin weathercocks, or iron crosses, and even plain
sheets of iron.

One of the most striking examples in support of the second proposition,
was the case of an American ship, reported in the Phil. Trans. for 1770.
During the night, in the midst of a storm, the crew reported that there
was a stream of fire in the rigging, just above the middle of the
lightning conductor. The captain saw a stream of fire, sometimes in
sparks, and sometimes only a steady light; and on examining the
conductor next morning, found that one of the links of its chain was
broken. Fortunately the two pieces, being kept in place by the fastening
to the shrouds, were only about three quarters of an inch apart. These
two broken ends formed a sort of points, and on its passage between them
the lightning had become visible. But this was all; no shock was felt,
nor anything which caused any suspicion that the fracture of the
conductor had in any way hindered the passage of the lightning. Franklin
also had shown by experiment that in a lightning rod where the upper end
was only connected with the part entering the ground by a very fine
brass wire, although the wire was melted by the passage of the
lightning, it still was conducted from top to bottom without any damage
to the house; and in other instances metallic wires, though partly
melted by the lightning, had still served as conductors. But it is not
contended from these examples that a very exact and continuous
connection of all the different parts should be dispensed with.

The lightning rod proposed by Regnier consisted of a piece of wood,
coated with resin, rising 2 metres (6 feet 7 inches) above the roof, and
having fixed on its top a sort of inverted funnel of copper, at the
upper end of which was fixed the point. To the lower edge of the funnel
were fastened ropes formed of twenty-seven annealed iron wires well
bound together, which were, at a suitable distance, connected with iron
bars, fastened to masts, and leading to moist earth. The point had a
small piece of platinum at its upper end.

[Illustration: Regnier’s System of Lightning Conductors]

The reporters observe that the wooden support may be employed by way of
extra precaution, though there was no known instance of lightning
leaving metal for wood; but it should be strong enough to resist the
wind. They approve of the method proposed for connecting the point with
the metal bars, metallic ropes being very suitable for this purpose, and
keeping them well away from the building was quite right; but they add
that the metallic bars should not only communicate with moist earth, but
also with water in wells or otherwise.


INSTRUCTIONS FOR ERECTING LIGHTNING RODS FOR POWDER MAGAZINES, _adopted
                   by the_ FORTIFICATIONS COMMITTEE.

                          _25th August, 1807._

A lightning rod is an electrical conductor terminating in a point and
carried down to the common receiver. It may be regarded as a metallic
tree, and divided into (1) the upper terminal, (2) the trunk, and (3)
the roots.

1. The upper terminal is a very pointed, conical or pyramidal spike of
metal having a base 3 or 4 centimetres (1½ inches) in radius. The point
is of gold or platinum, soldered to a copper rod 1 or 2 metres long (3
feet 3 inches to 6 feet 7 inches). This rod is joined to the rest of the
upper terminal, which is of iron, either by solder, a screw, or a pin.
It is important that all the parts of the upper terminal should be
joined with care so as to prevent fracture; at the bottom of the
terminal are several feet by which it can be leaded to the vault or
bolted to the framing of the roof. Several devices for giving some play
to the terminal so as to diminish the effect of vibration have been
proposed, but it is better to make the terminal strong enough to resist.
At the bottom of the terminal is joined the piece connecting with the
conductor; this ought to be very complete and continuous, especially at
the point of junction with the terminal. Frequently the terminal is
enlarged at this point to facilitate the passage of the lightning. To
preserve the terminal from rust it is sometimes gilded—it has been
proposed to tin it—more frequently it is merely painted; experience
shows that this is sufficient. Instead of making the whole terminal
conical or pyramidal, a square bar of iron, finished with a point of
copper tipped with gold or platinum, is sometimes used. This plan may
usually be adopted without danger, but they are more liable to be broken
or bent by vibration.

[Illustration:

  FIG: 1.
]

[Illustration:

  FIG: 2.
]

[Illustration:

  FIG: 3.
]

[Illustration:

  FIG: 4.
]

2. The trunk or conductor is made of iron bars 13 to 20 millimetres
square (½ to ¾ inch) notched at the ends and bolted together with a
plate of lead between the two (Fig. 1). For powder magazines a bar of 27
millimetres (1 inch) square is recommended. They follow the outline of
the roof, cornice, and wall, and each bar is fixed by a half collar
(Fig. 2) or cramp placed in the middle of the bar or as far as possible
from the junction of two bars. Instead of the iron bars ropes of copper
or iron wire, or even of hemp, may be used; these last may be used
provisionally, but for permanent conductors they have no advantage
either in economy or conductivity. The copper rope conducts the
lightning better, but its smaller size and cylindrical form, by
diminishing its absolute and relative surface, counterbalances its
superior conductivity. The great and real advantage of metallic, and
especially of copper ropes, is in their continuity and their
flexibility. The conductor is led down to the surface of the ground
where it is bent and led parallel to the surface towards a pit full of
water, or deep enough to allow the end of the conductor to rest in damp
earth; from 2 metres (6 feet 6 inches) above the ground to the pits the
conductor is enclosed in a channel or trough like the fuse of a mine,
the object of this is to protect the conductor from the dampness of the
soil and from contacts. These would be unimportant so long as there is a
perfect connection between the point of the conductor and the common
reservoir, but this continuity may be destroyed by degradation of the
conductor, and it is chiefly at the joints that this discontinuity is to
be feared. When the conductor has to be buried it should be in an oaken
trough, well put together and tarred or charred or surrounded by
powdered charcoal so that the metal cannot be rusted by infiltrations or
humidity; in some soils it is better to make the subterranean part of
the conductor of lead, taking care by increasing the surface to make up
for its inferior conductivity. Sometimes water pipes may be made use of,
but only when they serve to lead water away and when they terminate in
an isolated reservoir. It is important to lead the conductor far away
from water pipes carrying water to public fountains or into the interior
of houses.

3. If the conductor leads to a well full of water the roots (Fig. 3)
need not be more than a few spindles terminated in points and long
enough to be always immersed. When the conductor only leads to a bed of
earth it is supplied with a system of roots (Fig. 4), having for its
object the multiplication of the points for the escape of the lightning,
and these are increased in number according as the soil is a less good
conductor. The pits should be some distance from the foundations of the
building, so that the lightning may not damage them, and it is
important, by all possible means, to increase the natural humidity of
the soil. When the wells cannot be closed it is necessary that the
conductor should be insulated and plunged deeply in the water for fear
that the communication of the electricity to the well-chains or
pump-rods might cause accidents or alarm. After some other instructions
it is added that the dispersal of the electricity in the common
reservoir is, next to the continuity of the conductor, that which most
deserves the attention of the physicist and the engineer.

It has been remarked that a point extended its sphere of activity as far
as 10 metres (32 feet 9 inches), that beyond this distance its effect
became less sensible, and that when the points were too near together
they neutralised one another. So upon a building of a given size it is
necessary to set up so many that all parts shall be covered by their
spheres of attraction, which should meet and not overlap each other.
Lightning in passing from a cloud to the earth does not always take a
vertical direction, it sometimes follows the path of the rain drops,
which is inclined by the wind, so when a magazine is very lofty, or on
an elevated spot it is not useless to fix horizontal or inclined points
on the gables or angles. In some places the magazines are dominated by
other buildings; in these cases the neighbouring buildings should be
protected, or the magazines should have horizontal points towards them.
If the ramparts dominate the magazine it will be prudent to set upon
them a lightning rod on a mast. Trees are only struck by lightning
because their tops serve as points but their trunks are bad conductors,
hence it is prudent not to have plantations, especially of lofty trees
near magazines. However many points may be set up on a magazine they
should all be connected together, and all joined to the principal
conductor, and it would be well to have more than one principal
conductor so that if one loses its continuity the lightning may have a
path by the other. Stone, wood, and gunpowder are bad conductors, and
pieces of metal may without danger be used in the inside of magazines,
provided they are connected with the principal conductor by branch
conductors of suitable size: still it is prudent to keep the metal
outside.

[Illustration: Powder Magazine, with oblique as well as vertical rods]

Reference is then made to “Regnier’s System of Lightning Rods,” Appendix
F., p. 53, which is thought to be much too expensive.


    REPORT _on the foregoing Instructions made by_ LA PLACE, ROCHON,
  CHARLES, MONTGOLFIER, _and_ GAY LUSSAC _to the_ NATIONAL INSTITUTE.

                         _2nd November, 1807._

The reporters say that experience has taught that the point of a
lightning rod 4 or 5 metres (13 to 16⅓ feet) does not effectually
protect a space round it greater than one having a radius of 10 to 12
metres (32¾ to 39¼ feet). That when there are points or considerable
masses of metal on a building having a lightning rod it is absolutely
necessary to connect them by branches with the principal conductor. That
it is not less important that the metallic bars should be thoroughly
well connected together so that the electricity may find no resistance
in its path from the point to the common receiver. And lastly, that it
is necessary that the conductor should have a perfect communication with
moist earth, or better, with water. They then proceed to discuss the
instructions, or that part of them which relates to the construction of
the lightning rods. They recommend the use of gilded copper points,
notwithstanding the doubt concerning them which had been raised in
consequence of their deterioration by oxidation, and their being blunted
by lightning. They say that experience has shown that an iron rod 20
millimetres (·8 inch) square is more than sufficient to carry the most
violent discharge of lightning, and that it is consequently needless to
make them larger, as recommended in the Instructions; that it is only at
the joints that there is any cause for fear because, in spite of the
insertion of the piece of lead, the contact is not perfect; that it
would be easy by enlarging the bars at their junctions to increase the
number of points of contact, and by lengthening the bars to make fewer
joints. That in this respect the use of iron wire ropes would be very
advantageous, but they fear that the ropes would be easily destroyed,
and that the use of copper wire rope instead of iron would be too
expensive.

When the conductor reaches the ground too much care cannot be exercised
in making a free communication between it and the soil. It is upon this
that its good effect principally depends, for houses have been struck
although provided with a conductor, because it only communicated with a
very dry soil. M. Patterson, of Philadelphia, in the fourth volume of
the American Phil. Trans., has published a means of making a good
contact which seems useful. He proposes to lay the conductor in a bed of
galena worked into a paste with melted sulphur. The galena is a good
conductor, and would have the advantage of protecting the iron from the
damp. He has also proposed a simple means of providing for the easy
dispersion of the electric fluid in cases where the soil is not very
damp, which consists in making a hole in the ground and filling it with
charcoal, into which the conductor is plunged. But M. Guyton used the
conducting power of charcoal for this purpose more than thirty years
ago, and it has been applied in many ways. Charcoal, like galena, is a
good conductor, and this property renders its employment desirable in
cases where the soil is dry.

Upon the proposal to fix inclined or horizontal points they think that
vertical points will suffice; and with reference to the Regnier system,
they remark that it would certainly be very expensive, and that it would
not be necessary to adopt it until the usual system had been found
insufficient.


    INSTRUCTIONS _about_ LIGHTNING RODS _adopted by the_ ACADEMY OF
                               SCIENCES.

                    _First Part, 23rd April, 1823._

   PREPARED BY A COMMITTEE CONSISTING OF MM. POISSON, LEFEVRE-GINEAU,
                GIRARD, DULONG, FRESNEL, AND GAY LUSSAC.

[Illustration: Mode of attaching Conductor to Upper Terminal]

After some theoretical remarks the Committee describe the conductor they
recommend, giving the name of _tige_ (upper terminal) to the part rising
into the air above the roof, and that of conductor to that part
extending from the upper terminal to the ground. The upper terminal is a
square or round bar of iron tapering from base to summit. If from 7 to 9
metres (23 feet to 29 feet 6 inches) high, which is the smallest height
to be used on large buildings, it should be 54 to 60 millimetres (2·1 to
2·3 inches) square or diameter at the base, if 10 metres (32 feet 9
inches) high, it should be 63 millimetres (2·5 inches). About fifty-five
centimetres (1 foot 9½ inches) of the upper end is cut off and replaced
by a point of copper either gilded at the end or tipped with a little
piece of platinum. At the lower end of the terminal (A), 8 centimetres
(3·15 inches) above the roof, is fixed a base (B) to throw off the rain
which would run down the terminal, and above this base the terminal is
clasped by a collar (C), as shown in the drawing, to which is bolted the
conductor (D). The engraving shows the modification of the arrangement
as adapted to both round and square terminals. The conductor is a bar of
iron 15 to 20 millimetres (·59 to ·79 inches) square, joined firmly to
the upper terminal by bolting it tightly between the two ears of the
collar. The best way of joining the bars together is shown in figure 1,
p. 55. It is to be held up at a distance of 12 to 15 centimetres (4·7 to
5·9 inches) from the roof by crutches, and to be kept at a like distance
from the walls of the building. At 50 or 55 centimetres (19·6 to 21·6
inches) below the surface it is turned away perpendicularly from the
wall for a distance of 4 or 5 metres (13 feet 1 inch to 16 feet 5
inches) if it does not sooner meet with water. To avoid rusting the rod
is carried in a trench filled with charcoal, and then turned down a well
so as to have at least 65 centimetres (25·7 inches) in the water when at
its lowest level, where it terminates in three or four branches to
facilitate the exit of the electricity from the conductor.

If there is no well convenient, a pit should be made 13 to 16
centimetres (5·1 to 6·3 inches) in diameter, and 3 to 5 metres (9 feet
10 inches to 16 feet 4 inches) deep, down the middle of which the
conductor should be led and the hole filled with charcoal tightly
rammed. As the iron bars forming the conductor are not easily bent to
follow the lines of the building a metallic rope may be used. It is made
of four strands, each composed of 15 iron wires, and forming a rope of
16 or 18 millimetres (·62 to ·7 inches) in diameter. Each strand is
tarred separately, and the whole also well tarred when put together. It
is attached to the upper terminal in the same way as the bars by
pinching between the ears of the collar (c). At 2 metres (6 feet 7
inches) above the ground it is joined to the bars which form the earth
connection by being pinned into a socket formed at the end of the first
bar. Ropes of copper or brass wire may be used, and they need not be
more than 16 millimetres (·62 inches) in diameter.

It is necessary to connect any considerable metallic masses (lead roofs,
metal gutters, or tie rods) with the conductor, because if this be not
done, and the conductor be broken, or have a bad earth connection, the
lightning may leave the conductor for the metallic mass.

Modifications of this form of conductor for use on churches, ships, and
powder magazines (for the latter carrying the conductors on masts is
recommended) are then described.

The report says that the terminal of a conductor protects efficiently a
circular space round its base, having a radius equal to twice its
height; but that it is prudent to estimate that a conductor on a church
spire only protects a circle having a radius equal to the height of the
conductor.

The conductor should go the shortest way to earth. It should be on the
side most exposed to the weather, especially on spires.


                  _Second Part, 18th December, 1854._
 PREPARED BY A COMMITTEE CONSISTING OF MM. BECQUEREL, BABINET, DUHAMEL,
               DESPRETZ, CAGNARD DE LATOUR, AND POUILLET.

Notwithstanding the considerable advance in knowledge since 1823, the
instructions of that date have no need to be altered, at least in their
essential principles; but the methods of construction of buildings
having materially altered, and metal having largely replaced wood and
stone, buildings had, so to speak, become metallic masses, which would
have incomparably greater attraction for thunder clouds. The Palais
d’industrie in the Champs Elysees, for example, nearly 3 hectares (7·4
acres) in extent, and 40 metres (131 feet) in height had everywhere
enormous masses of iron, brass, and zinc.

The company undertaking the building had sought the advice of the
Academy as to the means to be employed to protect it from lightning, and
it had been found necessary to revise the instructions of 1823, in order
to introduce such modifications as were necessary.

Quoting the passage referring to the connecting of metallic masses with
the conductor, the Committee think that the time had come to enter into
fuller details on this point.

Formerly the use of metal was almost restricted to ridges, gutters, and
tie rods; now metal was used everywhere, and what is important, in large
surfaces and great masses; and this new system realised on a large scale
the first objection to lightning rods—it attracts the lightning.

When this objection was applied to lightning rods, it had only the
appearance of truth, but when applied to the masses of metal then used
in buildings, it was not only specious, but true, and founded upon well
established laws; these buildings do attract the lightning, and render
its effects more disastrous.

In the case of two buildings alike in size and shape, situated on the
same soil, one made of wood and stone as formerly, the other with much
metal as now, and both without lightning rods—if the conditions are such
that the lightning must discharge itself, it will always strike the
latter, and never the former; in the same way as on bringing to the
conductor of an electrical machine a ball of wood or stone, and one of
metal, it is always the latter which will receive the spark. Lightning
rods, therefore, are so much the more indispensable as the buildings
contain greater surfaces and greater masses of metal.

The nature of the soil must be taken into account, as well as the
buildings and other objects upon it. A dry soil, with a subsoil of dry
sand, chalk, or granite, does not attract the lightning, because it is a
bad conductor. Unless when accidentally wetted the buildings on it
participate to some extent in this immunity, at least if they are not
built in the modern style, and are not very large. But if there are at a
moderate depth underneath this dry ground, large metallic veins, vast
caverns, sheets of water, or only abundant springs—these will attract
the lightning, which will destroy everything in its path unless
protected. If the wet or metallic strata are very deep, the danger of an
explosion is diminished by the difficulty of passing the intervening
envelope, and by the weakening of the action of the cloud by the
increase of distance.

On the 19th April, 1827, the packet boat _New York_ was twice struck by
lightning. On the first occasion, having no conductor, it received
considerable damage; on the second, the conductor was fixed; it was made
of a pointed bar of iron, 1·2 metre (about 4 feet) long, and 11
millimetres (·43 inch) diameter at the base, and a surveyor’s chain
about 40 metres (131 feet) long, forming a connection between the foot
of the rod and the sea; the chain was made of iron wire 6 millimetres
(·24 inch) in diameter; the links were 45 centimetres (17·7 inches)
long, ending in loops, and joined together by two round rings. When
struck the chain was dispersed in burning fragments and globules, which
set the deck on fire in many places, notwithstanding the hail upon it
and the rain which fell heavily; the bar at the top was melted for a
length of 30 centimetres (11·8 inches) from the point, and down to a
diameter of 6 millimetres (·2 inches). The rest of the rod remained with
about 8 centimetres (3·1 inches) of the chain attached to it, the
longest piece of chain found was less than 1 metre (3 feet 3 inches)
long, and was blistered as by fire.

On the 13th June, 1854, the _Jupiter_ was struck by lightning. The
conductors were in place; that of the mainmast which was struck went 2
metres (6 feet 6 inches) into the sea, and had at its end a ball 2 kilos
in weight. After being struck the conductor had disappeared and the
pieces of it were scattered everywhere. The conductor, about 70 metres
(230 feet) long, was a cable of three strands formed of sixty brass
wires, each one half or two-thirds of a millimetre (·019 or ·026 inches)
thick. The cable was mostly in bits no bigger than pins, but there were
some pieces a few decimetres long, these had been turned violet colour
as by fire, and those first touched were still burning hot.

These two examples show that a conductor may be destroyed, but they also
show that it is not useless even then, since it will have received the
discharge and directed it, and so prevented greater mischief. The
_Jupiter_ received no damage; whilst not far off, a Turkish vessel,
which also had a conductor (but the chain of which did not reach the
water) having been struck by lightning in the same storm, had a hole
more than 30 centimetres (11·8 inches) deep, and almost such as would
have been made by a cannon ball, in her side just above the copper, and
near the water line.

The question is, are such accidents to conductors inevitable, or are
they the result of faulty construction? All the facts established in the
accounts of lightning and its phenomena, leave no doubt on this point.
All the lightning rods which have been destroyed were of bad materials,
insufficient, badly constructed, not in accordance with the principles
which theory has deduced from experience.

The conductor of the _New York_ had several faults; its upper terminal
was too small, and too much drawn out; its conductor had much too small
a sectional area; and the use of a chain in such cases should be
strictly excluded.

There is no example known in which lightning has been able to melt iron
rods 2 centimetres (·78 inch) in diameter, or 3 square centimetres (1·18
inch) in section; and copper may be used in still smaller sizes.

The conductor of the _Jupiter_, although better than the former, had
also a radical defect. The fragments of the conductor which were
examined bore but few traces of fusion, and none of these traces
extended to the entire thickness of the cable; they were also limited to
a group of some of the sixty wires of which it was composed. This seemed
to show that the discharge was not carried equally by all the wires, and
that those wires which it followed being insufficient to carry it, were
the ones melted, and the others were broken or volatilised with
explosion. Hence the breaking of the cable and dispersion of fragments
of some decimetres in length, which, though too hot to be touched, were
not hot enough to set wood on fire. This explanation, however, raises a
singular question, whether, in a cable of similar wires twisted and
bound together, the lightning can choose some wires in preference to the
rest, even when the whole of them are hardly sufficient to give it a
free passage.

Undoubtedly, yes; at any rate under certain conditions. No doubt if at
both ends of the cable, for the length of a decimetre, the wires first
tinned separately are afterwards soldered together, so as to make a sort
of metallic cylinder, electricity, whether natural or artificial, having
to pass along the cable, will not show a preference for one wire over
another; but where this is not done—if at the two ends, or, more
generally, at the two points of junction with other conductors, the
wires are isolated by layers of dust or oxide—if, in addition, the cable
only touches the terminals by its outside wires, then things happen very
differently. The electricity takes those wires that are in contact with
the terminal; these reduced to few in number become incapable of
carrying it; and the whole cable broken by the explosion exhibits the
phenomena shown in the case of the _Jupiter_.

The deficiency in each case was due to one cause—insufficiency of
sectional area. In the first case the insufficiency is apparent, the
iron wires 6 millimetres (·24 inch) thick were nine or ten times too
small; in the second, the insufficiency is more hidden, it results from
badly made junctions.

The two most fundamental rules for the construction of the rod and
conductors are—1st. That they shall have a sufficient sectional area.
2nd. That they shall be continuous and without a break from the point of
the upper terminal to the common receiver (the earth). But this
continuity may in strictness be interpreted in two ways: it may be said
that two pieces of metal in contact form a sufficiently continuous
connection; and it may be said, on the other hand, that most frequently
this simple contact is no more than a break in consequence of oxidation
and the interposition of foreign bodies.

The instruction of 1823, without adopting the first interpretation, does
not appear to have sufficiently recommended the second, which should
exclusively regulate all construction of lightning rods. No doubt it is
possible, by taking great care, to join and bolt together two pieces of
iron or copper closely enough to make a practically continuous
conductor, but when there are many joints we fear that evil might arise
from the negligence of workmen, and still more from the chemical
alteration of the surfaces, the deposition of foreign matter, and the
mechanical dislocation produced by time and repeated shocks.

Hence, the three following practical rules should always be observed:—1.
To reduce as much as possible the number of the joints. 2. To make all
the joints with hard solder, and they should be upon surfaces of at
least 10 centimetres (3·9 inches) square, and further strengthened by
straps and bolts. 3. Not to make the upper terminal so gradually pointed
as usual. The upper terminal of iron should be not less than 2
centimetres (·78 inch) diameter, the end should be filed down and a
screw tapped 1 centimetre (·39 inch) high and 1 centimetre diameter, and
to this a cone of platinum 2 centimetres diameter and 4 centimetres (1·5
inch) high, and consequently having an angle at the point of 28° or 30°
should be fitted, screwed, and carefully soldered.

In other respects the instructions of 1823 should be followed; no fact
which leads to a modification of the general rules there proposed 1, for
the sectional area of the conductors; 2, for the method of fastening to
buildings; 3, for the method of making the earth connection, has since
come to light.

The subject, however, is not exhausted, there still remains the
important and difficult question: what is the circle of protection
afforded by a well constructed lightning rod? The opinion generally
received at the end of the last century was that the circle of
protection had a radius of twice the height of the terminal, and the
instruction of 1823 adopted this opinion, but with some restrictions as
in the case of spires. It is important to remember that these rules rest
upon a more or less arbitrary basis, and this is said not to condemn
them, but only to prevent there being attached to them a value which
they do not possess.

More observations are required, and it is only with reserve that these
rules are admitted. They are neither general nor absolute, they depend
upon a variety of circumstances, and especially on the materials of the
buildings. For example, the radius of the circle of protection, which
would be sufficient for a building having only wood tiles or slate on
its upper portion, would not be sufficient for a building in which the
covering or the framing of the roof was of metal. In the former case the
active portion of the thunder cloud, although further from the lightning
rod than from the roof, would exert a greater action on the rod, whilst
in the latter the action on the rod and on the roof would be almost
equal at an equal distance.

A special note upon ships, and another on the Palais de l’Exposition
close the report.


 SPECIAL REPORT FOR THE NEW BUILDINGS OF THE LOUVRE, 18 DECEMBER, 1854,
                         BY THE SAME COMMITTEE.

Referring to the subject of the earth connection the Committee say; in
the earliest instructions, it is said that the conductors should
communicate with the water in a river, a pond, or wells, or at least
with moist earth. This rule, although quite correct in itself,
frequently leads to erroneous practice. It is sometimes thought that
lightning is extinguished by water, as fire is; and when water is scarce
the conductors are plunged into a well-cemented cistern. This is a most
dangerous mistake; the conductor should be in connection with the common
receiver, that is, the great water-bearing strata (nappes d’eau,) of
much greater extent than the thunder cloud. At other times where wells
are possible but costly, advantage is taken of the alternative allowed
by the instructions. Instead of wells the conductors are put in
connection with the earth, without being careful to see that it
preserves sufficient moisture in times of drought when storms are most
to be expected, and without being careful to see that the moist
connection is sufficiently large. They specially note this latter error,
as it appears to be still more common than the former. They do not
hesitate to say that recourse should never be had to this method of
connection with the common receiver. They recommend that in default of
rivers or very large ponds, the conductor should always be connected by
large surfaces with the inexhaustible subterranean water-bearing strata.

Secondly, where these strata are at a moderate depth below the surface,
the Committee consider it necessary to make use of a conductor with two
branches, the principal to descend to the subterranean water; the
secondary, leaving it at the ground level, is put in connection with the
surface. And for this reason; after great droughts thunder clouds exert
but a feeble influence upon a dry, badly conducting soil. All their
energy is felt by the subterranean waters; and the electricity will be
carried by the principal branch. On the other hand, after a summer
shower, when the surface soil gets moist, it is at once made a good
conductor. It is that which is affected by the thunder cloud: while, at
the same time, it screens the subterranean water from electrical
influence. In such a case it is indispensable that the surface of the
ground should be in direct connection with the conductor; and this the
secondary branch supplies.

There is a final question how the conductors should be connected with
the various metallic portions of the building. The ridges are throughout
of iron; but the interior arrangements require that, in some portions of
the building, there should be, properly speaking, only one floor, whilst
in other parts there are six. Each floor may be regarded as a great
metallic network, composed of several strong plate girders, crossed by
numerous joists analagous to rails, while these are, in their turn,
crossed by a multitude of smaller iron rods; and the meshes of this
network are filled with tiles. In enquiring into the effect of a thunder
storm upon those portions where there are six such floors one above the
other, it is easy to see that if the roof were a great continuous sheet
of metal, it would take up the whole electrical energy of the cloud, at
any rate, as far as the floors underneath it are concerned. In this case
it would be amply sufficient if the covering were well connected with
the lightning rods. But in this case the roof is metallic, only in a
very small portion; it may be said that the ridges only form a network
with very large meshes, and, consequently, is an insufficient shield,
through which the upper floor may still receive a considerable shock.
Therefore the Committee propose the following arrangements:—1st. The
principal pieces of each floor should be put in connection with the
conductor. 2nd. It is very desirable that all the joists of the upper
floors should be connected together by a rod bolted, and, if possible,
soldered to each, which rod should be connected with the conductors.
3rd. It seems probable that, in general, the roof frames are in good
connection with each other, and, consequently, it would suffice if all
the upper terminals are connected with them. If, however, it happens
either by changes of level in the gutters, or from other causes that the
connections become doubtful special iron connections must be made. 4th.
The zinc gutters and ridges should be connected with the lightning rods.


 REPORT _on the points of upper terminals made by Messrs. Delieul, by a
  Committee consisting of_ MM. BECQUEREL, BABINET, DUHAMEL, DESPRETZ,
      CAGNIARD DE LATOUR, REGNAULT, DE SENARMONT, _and_ POUILLET.

                           _5th March, 1855._

The committee examined the points presented by Messrs. Delieul, one of
platinum, made exactly as described in the report of the previous 18th
December; the other, a cone similar in form, size, and external
appearance, but rather less costly, being made of a cap of platinum,
fixed with hard solder upon the conical end of the iron rod. It was
thought that this second arrangement would not practically be inferior
to the other; but it must be made by a skilful workman, who knows how to
insure that the solder should take to the whole of the surfaces brought
together. They see no objection to the substitution of palladium, or
gold or silver of a standard of ·950 for the platinum. But all these
metals are costly; few workmen know how to work in them, or at least to
employ that precision, and take that minute care, which are
indispensable to success. These reasons have raised again a proposition
that was discussed in the former commission, which consists in making
the points of copper. The copper point is 2 centimetres (·78 inch) in
diameter, like the upper part of the iron rod, to which it is screwed
and brazed; its length is about 20 centimetres (7·87 inches), and it
terminates in a cone 3 or 4 centimetres (1·1 or 1·5 inches) high.

They see no reason why this should not be used with almost the same
confidence as the preceding forms. If there is ground to fear that it
may undergo changes from atmospheric influences, this is counterbalanced
by certain advantages. 1st, copper is with palladium, gold, and silver,
among the best conductors of heat and electricity; and the point of the
cone will be much less heated than the platinum point; and 2nd, the
terminal, with a copper point, is much less expensive, and can be made
everywhere.

On the report being put to the vote M. Despretz could not approve the
proposal to employ copper points, fearing that the deposition of
carbonate or some other badly conducting matter would diminish the
efficacy of the lightning rod.


    INSTRUCTIONS _upon_ LIGHTNING RODS _for_ POWDER MAGAZINES, _by a
 Committee consisting of_ MM. BECQUEREL, BABINET, DUHAMEL, FIZEAU, EDM
      BECQUEREL, REGNAULT, _le Maréchal_ VAILLANT, _and_ POUILLET.

                         _14th January, 1867._

After referring to some general principles, and to the construction of
lightning rods recommended in the reports of the earlier Committees: the
Committee recommend, that the upper terminal including the copper point
should be from 3 to 5 metres (9 feet 10 inches to 16 feet 5 inches)
high; that the junction of the conductor and the upper terminal, and
also the several joints of the conductor, should be covered with solder,
and insist very strongly upon the necessity of communication with the
_nappe d’eau souterraine_, which they define as “the water level in
neighbouring wells which never dry up, and which retain at least 50
centimetres (19·68 inches) in depth of water in the most unfavourable
seasons.”

The special arrangements to be adopted in setting up lightning rods for
powder magazines are: not to fix them on the building itself but outside
the surrounding walls. For each large sized magazine (27·89 metres, by
20 metres, and 11 metres high, equal to 91 feet 6 inches by 65 feet 7
inches, and 36 feet high) there should be three conductors—two near the
ends of the long side of the enclosing wall most exposed to storms, and
the third in the middle of the opposite side. The upper terminals should
be only 5 metres (16 feet 5 inches) high, and should be raised on a
pier, a mast, or other support 15 metres (49 feet 2 inches) high, down
which the conductor should be led to the ground. There should be a
circuit which the Committee call _circuit de ceinture_ carried entirely
round the enclosing wall to which each conductor should be joined, and a
conductor should be carried from the most convenient point of this
circuit to the underground water. For middle sized magazines two
terminals and supports, and for small magazines one terminal and support
will suffice; but in all cases there should be a _circuit de ceinture_.
This need not be deep below the surface, nor covered over; it may even
be in an open gutter, but a conductor must be led from it to the
underground water, even if in order to do this it is necessary to carry
the conductor several hundred metres or several kilometres. It need not,
however, be made of bars and carried all the way in a trench, but it may
be made of six wires 6 or 7 millimetres (about ·25 inches) in diameter,
and carried on posts like telegraph wires, except that they need not be
insulated.


  INSTRUCTIONS _by the Committee consisting of_ MM. ALPHAND, BELGRAND,
     FIZEAU, _Comte du_ MONCEL, ED. BECQUEREL, DESAINS, CH. SAINTE
   CLAIRE-DEVILLE, DUC, BALLU, MAGNE, DAVIOUD, FELIX LUCAS, _and_ R.
 FRANCISQUE MICHEL, _appointed to inspect the_ LIGHTNING RODS _on the_
                    MUNICIPAL BUILDINGS _of_ PARIS.

                           _20th May, 1875._

The Committee find that platinum tips are useless, and recommend instead
that the point of the terminal should be made of pure copper, 50
centimetres (19·7 inches) long, and terminating in a cone, forming an
angle of 30°. This should be scarfed, pinned, and soldered to the end of
the terminal. The terminal should be of wrought iron in one length, and
where possible galvanized; but on no account painted. The connection
with the conductor should be by a piece fitted and bolted; and, lastly,
the whole joint should be well covered with solder.

The Committee consider that on an ordinary building a terminal will
effectively protect a cone, having the point for its apex, and a base
whose radius is 1·75 of its height. But in practice the terminals may be
much farther apart, if there is a _circuit des faites_. This is defined
as a metallic conductor, which extends without break over the ridges of
all the buildings which it is intended to protect, and which is joined
by metallic contact to all the upper terminals and to the conductor, and
consequently to the underground water which alone forms the common
reservoir. All pieces of metal of any considerable size should be
connected with the conductor.

If the conductor is made of iron bars, they should be galvanized if
possible, and the joints should be fitted, bolted, and finally covered
with solder. If the bars cannot be galvanized, they should be well
painted. The Committee recommend the employment, especially in the
_circuit des faites_, of an arrangement for compensating for the
lengthening and shortening of the bars by the variations of temperature.
This is made by inserting in the circuit a curved band of copper which
will yield to the movement of the rods. If the conductor is made of
galvanized iron wire rope, each wire should be 2·5 or 3 millimetres (·09
to ·11 inch) in diameter, and there should be such a number of them that
the sum of their sectional areas shall be equal to one-fifth more than
that of a bar of iron 20 millimetres (·78 inch) square. The rope should
be all in one piece, and the joints with the terminal and earth
connection should be covered with solder.

The supports should not be insulated, and there should be as few as
possible of them. At the underground end of the conductor should be
fixed a large sheet or hollow cylinder of metal, and this should be
always, even in the greatest droughts, plunged at least 1 metre (3 feet
3 inches) into the subterranean water. If from any cause this water
cannot be reached, the conductor may be joined to one of the main
water-pipes of the city; but if the conductor cannot be led either to
the subterranean water or to a main water-pipe, no lightning-rod should
be erected. It would do more harm than good.

In the case of buildings of any importance, two or more conductors
leading to the subterranean water should be employed. It should be so
arranged that the underground part and the earth connection may be
easily inspected and cleaned from rust, and the whole should be
inspected and cleaned at least once a year, at the end of the autumn.
The Committee is of opinion that it would be better to put all the
lightning-rod work in the hands of special workmen, under the control of
an agent appointed by the administration, and not to trust it to the
blacksmiths and locksmiths usually employed. The Committee lastly
recommend that they should be permanently appointed, and meet every year
after the inspection, to report and decide upon the steps to be taken to
remedy any defects that may be discovered.


 REPORT _by the joint Secretary_ (FRANCISQUE MICHEL) _of the Lightning
     Rod Committee to the Prefect of the Department of the Seine_.

This report gives a detailed description of the state of the lightning
rods attached to the public buildings of Paris.

In most cases the upper terminals were of great length, some of them as
much as 9 metres (nearly 30 feet) in height; the conductors were in
almost all cases of iron, either in bars or wire rope; the earth
connections were of various kinds and extent.

The report frequently states that the points were blunted; that the
upper terminals and the conducting rods were deeply rusted; that
especially at the joints the conductors were seriously deficient; and
that the underground portion was greatly deteriorated by rust.

A description is given of an accident from lightning to the church of
St. Sulpice; but this building had no lightning rod. In the case of the
church of St. Clotilde there are five upper terminals, two on the two
spires, the remaining three along the ridge of the main roof. The
building was amply protected as far as its length was concerned, but the
transept was not so thoroughly protected. The five terminals were joined
to a conductor which went round the building, and was connected with the
ground. A second conductor led from one of the terminals to the ground,
where it terminated in a second pit. The conductors were made of iron
rods 18 millimetres (·71 inch) in diameter, joined by collars and pinned
and the whole covered with paint. They terminated in distributors
plunged in the underground water in walled pits. They were supported by
insulated collars. The building has an iron roof. The church had been
struck by lightning at least four times since the lightning rods had
been erected. The first time, twelve years ago, the lightning struck the
rod placed on the transept, and carried away the platinum tip of the
copper point. Since then the rod has received another discharge, and the
copper point is bent to the S.W. In January, 1872 or 1873, the lightning
struck the western tower, and shattered one of the stones above one of
the windows of the staircase.

“One of the platinum tips is gone, and many are blunted. The
conductivity of the conductor is very bad, and the joints are very much
damaged: hence the accident to the tower. The greater number of the
glass insulators are broken, or gone altogether.”

In the case of the church of St. Eloi, which had one terminal on the
spire, one conductor, formed of iron wire rope 2 centimetres (·78 inch)
in diameter, joined at 3 metres (9 feet 10 inches) above the ground to
an iron rod 25 millimetres (·97 inch) in diameter, which entered the
ground and ended without branches in a pit filled with charcoal. The
soil was dry and calcareous. The conductor was made up of many lengths
of rope, old pieces apparently having been used; the joints were in bad
condition, and needed soldering. The underground part was deeply rusted.

“In September, 1874, lightning struck the spire, twisted the conductor,
broke the terminal, threw down the part above the cross, and made great
cracks in the apse.”

During the building of the Mairie of the 20th Arrondissement, the
lightning struck a fir-pole in the scaffolding. It did not do any
damage, being carried away by the chain attached to the pole, from which
it took all the rust, and being thence conducted by some pieces of iron
roof framing lying on the ground.

There are several other accounts of accidents, but they are mostly
represented by the foregoing examples.


   INSTRUCTIONS _as to the application of_ LIGHTNING CONDUCTORS _for
                 protection of_ POWDER MAGAZINES, ETC.

            Issued with Army Circulars, dated May 1st, 1875.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

1. The principles adopted by Sir W. S. Harris, as shown in the
Appendices A and B, to this paper, still held to be sound.

2. The terminating plane of action of lightning is sometimes beneath the
surface of earth, which, if moist, forms good medium for diffusion of
electricity.

3. Dry soil is to be regarded as non-conducting matter.

4. Therefore conductor to be taken into soil permanently damp.

5–6. Underground magazines are usually in dry soil, and should

therefore be fitted with conductors as in the case of similar magazines
above ground.

8–9. Casemated batteries of modern construction, with magazines in
basement should have conductors on the parapet or terreplein from end to
end of battery, attached to vertical conductor into earth. Flagstaff
should have conductor. In large works there should be several points 5
feet above top of building. Iron verandahs and railings are good
conductors when with good earth connections.

10. Iron buildings are good conductors. But if covered with asphalte,
concrete, &c., rods or points must be provided projecting above
asphalte, &c., and with good earth connections. Iron shields should be
connected with conductors.

11. Copper is recommended as best conductor; it is not liable to
corrosion, and very durable.

12. But if exposed to injury, or likely to be stolen or corroded, copper
may be replaced by iron, provision being made for its smaller
conductivity—viz., ⅕th that of copper.

13. Copper rods to be ½ inch diameter; copper tubes to be ⅝ × ⅛ inch
thick; copper bands to be 1½ × ⅛ inch thick.

14. If the conductor be of iron, solid rods to be 1 inch diameter; solid
bands to be 2 inches wide × ⅜ inch.

15–16. The fusing temperature of copper is 1994° Faht.; whereas that of
iron is 2786° Faht. So far there is a marked advantage over copper. But
it rusts easily, and then the electrical resistance is immensely
increased. Roughly speaking, an equal conducting power may be obtained
either in iron or copper for the same cost, the number of iron
conductors being greater in proportion to the less cost, and the more
conductors being the better.

17–19. Expansion and contraction are to be carefully provided against;
_e.g._ by suitable bends at intervals in long lines of horizontal
conductors and by bearing collars, allowing of slip in vertical lines.

20. Soldered or welded joints are desirable, but not absolutely
necessary.

21. Gives engravings of connections recommended by Sir W. S. Harris,
where soldered joints cannot be used, and which fulfil the conditions
specified in sections 17–19.

22. Soldered or welded joints to be used where discharge is possible
with unsoldered joints, and likely to ignite dust or inflammable
substances near.

23. Iron may be connected by similar joints as for copper, or by screw
joints as for gas pipes. No white lead to be used, it being a bad
conductor.

24. Iron flat bands may be connected by rivets or screws, working in
slots, to provide for expansion, each surface in contact being at least
six times the sectional area of band.

25. Copper bands to be similarly connected. Joints between different
metals may be soldered, screwed, or rivetted, the extent of surface in
contact being regulated by the dimensions of the metal of the least
conducting power. Access of moisture to surfaces in contact must be
prevented, on account of local galvanic action and decomposition.

26. No precise limit can be fixed to protecting power of conductors. In
England the limit is usually assumed as being the radius of the height
from ground. It may be sufficiently correct for practical purposes, but
cannot always be relied upon.

27. Conductors do not attract lightning; they only diminish the
resistance due to the air. Even a change in the nature of the soil -over
which a cloud passes may produce a discharge.

28. One angle of a building may receive a discharge, though another
angle have a conductor. So every prominent part of a building containing
explosive material should have a conductor.

29. In buildings of uniform height, provide a solid rod 5 feet above it
at each end, and at each 45 feet in length; if the conductor be of iron
the top should be gilt.

30. Buildings not over 20 feet long to have one vertical conductor at
end, and a horizontal conductor on ridge.

31. If 20 to 40 feet long to have one vertical conductor in centre, and
one along ridge, as last.

32. If 40 feet long to have two vertical conductors; if 100 feet long
three conductors; in both cases with conductor along ridge.

33. Similar principles to be adopted in larger and more complicated
buildings.

34. Each prominent part should have a conductor. The value of three or
four points to terminals is not apparent unless the points are widely
separated.

35. Conductors are to be connected horizontally, _e.g._, by ridge or
eaves, which, when of metal, should be invariably connected with
conductor. All metal surfaces whatever to be also so connected.

36. Sir W. S. Harris considers the relative conductivity of the several
metals as being—of lead 1, tin 2, iron 2½, zinc 4, copper 12. So lead
cannot be altogether depended on.

37. Avoid long lengths of horizontal conductors without earth contacts,
as the currents might leave the conductor, and pass to earth, causing
danger. Avoid sharp angles.

38. Good earth connections most important. Conductors are to be led into
springs or wells or earth permanently wet. Not into watertight tanks.
Shingle, dry sand, or dry mould are not sufficient. Provide several
earth connections in all large systems of conductors as a precaution.

39. Lead conductors into ground in trenches 18 inches deep. Not less
than 30 feet of metal to be in contact with moist earth.

40. Lead a flow of water over trenches if possible, _e.g._, from rain
water pipes.

41. Trenches in rocky or dry soil to be 30 to 120 feet long, so as to
obtain all moisture possible.

42. Connections in trenches may be of old iron, forming continuous
metallic surface, the trenches to be filled with cinders or coal ashes.
Water pipes form excellent earth connections, but gas pipes are
dangerous.

43–44. Frequently inspect conductors, especially as to joints connecting
different metals and defects in iron from rust.

45–46. Galvanize iron, care being taken that the coating is good.

47. Great care to be taken in case of contact of zinc coating with other
metals, especially copper.

 _April 8th, 1875._

                                      FRED. E. CHAPMAN.
                                  _Inspector General of Fortifications._


           APPENDIX A.—BY THE LATE SIR W. SNOW HARRIS, F.R.S.

1. The earth’s surface and clouds are the terminating surfaces of
electric actions, and buildings, &c., are only points, as it were, of
earth’s surface in which the whole action vanishes.

2. Electricity when confined to substances resisting its progress, as
air, glass, dry wood, stones, &c., exerts a terribly explosive power.

3. But when confined to bodies, such as metals, offering small
resistance, its violent expansion or disruptive action is greatly
reduced or avoided altogether, and becomes a continuous current
comparatively quiescent. But if body be small, as wire, it may be heated
or fused. Resistance is so small that a shock has traversed copper wire
at the rate of 576,000 miles a second; resistance increases with length
and diminishes with area of section of conductor.

4. So a building metallic in all its parts, or a man in armour is safe.

5. So endeavour to bring buildings into the same passive or
non-resisting state as if of metal.

6. So conducting channels of copper should be systematically applied to
walls, either in plates united in series one over another, not less than
3½ inches wide and 1/16th and ⅛th of an inch thick, or of stout copper
pipe not less than 3/16ths of an inch thick, and 1½ to 2 inches
diameter, fixed to building by braces or copper nails or clamps.
Terminals to be solid metal rods, projecting above to a moderate and
convenient height. Earth connections to be by one or two branches,
leading out about a foot below ground—if possible into moist ground, but
if dry, use old iron or other metallic chains so as to expose a large
metallic surface.

7. All metals in roof, &c., of building to be connected with main
conductors; any prominent chimney to have a pointed conductor taken
along it to metals of roof.

8. An electrical discharge never leaves a perfect conductor to pass to a
very bad one, so the apprehension of lateral discharge is absurd.
Furious discharges have fallen on the conductors to the masts of H.M.
ships, and passed through copper bolts in bottom without injury even to
persons leaning against the conductors.

9. Metallic bodies have no specific attraction for electricity more than
wood or stone have; all matter is indifferent so far as regards a
specific attraction. Lightning falls indiscriminately upon trees, rocks
and buildings, whether with metals about them or not; _e.g._, at
Plymouth Dockyard in May, 1841, a granite chimney, 120 feet high,
without any metal in it, was struck, and yet it was within 300 feet of a
clock-tower of equal height, having metal weathercock, a dome covered
with metal and large conductor along it to ground. The damage ceased
where the chimney passed through a massive metallic roof, having a
conductor from it to the ground. Here the lightning fell on a building,
which, according to the popular idea, held no “invitation” in preference
to a structure which _did_ hold such “invitation.”

10. If efficient conductors provide free and uninterrupted course for
electrical discharge, it will follow that course without danger to
general structure; if _not_, then this irresistible agency will find a
course for itself and shake all imperfect conducting matter in pieces in
doing so. The great object is to provide a line or lines of small
resistance in given directions, less than the resistance in any other
line of the building. The conductor no more attracts lightning than a
gutter or water pipe attracts a flow of water.

11. It follows that a magazine if of metal would be safer than if built
in the usual way. Metallic gutters and ridges, with continuous metallic
communications to earth, are unobjectionable.

NOTE.—It is as wrong to isolate conductors from buildings by glass or
resin, as it would be to place rain water pipes 10 feet from the
building from which they should carry off the water.

An instance is given of an iron conductor which was placed 10 feet from
a house, the latter being, notwithstanding, struck at the point nearest
to the conductor, which was untouched.

12. Pointed terminations tend to break the force of lightning when it
falls on them. Before explosion a large amount of discharge passes off
through pointed conductors.

Pointed conductors should be solid copper rods, about ¾ inch diameter,
and a foot long, united by brazing to the conducting tube. It is not
necessary to gild the points, or form them of platinum. Sometimes even,
this would be detrimental, as platinum has only half the conducting
power of copper. The oxidations of the surface of conductor is of little
moment; and in case of copper very trifling. In any case the conducting
surface is better than the bad—or non-conducting air. The electric
telegraph wires work well, though enclosed by gutta percha or other
non-conducting matter. It is sufficient if the terminal solid rod be
even roughly pointed. But even a ball, a foot diameter, would be a point
as opposed to 1,000 acres of charged clouds.

NOTE.—Experience contradicts the idea that the conductor protects a
certain area. The foremast of a ship has been struck, though the
mainmast has been protected by conductor.

13. Copper linings to doors and windows of magazines, are not
objectionable, but useless for keeping out lightning. They should be
connected with the general system of conductors.


  APPENDIX B.—AS TO SOLID OR HOLLOW CONDUCTORS. BY SIR W. SNOW HARRIS,
                                 F.R.S.

1. A given quantity of electricity melts the same quantity of metal,
whether in a solid or hollow form. So far it is immaterial which form
the conductor has. But supposing the mass of metal to be so large that
the heating effect may be neglected. It is proved that the greater the
surface, the less is its intensity or power at any point, the intensity
approaching the second power or square of the surface inversely. It is
important to give the charge free room of expansion by increasing the
surface of conductor, so as to reduce the mechanical activity of shock
to the least possible. Rectangular flat bars may be employed.

2. A rain water pipe communicating with main conductor, should have
earth connection. All imperfect substances, as masonry, and ship masts,
transmit a certain portion of electricity without explosive action. One
great use of the conductor is to relieve the wood or masonry of the
quantity it cannot discharge without explosion.

3. Conductors of small iron rod or wire are very objectionable. They
commonly rust at the joints, and have fallen to pieces, and often been
knocked to pieces by lightning. Iron may, certainly, be employed with
advantage, but should be galvanized. Zinc is an even better conductor
than iron; and being spread over the surface is not open to the
objection of making a conductor of two metals of unequal conducting
power. A good and efficient conductor might be formed of galvanized
iron. It should be of wrought iron, galvanized, of 2 inches diameter,
with screwed joints of _extra_ thickness. Copper tubing is, however,
always to be preferred.

4. In dry or rocky soil, complete the conductor by leading old iron
chains out from the walls in several directions, or by leading a flow of
water over them. Fortunately a thunder storm is usually attended by
heavy rains. The iron chains should extend 30 to 50 feet, and be a foot
or 18 inches under ground. The termination in a large surface of moist
earth would be preferable to that in a well, as the action is a
superficial one of expansion in all directions. In the _tin_ leaf
coatings of the electrical jar, the charge is not influenced by the
thickness of metal.

                                                         W. SNOW HARRIS.


     REPORT ON THE DESTRUCTION BY LIGHTNING OF A GUNPOWDER STORE AT
         BRUNTCLIFFE, YORKSHIRE. BY MAJOR Y. D. MAJENDIE, R.A.

                 (_Abstracted by G. J. Symons, F.R.S._)

The Gunpowder exploded at 4.30 p.m. on August 6th, 1878, during the
greatest intensity of a violent thunderstorm. The building, was brick,
with brick arched roof, length 9 feet, width 5 feet, height 6 feet
(internal dimensions). The store had a uniform thickness of three
bricks, and was furnished at the one end with an iron door, at the other
end with a lightning conductor. The conductor consisted of a copper wire
rope, 10 gauge copper wire, the rope being 7/16 inch thick, having four
points at the top (one large one in the centre, and three smaller ones
round it), it extended to about 13 feet above the top of the building,
and about the same length was carried into the ground and terminated in
a drain. The conductor had been erected in 1876, by Mr. John Bisby, of
Leeds, and was fixed to a pole distant about 2 inches from the end of
the building opposite to that in which the iron door was fixed, it was
not connected with the iron door in any way. No one was near the store
when the powder exploded, and it seems probable that the earth
connection of the conductor was bad, that the mass of iron in the door
offered at least an equally good path—and that the gunpowder was ignited
by a flash passing between, the two imperfect conductors.

[Illustration: View and Plan of Bruntcliffe Gunpowder Store]

“The only structural damage effected was produced by the impingement of
bricks, which striking with great force, had in a few instances,
partially penetrated or displaced brick work in the dwelling-houses and
buildings, and a portion of the iron of an iron church was broken by a
piece of projected _débris_. A brick was driven through a window in one
of the houses at three hundred yards, and broke a bedstead. As far as I
have been able to discover no other structural injury was occasioned.”

This accident appears to suggest several conclusions:—

“In the first place it appears to me to afford a striking confirmation
of the principle which has been repeatedly and emphatically enunciated
by Sir William Snow Harris and other authorities on the subject of
lightning conductors, that in order to secure an efficient protection
for a given building, all the metal of the building, and as far as
possible the whole of the structure itself, should be brought into
actual connection with the system of conduction; in other words, that
the general conducting power of the mass of the edifice should be
completed, and all attractive and prominent parts allied in one
protective combination, so as to “bring the whole” (as it has been
expressed by Sir William Snow Harris) “as nearly as may be into that
passive or non-resisting state which it would assume, supposing the
whole were a mass of metal.” In the present case, assuming the conductor
itself to have been efficient, a point which there seems no sufficient
reason for doubting, the system of conduction was obviously defective.
Not only was the whole length of the building left unprotected, the
conductor having been on a pole at one end, and carefully insulated from
the building, but the iron door which was at the opposite end, was
absolutely unconnected therewith, and was not itself supplied with any
earth connection.”

“It appears clear, therefore, that even what may be deemed _per se_ an
efficient lightning conductor, _i.e._ a conductor, which considered
alone, offers a path of little or no resistance even to a powerful
electric current, does not afford a reliable protection to a building
unless it be scientifically applied, and with due regard to those
principles upon which the more eminent authorities on electrical science
are agreed. To a disregard of these principles, especially in respect of
the iron door being left out of the system of conduction, and
unconnected therewith, I believe the present accident may be
attributed.”


       REPORTS OF COMMITTEES ON THE POWDER MAGAZINES AT PURFLEET.

        (Phil. Trans., 1773, p. 42, and 1778, Part I., p. 232.)

              (_Abstracted by Prof. W. G. Adams, F.R.S._)

Report of a Committee consisting of the Hon. Henry Cavendish, Dr.
Watson, Dr. Franklin, Mr. J. Robertson, Mr. Wilson, and Mr. Delaval,
appointed by the Royal Society, “to consider of a method for securing
the powder magazine at Purfleet.”

A powder mill at Brescia having blown up in consequence of being struck
by lightning, the Board of Ordnance applied to Mr. B. Wilson to know in
what way the powder magazine could be protected. He recommended that a
blunt conductor should be employed, whereas Dr. Franklin recommended a
pointed conductor. The Committee met and Dr. Franklin read a paper on
the subject, and the report of the Committee was in conformity with Dr.
Franklin’s views.

The Committee went to Purfleet and examined the buildings. They found
that the barrels of powder, when the magazines were full, lay piled on
each other up to the spring of the arches; on each barrel were four
copper hoops, which with vertical iron bars formed broken conductors
within the building. These iron bars were ordered to be removed.

The Committee advised that at _each end_ of each magazine a well should
be dug in or through the chalk, so deep as to have in it at least four
feet of standing water. From the bottom of this water should arise a
piece of leaden pipe to or near to the surface of the ground, where it
should be strongly joined to the end of an upright iron bar, an _inch
and a half_ in diameter, fastened to the wall by leaden straps, and
extending ten feet above the ridge of the building, tapering from the
ridge upwards to a sharp point, the upper twelve inches of copper, the
iron to be painted.

Lead was mentioned for the underground part as less liable to rust, in
the form of a pipe as giving greater stiffness for the substance, and
iron for the part above ground as stronger, and less likely to be cut
away. The pieces of which the bar may be composed should be screwed
strongly into each other by a close joint with a thin plate of lead
between the shoulders. Each rod in passing above the ridge should be
strongly and closely connected by iron or lead, _or both_, with the
leaden coping of the roof, so making metallic communication between the
two bars of each building.

It was also advised that two wells be dug within twelve feet of the
doors, one to the north of the north building and the other to the south
of the south building, and that metallic communications be made between
the water in them and the leaden coping of the roof.

The Board house stood 150 yards from the magazines, on elevated ground,
and was a “lofty building with a pointed hip-roof, the copings of lead
down to the gutters, from which leaden pipes descend at each end of the
building into the water of wells of forty feet deep, for the purpose of
conveying water forced up by engines to a cistern in the roof.”

As to the Board-house, they thought it already well furnished with
conductors by the several leaden communications above-mentioned from the
point of the roof down into the water, and that by its height and
proximity it may be some security to the building below it; they
therefore proposed no other conductor for that building, and only
advised erecting _a pointed iron rod_ on the summit, similar to those
before described and communicating with those conductors.

Mr. Wilson dissented from that part of the Report which recommended that
each conductor should be pointed, because, _he says_, “by points we
solicit the lightning, and may promote the mischief by drawing the
charges from charged clouds, which would not discharge at all on the
building if there were no points on the conductors.” By experiments made
and appealed to at the Committee the difference in the effects between
pointed and blunted conductors is as twelve to one. Mr. Wilson states
that, “A thunder cloud, therefore, if it acted at 1200 yards distance
upon a point, would require a blunted end to be brought within the
distance of 100 yards, and beyond those limits would pass over it
without affecting it at all.” He also says, “The _longer_ the conductors
are above the building, the more danger is to be apprehended from them.
I have always considered pointed conductors as being unsafe by their
great readiness to collect the lightning in too powerful a manner.”

Mr. Wilson adds an account of an accident to St. Paul’s Church, and some
curious reasoning on it in support of his own views. (See Phil. Trans.
1773, p. 59–61.)

                  *       *       *       *       *

On the 15th of May, 1777, the Board House at Purfleet was struck by
lightning, and some of the brickwork damaged (See Phil. Tran., 1778, Pt.
I., p. 232). About 6 p.m., after heavy rain through the day, a heavy
cloud hung over the house for some time, and Mr. Nickson, who watched it
from the house and gives the account, says he suspected that some of the
conductors might find employment from it. He had not been long at the
window before a violent flash of lightning and clap of thunder came
together. The lightning struck one of the iron cramps that hold the
coping, and made a dent in the lead of the cramp and the stone adjoining
it, throwing some stone down and slightly disturbing about a cubic foot
of brickwork at A. The iron cramp was situated over a plate of lead, and
the ends of it, inserted in the stone, came within 7 inches of that
plate, which communicated with the gutter, and served as a fillet to it;
this gutter was part of the main conductor of the building. The
lightning struck through the stone, &c., to the corner of the plate,
fusing a very small portion of it. From this point no farther effect of
the lightning could be traced. At the distance of seven feet and a-half
from the place struck, a large leaden pipe went down from the gutter to
a cistern of water in the yard. It is remarkable that the surface of one
of the hip-rafters, four inches and a-half in diameter, covered with
lead (communicating with the gutter), and _reaching within twenty-eight
inches_ of the place struck, seems not to have been at all affected. The
distance from the point of the conductor on the house to the part struck
was forty-six feet.

[Illustration: View of Board House, at Purfleet]

A fresh Committee of the Royal Society, consisting of Mr. Henly, Mr.
Lane, Mr. Nairne, and Mr. Planta, recommended a channel to be made from
cramp to cramp round the parapet, filled with lead, and connected in
four places with the main conductor on the roof of the building.

Mr. Wilson again dissented from their report, and attributed the hanging
of a heavy cloud over the house (it being calm at the time) to the
presence of the pointed lightning conductor.

An account of Mr. Wilson’s elaborate series of experiments at the
Pantheon on a long cylinder to illustrate the effects of pointed and
rounded conductors occupies seventy pages of the Philosophical
Transactions; and another Committee of the Royal Society, consisting of
Sir John Pringle, Dr. Watson, Henry Cavendish, W. Henly, Bishop Horsley,
T. Lane, Lord Mahon, E. Nairne, and Dr. Priestley, report in favour of
having additional conductors ten feet high, with copper eighteen inches
long, finely tapered and acutely pointed placed upon the magazines. They
conclude that “elevated rods are preferable to low conductors terminated
in rounded ends, knobs, or balls of metal,” conceiving that, the
experiments and reasons, made and alleged to the contrary by Mr. Wilson,
are inconclusive.

Mr. Wilson’s objections are again urged by Dr. Musgrave, but called in
question by Mr. Nairne (see Phil. Trans., 1778, Pt. 2, p. 823), who
makes a series of experiments to illustrate the advantage of pointed
conductors.

Both Mr. Wilson’s and Mr. Nairne’s experiments agree in showing that
“pointed conductors draw off the electricity from a cloud at a much
greater distance than those which are blunted.” Mr. Wilson objecting
that this draws the charged cloud from a greater distance; and Mr.
Nairne concluding that “a charged body is exhausted of more of the fluid
by a pointed than by a blunted conductor,” and so is not likely to cause
so much damage since it discharges itself more gradually.


              EXPERIMENTS AND OBSERVATIONS ON ELECTRICITY.

           BY BENJAMIN FRANKLIN. Fifth edition. London, 1774.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The author shows that pointed bodies draw off electricity much more
effectually than blunt ones.

When the land is hot, “the lower air is rarified and rises; the cooler,
denser air above, descends.”

The clouds meet over the heated place, “and if some are electrified and
others not, lightning and thunder succeed, and showers fall.”

“As electrified clouds pass over a country, high hills and trees,
towers, spires, masts, chimneys, &c., as so many points, draw the
electrical fire and the whole cloud discharges there.”

Therefore it is dangerous to take shelter under a tree. It is safer to
be in the open fields, especially if the clothes are wet.

Metals are fused, possibly without heat; the lightning creating a
violent repulsion of the particles of the metal it passes through.

[He afterwards admits this opinion to be erroneous.]

Describes experiments with sharp-pointed metallic bodies, and says: “May
not the knowledge of this power of points be of use to mankind in
preserving houses, churches, ships, &c., from the stroke of lightning,
by fixing on their highest parts upright rods of iron, made sharp as a
needle, and gilt, to prevent rusting; and from the feet of these rods
lead iron wire down the outside of the building into the ground; or down
one of the shrouds of a ship and her side till it reaches the water.”

“Would not pointed rods probably draw the electrical fire silently out
of a cloud before it came nigh enough to strike, and thereby secure us
from that most sudden and terrible mischief?”

He mentions the case of the topmast heads of a ship being struck, but
having flames upon them like very large torches before the stroke.

He thinks that if there had been a good wire conductor from the heads to
the sea there would have been no stroke or damage.

He records the experiments on the 10th of May, 1752, at Marly, of M.
D’Alibard, who placed upon an electrical body a pointed bar of iron 40
feet high. In a thunder storm sparks of fire were attracted from it.

Again, at Paris, on the 18th of May, with the same result, by M. de Lor,
with a bar of iron 99 feet high upon a cake of resin 3 inches thick and
2 feet square.

Similarly in London in July, 1752, by Mr. Canton.

He refers to other experiments.

He experimented in 1752 with a kite of thin silk (as being able to bear
the wet), having a very sharp-pointed wire fixed to its top, above which
it rose about a foot. The kite was raised by twine, the part in the hand
being made of silk and kept quite dry.

The pointed wire will draw the electric fire from thunder clouds, and
when the rain has wet (_sic_) the kite and twine, so that it conducts
the electric fire freely, they will be electrified, and the electric
fire will stream out plentifully on the approach of the knuckle.

“Spirits may be kindled, &c., as with a rubbed glass or tube, and
thereby the sameness of the electric matter with that of the lightning
be completely demonstrated.”

September, 1752. He erected “an iron rod to draw the lightning into his
house in order to experiment on it.”

After many experiments, he concluded that “the clouds of a thunderstorm
are most commonly in a negative state of electricity, but sometimes in a
positive state.” The latter, he believed, rare.

“So that, for the most part, in thunderstrokes, it is the earth that
strikes into the clouds, and not the clouds into the earth.”

In the contrary (rare) case the cloud was, “I conjecture, compressed by
the driving winds or some other means, so that part of what it had
absorbed was forced out, and formed an electric atmosphere round it in
its denser state, so communicated positive electricity to my rod.”

“The electric fluid, moving to restore the equilibrium between the cloud
and the earth, takes, in its way, all the conductors it can find (_v._
page 132 of Franklin’s book)—as metals, damp walls, moist wood, &c.—and
will go considerably out of a direct course for the sake of the
assistance of a good conductor.”

“Explosions only happen when the conductors cannot discharge it as fast
as they receive it, by reason of their being incomplete, disunited, or
too small, or not of the best materials for conducting.”

He supposes that a wire ¼ inch diameter will conduct the electricity of
any one stroke of lightning ever known.

Iron is the best material, as least liable to fuse.

“Pointed rods erected on buildings and communicating with moist earth
would either prevent a stroke, or, if not prevented, would conduct it so
that the building should suffer no damage.

He gives instances of a small wire acting as conductor and saving the
building, though the wire, being too small, was utterly destroyed.

His theory as to the crooked course of lightning is as follows:

“Who knows but that there may be, as the ancients thought, a region of
this fire (electric) above our atmosphere, prevented by our air and its
own too great distance of attraction from joining our earth. Yet some of
it be low enough to attach itself to our highest clouds,” which thence
become electrified, &c.

“I am still at a loss about the manner in which clouds become charged
with electricity, no hypothesis I have yet formed perfectly satisfying
me.”

He describes how he and others have been struck down by electric shocks
without feeling pain or sustaining permanent injury.

For protecting powder magazines, erect a mast not far from it, and 15 or
20 feet above the top of it, with a thick iron rod fastened to it,
reaching down till it comes to water.

“In buildings the rod may be fastened to the walls, chimneys, &c., with
staples of iron. The lightning will not leave the rod (a good conductor)
to pass into the wall (a bad conductor) through these staples. It would
rather, if anywhere in the wall, pass out of it into the rod to get more
readily into the earth.”

If the building be very extensive, two or more rods may be placed at
different parts for greater security.

It is well not to sit near the chimney, or gilt objects, during a
thunderstorm.


AN ESSAY ON THE CAUSE OF LIGHTNING, _and the manner by which the thunder
 clouds become possessed of their electricity, deduced from known facts
 and properties of that matter, to which are added plain directions for
constructing and erecting safe conductors. By_ JOHN SIMMONS. 8vo. 1775.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

“As on the earth the operation necessary for the excitation and
collection of the electric fluid is attrition.” ... “So we may
rationally conclude that attrition is the means of excitation and
collection of electric matter in the clouds as well as on the earth.”

By metallic conductors buildings may be preserved from the effects of
lightning

Electricity ascends from the earth to the clouds by means of moist air.

“A conductor is a continuation of metal from a certain height above the
highest part of a building to moist earth or water” ... “for easy and
safe passage of lightning.”

Metal is the best of all conductors.

The author quotes from Franklin “buildings that have their roofs covered
with lead and spouts of lead continued from roof into ground to carry
off the water, are never hurt by lightning when it falls on such a
building.”

The conductor may be made of any metal, and flat or round.

But nowhere less than ¾ inch diameter except at terminal.

But iron rusts, so copper or lead should be used. Lead is best, used in
strips 4 inches wide and ⅒th inch thick.

Good earth contact required in moist earth (going therein at least 5
feet) or water.

The several lengths of the conductor must be well in contact by being
screwed, if of iron; soldered, if of lead.

The upper terminal to be iron or copper rod 9 or 10 feet long, ¾ inch
diameter, and 2 to 5 feet above top of highest chimney or other part of
building.

It should be pointed as this attracts electricity better.

Lead roofs to be connected with conductor. (Examples given of house and
ship struck.)

No building or object is known to have been struck by lightning within
50 feet of a proper conductor. But a tree has been shivered within 52
feet, so we may conclude that protecting influence extends to 50 feet
horizontally in every direction from the point of conductor.

In gunpowder stores, conductors are not to be fixed to the buildings,
but at (say) 12 feet away, fastened to a standard, the top being as high
above the building as it can be conveniently.

No metal on sides or roof of the building is to be exposed to the
lightning so as to attract it.


                 A TREATISE on ATMOSPHERIC ELECTRICITY.

                         BY JOHN MURRAY. 1830.

              (_Abstracted by Prof. W. G. Adams, F.R.S._)

In Chapter V., on lightning identified with electricity, the author
speaks of fire-balls and the Aurora Borealis, and ascribes the formation
of shooting stars to electrical action. He does not believe they come
from distant space into our atmosphere, but regards them as concretions
formed by a flash of lightning darting through gaseous media and
atmospheric air _expanded by heat_, carrying metallic dust and earthy
particles ejected from volcanoes, or carried up by _evaporation_ or
other causes, and diffused over an immense surface in the upper regions
of the air. “The lightning carries, like a _ploughshare_, the
accumulated matter in its progress, and, by the powerful electrical
attraction thus excited, these particles will be drawn into the vortex
of the lightning instantaneously; for, the lightning finally
encountering an electricity of an opposite kind, an explosion ensues,
and the collected mass is instantaneously fused and agglutinated, while
the meteorite thus formed tumbles to the ground.... We therefore do not
see the necessity of considering meteoric stones _extra atmospheric_.”

In this way John Murray goes on page after page, but the above will
probably be sufficient notice of his work.

The following are the conditions he lays down for a good conductor:—

1. A finely pointed summit to offer an unresisting entrance.

2. A sufficient length to anticipate, as it were, the descending
electricity, and receive it on its summit before it could reach any part
of the building.

3. A superior conducting power in the material of the rod to facilitate
its passage to the earth.

4. A sufficient thickness to prevent its fusion, which, however, will
greatly depend on the resistance it has encountered in entering the
conductor. And, finally

5. A safe conduction to a well or moist surface below ground.

He says: “Let the wires below ground in contact with moisture pass
through a cylinder of zinc before they diverge to form the root, the
copper wires will in this case always remain free from any oxidation.”


 HARRIS’S LIGHTNING CONDUCTORS. REPORT _to the Committee upon_ MR. SNOW
               HARRIS's _and other_ LIGHTNING CONDUCTORS.

        (February 11th, 1840. Parliamentary Paper. Fcap. folio).

               (_Abstracted by Professor W. E. Ayrton_).

Instances are given of ships not provided with lightning conductors
being struck and damaged, whilst others lying near, and provided with
conductors, were not injured. The question of lightning conductors
attracting lightning considered, and evidence shown to the contrary.
Lateral discharge from a lightning conductor considered. Evidence
against it, if only the conductor were continuous and of sufficient
size. Faraday considered that a man leaning against one of Harris’s
conductors when the electricity descended would not be hurt. Proposition
to place a globe of glass on the head of the mast in place of a
lightning conductor considered, and the conclusion arrived at that it
would do harm.

Wheatstone stated that “in the Report of the Committee of the Academy of
Sciences of Paris, appointed to investigate the utility of lightning
conductors, there is no instance on record of an iron rod of ½ inch in
diameter being fused or even made red-hot by a flash.”

Mechanical objections to lightning conductors on ships considered and
discussed. Decided that the application of Mr. Harris’s conductor tended
rather to strengthen than weaken the mast and spars. Then follows a
large number of letters, giving accounts of accidents from lightning to
ships, &c.

Decision arrived at that on the whole Mr. Harris’s conductor is the best
of those examined.


THE DIFFERENCE BETWEEN LEYDEN DISCHARGES AND LIGHTNING FLASHES. BY C. V.
          WALKER, Hon. Sec. Lon. Electrical Soc. London. 1842.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The author alludes to the experiments of Franklin, &c.

The distance to the lower surface of clouds, observed by Le Gentil and
others, shows an average of 1000 to 2000 feet, whereas the greatest
length of spark with a large machine is 3 to 4 feet.

The inductive action bears some inverse ratio to the distance.

Leaves of trees have a remarkable property of silently drawing off
electricity.

He gives the particulars of a large number of experiments, with
arguments thereon, to prove the theory of the difference between Leyden
discharges and lightning.

Quotes examples of lightning on conductors and buildings to show that
the conductor takes part only of the charge, the remainder taking other
paths. Contiguous semi-insulated bodies must not be left unconnected
with the lightning rod.

He quotes, with approval, the advice of Faraday, viz., to tie together
with a metallic connection all contiguous readily-conducting bodies.

Cites numerous other opinions to the same effect, viz., that all
metallic parts of a building should be connected with the conductor.

He sums up by stating “that the Leyden charge differs considerably not
so much in _nature_ as in _degree_ from that of the cloud, inasmuch as
the proximity of the coatings in the one case is infinitely small
compared with the distance in the other,” &c.

He expresses great confidence in Sir W. S. Harris’s system for
protecting ships.


 THE EFFECT OF A LIGHTNING FLASH ON THE STEEPLE OF BRIXTON CHURCH, AND
OBSERVATIONS ON LIGHTNING CONDUCTORS GENERALLY. BY C. V. WALKER. London.
                                 1842.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The author refers to Faraday’s experiments, as shewing instances of
lateral discharge, and says, “unless precautions are taken to prevent
its proceeding from a lightning conductor, that instrument literally
invites the enemy within doors.”

He gives detail of the accident at Brixton, there being no lightning
conductor.

The stroke did much damage to the steeple and then passed off harmlessly
by the metal gutters and rain-water pipes.

One side of the steeple was drenched with wet and carried off part of
the stroke.

He quotes examples of the apparently protective action of high trees.

Lofty trees near lofty buildings would materially mitigate, if not
prevent, the violence of the stroke.

The accident at Brixton shows that the lightning takes not simply the
_shortest_, but, in addition, the _largest_ path.

Had the steeple been provided with a lightning conductor outside,
passing near the clock face or the bells, or water pipe, it is more than
probable that a flash would pass from it to these vicinal conductors.

If _outside_ the tower the danger would be greater. He recommends that
the _metal_ cross on the steeple be _replaced_ by a _stone_ one, and
that the present iron rain water-pipes be connected by copper rods or
plates, which are also to be connected with the lead work of roof.

The bells are also to be connected with each other and with the
conductor.

Every bolt-clamp or other piece of metal within “striking distance” of
the conductor, unless in direct communication with it, is liable to
cause lateral discharge.

The odour developed by lightning was, at Brixton, decidedly sulphurous,
as a piece of stone which was shattered by the stroke retained the odour
of sulphur distinctly for several hours.


ON THE NATURE OF THUNDERSTORMS; AND ON THE MEANS OF PROTECTING BUILDINGS
 AND SHIPPING AGAINST THE DESTRUCTIVE EFFECTS OF LIGHTNING. BY W. SNOW
                          HARRIS, F.R.S. 1843.

                    (_Abstracted by Prof. Ayrton._)

_The backstroke may do injury_, that is, a person may be killed in
consequence of a flash of lightning passing between the clouds and the
earth at some distance from the person.

In the Phil. Trans. for 1787, Mr. Brydone writes to the President of the
Royal Society, and mentions the case of two men riding in two carts, the
front one drawn by two horses, these horses and the man driving them
were killed;, the man on the hinder cart and a shepherd at a distance,
saw the occurrence and heard a report but observed no lightning.

_A metallic screen appears to protect the interior from the action of a
current, as well as from static induction._

Dr. Franklin found he could not destroy a wet rat by artificial
electricity, although he could a dry one.

The first lightning conductor was erected in England at Payneshill, by
Dr. Watson, in 1762.

The lightning conductor should expose a large surface, and should be
united with all the great masses of metal in its vicinity. For
stationary elevations the conductor should consist of solid or tubular
rods or flat plates of metal. We must consider the _mechanical_ action
the lightning may produce on the conductor, as well as any possible
heating action. Sir W. Snow Harris mentions that there were no signs of
fusion in the fragments of the linked brass rod, at Charles Church,
Plymouth, torn to pieces in 1824, or in the small pieces of the
conductor at the Hotel des Invalides, at Paris, consisting of a strand
of twenty iron wires, and which was smashed in 1839.

He says the benefical effect of _superficial_ conductors appears to
depend on the removal of the electrical particles further out of the
sphere of each other’s influences.

“Thus we find,” says Sir W. Snow Harris, “in a variety of cases of
damage by lightning that the passing charge, in striking on large
expanded sheets of metal has become comparatively tranquil, and has been
traced no further, whilst in striking on large masses of metal exposing
but a small surface, it has assumed an intensely active state.”

He goes on to state that the resistance of the conductor must be kept as
low as possible, and as neither the resistance nor the heat developed is
increased by rolling the wire out into a flat surface, he argues that
“there is, consequently, no disadvantage in giving a lightning rod as
much superficial capacity as possible, as regards conducting power,
whilst, on the contrary, the diminished intensity attendant on it is
very advantageous: this effect of superficial conductors appears to
depend on the removal of the electrical particles further out of the
sphere of each other’s influence.”

_What quantity of metal is requisite for a lightning rod?_ He concludes
from the results of a number of accidents that “a copper rod ¾ inch
diameter, or an equal quantity of copper under any other form, would
withstand the heating effect of any discharge of lightning which has yet
come within the experience of mankind.”

_Practical deductions._—“From the various enquiries contained in the
first 123 pages of this book, we arrive at the following deductions:—

“1st. Copper is the best kind of metal for a conductor.

“2nd. The quantity of metal should not be less than that represented by
the section of a solid cylinder ½ inch diameter.

“3rd. The metal should be placed under as great an extent of surface as
is consistent with strength, and should be perfectly continuous.

“4th. The conductor should involve in its course the principal detached
masses of metal in the building.

“5th. It should be placed as close as possible to the walls which are to
be defended, and not at a distance from them, and be carried at once
directly into the ground.

“6th. It should be attached to the most prominent points of the
building, and if the length be very considerable its dimensions should
be increased.

“Lastly. In extensive ranges of buildings, all the most prominent parts
should have long pointed rods projecting freely into the air, and the
greater the range of building the higher they should be.

“In particular cases, in which expense must necessarily be considered,
wrought iron tubing may be employed; it should not, however, be less
than 2 inches in diameter, and 3/10ths of an inch in thickness.”

Insulating the lightning conductor from the building is quite valueless.

The method of fixing lightning conductors to ships is explained at
considerable length.

_Range over which the protecting power of the lightning rod
extends._—Great doubts exists as to the answer to this question, since
in many cases one portion of a building has been struck while a
lightning rod in good condition existed close by.

For example, the powder magazine at Bayonne was 56 feet long, 36 feet
wide, covered with thick vaulted masonry and a sloping roof with gable
ends, protected by plates of lead; the gutters were also of lead, and
there were the usual spouts for discharging the rain. The lightning rod
projected about 20 feet above the building, and was attached to the lead
of the roof by a metallic socket through which it passed, and which was
soldered to one of the lead coverings. Instead of being carried,
however, directly into the earth at the foot of the wall, it was turned
outward at about 2 feet from the ground, and being bent at right angles,
was continued on semi-insulating posts of wood into a trench filled with
charcoal, distant 33 feet from the wall.

On the 23rd of February, 1829, the building was struck, the point of the
conductor melted, and the leaden plates by which it was attached to the
wood posts at the foot of the wall, were more or less torn and
perforated by holes. No damage, however, ensued to the building in the
course of the conductor. At the south-west corner, a sheet of lead
covering the gable end was torn out immediately over a point where two
stones of the cornice were united by an iron cramp.

Sir W. Snow Harris considers the possibility of this damage having
arisen “from the conductor (in consequence of being continued at so
great a distance from the building) not offering a sufficiently easy
line of transit for the discharge to the earth,” but he rejects this
explanation and concludes that the damage arose from the lightning
striking the building in two points.

Again, the Heckingham poorhouse, although armed with eight pointed
lightning rods, was struck, in 1787, at a point _m_, 70 feet from the
nearest conductor _c_.

[Illustration: View and Plan of Heckingham Poorhouse]

[Illustration: View and Plan of Heckingham Poorhouse]

The squares at _a_, _b_, _c_, _d_, _e_, _f_, _g_, _h_, indicate chimneys
to which lightning conductors were attached. The centre range was 108
feet long, the flanks each about 160 feet long: the details of the
lightning conductors are not given. One portion of the lightning
discharge struck one of the conductors and was carried off by it without
damage to the building, one portion struck the building at the point _m_
and also the shed at _s_, doing some damage, and a third portion struck
the ground immediately in front of the building near a gate, G.

The ship _Ætna_ was struck in 1830 by several heavy electrical
discharges when at Corfu. These for the most part passed down a chain
conductor attached to the mainmast. One of the discharges, however,
struck the ship near the bow, and exploded about 12 feet above the
forecastle close to the foremast, knocking people down, &c.

The Board-house at Purfleet was a lofty building with a pointed roof,
well leaded and connected by lead gutters and pipes with the earth, and
with wells 40 feet deep for the purpose of conveying water forced up to
a cistern on the roof. It was, therefore, only thought necessary to add
an iron spike about 10 feet long to the middle of the highest part of
the roof. The building, however, in 1777, was struck and slightly
damaged at a point 46 feet from the conductor.

Several other examples illustrating how small an area a lightning rod
protects follow.

Sir W. Snow Harris further concludes that experience shows that
lightning will not leap from a lightning rod to a piece of insulated or
semi-insulated metal near it, although a discharge may take place
between the rod and a distant metallic mass in connection with the
earth, but not otherwise in connection with the rod.

He lastly considers the question, formerly much debated as to whether a
lightning rod attached to a house will attract to the house a discharge
that otherwise would not have struck it, and he concludes that there is
no foundation for the erroneous impression that the existence of a
lightning conductor can ever cause damage.


 AN ACCOUNT OF THE CHIMNEY OF THE EDINBURGH GAS WORKS. BY G. BUCHANAN,
                             C.E., F.R.S.E.

     [Proceedings of the Royal Scottish Society of Arts, 1850–51.]

                 (_Abstracted by G. J. Symons, F.R.S._)

This chimney has a total height of 341½ feet (329 feet above ground), it
is circular; at the top the internal diameter is 11 feet 4 inches, and
the external 13 feet 10 inches; and at the bottom, internal diameter 20
feet, external 26 feet 3 inches.

Respecting the conductor Faraday was consulted, and replied as follows:—

“The conductor should be of ½ _inch copper rod_, and should rise above
the top of the chimney by a quantity equal to the width of the chimney
at the top. The lengths of rod should be well joined _metallically_ to
each other, and this is perhaps best done by screwing the ends into a
copper socket. The connection at the bottom should be good; if there are
any pump pipes at hand going into a well they would be useful in that
respect. As respects electrical conduction, no advantage is gained by
expanding the rod horizontally into a strap or tube—surface does
nothing, the solid section is the essential element.[4] There is no
occasion for insulation (of the conductor) for this reason. A flash of
lightning has an intensity that enables it to break through many hundred
yards (perhaps miles) of air, and therefore an insulation of six inches
or one foot in length could have no power in preventing its leap to the
brickwork, supposing that the conductor were not able to carry it away.
Again, six inches or one foot is so little that it is equivalent almost
to nothing. A very feeble electricity could break through that barrier,
and a flash that could not break through five or ten feet could do no
harm to the chimney.

Footnote 4:

  The very reverse of what was formerly held by high authorities.—[Note
  by Editor of Proc. Roy. Scot. Soc. of Arts.]

“A very great point is to have no insulated masses of metal. If,
therefore, hoops are put round the chimney, each should be connected
metallically with the conductor, otherwise a flash might strike a hoop
at a corner on the opposite side to the conductor, and then on the other
side on passing to the conductor, from the nearest part of the hoop
there might be an explosion, and the chimney injured there or even
broken through. Again, no rods or ties of metal should be wrought into
the chimney parallel to its length, and therefore to the conductor, and
then be left unconnected with it.”

In answer to some further inquiry, Professor Faraday again wrote:—

“The rod may be close along the brick or stone, it makes no difference.
There will be no need of rod on each side of the building, but let the
cast-iron hoop and the others you speak of be connected with the rod,
and it will be in those places at least, as if there were rods on every
side of the chimney.

“¾ rod is no doubt better than ½ inch, and except for expense I like it
better. But ½ inch has never yet failed. A rod at Coutt’s brewery has
been put up at 1½ inch diameter—but they did not mind expense. The
Nelson column in London has ½ inch rod, ¾ is better.

“I do not know of any case of harm from hoop-iron inclosed in the
building, but if not in connection with the conductor, I should not like
it; even then it might cause harm if the lightning took the end furthest
from the conductor.”

The following paragraph states what was done:—

“The electric conductor stands 6 feet above the iron top-plate, ⅝-inch
round copper, made fast to stone and brickwork with 7⅞-inch copper
holdfasts let 4 inches into the masonry or brickwork, with a head on the
inside and an eye on the outside to receive the rod as it was carried
up. By these holdfasts an ascent can easily be made to the top by a
small tackle suspended to the holdfasts. The conductor is metallically
connected to all the ironwork on the stalk—the plate on the top,
projecting cope, malleable iron hoops, bolts on the top of stone
pedestal, and also the ascending chain. The rod descends into a well
about 10 feet from the foundation, and is immersed about 8 feet deep in
water, and the end turned up 2 feet in a horizontal direction, and
flattened.”


PAPERS _relative to_ SHIPWRECKS BY LIGHTNING, _as prepared by_ SIR SNOW
            HARRIS, _and presented by him to the Admiralty_.

         (August 5th, 1854. Parliamentary Paper. Fcap. folio).

               (_Abstracted by Professor W. E. Ayrton_).

Number of merchant ships destroyed by lightning, loss to the country.
Application of lightning conductors to ships in 1820. Mode of applying
them. Mechanical difficulties; how overcome. The saving to the Exchequer
which has resulted.

Long account of various ships in the Royal Navy not provided with
lightning conductors, struck by lightning and damaged. Loss of life and
injury that has resulted. Long account of ships provided with lightning
conductors, and so preserved.

Sir Snow Harris states that “although his system of lightning conductors
ought to guard against all those violent and regular shocks of lightning
falling within the ordinary experience of mankind, it is not to be
expected that the system could guard against every possible kind of
atmospheric electrical discharge, be the circumstances what they may,
such as thunderbolts, fire-balls; nor is it expected that it should
guard against meteorolites, or against sweeping electrical action mixed
up with convulsions of nature; nor can it quiet those minor electrical
effects producing electric glow; nor can it always obviate that
tremendous concussion and expansion of the atmosphere in cases in which
a thunder-cloud discharges its lightning in a dense explosion on the
masts, and which may rupture, or mechanically tear to pieces, frangible
matter.”


  STATISTICS OF BUILDINGS AND SHIPS STRUCK BY LIGHTNING. BY F. DUPREZ,
                         MEMBER OF THE ACADEMY.

   [Académie Royale de Belgique, Extrait du Tome 31 des Mémoires, 5th
                            December, 1857.]

          (_Abstracted by Professor T. Hayter Lewis, F.S.A._)

M. Duprez refers to the Report of a Committee of the Institute of
France. (Vide _Comptes rendus_, 1852–6.)

He divides the subject into the following heads:—

1. The frequency with which lightning rods are struck.

2. Their terminal points and the effects of the stroke on them.

3. The conductors and their ground connections.

4. The protective power of the lightning rods.

1. _Concerning the frequency with which lightning conductors are struck
by lightning._

The author cites 144 cases of lightning rods having been struck. Of
these seventeen were struck two or three times, so that the total number
of electric discharges on them was 168, as far as recorded.

But very many cases are not recorded at all, _e.g._, from 1793 to 1813
only two cases were noted. The great number of lightning rods struck
would seem at first to support the idea that they attract lightning.

But we must compare the number of rods struck with those fixed, and we
find from a communication made in 1777 to the Academy of Berlin, that,
even then, a large number were fixed to the most important edifices of
N. Italy and England.

The same in 1784 to those in the ports of France and to the ships in the
said ports.

In 1794 the fortresses of Russia were ordered to be so protected.

In 1769 there were 166 edifices in Hamburg alone, and 104 in its
environs, with conductors.

If the number of conductors were so great in the last century, we must
conclude that the number of those struck must be very inconsiderable as
compared with those fixed.

In Hamburg, _e.g._, not one rod is recorded as having been struck.

In 1785, Ingen-Housz reports that of all the lightning rods placed by
his direction on the Austrian powder magazines and other buildings only
one had been struck.

In 1772, Franklin wrote, that during the twenty years in the course of
which lightning rods had been fixed in America he knew of five cases
only in which these rods had been struck.

Sir W. S. Harris reports in 1854, as the results of twenty-two years’
experience, that the number of vessels struck unprotected by lightning
rods, as compared with that of vessels protected by his plan, was as
three to two.

The above show that the idea of danger from lightning rods is not well
founded.

Besides which it must be remembered that they are frequently placed in
the most exposed positions, _e.g._, of the 144 rods struck, seventy-four
were on ships, and fifteen others on buildings which had been struck
before.

One would think that the number of terminals placed on a building would
diminish the chances of their being struck, but it does not seem to be
so; _e.g._, twelve buildings in the first list had many terminals
communicating with a common conductor or different conductors.

Yet the lightning struck, with explosive effect, one or other of the
rods of these buildings.

And in each of two cases the lightning struck at once the three rods
fixed to a building.

Of the 144 cases above cited:—

         74 were to lightning rods fixed on ships
         30 were to lightning rods fixed on towers
          9 were to lightning rods fixed on powder magazines
         31 were to lightning rods fixed on ordinary buildings.
        ———
        144

In forty-four cases where one of Sir W. S. Harris’ conductors was fixed
to each mast of a ship, the mainmast was struck twenty-seven times; the
foremast was struck fourteen times; the mizen was struck twice; both the
main and foremast twice.

2. _As to the points of the lightning rods struck, and the effect
produced on them._

(Sir W. Snow Harris’s system as adopted in the British Royal Navy since
1830 is described. They are formed of bands of copper let into the
masts. They have no upper terminals or points, and fifty-five are
included in the list already quoted of 144 lightning rods struck.)

Of the eighty-nine cases remaining in the list, only fifty-one are
recorded as having their upper terminals ended with points.

Of these, thirty had their points melted to a greater or less extent;
six of them were of copper or brass; five were of copper gilt or iron
gilt; one was of brass silvered; and four were of platinum. The others
are not distinctly described, and the sizes seldom given.

One of brass was 25·4 centimetres (c. 10 inches) long, and 5 millimetres
(⅕th inch) diameter at its base, and was melted for ¼th of its length.

One of copper was 24 centimetres (c. 9½ inches) long, and 9 millimetres
(c. ⅓rd inch) diameter at base, and was almost all melted.

One of platinum was 8 centimetres (c. 3 inches) long, and 1 centimetre
(c. ⅓rd inch) diameter at base. This was melted for a length of 5 or 6
millimetres (c. ⅕th inch.)

It results from the above facts that the points of the lightning rods
have been much too slender.

The Institute of France recommends, therefore, for the points 2
centimetres diameter (c. ¼th inch) at base, and only 4 centimetres (c.
1½ inches) high, with an angle of opening of 28 to 30 degrees.

It has been urged, especially in Germany, against the employment of
pointed upper terminals that these points are fused by the lightning,
this fusion being regarded as dangerous on account of its action on
inflammable substances near.

As to this, the author cites three cases of buildings set on fire,
though protected by lightning rods. But the precise cause of the fire
was not ascertained.

Several observations show that the melted metal trickled down the side
of the lightning rod.

At Strasbourg the metal was pressed down on one side, and had bent like
wax softened by heat. At other times the lightning disperses the melted
metal in all directions. (Examples quoted.)

With these facts before us we cannot altogether deny that some danger
may arise from the fusion of the metal at the point of the terminal. But
this danger can be much lessened, if not removed, by adopting the size,
etc., of the lightning rods recommended by the Institute of France.

Besides fusion, the points sometimes show distinct traces of mechanical
action caused by lightning.

The author quotes six examples of this where the points had been curved.

This shows the necessity of strengthening the points of the upper
terminals. The curvature arises, probably, from the points being much
heated by the lightning, and acted on by the wind.

One case is noted of a point which had the appearance of having been
struck violently by a hammer.

Also of one in which the base of a point, where it was screwed to the
rest of the upper terminal, was split for a length of 11 millimetres (c.
½ inch).

Also of a platinum point screwed on the upper terminal (copper), and
retained by a pin, where the stroke tore away the pin, the point falling
intact at the foot of the lightning rod.

3. _Of Conductors of lightning rods struck, and their contact with the
ground._

The author refers to forty-one cases of lightning rods struck when not
on Harris’s principle.

Of these, 5 were of copper bands soldered together; 5 were of copper
wire either as rope or chain; 1 was made of bands of sheet iron; 11 were
of bars of iron joined by screws or by solder; 3 had pieces of lead
between the parts where they were screwed together; 3 were of simple
iron wire, or of rope or chain of iron wire; 3 were of iron joined
together by hooks; 12 are described as chains (metal not specified); 1
is described merely as a conductor.

The dimensions of the above are seldom given.

The largest bands reported are 16 centimetres (c. 6¼ inches) in width.

The largest bars reported are 55 centimetres (c. 2¼ inches) in width and
15 centimetres (c. ½ inch) in thickness.

The description of the earth connection is also imperfect.

Of eighty-nine lightning rods described as struck, only twelve are noted
as having their ends in running water or wells, and one in damp soil.

Fifteen simply entered the ground, it being noted expressly of six of
these that it was dry.

In three cases were the lightning rods were struck the author found that
the part at the base and in the damp earth had terminated in a plate of
lead, protected above the ground by a wooden enclosure.

Three conductors of ships did not communicate with the sea.

Twenty-three cases are noted of ordinary conductors (not on Sir W. S.
Harris’s principle).

The lightning melted, or reduced almost to powder, three.

The first was on a house, and was of copper wire, the diameter not
known, ending with a chain of iron buried in the earth.

The second was on a ship’s mainmast, and was of iron wire 6 millimetres
(c. ¼ inch), diameter, 46 centimetres (c. 18 inches) long, folded at
their extremities, and united by rings.

The third (also to a ship) was a rope of three strands formed in the
whole of 60 brass wires, each being one half to two-thirds of a
millimetre thick.

The two last conductors had their ends in the sea.

The parts of these conductors, in place of being soldered or screwed
together, were joined merely by hooks and rings like a surveyor’s chain.
Evidently a bad form as their contact is imperfect.

In three other conductors, whose different parts were screwed together
with lead between them, the stroke melted the lead.

This shows the danger of lead from its fusibility, in addition to its
less conducting power.

The author gives examples of this, wherein a leaden pipe, 8 centimetres
(c. 3¼ inches) external diameter, and 13 millimetres (c. ½ inch) thick,
was melted.

He quotes Arago as calling attention to the importance of the form of
the bends in conductors, abrupt bends being dangerous.

Two examples are quoted to prove this, the conductors having been broken
by the lightning stroke at a sudden bend.

To provide lest the lightning, after having struck the lightning rods,
should abandon them for larger masses of metal near them, these masses
should be made to communicate with the conductors.

Cases are cited where the lightning quitted the conductor and struck
metallic bodies near. Also, in respect of painting conductors, the
author quotes a case where part of a bell wire adjoined a lead pipe
which communicated with the conductor. Part of the wire was painted in
oil colour, the other part not. The latter was melted, the first not,
but the paint (though otherwise uninjured) had ceased to adhere to it.

Three examples are cited of danger from conductors ending in watertight
tanks.

In one case the stroke broke the conductor.

In another it left the conductor and injured the building.

In the third it merely melted the point of the upper terminal.

Nevertheless, it often happens that the lightning, in spite of imperfect
communication with the earth, disperses itself inoffensively.

Out of fifteen cases of lightning rods struck, in which the conductors
were simply buried, more or less, in the soil, they carried off the
stroke in eleven without the buildings being injured, or any trace being
left of it, except that the ground was upheaved where the latter was too
dry.

The French Institute, in their report on the protection of the Louvre,
considered it necessary to employ, under certain circumstances, a
conductor with two branches, the one descending into a subterranean
source of water, the other communicating simply with the surface of the
earth.

On the other hand, Arago thought that conductors need not enter the
ground, but communicate only with a metallic surface lying on the
ground.

This view is confirmed by the cases which the author mentions where the
surface of the earth being wetted by rain formed a conductor.

Nevertheless, the two branches are desirable, in case one should fail.

Fifty-five conductors on Sir W. S. Harris’s system are recorded as
having been struck, but the damage was quite trivial.

Two electrical phenomena are to be noted as sometimes occurring when a
lightning rod is struck.

First, when a conductor is formed of metallic plates a peculiar noise is
heard like water pouring on a fire.

Second (independently of the form of the conductor), electric sparks are
emitted from bodies near. The author cites example at Berne, 1815.

4. _Protective agency of lightning rods._

Out of 168 cases of lightning rods struck (_vide_ page 91) there are
only twenty-seven (c. ⅙th) in which the buildings or ships have not been
preserved, and of this sixth many of the conductors were imperfect;
_e.g._, four terminated in earth which was unusually dry, and two of
them were of insufficient size.

Another was formed of pieces having their ends hooked.

Two conductors ended in watertight tanks.

Another was in the form of a surveyor’s chain, the parts not being,
consequently, in close contact.

Others were badly jointed, or had imperfect communication with the
ground or with the sea.

In two cases the stroke broke the conductor at points where its
direction was abruptly changed.

In two other cases the lightning left the conductors struck, and fell
upon buildings near without causing damage to those on which the rods
were fixed.

In the instance of a lightning rod fixed to the mainmast of the
_Jupiter_ (1854), the conductor was made of sixty brass wires, one half
to two-thirds of a millimetre (0·02 inch) thick, and was broken by the
stroke into thousands of pieces. The Institute Committee concluded that
the lightning was not conducted by all the wires of the conductor. Those
which it followed were insufficient to transmit it; some were melted,
some broken. The Committee recommended, therefore, that each metallic
wire be tinned separately at the extremity of the conductor, and
soldered thereto for a length of about a decimeter (c. 0·4 inch), so as
to form a metallic cylinder.

In the last six cases the particulars of the lightning rods are not
given sufficiently to show the cause of their failure, but five are
described as being of chain or ropes of metal wire.

It results from the above facts that when the lightning rods have proved
insufficient protection, their failure has been owing to defects in
their construction; it is rather surprising to find how well buildings
and ships have been protected, even when the lightning rods have not
been well constructed.

In every one of the fifty-five cases where Sir W. S. Harris’s rods were
fixed they have protected the ships, except that not having points some
slight damage has sometimes occurred to the tops of the masts.

This shows their superiority over ropes or chains.

Arago thought that lightning rods were protection against ordinary
lightning, but not when it assumed the form of fire-balls. The author
cites several examples to show that this opinion was not well founded.

He considers a perfectly constructed lightning rod to be a perfect
safeguard.

But he adds that the lightning stroke produces electric disturbances in
its vicinity, although the building be intact.

He cites an example of this in respect of a prison whose inmates (300)
experienced a great enfeebling of their muscular power during some
seconds.

Very few records exist relating to the area of action of lightning rods,
and the elements for determining their protective power are slight. The
author gives a table showing the heights of points, horizontal
distances, &c., in certain cases, and cites four instances of ships
whose foremasts were struck although the mainmasts had lightning rods,
and one where the mizen was struck though the fore and mainmasts were
protected.

                        TABLE GIVEN BY M. DUPREZ.

 ┌─────────────────────┬───────────────────────┬───────────────────────┐
 │                     │      IN METRES.       │   IN ENGLISH FEET.    │
 ├─────────────────────┼─────┬─────┬─────┬─────┼─────┬─────┬─────┬─────┤
 │                     │ 1st │ 2nd │ 3rd │ 4th │ 1st │ 2nd │ 3rd │ 4th │
 │                     │Case.│Case.│Case.│Case.│Case.│Case.│Case.│Case.│
 ├─────────────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┤
 │Length of upper      │  1·5│  3·4│  1·5│  2·3│    5│   11│    5│    8│
 │  terminal, or height│     │     │     │     │     │     │     │     │
 │  of point above     │     │     │     │     │     │     │     │     │
 │  that portion of the│     │     │     │     │     │     │     │     │
 │  building on which  │     │     │     │     │     │     │     │     │
 │  the upper terminal │     │     │     │     │     │     │     │     │
 │  was fixed.         │     │     │     │     │     │     │     │     │
 │Vertical height of   │  1·5│  7·6│  6·7│ 71·2│    5│   25│   22│  232│
 │  point above the    │     │     │     │     │     │     │     │     │
 │  place struck.      │     │     │     │     │     │     │     │     │
 │Horizontal distance  │ 15·2│  7·3│ 17·4│ 59·9│   50│   24│   57│  197│
 │  of place struck    │     │     │     │     │     │     │     │     │
 │  from the base of   │     │     │     │     │     │     │     │     │
 │  upper terminal.    │     │     │     │     │     │     │     │     │
 └─────────────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘

These instances show that we should be misled in considering, as being
protected, a circular space whose radius was double the height of the
lightning rod.

The protected radius appears to be only equal to double the simple
height of the upper terminal above any required point, and reckoned
horizontally from a point vertically under the conductor.

[It will be observed that M. Duprez here contradicts himself in two
consecutive sentences, and in a subsequent part of his work (p. 30) of
the Memoir, he again says: “Aucun des cas indiqués dans le numéro
précédent n’infirme la règle généralement admise, savoir que la sphère
d’action d’un paratonnerre s’étend, dans toutes les circonstances, à un
espace circulaire d’un rayon égal au double de la longeur de la tige,
c’est-a-dire de la hauteur de la pointe au-dessus de la partie du
bâtiment sur laquelle la tige est fixée.”

But the table given by M. Duprez gives two instances in which the stroke
fell within the radius of once the height.—Ed.]


                                RESUMÉ.

In the paragraphs which the author numbers 1, 2, 3, 4, and 6, he refers
to former statements as to the proportion of lightning rods struck, &c.
(_Vide_ page 91, &c.)

5. There being several terminals on an edifice does not seem to diminish
the chances of each being struck.

7. In vessels, when the three masts have lightning rods, the mainmast is
most frequently struck.

8. Refers to Sir W. S. Harris’s lightning rods as being without terminal
rods or points.

9. The points of ordinary lightning rods have been made too slight.

10. Out of fifty-one cases of lightning strokes, thirty points have been
more or less melted; and the fusion is not without danger to the
buildings.

11. The lightning often leaves traces of mechanical action more or less
decided.

12. Refers to defective constructions of ordinary lightning rods.

13. Lead plates in conductors composed of bars joined together are
dangerous.

14. So are abrupt bends.

15. Conductors should communicate with the masses of metal near.

16. And must not end in watertight tanks. But

17. Conductors often protect buildings, though the ground connections
are imperfect.

18. It is well for a conductor to have two branches, viz., one in water,
and the other on the surface of the ground.

19, 23. Refers to the complete efficiency of Sir W. S. Harris’s
conductors.

20. Mentions the noise, electric sparks, &c., given off during a stroke,
as before stated (page 95).

21. Mentions the efficacy of lightning rods generally.

22. Their failure being owing to defective construction.

24. There is no proof that the electricity being in the form of a ball
has been the cause of any conductor’s inefficiency.

25. The lightning rarely bursts on a building or ship without striking
the lightning rod placed on it. Exceptions have, however, occurred in
ten cases, as here described. But

26. None of these instances invalidate the rule generally admitted, that
the protective action of the lightning rod extends, under all
circumstances, to a circular space whose radius is equal to double the
length of the upper terminal, _i.e._, the height of the point above the
part of the building on which the upper terminal is fixed.


                      ON ATMOSPHERIC ELECTRICITY.

                   BY REUBEN PHILLIPS. LONDON, 1863.

                  (_Abstracted by W. H. Preece, C.E._)

This is a pamphlet of seven chapters, and fifty-seven pages, written to
ventilate the author’s own notions of the nature of electricity and its
production in the atmosphere. He considers electricity to be two fluids
of a species of substance, consisting of separated subsidiary atoms.
“Electricity is comparable to a flying bullet; the _vis vivâ_ of the
bullet is like electrical intensity, and the mass of the bullet answers
to the quantity of electricity.” What the subsidiary atoms are like he
does not say.

Chapter I. is a fair resumé of what is known of the electricity evolved
by the friction of wet steam against solids in the hydro-electric
machine. He agrees with Faraday that the cause of the evolution of
electricity by the liberation of confined steam, is not evaporation, but
the friction of the water particles against the sides of the jet-piece
or orifice. Pure gases do not excite electricity; but impure air, when
compressed does, from the friction against the orifice of those
particles of water which are suddenly condensed by the cooling influence
of the expanding air.

Chapter II. is an attempt to show that electricity is evolved by the
friction of “gaseous matter” against water, or _vice versâ_. Ordinarily
the issuing vapour in the hydro-electric machine is positively, and the
boiler negatively, electrified; but cases occur where this is reversed.
According to the author, water by friction against gaseous matter or
air, becomes positively electrified.

Chapter III. applies this theory to thunder clouds, which are formed by
the rapid inter-mixture of masses of the atmosphere thrown into
circulation by heat. There are some capital descriptions of thunder
clouds. They are often accompanied by whirlwinds, and always by rain. It
is the friction of the whirlwind on the drops of rain that developes
electricity—the rain being positively, and the air negatively,
electrified. Hail is due to the ascending current of air carrying the
drops of water to the region of snow and frost! His notions are somewhat
hazy, thus:—“Much of the positive electricity is conveyed to the earth
by the lightning; but the corresponding negative electricity from being
carried upwards with the vertical wind, cannot so easily escape to the
earth, so that the storm cloud contains, on the whole, more negative
electricity than positive electricity” (p. 38.)

Chapter V. contains the author’s explanation of fire-balls, which he
supposes to be a “glowing discharge,” preparatory to the final spark or
flash of lightning. “Probably most of the shooting stars are merely
electrical fire-balls high up in the atmosphere”(!)

Chapter VI. is devoted to the Aurora Borealis, which plays about the
magnetic pole, and is an electrical phenomena of the upper strata of the
atmosphere; and Chapter VII. is an attempt to explain the auroral light
as “probably produced by the collision of the subsidiary atoms when they
are in the act of electro-apposition.”

The pamphlet is said to be a condensed account of the discoveries of the
author in matters connected with atmospheric electricity—discoveries
which were described in papers handed to the Royal Society, but which
that Society did not read. The Royal Society were wise.


    LE COUP DE FOUDRE DE L’ILE DU RHIN PRES DE STRASBOURG. PAR M. F.
                       HUGUENY. 4to. Paris. 1869.

                 (_Abstracted by G. J. Symons, F.R.S._)

A very full account of an accident by ball lightning. The facts are set
out as clearly as possible, the authority is given for every statement,
and most carefully engraved plans and engravings are given of all the
necessary details. It does not bear upon the question of lightning
conductors except in that it shows that a discharge of globular
lightning traversed a horizontal distance of 919 yards, passed in front,
but below the top, of a building which had three good conductors upon it
and struck a chestnut tree, which was by no means the highest tree in
the locality.


     DIRECTIONS FOR CONSTRUCTING LIGHTNING RODS. _From_ “_Essays on
              Meteorology_,” _by_ PROFESSOR JOSEPH HENRY.

          (Smithsonian Miscellaneous Collections. 8vo., 1871.)

                     (_Abstracted by A. J. Frost_).

1. The rod should consist of round iron, of not less than ¾ of an inch
in diameter. A larger size is preferable to a smaller one (ordinary gas
pipe may be employed). Other forms of rod, such as flat or twisted, will
conduct the lightning, and in most cases answer sufficiently well. They
tend, however, to give off lateral sparks from the sharp edges at the
moment of the passage of the electricity through them, which might, in
some cases, set fire to very combustible materials.

2. It should be throughout its whole length in perfect metallic
continuity, either by screwing the parts firmly together or by welding.

3. The rod should be covered with a coating of black paint.

4. It should be terminated above with a single point, the cone of which
should be encased with platinum not less than 1/20 inch in thickness.

5. The shorter and more direct the rod is in its course to the earth the
better; acute angles should be avoided.

6. It should be fastened to the house by iron eyes, which may be
insulated by cylinders of glass; this, however, is not absolutely
necessary.

7. The connection to the earth should be as perfect as possible—in
cities nothing is better for this purpose than to unite it to the gas or
water pipes. When a connection cannot be formed in this way the rod
should terminate in a well containing water, or if this is not
practicable it should terminate in a plate of iron, or some other metal
buried in moist ground. It should, before it descends to the earth, be
bent, so as to pass off nearly at right angles to the side of the house,
and be buried in a trench, surrounded with powdered charcoal.

8. The rod should, in preference, be placed on the west side of the
house, and on chimnies where a current of heated air ascends during the
summer season.

9. A single rod may be placed on small houses, and its elevation should
be at least half of the distance to which its protection is expected to
extend.

10. Metallic roofs should be united with the lightning rods.

11. As a general rule, large masses of metal within the building,
particularly those which have perpendicular elevation, ought to be
connected with the rod.


ON LIGHTNING AND LIGHTNING CONDUCTORS. BY W. H. PREECE, Mem. Inst. C.E.

  (Journal of the Society of Telegraph Engineers, 27 November, 1872.)

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The author refers to the Escurial having been on fire seven times—four
of them certainly from lightning; yet no lightning conductor is fixed
even now.

The average deaths from lightning in England are eighteen per annum; in
France, ninety-five.

From January 1, to July 31, 1872, 9·26 per cent. of instruments, of
different forms, used in the telegraph offices, were injured by
lightning.

Electricity is force, not matter, and _Current_ is a well-defined term
which implies a transference of electricity from one place to another.

Thunderstorms differ only in degree from the phenomena which cause the
ordinary snapping sparks from the machine.

In any case there must be two conducting masses in opposite electrical
states, separated by a non-conductor or dielectric.

The light is the effect of the discharge, and is simply incandescent
matter. It indicates the path of the discharge and nothing more.

Death by lightning is painless.

_Potential_ is that function of electricity which determines its motion
from one point to another.

The path of electrical discharge is prepared beforehand by induction.

The particles of air, &c., are in a state of “tottering equilibrium.” A
moving ship, a man on horseback may destroy this, and we have a
discharge with all the effects of light, heat, and mechanical energy.

It is very doubtful whether thunder-clouds are themselves the sources of
electricity, producing thunder and lightning; they are more probably,
mere accumulators as the coatings of a Leyden jar.

Clouds have been known to be absent during a discharge.

Moreover, the charge of a Leyden jar exists not in the coatings but in
the dielectric separating them.

So the discharge exists in the air and not in the clouds.

Sheet lightning is a mere reflection of forked.

Evidence proves that some such phenomena as ball or globular lightning
exists, and an explanation of it has been given by C. Varley.

Discharge is invariably through the line of least resistance. It may be
through metals, bricks, trees, animals, and not always in a single
track; it is often divided into two, three, or even four lines.

Thus, an electrical discharge in air, is simply a discharge between two
electrified conductors, of such different potentials as to break the
resistance of the dielectric separating them.

There is nothing hidden, mysterious, or unknown in it.

A ship is a prominent object; generally a conductor, and reduces the
line of resistance between the sea (inner coating) and the cloud
(exterior coating of the condenser) determining discharge.

Trees, buildings (except tall spires, &c.) are less prominent.

The effects of lightning experienced on telegraph wires, poles, and
instruments by direct discharge are less numerous than those by
induction, and seldom destructive.

There were only two cases in the past season where line wires (No. 8
iron, diameter 0·170 inch) were absolutely fused.

Accumulation of a charge upon a cloud converts it into a powerful
inducing body.

It induces in the wire an opposite electrical state. Discharge takes
place. The cloud suddenly loses its coercive power. The wire recovers
its neutral condition, and produces a powerful current in opposite
direction.

Wires are affected although buried two feet underground. Unprotected
poles are often destroyed. In one case, twenty successive poles were so.

Instruments have had their cases burst out, wood-work has been burnt,
and the wires of electro-magnets, &c., been fused.

Clouds are not perfect conductors, so do not part with all their
discharge at once. There may be several successive discharges.

_Protection._—Sir. W. S. Harris’s system approved.

_Houses._—Unnecessary expense is often incurred in protecting them.

A warm flue, terminating in a metal grate, is a dangerous conductor, as
it ends in the room and not in earth: hence so many accidents indoors. A
lightning conductor should expose a prominent metallic point, and offer
a path of little or no resistance thence to earth.

Hitherto expensive plates or ropes have been used for this. But the
author thinks galvanized iron wire ¼ inch diameter amply sufficient for
any dwelling house.

Telegraphic poles, protected by lightning conductors of No. 8 wire (½
the above size), have never been injured.

In one case, fifteen per cent. of unprotected poles have been struck.

But no case of damage has occurred for many years since the poles were
earth-wired. The cross-arms are often damaged as far as the earth wires,
never below.

The author can conceive no case in which ½ inch standard galvanized iron
wire is not ample.

The conductor should be solid and continuous from the gilded or platinum
point to the ground.

Joints should be well soldered. Chains and linked rods should not be
used.

Earth connections should be formed with iron gas- or water-mains, or be
several feet in coke, or in a well.

Each conductor should make a separate earth.

All masses of metal in the line of probable discharge are to be
connected with conductor.

Conductors should be examined periodically, they should not be
insulated, nor be near soft metal gas-pipes, nor bent in acute angles.

The area of protection appears to be that of a cone, whose radius is
equal to the height of the conductor.

One conductor is enough for small houses, but each stack of chimneys
should have one in connection with the main conductor.

Lead roofs and iron pipes are easily made into protectors for buildings.

Details given for protecting telegraph apparatus.

The telegraph companies abandoned the use of protectors. The Post Office
re-introduced them with good results. The Indian telegraph apparatus is
protected, and accidents scarcely ever occur.

_Prevention._—Points prevent the accumulation of charges. But with very
tall conductors—as to spires—a current results constantly in one
direction, producing electrolytic action and destruction of conductor,
as proved by one at Llandaff Cathedral.

So earth should be made with large masses of metal, as gas- or
water-mains.

Galvanised iron fastenings should not be used to secure copper
conductors to buildings, as galvanic action would be set up.

_Appendix._—Letters quoted from Mr. Latimer Clark and Dr. Faraday as to
damage to underground wires from lightning.

The _Discussion_ on Mr. Preece’s paper was conducted by Prof. Abel, Capt
D. Galton, Mr. G. J. Symons, who referred to Dr. Franklin’s suggestion
as to cold fusion, Prof. Ayrton, who entered at length into the system
of prevention used with the Indian telegraphs, Sir W. Thomson, and Mr.
Latimer Clark.

Mr. Preece replied, more especially alluding to the phenomena of fire
balls.


LIGHTNING RODS AND HOW TO CONSTRUCT THEM.——BY JOHN PHIN, C.E. New York.
                                 1873.

                  (_Abstracted by W. H. Preece, C.E._)

The author is not an electrician nor a patentee, but the Editor of an
engineering paper called the _Technologist_. The book is written chiefly
to counteract the machinations of a great nuisance in the United States,
called the “lightning rod man.” The Author thinks a good rod as
important as a fire insurance policy. Every case of injury that he has
examined was due to defective rods, or to the absence of them. The
lightning rod is an American invention. He mentions several cases of
marked immunity from accident due to proper conductors, notably St.
Paul’s and the Monument, London; the Cathedral, Geneva; and St. Mark’s,
Venice.

The lightning rod should form the path of least resistance, and it may
be of iron or of copper. If of iron he prefers a flat bar 1 inch by ¼
inch, weighing 13 ounces per foot, or No. 00 copper, weighing 6½ ounces
per foot. He also advocates copper rope.

He thoroughly believes in the conduction through the mass of the metal,
and quotes (p. 12) several experiments in support of that view.

He believes in a good earth and in connecting all waterspouts, eaves,
gutters, and metal work generally with the earth and with the conductor;
he thinks one good rod enough, and sees no reason why lightning rods
should not be painted, indeed, thinks it better to do so, for they
become less unsightly; he has no faith in points, nor in gilding, or
platinising; he recommends instead cast iron caps to chimneys; he
discards insulation as absurd, and suggests that rods may be tacked, or
stapled, or strapped to buildings, although he prefers staples;
recommends strongly that wet earth should be reached, and that as large
a metal surface as possible should be exposed to the ground and embedded
in coke; he does not like any connections with the gas pipes.

He suggests that iron conductors may be welded or have merely butt
joints, but recommends solder with copper, after being bound with fine
wire.

He adduces the fact that Mr. Brooks, of Philadelphia, measured the
resistance of three rods attached to three buildings that had been
damaged, and found the average to be above the resistance of one hundred
miles of telegraph wire.


  TRAITÉ DES PARATONNERES, &c. PAR A. CALLAUD. Paris. 1874. Royal 8vo.

                 (_Abstracted by Latimer Clark, C.E._)

This work consists of 171 pages. It commences with a short history of
the subject, which occupies the first chapter. The remaining nineteen
chapters treat successively of the collecting points and their mode of
action; the conducting rods and the methods of attachment to different
classes of building, and their connection with the earth, with
concluding observations.

The second chapter treats of the height of conductors and the area
protected, in which he follows the usual rules, and recommends lofty
rods, their office being not only to safeguard the building, but to
withdraw electricity silently from the air and thus prevent strokes of
lightning or diminish their violence.

In Chapter III., after citing the opinions of many other writers, he
strongly advocates protectors furnished with sharp points of platina, or
some inoxydisable metal, securely screwed and soldered on to copper
rods, and condemns points of iron or copper. Throughout the work he
treats cost as a secondary consideration and considers it false economy
to spare any expense necessary to ensure the thorough perfection of the
whole system.

In Chapters IV., V., and VI. he gives drawings of connections and of
various forms of weathercocks.

In Chapter VII. he recommends multiple points, especially in mountainous
countries and where storms are prevalent. He also points out that many
buildings are naturally protected by the metal roofs and ornaments
belonging to them. So long as these are connected with the ground, he
prefers that the projecting rod should be of round iron of considerable
length and in one piece, and the conducting cable should wind round it
as a collar, and be strongly attached to it by set screws and soldering.
He does not advise that all the masses of metal within a building should
be connected with a conductor, especially if they are in proximity with
human beings, but with a well-made conductor he considers it safer to
leave them isolated. (Chapter IX.)

For the conductor he recommends Gay Lussac’s construction, viz., a rod
of iron about ⅝ inch square, carried by iron supports, or a twisted
cable of iron wires having a diameter of ⅝ inch to ¾ inch, well tarred
or galvanised, 6 or 8 feet from the soil these are securely united to an
iron bar ⅝ inch to 1 inch diameter. If of copper they may be smaller.
Has seen rods of copper of ⅜ inch effectually protect churches, but
regards this as a minimum size for a length of 80 feet and ¾ inch as a
maximum. The single wires of the cords may have a diameter of 1
millimetre; the joints are made by splicing the strands together and
soldering them. (He recommends conductors of straw in some cases for
country use. Chapter X.)

The conductor is led along the ground in a channel of half drain tiles,
surrounded with coke and terminates in a copper grapnel embedded in a
basket of coke. (Chapter XIII.)

Chapters XIV., XV., and XVI. gives details of the construction of
lightning conductors for tall chimneys, powder magazines, and ships.

In Chapter XVIII. he gives numerous examples of the utility of
conductors, and in Chapter XIX. he gives a _resumé_ of his instructions,
again insisting on the perfect continuity of the connections and the
perfection of all the parts; these instructions are also embodied in a
note read before the Academie des Sciences, in 1862, a copy of which is
given at page 167 of M. Callaud’s work.


BLITZABLEITER-ANLAGEN. PROF. C. ZENGER’S SYMMETRISCHE BLITZABLEITER. C.
                         Korte and Co., Prague.

                 (_Abstracted by G. J. Symons, F.R.S._)

This is really a trade circular, but it gives, in a compact form, the
considerations which have induced Prof. Zenger to propose his new
system, and a description of the mode in which it is carried out. In the
first place it may be well to reprint from the _Meteorological
Magazine_, Vol. VIII. (1873), page 155, the report of the paper read by
Prof. Zenger at the British Association Meeting.


  PROF. ZENGER, ON THE ACTION OF SYMMETRICAL CONDUCTORS AND LIGHTNING
                              CONDUCTORS.

  Professor Zenger read a paper, on this subject, illustrating it with
  the well-known experiment in physics of placing two insulated
  hemispheres of brass plate in contact with another insulated sphere
  of brass. If the former were charged with electricity and removed
  from the inner brass sphere, there was found no trace of electricity
  on its surface. The electricity was shown to be accumulated on the
  surface of the outer spherical conductor, with equal tension in
  every point of the surface. Professor Zenger showed that if the
  outer hemispheres were replaced by two circular wires, no action
  whatever in the inner conductor was found. He said it was easy to
  see that this simple experiment might prove useful in regard to the
  construction of electric apparatus and of lightning conductors to
  protect buildings, and even whole cities, from the destructive
  action of atmospheric lightning. He had, therefore, endeavoured to
  ascertain the effects if any other form of a symmetrically-arranged
  conductor were used, instead of a circular form. In the first
  instance, he had tried the parabolic wires joined to the
  electroscope; next, a rectangular wire with five different openings.
  If placed exactly in the middle of the rectangular wire, no action
  was observed; if placed eccentrically, however, there was small but
  increasing action; and if he placed a needle or another
  sharp-pointed instrument between the protecting wire and the
  electroscope, he still better observed the different action produced
  by placing the electroscope in an eccentrical position. He therefore
  thought that it was possible by symmetrical wires placed on
  buildings, or over whole cities, so to procure an entire protection
  from atmospherical electricity. If the electric clouds should even
  enter between the objects protected and the protecting wires, their
  activity would be greatly diminished, for the wires would become
  immediately charged, and nearly all the electricity accumulated on
  their surface without any danger to the protected buildings.

  Mr. Glaisher, who had taken the chair in the temporary absence of
  the president, said their thanks were due to Professor Zenger for
  his communication upon a subject so important. What they wanted to
  know was the distance at which buildings were protected by a
  lightning conductor, and Professor Zenger’s assertion that the
  sections of a globe were as effective as the whole globe itself,
  would be an important addition to scientific knowledge if proved to
  be so.

  Professor Clerk-Maxwell, who said he had paid some attention to the
  subject of shielding bodies from electrical action by means of the
  wire, feared that the form that Professor Zenger had given them
  would be rather difficult to work out mathematically.

  Professor Zenger said that the correspondent of the _Engineer_
  newspaper had just informed him that the instrument hut of the
  Atlantic Telegraph Company at Valencia was protected by wires on the
  principle he had just mentioned, and the plan of protecting the hut
  had been devised by Mr. Cromwell Varley.

We now pass on to Messrs. Korte’s paper, which refers entirely to the
application of this symmetrical principle to buildings. They begin by
claiming that Prof. Zenger’s system is the only one based upon
scientific investigations and practical experiments, and that although
far better than the primitive arrangements generally adopted it costs no
more. They urge that the conductors should be symmetrically arranged,
and yet they say that they should lead to the side of the house most
exposed to the weather. They recommend that the upper terminal should be
a long oval of gilt brass, something like a blunt spear-head, and that,
in ordinary cases, a single copper rod of 0·20 inch diameter (_not_ a
rope of that size) will be sufficient; it is to be taken through
porcelain insulators, and the earth terminal is to be a copper plate
nearly ¼ of an inch thick, buried from 6 to 9 feet deep in coke.


PROTECTION OF LIFE AND PROPERTY FROM LIGHTNING. By W. MCGREGOR. Bedford,
                          1875. 8vo. 43 pages.

                 (_Abstracted by Latimer Clark, C.E._)

Mr. McGregor does not give any new facts in connection with lightning,
but discusses the theory and action of conductors, and quotes numerous
opinions from other writers, with practical suggestions and precautions
to be observed in fixing conductors.

Among the principal opinions adduced are the following:—

1. Professor Jenkin’s statement, that if a conductor be armed with a
point, the electricity passes into the air rapidly in times of
excitement by induction, and so equalises the tension of the surrounding
atmosphere as to mitigate, or, in some cases, to prevent the discharge
of lightning.

2. De la Rive’s observation that a slight break of continuity in a
conductor is filled by a succession of brilliant sparks during a storm,
though there be no lightning; that blunt points or balls are equally
effective when struck, but are more usually accompanied by explosion
than by continuous discharge.

3. The opinions of De la Rive, Dr. Mann, and Preece, that a conductor
practically protects a conical space—of which the radius is about double
the height—and that the conductor should therefore extend to some height
above the building.

4. Ganot’s opinions that a conductor should terminate in a point or
points, have sufficient sectional area, be thoroughly connected with the
earth, and be connected with lateral metallic surfaces of large extent
if it passes near them; either iron or copper may be used, and existing
rain and water pipes, &c., may be utilised; but the joints should be
made carefully and tested. Chimneys with soot act as dangerous
conductors, and should therefore be protected.

The author does not give any precise directions as to the best form or
size of conductors.


       LYNILDENS FARLIGHED I NORGE. BY H. MOHN, Kristiania. 1875.

                    (_Abstracted by C. Terkelsen._)

The author, having been specially commissioned to enquire into and
investigate the danger of lightning in Norway, found that lighthouses,
telegraph stations, and other much exposed buildings, which were
provided with conductors, did not by far suffer so much as churches,
which in the most cases were unprotected.

Out of about 100 churches reported to have been struck by lightning,
only three were provided with lightning conductors: on the first,
Kongsberg, the conductor was in good order, and the church was
comparatively uninjured; the second church, Fossnes, built of wood, had
a conductor, but made of zinc wire, which melted, and of course left the
church unprotected; on the third, Brónó (struck 17th October, 1872), the
wire had rusted, where it joins the earth, and the church was destroyed.

The author gives a full description of the different cases.

Of 100 churches struck by lightning, fifty-six were totally destroyed,
and had to be rebuilt; twenty-four of that number were churches built of
stone, twenty-nine of wood; the building material of the remaining three
is unknown. It would thus appear that stone buildings are almost as much
exposed to be damaged by lightning as wooden ones. Of the above-named
churches only one can be said to have been saved by a lightning
conductor, viz., Kongsberg. In 1820 the lightning struck the church, set
fire to a great part of the wood-work, and did other damage. The tower
was then covered with sheet iron. In 1852 the lightning struck the tower
again, which, however, then was provided with a conductor consisting of
two thin copper plates, 2½ inches wide, fastened on the north and south
side of the tower, and both beginning with the iron rod, on which the
vane is fastened; but this rod did not end in a point, but in a gilt
cross. The conductors were carried down the brickwork of the church to
the field, and across the market place, and ended in an old water-butt.
When the concussion took place one of the lightning conductors was
disabled; but no material injury was done to the tower. In 1872, July
16th, the lightning struck a farmhouse about 700 feet from the
above-mentioned church; the farmhouse being about thirty feet, and the
tower about 150 feet high.

The construction of a lightning conductor ought to be as follows: It
consists of the following three chief parts. (1) The receiver; (2) the
conductor; (3) the earth connection. The receiver consists of a copper
point 8 inches long and ¾ inch thick; which is screwed into an iron rod,
1½ to 2 inches thick. The screw must fit well and the flats of the
copper and iron fittings must be well connected and afterwards soldered
round the joint to prevent water and air from rusting the iron. There
are various ways of fastening the receiver to the building, but the
engineer is generally guided by circumstances. The conductor may be made
of iron or copper in the shape of rods or wire twisted like rope. If
made of iron rods they should be round and ⅝ to ¾ inch thick; if iron
wire-rope is used the thickness must be equal to a rod of ¾ inch; if
made of copper the rod must be at least ¼ inch thick, or if made of
copper wire-rope ⅜ inch. In both cases the conductor is put in metallic
connection with the receiver, and then guided into earth.

The earth connection is merely a continuation of the conductor and must
be buried as deep as possible in the earth, and reach the water, if it
is to be found.

The end which reaches the water may be constructed in various ways,
according to circumstances, but it is of the greatest importance that
the earth conductor never gets dry. If there is great difficulty in
getting at the water, the earth conductor may be constructed in the
following manner. It is made of copper, and has joined to it as many
branches as are thought necessary. Each branch has rivetted or soldered
to it a copper plate 1 or 2 feet square; they are carried as far away
from the building as possible, and buried deep into the earth. Besides
this there must be laid an extra conductor, perfectly metallically
connected with the chief conductor just under the surface of the earth,
alongside of it, out from the building, with as many branches, and as
long, as possible. This conductor becomes efficient, as soon as the
surface of the earth gets wet through rain, which generally falls during
a thunderstorm.


LECTURE DELIVERED BEFORE THE SOCIETY OF ARTS, _28th April, 1875_. By R.
                             J. MANN, M.D.

                 (_Abstracted by E. E. Dymond, F.M.S._)

Draws attention in the first place to certain established principles.

Different powers of various substances for conducting electricity.

Electrical induction.

In dull fine weather the surface of the earth negative, the surrounding
air commonly positive, the surface of the sea positive.

How a thunder storm begins, gradually approaching cloud, lightning
between it and earth. According to Delisle and Petit, a lightning stroke
_may_ extend 9 or 10 miles, but for ordinary circumstances the striking
distance varies between 650 and 6,500 feet. The lightning stroke follows
the line of least resistance, and invariably falls upon the most
prominent conducting substance, and passes through substances affording
an easy way and offering small resistance without disturbing their
molecular condition; shatters bad conductors; heats, sometimes melts,
good but insufficient ones.

Describes the various forms of lightning—flash, diffused, sheet, and
ball.

A continuous rod of good conducting metal must be carried from the top
of the building to the ground. Describes varying carrying capacities of
iron, zinc, or copper; recommends from his experience in South Africa,
42–strand rope of 1/16th inch galvanised iron wire.

The disintegrating energy is mainly expended on the extremities of the
conductor.

In Natal he used to enclose the top of the rope in a tube of stout zinc,
finished at the top by a gilded ball of wood, and he opened the strands
of the wire above it into a brush. The French electricians strongly
recommend a cluster of points.

The earth contact must be good and damp. The French system of Callaud
described.

Gay Lussac recommended that all large metallic masses should be brought
into connection with the conductor, and the conductor not insulated from
the building. M. Callaud, on the contrary, adopts insulating supports
for the conductor, and condemns the connecting of metals in the
building.

The metals used in the construction of the buildings may be utilised as
conductors; rain pipes, metal ventilating pipes, but not soft metal gas
pipes.


  ON THE PROTECTION OF BUILDINGS FROM LIGHTNING. BY PROFESSOR J. CLERK
                            MAXWELL, F.R.S.

     (Reprinted from the _Report of the British Association for the
                    Advancement of Science_, 1876.)

  Most of those who have given directions for the construction of
  lightning conductors have paid great attention to the upper and
  lower extremities of the conductor. They recommend that the upper
  extremity of the conductor should extend somewhat above the highest
  part of the building to be protected, and that it should terminate
  in a sharp point, and that the lower extremity should be carried as
  far as possible into the conducting strata of the ground, so as to
  “make” what telegraph engineers call “a good earth.”

  The electrical effect of such an arrangement is to _tap_, as it
  were, the gathering charge, by facilitating a quiet discharge
  between the atmospheric accumulation and the earth. The erection of
  the conductor will cause a somewhat greater number of discharges to
  occur at the place than would have occurred if it had not been
  erected, but each of these discharges will be smaller than those
  which would have occurred without the conductor. It is probable,
  also, that fewer discharges will occur in the region surrounding the
  conductor. It appears to me that these arrangements are calculated
  rather for the benefit of the surrounding country, and for the
  relief of clouds labouring under an accumulation of electricity,
  than for the protection of the building on which the conductor is
  erected.

  What we really wish is to prevent the possibility of an electric
  discharge taking place within a certain region, say, the inside of a
  gunpowder manufactory.

  If this is clearly laid down as our object, the method of securing
  it is equally clear.

  An electric discharge cannot occur between two bodies unless the
  difference of their potentials is sufficiently great compared with
  the distance between them. If, therefore, we can keep the potentials
  of all bodies within a certain region equal or nearly equal, no
  discharge will take place between them. We may secure this by
  connecting all these bodies by means of good conductors, such as
  copper-wire ropes; but it is not necessary to do so; for it may be
  shown by experiment that if every part of the surface surrounding a
  certain region is at the same potential, every point within that
  region must be at the same potential, provided no charged body is
  placed within the region.

  It would therefore be sufficient to surround our powder-mill with a
  conducting material (to sheathe its roofs, walls, and ground-floor
  with thick sheet-copper), and then no electrical effect could occur
  within it on account of any thunderstorm outside.

  There would be no need of any earth-connection. We might even place
  a layer of asphalt between the copper floor and the ground, so as to
  insulate the building. If the mill were then struck with lightning,
  it would remain charged for some time, and a person standing on the
  ground outside and touching the wall might receive a shock; but no
  electrical effect would be perceived inside, even on the most
  delicate electrometer. The potential of every thing inside, with
  respect to the earth, would be suddenly raised or lowered, as the
  case might be; but electric potential is not a physical condition,
  but only a mathematical conception, so that no physical effect could
  be perceived.

  It is therefore not necessary to connect large masses of metal, such
  as engines, tanks, &c., to the walls, if they are entirely within
  the building.

  If, however, any conductor, such as a telegraph wire or a metallic
  supply-pipe for water or gas, comes into the building from without,
  the potential of this conductor may be different from that of the
  building, unless it is connected with the conducting shell of the
  building. Hence the water or gas supply-pipes, if any enter the
  building, must be connected to the system of lightning-conductors;
  and since to connect a telegraph-wire with the conductor would
  render the telegraph useless, no telegraph from without should be
  allowed to enter a powder-mill, though there may be electric-bells
  and other telegraph apparatus entirely within the building.

  I have supposed the powder-mill to be entirely sheathed in thick
  sheet-copper. This, however, is by no means necessary in order to
  prevent any sensible electric effect taking place within it,
  supposing it struck by lightning. It is quite sufficient to enclose
  the building with a network of good conducting substance. For
  instance, if a copper wire, say No. 4, B.W.G. (0·238 inch in
  diameter), were carried round the foundation of a house, up each of
  the corners and gables, and along the ridges, this would probably be
  a sufficient protection for an ordinary building against any
  thunderstorm in this climate. The copper wire may be built into the
  wall to prevent theft, but it should be connected to any outside
  metal, such as lead or zinc on the roof, and to metal rain-water
  pipes.

  In the case of a powder-mill, it might be advisable to make the
  network closer by carrying one or two additional wires over the roof
  and down the walls to the wire at the foundation. If there are
  water- or gas-pipes which enter the building from without, these
  must be connected with the system of conducting-wires; but if there
  are no such metallic connections with distant points, it is not
  necessary to take any pains to facilitate the escape of the
  electricity into the earth.

  It is desirable, however, to provide for the safety not only of the
  building itself, but of the system of conductors which protects it.
  The only parts of this system which are in any danger are the points
  where the electricity enters and leaves it. If, therefore, the
  system terminates above in a tall rod with a sharp point, and
  downwards in an “earth wire,” the external discharge will be almost
  certain to occur at the ends of these electrodes, and the only
  possible damage will be the loss of a few particles from their
  extremities; but even if the rod and wire were destroyed altogether,
  the building would still be safe.


 ON BOILER AND FACTORY CHIMNEYS AND LIGHTNING CONDUCTORS. BY R. WILSON.
                                 1877.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The author refers to the wide-spread disbelief in the efficiency of
conductors, the common opinion being that metallic bodies, especially
when pointed, attract lightning, and are therefore dangerous. This is
quite erroneous.

“On an electrified cloud passing over a pointed conductor, the opposite
and induced electricity of the earth is discharged from the point of the
conductor, and the cloud and air are often thereby neutralized without
producing lightning at all. But when a discharge does take place, the
conductor offers a line of comparatively small resistance.”

The author further says that, “if electrified clouds be driven to the
erection in such masses that the opposite electricity does not stream
away from the point of the conductor in sufficient quantities to prevent
a spark from passing, the spark or flash will pass from cloud to
conductor in preference to any neighbouring point.”

He refers to the safety of conductors, as shown by Sir W. S. Harris’s
reports.

When injury to buildings has occurred where lightning rods are fixed,
they have been “ignorantly and wrongly applied,” or joints have rusted,
the rods been broken, or earth contact has become imperfect.

He refers to Harris and Faraday as to sectional area of conductor.
Considers a rope to be better than a rod, as it is less liable to be
fractured and to have badly formed joints.

The upper extremity should project into the air as high as the diameter
of the chimney top.

The rod should not be inside a chimney, as gases are liable to injure
it.

The conductor should communicate with all metal in the chimney.

Insulation is not required.

All contact between copper and iron should be avoided on account of
galvanic action.

Earth contact should be tested every year. Anderson’s galvanometer
approved of for this.


NOUVEAU PARATONNERRE ACCEPTÉ PAR L’ACADÉMIE DES SCIENCES. PAR JARRIANT.
                           8vo. Paris. 1877.

                 (_Abstracted by G. J. Symons, F.R.S._)

This pamphlet is really a letter by M. Francisque Michel respecting some
new patterns of lightning conductors made by M. Jarriant, and submitted
to the Académie des Sciences by M. le Comte du Moncel. The author states
that there have been many theories as to the advantage of conductors
rising to great heights above buildings, and that, on the other hand,
some persons have urged that buildings should bristle all over with
points, and thus prevent any disruptive discharge. He thinks that, owing
to the translation of the storm-cloud by the wind, these short points
will not always have time to act, and says that the only rational plan
is to place a conductor high above the house it is intended to protect,
and so constructed that it, and it alone, offers a path of scarcely
appreciable resistance to the electric discharge. He says that in
Germany they put a metal sphere on the top of the conductors, but in
France, both the Academy and the Commission of the City of Paris have
advised that they should terminate in a point.

M. Francisque Michel says that formerly a conductor was supposed to
protect all objects within a cone whose base had a radius of twice the
height of the conductor; but that he and M. Félix Lucas had investigated
the question geometrically, and have arrived at the conclusion that the
radius cannot exceed 1·75 of the height. Hence, in many buildings, it
became necessary either to increase the number of the conductors or to
make them more lofty, both alternatives leading to increased expense. M.
Jarriant’s design, which consists of galvanized angle iron bolted
together, enables the increased elevation to be obtained at a price
twenty per cent. below that of the old patterns. The angle irons
themselves offer much surface, their angles are useful for discharging
electricity, and they carry at the top the copper terminal recommended
by the Académie.


    A PRACTICAL TREATISE ON LIGHTNING CONDUCTORS. BY HENRY W. SPANG.
                          Philadelphia. 1877.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

“The identity of electricity, manifested by friction, with that
contained in the atmosphere, was not fully verified until Franklin’s
experiment with his kite in June, 1752.”

“In restoring the equilibrium between the opposite electricities of high
potential, the discharge will pass by the shortest path, even though a
poor conductor, in preference to a longer path through a good
conductor.”

The electricity of the earth is usually negative—of the atmosphere,
usually positive.

He quotes experiments at Kew to this effect.

The friction of solid and liquid particles against the earth, and
against each other in the air, produced by the wind, is a source of
atmospheric electricity.

The height of the lower part of the thunder-clouds above the sea in the
United States averages about 2,500 feet.

Dense thunder-clouds are good conductors, and are electrified to a
certain extent by the induction of the electricity contained in the
surface-earth. As electricity accumulates in the thunder-clouds it acts
by induction on the surface-earth, and causes a corresponding increase
of potential in the earth and the objects thereon.

He alludes to the vitreous tubes (fulgurites), 5 feet to 75 feet deep,
as being formed by electricity passing to the subterranean water-bed
through sand or other dry earth.

A highly positively electrified cloud within 3,000 feet of a building
causes the latter to be intensely negatively electrified by induction.

So also the earth beneath the building and the upper portion of the
subterranean water bed.

Whatever offers the _least_ resistance to the stroke will be its chosen
path and it will never leave a very good line of conductors, which is in
a short path between two opposite electricities, for an inferior one.

151 persons are killed by lightning annually in the United States,
France, England, and Switzerland.

He quotes Sir W. S. Harris’s system for the Navy as preventive.

There is no absolute safety anywhere out of doors. It can only be found
inside a structure having good conductors, with good earth connections.

Conductors cannot prevent disruptive discharge. They simply furnish a
good path for lightning which passes over them without doing any damage.

_Protective Area._—A committee appointed in 1875 by the Prefect of the
Seine reports as protected, a circular space whose radius is equal to
1·45 [Should be 1·75, see page (67). Ed.] of height of conductor. But
this is not always to be relied upon.

It is necessary that a conductor extend along the ridge, gable ends, and
eaves of a house, and above each chimney.

Lightning is electricity of very high potential, and the difference of
conductivity between the resistance of copper and iron to a lightning
discharge is small and practically amounts to nothing.

Iron rod conductors not to be less than 7/16 inch diameter. No case is
recorded where such a rod, properly connected with the earth, has been
fused or greatly heated by lightning.

Paint or an ordinary amount of rust does not affect conductivity.

A conductor of large surface exercises a much greater protective action
than the same quantity of metal in the form of a wire or solid rod.

Not because electricity in motion resides on the surface, but that the
expansive action of a discharge may have a wider scope _through_ the
metal.

So iron rain water-pipes are good conductors, and should be connected
with metal spouting, conductor on ridge, &c.

Cable conductors bend easily and can be made in one length, so often
answer better than bars.

If earth connection is good, rusty joints are of little consequence.

Conductors are not to be insulated.

Iron pipes for gas, water, heating, &c., also iron columns extending
from basement to near the roof are to be connected with conductor and
earth terminals.

The pipes on each side of gas meter are to be connected by iron bands.

Air terminals are to rise about 4 feet above each chimney or other
elevated projection.

High steeples to have horizontal conductors round them at every 20 feet
in height connected with vertical conductors.

One terminal in the centre of a building not over 25 feet long or wide
is sufficient, or one at each end of the ridge. One to each 20 feet of a
large building, with one at each end and to each chimney, &c.

When the horizontal portion of a lightning conductor, or path along the
roof of a building from ridge to eaves (_sic_) exceeds 50 feet in
length, the path becomes rather indirect for a lightning discharge,
which is then apt to select a shorter route through the building.

The upper part of terminal need not be gilt.

Points are practically of no use.

Chimneys are very likely to be struck, owing to the heated air rising
from them.

Provide against this by metal caps.

There is danger also, owing to the vapour rising from them, from barns
stored with new hay or grain, stables, schools, churches, &c.,
containing many people, flocks of sheep, &c.

Earth terminals must be in moist ground.

The author quotes Prof. F. Jenkin as to the difference of conductivity
between well moistened and perfectly dry earth (as porcelain, &c.) in
electricity of low potential, as 1,000,000,000,000 to 1.

Gas and water mains usually 4 feet or so deep in dry earth, therefore
not good conductors.

Examples quoted of injury to their joints by lightning, which passed
from conductors to the mains.

Suggests, as earth terminal, an iron pipe, 10 feet long, 2 inches
diameter, open at each end, perforated at sides, put in vertically, and
having the water from pipes for rain and waste led into it.

To be 8 feet from foundation.

Gives engravings of numerous forms proposed for conductors, most of them
being defective, and none show improvement on Franklin’s round rod.

Copper rods held by iron staples, and connected with iron earth
terminals, are bad, owing to galvanic action.

Copper wires in cable conductors become brittle, and snap when vibrated
by the wind; sometimes, also, they are eaten away by electrolytic
action.

He gives a drawing of a house protected as suggested by him, viz., by
metal rain water-pipes connected with the metal gutters and ridge; also
with his improved earth terminal by a good iron bar conductor.

Gas, water, and other pipes are to be connected together, and with
conductor.

These often give better path for lightning than the conductors.

But dangerous if without proper earth terminal.

He disagrees with Prof. C. Maxwell’s theory as to disconnecting the
metal covering, &c., of buildings from the earth.

Lightning conductors detached from buildings do not afford absolute
protection.

Lightning has great affinity for gas-holders, so one of the nearest
guide columns should be connected by a metallic conductor with the pipe
leading to street main, and also with a vertical earth terminal.

When a telegraph line is altogether metallic, well insulated upon poles,
&c., and not metallically connected with the earth, the electricity of a
storm-cloud will not exert so strong an inductive influence upon it as
upon a line whose ends terminate in the earth.

Line wire is often melted, poles and apparatus shattered, and employés
sometimes killed.

As a remedy, a galvanised iron wire is now fastened to every fourth pole
by iron staples, from 4 inches above the top of the pole to a coil about
10 feet long of iron wire beneath its lower end.


       UEBER BLITZABLEITER UND BLITZSCHLÄGE IN GEBÄUDE WELCHE MIT
    BLITZABLEITERN VERSEHEN WAREN. VON G. KARSTEN. Kiel. 8vo. 1877.

                  (_Abstracted by R. Van der Broek._)

In this pamphlet Dr. Karsten gives an account of two cases in which
buildings that were provided with lightning conductors were damaged by
lightning. The author states that the statistics for the year 1873 show
that in Schleswig-Holstein twenty-six per cent. of all the cases of fire
were caused by lightning; 1/130th part of these cases occurred in the
towns and the remainder in the country.

Do lightning conductors guarantee absolute protection? The author
answers this question as follows: There is no absolute certainty in
empirical matters; each new case may direct our attention to
circumstances that had been overlooked. If lightning conductors cannot
be said to ensure perfect safety, they certainly afford a very high
degree of protection.

The flash of lightning which struck the church at Garding, on the 18th
of May, 1877, fractured the conductor in fifteen places and pierced the
wall of the steeple in two places. The inefficiency of the conductor
resulted from the carelessness with which it was fixed; the line was
laid down the north side of the steeple and fastened with twenty-five
wall eyes; these wall eyes were hammered too deep into the wall, thus
damaging the line and forming a short and sharp bend in each case,
besides also unduly straining the wire. The damage to the steeple was
the consequence of a neglected secondary circuit. There are an
excessively large number of tie-rods in the steeple; the heads of these
rods are not connected together, neither are they, except in one case,
in close proximity to any of the larger masses of metal that are about
the building. The conductor passed close to one of those heads; the
south side of the steeple, where the opposite head is, becoming wet
through the rain, a secondary circuit was formed, and a return shock
followed; the damage to the steeple was trifling.

The rod was provided with a conical point rather blunt but surmounted by
a short platinum point. The copper line-wire was of good material—not of
a uniform thickness, but at the weakest places not weighing less than
240 grammes per lineal metre (8 oz. per yard or rather less than ¼ inch
diameter if solid). The earth-plate was sunk into a well 10 metres deep,
and tested faultless after the discharge.


  ÉTUDE SUR LES PARATONNERRES LEUR CONSTRUCTION LEUR INSTALLATION. PAR
                      JARRIANT. 8vo. Paris. 1878.

                 (_Abstracted by G. J. Symons, F.R.S._)

This pamphlet opens with two pages devoted to the consideration of
Michaëlis’s work published in 1783, “De l’effet des pointes placées sur
le Templè de Salomon;” then it becomes more practical, refers to the
Academy of Bordeaux propounding in 1750 the question as to the identity
of lightning and electricity, and to Franklin’s letter in the same year
to Collinson, giving his reasons for believing in the analogy; states
that the experiments suggested by him were repeated by Buffon and
Dalibar in March, 1752, and subsequently repeated at Marly before Louis
XV. Then the writer refers to the erection of the first conductor in
France, to the popular displeasure which it excited, and to the long
legal process before the proprietor was allowed to keep it in position.

The author thinks that in many cases it is better to slightly increase
the number of conductors than to make them of excessive length, because
the latter course causes them to fatigue and jar the roof timbers by
their vibration with the wind.

Respecting platinum points he speaks strongly and to the following
effect:—“I have already mentioned that Franklin’s first conductor was
melted. Since then, the upper terminals of conductors have been made of
platinum, because it is the least fusible, the least oxidizable of all
metals, and a very suitable one for making into points. Moreover, the
sharper a point the greater its preventive action, and hence I condemn
every conductor without a platinum point. Although some manufacturers
employ simple copper cones, which may certainly last some time without
deterioration, believing in the desirability of the points being always
in perfect order, I reject their system entirely.”

Few persons are used to making platinum points, it is a Parisian
speciality, those which the author prefers, form a cone of about 10
degrees at the opening of the point and are about 1½ inches long, then
screwed and soldered into a mass of copper forming a nut on the conical
copper rod, which is 1 foot or 1 foot 6 inches long. The platinum point
thus mounted can only give rise to a galvanic action so extremely feeble
as not in the least to affect the durability of the apparatus. Some
persons for the sake of cheapness suppress this platinum point, but they
are wrong, the saving is slight and the result defective. The author
objects to conductors made of bar iron because the joints are always
defective, and if the section be too small they may be so heated as to
set fire to the charcoal in which the lower extremity is buried.(!)
However, the author prefers a rope, but he does not say whether of iron
or copper, and he puts a strand of hemp in the middle so as to make it
more pliable.

“Arrived at the ground the conductor ought not to be in immediate
contact with the earth, for the damp would slowly destroy it; we avoid
this (?) by making it pass through a trough filled with coke. Experience
has shown that iron thus buried in coke undergoes no change even during
thirty years.... Broken coke is better than charcoal because of the
great quantity of water which it absorbs.”

The author then says that after passing through this trough the
conductor must be continued into a well, or into very moist earth, and
should end with a discharger like a fork with many prongs.

He recommends that all the iron be galvanized.

Although the concluding paragraph, coming from a manufacturer, sounds
rather like self-recommendation, it undoubtedly contains important
truths. M. Jarriant says:—

“I cannot too strongly advise that in erecting conductors those
specialists should be employed, whose studies and constant practice
enable them to ensure perfect work. It is necessary also that every
workman should remember that in placing a lightning conductor he holds
in his hands the lives of men, that he should feel conscientiously
interested in the perfection of his work, and, finally, that he should
feel that it is a mission which he fulfils, and not a mere matter of
trade at which he works.”


REPORT ON THE LIGHTNING CONDUCTORS OF THE SMALL ARMS AMMUNITION FACTORY
  AT DUM DUM, CALCUTTA. BY W. P. JOHNSTON. Government Telegraph Press.
                               1878. 4to.

                  (_Abstracted by W. H. Preece, C.E._)

This is an interesting report of a careful inspection and an electrical
testing, by a skilled electrician, of the lightning conductors at this
place. Although most carefully protected by well arranged and adequate
copper rods, copper bands, iron rods, and iron tubes, and terminated in
points, it was found that the points were covered either with rust or
with paint, and that the earth connections were so bad as to render the
buildings unsafe, although there was no difficulty in obtaining a good
earth at any part of the factory.


   ATMOSPHERIC ELECTRICITY. BY DAVID BROOKS. Philadelphia. 1878. 8vo.

                  (_Abstracted by W. H. Preece, C.E._)

A pamphlet by a distinguished American telegraph engineer, giving his
view on the magnitude and origin of atmospheric electricity, which he
attributes principally to the friction of air on ice in the Polar
regions, and which circulates southwards in the higher regions of the
air, and northwards in the crust of the earth. Hence also Aurora
Borealis which is always preceded by high winds and most frequent when
the earth is covered with snow.

Thunderclouds are usually about 2 miles high and from 13 to 23 miles
thick. Lightning is much less frequent in mountainous than in plain
countries. Copper lightning conductors are often applied to iron ships
and iron buildings, but absurdly, as they are in such cases superfluous.

The author advocates immense earth plates where there are no gas- and
water-pipes, which he calls the best lightning rods ever erected,
because they are electrically in perfect connection with the earth. The
track of a railway makes a capital earth. He has never known an accident
where proper conductors were used, whereas he has known many accidents
from imperfectly and improperly constructed lightning rods, though of
the latest and most approved patents.


CATALOGUE MESSRS. A. COLLIN ET FILS, Article PARATONNERRES. Paris. 4to.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

The authors state that a Municipal Commission has recommended, to the
exclusion of all other points, copper about ¾ inch diameter, terminating
in a cone of 30°.

As to the area protected Messrs. Collin refer to the reports of the
Academy in 1823 and 1854, admitting, as a limit of protected area, a
circumference of which the radius equals double the height of the upper
terminal for slightly elevated buildings, and simply the height for
towers, &c., but this rule is badly defined.

The authors quote formulæ based upon the assumed altitude of the storm
cloud, but state them to be unreliable.

The Academy in 1854 reports that an electrified cloud is equally
attracted at equal distances by a metallic part of the roof and by the
terminal of the conductor.

Exposed points of pinnacles, &c., are to be united to main conductors.

If copper be too expensive use iron wire.

The conductors are to be supported at about 10 centimetres (4 ins.) from
walls and roofs.

The Academy recommends them to be isolated on glass or porcelain, but
the New Commission rejects this, and suggests that all metallic parts be
united to the conductor,—also recommends that wells be sunk to water
level, as earth connections.

But this would often entail a depth of 20 to 100 metres, or even more.
So the conductors may be sunk into moist earth and surrounded with coke,
and if necessary, may terminate in a sheet of copper.

A good earth is very important. Connection with water mains advised.

The authors have fixed 8,000 lightning conductors on their principle
without failure.

They give engravings of the various parts.

They engrave a diagram of a powder magazine which they propose to
protect by a tall isolated lightning conductor fixed at a distance from
it, and at such a height as that it will be included in a cone whose
radius is equal to the height of the conductor.


              THE SCIENTIFIC AMERICAN, NOVEMBER 1st, 1879.

                   (_Abstracted by Alfred J. Frost._)

We learn that a lightning rod company in Cincinatti has patented a
system of lightning protection, which consists of an iron rod running
along the ridge of the building with points at each end projecting
upwards. It is supported upon large glass insulators, and has no
electrical connection with the building, and no rod running to the
ground. It is said that there are many public buildings in Iowa which
have been provided with this system of lightning rods.

Professor Macomber, of the Iowa Agricultural College, in reply to an
inquiry, says that it would be possible that a house insulated with a
glass foundation could be struck by lightning, but adds, “By insulating
a building the tendency to be struck by lightning would be very much
lessened, and the severity of the shock much decreased. Practical
illustrations of this can easily be obtained by means of an electrical
machine. A spark can be made to pass from the machine to an insulated
body, although the force of the shock will be much less than when not
insulated. Practically, it would be almost impossible to insulate a
building, because after rain commenced to fall it would wet it so that
communication with the earth would be established.”


 REMARKS ON THE ATMOSPHERIC ELECTRICITY AND ON THE ACTION OF LIGHTNING
     CONDUCTORS. BY PROF. DR. G. KARSTEN. 2nd edition. Kiel, 1879.

                  (_Abstracted by H. Van der Broek._)

The author of this pamphlet, Prof. Dr. G. Karsten, states that
thunderstorms are particularly dangerous in Schleswig-Holstein. He
attributes that fact to the scarcity of woods in that province, not more
than five per cent. of the surface being wooded; whilst in the Prussian
empire the proportion of woods is twenty-three per cent.

Woods promote a uniform dampness of the atmosphere and lessen the
up-current of air, which up-current contributes considerably to the
formation of thunderstorms; and the woods thus cause the discharges of
the electricity to take place principally between the clouds.

We do not yet know with certainty what the causes of atmospheric
electricity are, but we do know under what conditions or circumstances
thunderstorms may occur.

Thunderstorms are only formed when a violent condensation of the
rarified particles of water, which the atmosphere contains, takes place.
Such a sudden condensation, and the consequent formation of a
thunderstorm, may occur when two different masses of air—the one moist
and warm, the other dry and cold—intermix rapidly. The former of these
currents we call the South, or Equatorial current, the latter the North,
or Polar current. If these currents penetrate each other, or intermix
slowly, long continued falls of snow and rain ensue; if they mix rapidly
thunderstorms are formed during the warmer seasons, and sometimes also
during the colder seasons.

The Schleswig-Holstein Provincial Fire Insurance Association alone paid,
in sixteen years, the sum of £102,832 (an average of £6,427) for damages
caused by lightning. This province loses altogether £12,500 per annum
through fires caused by lightning.

The author’s very interesting remarks on the construction of lightning
conductors are briefly summarised in the following general rules:

  1. Copper and iron form the best materials for lightning conductors;
      lead and zinc may be used for secondary conductors.
      (Nebenleitungen.)

  2. If the conductor be constructed of iron, it should weigh from 1,200
      to 3,400 grammes per metre (2½ lbs. to 7 lbs. per yard), according
      to its length; a copper conductor should weigh, under the same
      circumstances, from 250 to 600 grammes per metre (½ lb. to 1¼ lbs.
      per yard).

  3. The conductor must be connected with all the projecting corners and
      pointed parts of the building.

  4. There must be no sharp curves or bends in the conductor.

  5. The conductor must be connected with all the large and extensive
      masses of metal that may be about the building. This connection
      may be made by wires leading towards the rod, as well as in the
      direction of the earth contact.

  6. The rods must be surmounted by good points, which must not be
      liable to be fused by the discharges of the electricity.

  7. The height of the rods must be in proportion to the size and shape
      of the buildings; but it is better to erect several short rods
      than one extraordinarily long one.

  8. In making the connection with the earth all sharp curves must be
      avoided.

  9. The underground part of the conductor must be made of galvanized
      metal, so as to minimise the effects of oxidation, or, in case a
      layer of coke is used, to prevent the action of the sulphur.

  10. The earth-contact should terminate in a plate, which, if possible,
      should always be immersed in water. If this can be so arranged the
      plate must have a surface ⅒th of a square metre (1 foot square)
      for conductors for small buildings, whilst a plate of a surface of
      2 square metres (5 feet square) will be sufficient for conductors
      for the largest buildings.

  11. Where a permanent contact with water cannot be established,
      several plates of a larger size must be used, and laid in a
      stratum of coke.

  12. In the case of very large buildings, provided with several rods
      and secondary conductors, several earth-contacts should be made
      which should be connected with each other.

With reference to the upper terminal point, the author remarks, in an
appendix to the second edition of his pamphlet, that it should be made
of a conical form of a basis of from 20 to 30 millimetres (0·8 in. to
1·2 in.), and of a length of 150 millimetres (6 inches); it must consist
of pure copper and be gilded. It is useful to provide it with a platinum
needle 15 millimetres (half an inch) long, and about 4 millimetres (0·2
inch) thick at its base; or with a cone of chemically pure silver, the
proportion between whose base and height must be as 2 : 3.


        LIGHTNING CONDUCTORS. BY RICHARD ANDERSON, London, 1879.

            (_Abstracted by Prof. T. Hayter Lewis, F.S.A._)

 _Historical Facts_—

The following are brief references to some of the principal facts
recorded in this volume:—

1600 A.D. Dr. Gilbert showed that magnetic and electrical phenomena were
emanations of one force.

1650. Otto Von Guericke constructed a little electrical machine (mainly
of a ball of sulphur on a revolving axis).

Sir I. Newton constructed a machine of glass, but used it merely for
amusement.

1675. The polarity of a ship’s compass was found to be reversed by a
stroke of lightning.

1708. Dr. Wall said that the light and crackling of rubbed amber seemed
in some degree to resemble lightning and thunder.

1709. F. Hauksbee, F.R.S., showed the similarity between the electric
flash and lightning.

1720. S. Gray, F.R.S., showed this by experiment, but was discredited.

1745. The first great step in this science was made at Leyden, by J. N.
Allamand and P. van Musschenbroek, who discovered the properties of the
Leyden jar. The priority of this invention disputed by Dr. Winckler, of
Leipzig; a mania for experiments arose. Louis XV. tried them,
unsuccessfully, on 180 of his Guards; but with perfect success on 700
Carthusian Monks.

1746. _Dr. Franklin_, of Philadelphia, saw some electrical experiments,
and in

1747 received a glass tube and some books on electricity from London;
then began to make experiments; sold his business, bought apparatus and
made electricity his study. Discovered that electricity passed most
easily and quickly through sharply pointed metals; that it was positive
and negative; and that lightning and electricity were identical. He sent
these results to the Royal Society, who refused to allow them to appear
in their Transactions; he then published them in a pamphlet. It was not
appreciated in England, but met with great applause in France, and was
also translated into German, Italian and Latin.

1747. The subject was taken up in England in a thoroughly practical
manner. Dr. Watson, Mr. Folkes, Lord C. Cavendish, Dr. Bevis, &c.,
experimented on a wire stretched across the Thames. The charge was found
to come back by the water. The same result followed through moist earth.
A gun was fired at a distance of four miles; the passage of the charge
appearing to be instantaneous.

New experiments were made by Dr. Watson with glass rods, 2 and 3 feet
long and 1 inch diameter. These showed that the rods, &c., contained
electricity only as a sponge holds water.

1752. Experiments by Messrs. Dalibard and De Lor, at Marly-la-Ville,
near Paris, in May, described.

1752. July. Franklin tried his Kite successfully, then his fame was
established, and he erected, on his own house, the first lightning rod.

1753. Prof. Richmann, St. Petersburg, was killed whilst experimenting.
The use of conductors opposed, violently in France, by Abbé Nollet.

1755. An earthquake at Massachusets, was laid to the charge of the
numerous lightning conductors. Franklin pushed their use by means of his
publication, “Poor Richard,” which had an enormous circulation;
particulars given showing success of lightning conductors.

1762. The first lightning conductor used in England, and Dr. Watson
asked to send in designs for lightning rods for ships. He did so, but in
an unpractical way, and they were disused.

1764. St. Bride’s steeple struck.

1769. The Dean and Chapter asked Royal Society for advice as to
protecting St. Paul’s. Committee of Royal Society disagreed as to
whether rods should be pointed. Pointed rods were used.

1769. The first conductor fixed to a public building in Europe was to a
church steeple in Hamburg.

De Saussure, at Geneva, had some difficulty in explaining to the
citizens that his conductors were not dangerous to his neighbours. There
was a great fear, generally, as to their use, _e.g._, a lightning rod
was erected, secretly, by the Priests at the Cathedral of Siena, and
excited great terror in the townsmen when discovered, but a terrific
stroke of lightning left the tower uninjured.

1772. Dr. Ingenhousz’s experiments.

1774. The University of Padua protected by conductors.

1777. A building at Purfleet was struck though it had a conductor, but
this was shown to be defective.

Sir J. Pringle had to resign his Presidency of the Royal Society because
he advocated points, but experiments were made and ended in favour of
points.

1778. The Venetians decreed that lightning rods should be erected
throughout the Republic.

1819. Electro-magnetism discovered by Œrsted.

1822. Sir W. S. Harris took up the question of providing good conductors
for ships, and afterwards made a list of 250 accidents to ships in 40
years; also of 200 seamen killed or wounded in that time. At this time
no importance was attached to the subject in England, except in the case
of Sir W. S. Harris. He insisted on the necessity of lightning rods. A
commission of inquiry was appointed by H.M. Government to investigate
the best method of applying lightning rods to H.M.’s ships, and they
reported (in 80 pages folio) that lightning rods were rather new fangled
things, but might be tried, without special harm to anybody. So most
ships were fitted with them after Sir W. S. Harris’s design. He was
knighted in 1847. An iron built ship, metal rigged, is as well protected
from lightning as Solomon’s Temple. Harris combated the opinion of those
who said that lightning rods attracted lightning.

Even in 1826 a government engineer recommended, on this ground, that all
lightning rods should be pulled down, and, in 1838, the Governor-General
of India ordered this by the advice of his “scientific officers.” This
was not countermanded until several buildings had been destroyed.

Army circulars are now regularly issued, containing Sir W. S. Harris’s
suggestions. (These quoted by Mr. Anderson).

Sir C. Barry suggested that Sir W. S. Harris should design lightning
conductors for new Houses of Parliament. He reported in 1855. He used
conductors of 2 inch copper tubes, ⅛th-inch thick, to towers and other
elevated parts, secured to masonry by metal staples. The cost was
£2,314.

As to conductors, Le Roy recommended that they should rise not less than
15 feet above chimney and summit of any edifice.

Mr. Anderson gives technical names of parts of lightning rods in
different countries. Chains first used, and gave rise to many accidents.
Tin and lead conductors tried; lead especially, from its easy
application to sharp curves, &c., but it is liable to be broken, and is
a bad conductor; so it went out of use.

Some particular buildings are constantly under attack from lightning,
_e.g._, Church of Rosenberg in Carinthia, not standing in a very high
position, but greviously damaged in 1730, &c.; rebuilt in 1778, with
lightning rod, and not injured since. Some of these effects may be
explained on meteorological grounds: the height and thickness of the
charged clouds only slightly varying, perhaps, in districts where there
are prevailing winds. The height of clouds sometimes enormous. Instances
are given of their being 15,000 to 25,000 feet above the sea. But
sometimes clouds are almost flat on the earth, two instances are given
of this. A remarkable and often fatal discharge is the “return stroke,”
always less violent than the direct stroke, but often very powerful, and
caused by the inductive action exerted by a thunder-cloud. Men and
animals are charged with opposite electricity to the cloud. When the
latter is discharged by the recombination of its electricity with that
of the ground, the induction ceases, and all bodies charged by induction
return to a neutral condition. Hence the dangerous “return stroke.” Lord
Mahon first demonstrated this by experiment. _As to origin_ of
atmospheric electricity, De Saussure considered it due to the
evaporation of water by the sun’s heat. Peltier (1765–1845) considered
the earth itself to be one immense reservoir of electricity. As light
comes from the sun, so electricity is generated by heat from the
interior of the globe. No electricity is produced by atmosphere, nor
held by it, except temporarily.

There is no recorded case in which a well made lightning rod, with “good
earth,” did not do its duty.

In 1822 there was an extraordinary number of thunder storms in France,
so lightning rods were ordered by Minister of Interior for all public
buildings, and he applied to the Academy of Sciences for advice. 1823. A
Committee (Gray Lussac, &c.) reported. They laid it down, as a rule,
that a lightning rod protected a circular area, having a radius of
double the height of the rod; and they said nothing about regular
inspection of lightning rods. So disasters occurred, and another
Committee was appointed (Pouillet, &c.). They reported 1854. The theory
as to the protected area was abandoned. It was recommended that
lightning rods should have as few joints as possible. The joints to be
well soldered, the points to be of copper (not platinum), and not to be
very finely pointed. The rods to be of copper, not iron. The Louvre was
well protected by lightning rods, but slightly injured, 1854. Another
Committee was appointed, and, 1855, Pouillet again reported on its
behalf. It recommended that the points (always of copper) should be
thicker, and the rod to have a never-failing connection with water or
moist earth, 1866. Several French powder magazines were struck though
provided with lightning rods, and the Minister of War asked the Academy
for another report. Another Committee (Becquerel, &c.) was appointed,
and, 1867, Pouillet again reported. He defines lightning as an immense
electric spark passing from one cloud to another, or from cloud to
earth, to restore equilibrium. The best protection for a building would
be iron rods surrounding it on all sides, and passing deep into ground.
Conductors should be inspected every year.

The conductor now remains essentially as Franklin invented it. Of the
inner nature of “lightning” we are utterly ignorant. The first
conductors were always of iron as being cheap.

Sir H. Davy pointed out the different conducting powers of different
metals. Becquerel, Lenz, Ohm, and Pouillet made similar investigations,
with the following results:—

 ───────────┬─────────┬─────────┬─────────┬─────────┬─────────┬─────────
            │ Silver. │ Copper. │  Lead.  │  Tin.   │  Iron.  │Iron = 1
            │         │         │         │         │         │Copper =
 ───────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────
            │         │         │         │         │         │
 Davy       │  109·1  │   100   │  69·1   │         │  14·6   │  6·85
            │         │         │         │         │         │
 Becquerel  │  73·5   │   100   │   8·3   │  15·5   │  15·8   │  6·33
            │         │         │         │         │         │
 Lenz       │ 136·25  │   100   │  14·62  │  30·84  │  17·74  │  5·64
            │         │         │         │         │         │
 Ohm        │  35·60  │   100   │   9·7   │  16·8   │  17·4   │  5·75
            │         │         │         │         │         │
 Pouillet   │  81·26  │   100   │         │         │ 18·2 to │ 5·49 to
            │         │         │         │         │  15·6   │  6·41
 ───────────┴─────────┴─────────┴─────────┴─────────┴─────────┴─────────

 (The difference being owing, probably, to the greater or less purity of
                               the Metals.)

1815. Brass wire rope generally used in Bavaria, but a steeple was
struck down though with a brass wire conductor 1 inch diameter. The real
defect was “bad earth,” but attributed to bad form of conductor; so this
was abandoned. Brass not a reliable metal, and often destroyed by smoke.
Purity of copper essential.

Professor Matthiessens’ experiments shewed that the conductivity of
copper varied from—

                         Pure               100·
                      to Australian          88·86
                         Russian             59·34
                     and Spanish, Rio Tinto  14·24

Hotel de Ville, Brussels, lightning rods designed by Professor Melsens
on the principle of a great number of small ones in preference to one of
large size, and covering building with network of metal, having many
points and many earth contacts. He considers that the relation of
section to surface of the lightning rod has a marked and definite,
though unknown, result.

Author describes weathercocks and methods of fixing them.

_Lightning rods generally_—methods used in France: Terminal rods,
usually of wrought iron, galvanized; their height depends on the size
and area of building it protects. This is generally to be considered to
be within a cone of revolution, of which the radius = height of rod
above ridge × 1·75.

Points described. The conductors are of iron, rebated, soldered, and
bolted at joints, with lead between. Bent plates of copper introduced to
provide against contraction and expansion. In large buildings, metallic
connections are formed on ridge by iron bars-¾ in. × ¾ in.

Precautions are taken against the destruction of iron underground, viz.,
by enclosing it in vertical sprints of wood, tarred or creosoted, rising
a few inches above ground, or by a coating of tar or by a wrapper of
sheet lead. The earth connection is a trough filled with broken
charcoal, through which the conductor passes, ending in several
branches, or in a grating between layers of charcoal. Galvanized iron
cables sometimes used, and (rarely) copper of ½ in. diameter.

_America._ Gutters and water pipes, &c., used where possible. If the
roof be of wood, slate, &c., a conductor is laid along ridge, and
connected with gutters and rain water pipes. If these latter be less
than 3 in. diameter, the conductor is often extended from roof down the
side of building close to the pipe. All metal chimney caps, railings,
water and gas pipes, and other large or long pieces of metal, inside and
out, are connected with conductor. The upper terminal usually projects 4
ft. above chimney or other highest part of building. It is a round rod,
7/16th in. diameter, hammered out to join it to conductor. A building 25
ft. wide and broad has one terminal in centre and one at each end. In
larger buildings, one terminal to each 20 ft. of roof. Not always
pointed.

Steeples have horizontal conductors at every 20 feet, connected with
vertical conductors, to provide against discharge in centre, caused by
deflection of discharge in the air by rain. Conductors are fixed to
buildings by iron staples or straps; the earth connections are similar
to ours. Also are used iron pipes, about 3 in. diameter and 10 ft. long,
placed vertically in moist earth and carefully connected with conductor.

_Newall’s system_: Copper conductors are the best, and in the end,
cheapest. Terminal rods are usually 3 to 5 ft. long, and ⅝th to ¾ in.
diameter, branching out at top.

_German_ “reception rod” described as being of iron, 10 to 30 ft. long;
the area of protection theory discredited. The electric fire, seeking
its nearest path to earth, is not to be diverged from it to the rod.
These high rods of no use except, _e.g._, near high trees, and are often
dangerous from being blown down. Barns containing new hay are likely to
be struck, as hay sends out stream of warm air.

Designs explained for protecting private houses by short terminal points
to chimneys, gables, &c. A copper rope at least ⅝th in. diameter should
be used; a copper rod, ½ in. diameter, has never been fused, so far as
is known. In chimneys of manufactories, where rope is liable to
corrosion, a greater thickness should be used.

Laughton-en-le-Morthen steeple injured, though with lightning rod, but
this was only a small, thin copper tube, ⅞th in. external diameter, and
1/32 in. thick; weighing 8oz. per foot, or equal to a rod about 0·12 in.
diameter, the joints were corroded, and the earth contact was imperfect.
Nevertheless, only one buttress was injured. It is of little consequence
whether the conductor be inside or outside, if it be carried to earth by
the shortest route. At first it was more generally put inside in France,
but this was given up for fear of accidents. But it is beyond
controversy that a good conductor is absolutely harmless to all
surrounding objects, and a man might lean against a copper half-inch
rod, carrying off a heavy stroke of lightning into “good earth,” without
being aware of its passing.

It is useless and dangerous to isolate conductors from buildings. All
masses of metal should be connected with conductors.

Prof. Clerk Maxwell’s theory described (as to disconnecting the
conductors, &c., from the earth): He states that it is not necessary to
connect masses of metal, as engine tanks, &c., if entirely within the
building, unless a conductor as, _e.g._, telegraph wire, water or gas
pipe come into the building from outside, then they must be connected
with conductor.

List of accidents from lightning, also deaths or injuries in England and
Wales, Prussia, United States, Sweden and Austria.

Particulars of damage to St. George’s Church, Leicester, 1846, and to
West-end Church, Southampton. Also, to Merton College, Oxford, and St.
Bride’s Church, Fleet Street, none of these having lightning rods.

Wrexham Church struck, this had a copper conductor, but it was too small
and the earth contact was doubtful.

List of buildings struck at home and abroad from 1589 to September,
1879, the authorities for the statements being given.

List of powder magazines struck between 1732 and 1878.

_Earth Connections._ Franklin’s report, 1772, strongly urges the
importance of this, in speaking of the powder magazine at Purfleet. In
ordinary cases, moist earth is sufficient, but in such a case as this he
recommends that a well should be dug at each end of magazine, with 3 to
4 ft. of water in it.

The importance of “good earth” is shewn by numerous accidents to
buildings, as, _e.g._, in 1779, the church of St. Mary, Genoa, and, in
1872, the cathedral of Alatri, in which latter case, the discharge left
moist earth to pass off by a water pipe, which it broke; but the church
was uninjured. Also at Clevedon Church, where the conductor passed into
a drain which was dry, but the stroke merely injured one buttress and
passed off by gas and water pipes.

Mr. Anderson states that earth contacts must be large. That it is
important that metal work be connected with lightning rod in at least
two parts, to realize a closed metallic circuit, and so offer entry and
exit. The earth contacts of the eight conductors of the Hotel de Ville,
Brussels, described, viz., their being enclosed in an iron box, 8 in. ×
3 in. × 3½ in., with three series of conductors (details given): one
passing into a well, another to the gas main, the third to water main.

In ordinary buildings, the grating, with charcoal, coke, or cinders,
&c., as before described, may be sufficient; but with large buildings,
contact with water is absolutely necessary.

_Periodical inspection._ Author strongly urges this because conductors
deteriorate from action of wind and weather above ground; the “earth”
often becomes bad, owing to new drains, &c.; buildings may be altered in
regard of the quantity and position of metals. An instance is given of
damage to a building owing to the change of position of iron safe.
Conductors are often displaced by workmen; and the number and position
of new gas and water mains, new trees, &c., also influence the power of
conductors.

_Appendix._ This contains a very full list of books relating to
lightning conductors.


REPORT UPON LIGHTNING DISCHARGES IN THE PROVINCE OF SCHLESWIG-HOLSTEIN.
                   BY DR. LEONHARD WEBER. 1880. 8vo.

                  (_Abstracted by Alexander Siemens_).

The serious damage caused in Schleswig-Holstein by lightning led to an
official inquiry into the subject, the following is an abstract of the
first report of the commission.

It is stated that trees, by their gradual but uninterrupted discharge of
electricity, have a dispersing effect upon thunder-clouds, and tend to
lessen the energy of lightning. In six cases out of the twelve examined,
houses with trees close by, were struck, but not so heavily as in
another case where the building had no protection whatever. Trees do
not, however, afford complete protection to neighbouring buildings,
their conductive capacities not being sufficient to convey, in the
immeasurably short time required, such heavy discharges of electricity
as lightning flashes. This is instanced by their being often wholly, or
partially, destroyed by the current, or, as occurred in four cases, by
their passing it over to better conductors, buildings, &c.

If a thunder-cloud passed over a perfectly plane surface, the discharge
would take place in a vertical line between earth and cloud, but
prominent objects, such as isolated trees, buildings, lightning
conductors, and iron pumps, reaching down to underground water, act as
attractive points, and divert the discharge, the path of which is also
influenced by any conductors which happen to come between them and the
thunder-cloud, such influence depending upon the capacity of the
conductors. So that, generally an electric discharge chooses that path
which, taking the distance into account, offers the best means of
conduction.

It is frequently found that inflammable material is struck by lightning
without being ignited, on account, it is presumed, of the short duration
of discharge not allowing the material to become sufficiently hot to
burn, but whether the duration of discharge is dependent upon the nature
of the charge of the thunder-cloud, or solely upon the condition of the
objects struck, has not been ascertained. The latter is, however, not
without influence, as in two of the four cases which resulted in fire,
the cause was presumably due to newly gathered hay stored at the top of
the houses struck, and in the other two cases to trees, which were
struck at the same time, the hay and the trees being bad conductors, and
prolonging the duration of discharge.

Four cases are given of buildings having lightning conductors being
struck.

The first case is that of a windmill, the conductor of which terminated
in a sheet of metal placed in a well near the building. The discharge
was exceedingly heavy, but beyond the platinum point being almost
entirely fused, no other damage was done.

The second is that of a house with two separate lightning conductors,
each ending in a copper plate, spirally coiled up, and laid in
underground water. One of the conductors was struck, and the lightning
passed from it, and, running horizontally along the thatched roof of the
house, descended by the other, causing no damage.

The third case refers to a church and, adjoining it, a school building.
A portion of the discharge was diverted from the conductor by an anchor
in the church wall three metres off (which it magnetized), and forced
its way through the ceiling of the school-house to a number of gas
brackets, which were turned up towards the ceiling. It was ascertained
that the ground floor of the house was completely under water, and well
connected to earth through the gas mains and an iron pump, a good
continuous conductor thus being formed.

Accordingly, the report recommends that lightning conductors should be
connected to the large masses of metal, such as gas and water mains,
which are found in our houses.

In the fourth instance a church had a lightning conductor, which was
connected to the top of two large iron supports running through the
steeple to the nave, and which terminated in a coiled earth-plate, 1 sq.
metre (11 sq. ft.), supposed to lie in water 7 metres (23 ft.)
underground. The lightning struck the conductor and, passing to the iron
supports, sprang from one through the outer wall, close to an iron
window frame, and from the other across the stucco ceiling, going to
earth 100 feet off through the altar gilding, which it blackened. It was
subsequently found that the copper earth-plate was only ⅓ metre (1 ft. 1
in. sq.), and that it was buried loosely round the rod in dry sand, the
rod itself reaching 2 to 3 metres further down, and just touching water
without an earth-plate, and also that the two supports had no earth
connection, thus forming a great danger instead of a safeguard to the
church.


DIE KONSTRUKTION UND ANLEGUNG DER BLITZABLEITER ZUM SCHUTZE ALLER ARTEN
VON GEBÄUDEN SEESCHIFFEN UND TELEGRAFEN STATIONEN. VON DR. OTTO BUCHNER.
                           Weimar. 1867. 8vo.

                  (_Abstracted by R. Van der Broek._)

The book is divided into two parts:

  1. General, or Introductory, and

  2. Practical.

The first, or Introductory part, is sub-divided into:

  1. Historical and statistical notes;

  2. The theory of atmospheric electricity, and of the lightning
  conductor; and

  3. A chapter on natural lightning conductors.

The great philosopher, Lichtenberg, of Gottingen, said in the year 1794:
“People are struck and their dwellings are destroyed by lightning
because they will have it so. It does not matter to us whether
parsimony, carelessness, ignorance, or anything else is the cause of
this.” The author asserts that this dictum may be equally applied to the
present generation.

Professor J. H. Winkler, of Leipzig, discovered, in the year 1746, that
electricity is the principal cause of thunderstorms.

The first lightning conductor in Germany was erected 1769, at Hamburg,
on the steeple of the Jacobi Church.

Between the years 1835 and 1863, a period of 19 years, 2238 persons were
_killed_ by lightning in France. The maximum in one year (1835) was 111
and the minimum 48. The total number of persons _struck_ by lightning
amounted to 6714; of this large number 1700 persons would have escaped,
if they had been careful to avoid the neighbourhood of trees, whilst the
storms were raging. The greatest number of the accidents caused by
lightning occur during the months of July and August; not a single fatal
case is on record for the months of November, December, January, and
February. The annual average number of persons killed by lightning was 3
in Belgium, 22 in England, and 10 in Sweden. In the low-lying
Departments of France the average is 2 or 3; the average increases
rapidly for the Mountainous Departments to 24, 28, 38, 44, and (in
Auvergne) 48. The per centage of males in France is 67, females 10, and
in the remaining cases the sex was not stated. In Prussia the proportion
is 184 males to 105 females, in Sweden 5 males to 3 females.

The largest number of persons killed by _one_ discharge is 8 or 9.

The author states that the return shock is only mechanical in its
effects.

Professor Müller lays down the following conditions for lightning
conductors:—

1. The rod must end in a very sharp point.

2. There must be no want of continuity between the extreme point and the
earth contact: and

3. The different parts of the conductor must be of the requisite
dimensions.

In practice we find that the first mentioned condition is incorrect, as
sharp points are too liable to be fused.

The rod must be made of a pyramidal or a conical form. Short rods of not
above 2 metres (6 feet 7 inches) in length may be made of a cylindrical
form. The best form of rod is one tapering from a base of from 50 to 60
millimetres (2 inches to 2·4 inches) in diameter to a diameter of not
less than 14 millimetres (0·56 inches). As it is difficult to fix rods
of a height of 10 metres (33 feet), it is better to erect one long rod,
and several shorter ones on different parts of the roof and connect them
together. The principal rod should have a height of from 2½ to 3 metres
(8 to 10 feet) and the secondary rods (_Nebenstangen_) should be at
least 1 metre (3 feet 3 inches) high.

The form of point universally used in Germany is a strongly firegilded
copper cone.

Kuhn advocates the use of chemically pure silver for the points. His
arguments in favour of this metal are incontrovertible. The conducting
power of silver is 1·36; that of pure copper being 1. The fusibility of
silver (1,000 c.) is sufficiently high for the purpose. The atmosphere,
unless it contains sulphur in a gaseous or a liquid form, has no effect
on silver. Silver is cheaper than platinum, and not more expensive than
a gilded copper cone, and it can be easily soldered to other metals.

The point should be screwed on, as well as soldered to the rod. All
other but the conical form of point should be rejected.

The best material for the earth contact is galvanised iron.

As regards the protection of sea-going vessels, Snow Harris’s
arrangement, converting, as it were, the vessel into one mass of metal,
is perfect.

The first practicable lightning conductor for the protection of
telegraph wires was constructed by Steinheil in 1846. His arrangement
was somewhat modified by Breguet and Fardely. Meiszner introduced a real
improvement.

On the Prussian railway telegraphs two “point-systems” are in use, one
for small stations, and the other for larger stations.

It is desirable that all lightning conductors be examined once a year.
The metallic connection throughout must be perfect, the point must be
kept free from rust, and the earth contact must be good. The whole
circuit should also be tested by means of a battery and a galvanometer.


EARTH CONNECTIONS OF LIGHTNING CONDUCTORS. BY LIEUT.-COL. STOTHERD, R.E.

     (Journal of the Society of Telegraph Engineers, May 12, 1875.)

                  (_Abstracted by W. H. Preece, C.E._)

Arguing from the case of a powder magazine at East London, Cape of Good
Hope, when the iron conductor was led into a cemented water-tank,
frequently dry, and where it was destroyed, the author raises two
questions:

1. Should such tanks be used for earth?

2. Is iron the proper metal to use?

He gives a decided negative reply to the first, and advocates the use of
galvanized iron properly protected from atmospheric action. He suggests
rods 1 inch in diameter, or bands 2in. × ⅜in. thick.

In the discussion which followed it was mentioned that the ground about
Torquay is so insulated that plates had to be carried out to sea to
secure a good earth for the telegraph there, and that of the numerous
churches which had been inspected, there was not a single conductor that
could be passed. It was pointed out that when copper conductors were
fixed with iron wall-eyes—a frequent thing—galvanic currents were set
up, and the conductor destroyed at the ground line.

It was stated that the earth connection of a supposed perfect conductor
was found to be equal to a resistance of 1,000 Ohms.

Mr. Preece, Major Malcolm, R.E., Dr. Mann, Mr. Pidgeon, Mr. Kempe, Mr.
Graves, Mr. Spagnoletti, and Mr. Latimer Clark, took part in the
discussion.


  REMARKS ON SOME PRACTICAL POINTS CONNECTED WITH THE CONSTRUCTION OF
LIGHTNING CONDUCTORS. By R. J. MANN, M.D., F.R.A.S. (_Quarterly Journal
                     Meteor. Soc._, October, 1875).

                 (_Abstracted by G. J. Symons, F.R.S._)

States that there are certain principles accepted as established facts,
_e.g._, that conductors should be of metal of high conductivity, and of
adequate dimensions. That in 1854 the French electricians held that a
“quadrangular iron bar ¾ in. diameter, was sufficient in conducting
power for all purposes.” Since then, wire ropes, owing to their
pliability, have nearly superseded solid rods, and copper has been
preferred to iron because of its higher conducting power and less
liability to oxidise. But provided that the iron be galvanized, and of
five times the sectional area of a copper conductor, considers the metal
immaterial.

Author states that the resistance of a conductor increases with its
length, therefore sectional area of conductor must be increased for
lofty buildings. Modern French electricians employ copper rope 0·4 to
0·8 in. diameter. M. R. Francisque Michel considers galvanized iron wire
rope 0·8 in. diameter sufficient for all ordinary cases. Copper wire
rope 0·5 in. diameter (6¾ oz. per foot) recently applied to St. Paul’s
Cathedral.

Importance of perfect earth connection strongly insisted upon, but it is
matter of some difficulty, and the oxidation of the earth terminals, and
their inefficiency doubtless lead to most of the reported failures of
lightning conductors. Author quotes Pouillet and Becquerel, as saying,
that for the efficient discharge of the lightning, which could be
carried by a copper rod 0·8 in. diameter, contact must be obtained with
1,200 square yards of moist earth, but this large requirement can only
easily be obtained in towns by connection with the water mains. Various
modes of obtaining adequate earth contact by iron harrows, Callaud’s
grapnel in basket of coke, &c., described.

Explains the rationale of testing goodness of earth currents by the
galvanometer. Calls attention to the destruction of upper terminals of
conductors to factory chimneys by the emission of sulphurous fumes, and
suggests that they might be cased in lead.

Calls attention to the importance of every joint being made absolutely
perfect.

Urges the superiority of points for upper terminals, owing to their
facilitating silent discharge, and rendering lateral discharges from the
conductor less probable.

Thinks that multiple points of copper kept fairly sharp and clean are,
on the whole, the best upper terminals.

Considers that all large masses of metal in a building should be
connected with the conductor; but quotes M. Callaud, who holds the
opposite view. Dr. Mann, however, points out that if the conductor be
efficient and perfect, the accidents which M. Callaud contemplates, and
on which he bases his arguments, could not occur.

Calls attention to the ready path afforded by the column of heated smoke
discharged by chimneys, and hence alludes to the placing of a coronal
conductor, as well as a multiple point on important chimneys.

Suggests the utilization of rain water pipes, by perfecting their
joints, and securing a good earth connection at their base.


  ON THE PROTECTION OF BUILDINGS FROM LIGHTNING. By R. S. BROUGH, 4to,
                            MUSSOORIE, 1878.

                  (_Abstracted by W. H. Preece, C.E._)

A carefully prepared theoretical and practical paper, adapted for use in
India. Author advocates the use of iron from its higher temperature of
fusion, and greater specific heat than copper, its long protection from
decay by galvanization and its cheapness. He prefers wire cables from
the absence of joints in them. He gives precise instructions for the
formation of a good earth, and advocates periodic electrical tests.


LIGHTNING CONDUCTORS. By Professors AYRTON and PERRY. (_Journal Society
            of Telegraph Engineers._ Vol. V., 1876, p. 412.)

                  (_Abstracted by W. H. Preece, C.E._)

The authors controvert Clark Maxwell’s views that a building would be
perfectly protected from lightning by being enclosed in a network, or
cage of wires, without the use of the earth. They object to the
application of the laws of static electricity alone to such a case.
Current induction intervenes, and this is not subject to the screening
action of a cage. Hence, though a metallic cage may assist the
protection of a house, it does not do so perfectly.


   ON THE PROPER FORM OF LIGHTNING CONDUCTORS. By W. H. PREECE, C.E.
                 (_British Association Report_, 1880).

                 (_Abstracted by G. J. Symons, F.R.S._)

Author states that ever since lightning conductors have been used, there
have been disputes as to whether the discharge passes over the surface
of conductors or through their mass. Snow Harris, Henry, Melsens, and
Guillemin have held that it passed over the surface; Faraday held the
opposite view.

The arguments in favour of the surface form are, in the opinion of the
author, deductions from exploded theories, from imperfect experiments,
or from erroneous interpretations of well ascertained facts. No direct
experiments have ever been made to solve the question, as far as the
author knows. Quantities of electricity, that is static discharges from
condensers, are in incessant use for telegraphic purposes, and are found
to follow exactly Ohm’s laws, even with the most delicate apparatus. The
knowledge of the flow of electricity through conductors, of the
retarding influence of electrostatic capacity upon this flow, and of the
distribution of charge, has become so much greater of late years through
the great extension of submarine telegraphy and the labours of Sir
William Thomson, Clerk Maxwell, and others, that the author questions if
any English electrician would now be found to argue in favour of the
surface form. Nevertheless, as ribbons and tubes still continue to be
used, and it appeared very desirable to settle the question
experimentally, the author determined to try and do so.


                  _First Experiments, June 28, 1880._

Dr. Warren de la Rue, who is always ready to place his splendidly
equipped laboratory at the service of science, not only allowed the
author to use his enormous battery and his various appliances, but aided
him by his advice, and assisted him in conducting the experiments.

Copper conductors, 30 feet long, of precisely the same mass, (_a_) drawn
into a solid cylinder, (_b_) made into a thin tube, and (_c_) rolled
into a thin ribbon, were first of all obtained. The source of
electricity was 3,240 chloride of silver cells. The charge was
accumulated in a condenser of a capacity of 42·8 microfarads. It was
discharged through platinum wire of ·0125 diameter, of different
lengths. The sudden discharge of such a large quantity of electricity as
that contained by 42·8 mf. raised to a potential of 3,317[5] volts is
very difficult to measure. It partakes very much of the character of
lightning. In fact, the difference of potential per unit length of air
is probably greater than that of ordinary lightning itself. It
completely deflagrates 2½ inches of the platinum wire, but by increasing
the length of the wire it could be made to reproduce all the different
phases of heat which are indicated by the various shades of red until we
reach white heat, fusion, and deflagration. Hence the character of the
deflagration, which is (by its scattered particles) faithfully recorded
on a white card to which the wire is attached, is a fairly approximate
measure of the charge that has passed, while the length of wire, raised
to a dull red heat, is a better one, for any variation in the strength
of the current within moderate limits is faithfully recorded by the
change of colour.

Footnote 5:

  The electromotive force of the chloride of the silver cell is 1·03
  volt.

Experiment 1.—Similar charges were passed through the ribbon, tube, and
wire, and in each case 2½ inches of wire were deflagrated. No difference
whatever could be detected in the character of the deflagration.

Experiment 2.—Ten inches of wire were taken and similar charges passed
through. In each case the wire was raised to very bright redness,
bordering on the fusing point, and in two cases the wire broke. In each
case the wire knuckled up into wrinkles, and gave evidence of powerful
mechanical disturbance. The same wire was not used a second time. No
difference could be detected in the effect through the different
conductors.

Experiment 3.—Silver wire of the same diameter and length was used, and
similar charges transmitted through it. Redness was barely visible, but
the behaviour of the wire was similar in each case.

The conclusion arrived at unhesitatingly was, that change of form
produced no difference whatever in the character of the discharge, and
that it depended simply on mass.


                  _Second Experiments, July 19, 1880._

As it might be urged that the length of conductor tested was so short,
and its resistance so small that considerable variations might occur and
yet be invisible, similar lengths (30 feet) of lead—a very bad
conductor, its resistance being twelve times that of copper—were
obtained, drawn as a wire, made as a tube, and rolled as a ribbon, each
being of similar weight.

Experiment 4.—Charges from the same condenser, 42·8 mf., but with 3,280
cells, were passed through, and the discharges observed on 6 inches of
platinum wire 0·0125 inch diameter, which in each case was heated to
bright redness. No variation whatever could be detected, whether the
wire, the tube, or the ribbon were used.

Experiment 5.—In order to form some idea as to how closely any variation
in the character of the discharge could be estimated, a long piece of
platinum wire was used, and the length adjusted until just visible
redness was obtained; then a diminution of 10 per cent. (3 feet)
produced a marked change to dull redness, and further excisions raised
the temperature to brighter and still brighter red.

The conclusion arrived at was that any change in resistance of 5 per
cent. would have been clearly and easily discernible.

It therefore appears proved that the discharges of electricity of high
potentials obey the laws of Ohm, and are not affected by change of form.
Hence, extent of surface does not favour lightning discharges. No more
efficient lightning conductor than a cylindrical rod or a wire rope can
therefore be devised.


       ÉTABLISSEMENT DE LA FORMULE RELATIVE AU RAYON D’ACTION DES
  PARATONNERRES. Par EMILE LACOINE. (_L’Electricité_, October, 1880.)

                 (_Abstracted by G. J. Symons, F.R.S._)

This author gives a formula for determining the area protected, which he
considers to vary with the height of the storm cloud, and the elevation
of the ground. He states that the mean elevation of the storm clouds at
Constantinople is as low as about 325 feet. He says that conductors
placed near the extremities of a building have their radius of
protection diminished, and therefore recommends a line conductor running
round the building. (The _circuit des faites_ of the Paris Municipal
Commission, see ante page 68).

He says that his formula leads to nearly the same results as have
hitherto been adopted, but he gives three examples, the results of which
are—length of conductor being 1·00, radius protected is respectively
3·80, 1·10, and 2·20.


 ON THE SPACE PROTECTED BY A LIGHTNING CONDUCTOR. By W. H. PREECE, C.E.
                      (_Phil. Mag._, Dec., 1880.)

                 (_Abstracted by G. J. Symons, F.R.S._)

In the early part of this paper the author discusses the distribution of
electricity in the space between the storm cloud and the earth’s
surface, and points out that the air in an electric field is in a state
of tension or strain; and this strain increases along the lines of force
with the electromotive force producing it until a limit is reached, when
a rent or split occurs in the air along the line of least
resistance—which is disruptive discharge, or lightning.

Since the resistance which the air or any other dielectric opposes to
this breaking strain is thus limited, there must be a certain rate of
fall of potential per unit length which corresponds to this resistance.
It follows, therefore, that the number of equipotential surfaces per
unit length can represent this limit, or rather the stress which leads
to disruptive discharge. Hence we can represent this limit by a length.
We can produce disruptive discharge either by approaching the
electrified surfaces producing the electric field near to each other, or
by increasing the quantity of electricity present upon them; for in each
case we should increase the electromotive force and close up, as it
were, the equipotential surfaces beyond the limit of resistance. Of
course this limit of resistance varies with every dielectric; but we are
now dealing only with air at ordinary pressures. It appears from the
experiments of Drs. Warren de la Rue and Hugo Müller that the
electromotive force determining disruptive discharge in air is about
40,000 volts per centimetre, except for very thin layers of air.

If we take into consideration a flat portion of the earth’s surface, and
assume a highly charged thunder-cloud floating at some finite distance
above it, they would, together with the air, form an electrified system.
There would be an electric field; and if we take a small portion of this
system, it would be uniform.

If the cloud gradually approached the earth’s surface, the field would
become more intense, the equipotential surfaces would gradually close
up, the tension of the air would increase until at last the limit of
resistance of the air would be reached; disruptive discharge would take
place, with its attendant thunder and lightning.

[Illustration:

  Fig. 1.
]

If the earth-surface be not flat but have a hill or a building, as A or
B, upon it, then the lines of force and equipotential planes will be
distorted, as shown in fig. 1. If the hill or building be so high as to
make the distance HD equal to the limit of resistance (fig. 2), then we
shall again have disruptive discharge.

[Illustration:

  Fig. 2.
]

If instead of a hill or building we erect a solid rod of metal, G H,
then the field will be distorted as shown in fig. 2. Now it is quite
evident that whatever be the relative distance of the cloud and earth,
or whatever be the motion of the cloud, there must be a space _d d´_
along which the lines of force must be longer than _c c´_ or H D; and
hence there must be a circle described around G as a centre which is
less subject to disruptive discharge than the space outside the circle;
and hence this area may be said to be protected by the rod G H. The same
reasoning applies to each equipotential plane; and as each circle
diminishes in radius as we ascend, it follows that the rod virtually
protects a cone of space whose height is the rod, and whose base is the
circle described by the radius G _c_. It is important to find out what
this radius is.

[Illustration:

  Fig. 3.
]

Let us assume that a thunder-cloud is approaching the rod A B (fig. 3)
from above, and that it has reached a point D´ where the distance D´ B
is equal to the perpendicular height D´ C´. It is evident that if the
potential at D´ be increased until the striking-distance be attained,
the line of discharge will be along D´ C´ or D´ B, and that the length A
C´ is under protection. Now the nearer the point D´ is to D the shorter
will be the length A C´ under protection; but the minimum length will be
A C, since the cloud would never descend lower than the perpendicular
distance D C.

Supposing, however, that the cloud had actually descended to D when the
discharge took place. Then the latter would strike to the nearest point;
and any point within the circumference of the portion of the circle B C
(whose radius is D B) would be at a less distance from D than either the
point B or the point C.

“_Hence a lightning-rod protects a conic space whose height is the
length of the rod, whose base is a circle having its radius equal to the
height of the rod, and whose side is the quadrant of a circle whose
radius is equal to the height of the rod._”

Upon this rule the author makes the following concluding remarks:

“I have carefully examined every record of accident that I could
examine, and I have not yet found one case where damage was inflicted
inside this cone when the building was properly protected. There are
many cases where the pinnacles of the same turret of a church have been
struck where one has had a rod attached to it; but it is clear that the
other pinnacles were outside the cone; and therefore, for protection,
each pinnacle should have had its own rod. It is evident also that every
prominent point of a building should have its rod, and that the higher
the rod the greater is the space protected.”


 SHORT ACCOUNT OF THE STRIKING BY LIGHTNING OF THE RAILWAY TERMINUS AT
 ANTWERP, ON THE 10TH OF JULY, 1865. BY M. MELSENS, Member of the Royal
                          Academy of Belgium.

                  (_Abstracted by R. Van der Broek._)

On the date mentioned, between three and four o’clock in the afternoon,
a violent storm burst over Antwerp, during which the lightning struck
the Railway Terminus, without, however, occasioning any other damage
than the perforation of a single hole in one of the glass squares of the
roof.

The author states that the effect of the discharge on this square of
glass, which was about 4^{mm} (0·2in.) thick, was remarkable; it
appeared as if it had been traversed by a projectile from below, the
perforation, viewed from above, being broken and chipped, whilst viewed
from below it showed a clean edge. The sinuosities caused by the
chipping on the upper surface had rounded edges, and the glass appeared
to have been subjected to incipient fusion. Not a single fragment of
glass was found on the glass squares or in the gutters of the roof.

The author arrives at the following conclusions: The square of glass was
pierced in the same manner as any square of similar nature and
dimensions, placed in identical circumstances, would be, were it
traversed by a spherical projectile fired at a low velocity from a
firearm. The fracture resembled one that would be produced by a missile
thrown from below, that is to say, from the earth to the sky.

The form of the opening indicated that the earth was positively
electrified.

The author notices that, according to M. F. Duprez, negative electricity
generally shows itself in abnormal conditions of the atmosphere, during
storms, rains, &c., and when the wind blows from the western quarters
between N. and S. Now, on the day in question, it rained and the wind
blew from the west.

The author publicly thanks M. Ruhmkorff for his skilful and
disinterested co-operation in proving the correctness of his (the
author’s) view of the distribution of the electricity at the Antwerp
discharge. M. Ruhmkorff has, at request, pierced squares of ordinary
glass about 1^{mm} (0·04in.) thick by the discharge of his great
induction apparatus charged by a powerful Leyden battery.


  ON LIGHTNING PROTECTORS WITH POINTS, CONDUCTORS, AND MULTIPLE EARTH
 CONNECTIONS, A DETAILED DESCRIPTION OF THE LIGHTNING PROTECTOR ERECTED
ON THE TOWN HALL OF BRUSSELS IN 1865, WITH AN ACCOUNT OF THE PRINCIPLES
ADOPTED IN THE CONSTRUCTION, BY M. MELSENS, MEMBER OF THE ROYAL ACADEMY
                        OF SCIENCES OF BELGIUM.

                  (_Abstracted by R. Van der Broek._)

As the author states in his preliminary observations that it is
impossible to give a complete condensed description of the Lightning
Protector, which he erected on the Town Hall at Brussels, we will merely
draw attention to a number of facts, regarding the system followed, some
of them, we believe, of a novel description.

M. Daniel Colladon, the author states, has observed that as a rule
lightning does not strike a single part or prominent point of the
objects that are struck or destroyed by it; and that, in the majority of
cases, it does not strike in the form of a single spark, but in the form
of a sheet with one or more principal centres of intensity. The
correctness of this observation, the author considers fully borne out by
the ravages which the electric discharge committed on the Town Hall at
Brussels, on the 10th September, 1863. He gives an elaborate description
of the effects of the flash on the building. It is interesting to note
that the ravages principally took place at the side exposed to the west
north-west wind, which was blowing at the time the building was struck.

In the ensuing winter the Municipal Council of Brussels took into
consideration the necessity of protecting the Town Hall against a
similar disaster, and the author was requested to superintend the
erection of lightning protectors on the building.

The characteristics of the author’s system, as exemplified by the
lightning protectors erected on the Brussels Town Hall, may be briefly
summarised as follows:—

  1. The points are very numerous—of three kinds; some long, sharp, and
      gilded, others of middling length, made of iron; and finally some
      small and very sharp, consisting of copper.

  2. The points are replaced by _aigrettes_ (brushes of points diverging
      from a common base).

  3. The conductor is not insulated.

  4. The connections are simple and unchangeable, the joints are each
      embedded in a mass of zinc.

  5. The surface exposed to the air is considerable.

  6. The conductor consists of thin, and numerous wires, which are very
      flexible, so as easily to be led round all the corners of the
      buildings.

  7. The conductor is made of galvanised iron.

  8. The earth connections are multiple: firstly, a well within which a
      large surface of metal is plunged; and, secondly, two enormous
      networks of metal pipes, offering an immense contact surface with
      the earth. One of these networks is in direct communication with
      all the reservoirs and all the water sources of the environs of
      Brussels and also in indirect communication with two rivers and
      two canals.

The author has arrived at the conclusion that the height of the rod is a
secondary question, as the radius of protection has not been determined
by irrefutable proofs, and as that length is, in comparison with the
distance and the extent of the thunder-clouds, so small a factor that it
may safely be neglected. The author states that he has been greatly
gratified to meet with the same opinion in a paper which Mr. W. H.
Preece published in Vol. I., No. 3, page 366, of the Journal of the
Society of Telegraph Engineers for 1872: “When we consider the distance
of the cloud and the area of its surface, the height of a building
vanishes in the general figure.”

The author points out that M. Perrot has endeavoured to demonstrate by
experiment that the neutralizing area of a lightning protector
surmounted by a crown of sharp points is far more extensive than that of
an ordinary protector. M Perrott further thought, and MM. Babinet and
Gavarret shared his opinion, that it is sufficient to shelter the
ordinary protector from discharges of lightning by arming it with
numerous, long, sharp, and well conducting divergent points. M. Gavarret
after having repeated Mr. Perrott’s experiments, found the results so
conclusive that he wrote to the author in the beginning of 1865: “It is
at the present time no longer permitted to erect lightning protectors
with single points.”

The metal of which the points are made must be a very good conductor.
With regard to their conductivity, the metals follow each other in the
following order: copper, silver, iron, platinum. No metals are used but
those which resist fusion. The author rejected platinum and silver: the
former because it fuses very readily by the electric discharge; and the
latter, because it has, in his opinion, no advantage over copper.

The conductor, although galvanized, received several coats of paint; but
the points (_aigrettes_) of course remained metallic. With regard to the
general principle of connecting the protector with any masses of metal
which may be about the building, the author has ever since 1865
endeavoured to demonstrate, that it is not sufficient, as might at first
sight be supposed, to form that connection at one single point; there
must be at least two points of contact, so as always to ensure a closed
metallic circuit.

The contact with the water presents a surface of about ten square metres
(12 sq. yds.), bringing both surfaces of the cylinder into account.

With regard to the earth connection, the author quotes M. Perrot, who
remarks that with the ordinary protector the surface immerged offers a
resistance at least 10,000 times greater than the conductor itself; it
is therefore necessary to increase the surface of the earth-plate as
much as possible.

In order to retard as much as possible the oxidation of the cylinder,
the author introduced two hectolitres (6 bushels) of lime into the well,
thus rendering the water alkaline.


DE L’APPLICATION DU RHE-ÉLECTROMÈTRE AUX PARATONNERRES DES TÉLÉGRAPHES.
                            PAR M. MELSENS.

                  (_Abstracted by R. Van der Broek._)

In this pamphlet the author describes in § 1 an apparatus to show the
presence of atmospheric electricity in telegraph wires.

In §§ 2 and 4 he explains how the apparatus is joined up in the Belgian
telegraph offices.

§ 3 contains a résumé of observations made at the government telegraph
offices between June, 1875, and March, 1876.

The author states in this paragraph that, on the 19th of June, 1875, the
Rheo-Electrometer at the office at Louvain, showed a deflection of 85°
East, although there was not the slighest appearance of atmospheric
electricity. The fact was, that at the time a thunder storm was raging
at Beverloo, distant from Louvain about 40 kilometres (25 miles).


         TROISIÈME NOTE SUR LES PARATONNERRES. PAR M. MELSENS.

                  (_Abstracted by R. Van der Broek._)

On the 3rd of July, 1874, the church of Ste. Croix, at Ixelles, was
struck by lightning. The building was provided with a lightning
protector, which was constructed as follows: The point consisted of a
platinum cone of about 30° (the form officially adopted in France in
1855), all the supports of the protector were soldered with zinc. This
was attached to the steeple, and rose to 53 metres or 174 feet above the
pavement. It consisted of an iron rod 18 mm. (0·71 in.) in diameter (M.
E. Sacré’s system). The conductor passed from the principal roof along
the roofs, descending to a point near a pump, behind the vestry, where
the well (W) was situate. There is an abundance of water in the well,
which is about 7 m. (23 ft.) deep. The conductor terminated in the well,
by a cast-iron plate 0·65 m. (2 ft. 1 in.) by 0·50 m. (1ft. 8 in.), thus
presenting a surface of 0·654 ⬜ m. (7 sq. ft.). A little in front of the
transept there is a supplementary rod B 5·25 m. (17 ft. 3 in.) high, 11
m. (36 ft.) distant from the point (c in diagram) which was struck; and
22 m. (72 ft.) distant from that point there was a second rod D, whose
height was 9 m. (29½ ft.) above the top of the roof.

The damage to the church was trifling, but the author contends that the
fact of the church having been struck at all, proves that a building
armed with a protector constructed on the usual principle is not
completely protected.

[Illustration: Plan and Elevation of Church of Ste. Croix, at Ixelles]

           A. Principal conductor on steeple.
        B. D. Two supplementary receiving rods.
           C. Stone cross at end of transept, which was struck,
           W. Well in which conductor made earth connection.


         QUATRIÈME NOTE SUR LES PARATONNERRES. PAR M. MELSENS.

                  (_Abstracted by R. Van der Broek._)

This treats § 1 of observations on the distribution of the spark of
electric batteries and machines over numerous metallic conductors of
different sections, lengths, and nature, and on the passage of
electricity of tension in bad conductors.

§ 2. Effects of soldered joints on the conductivity and the resistance
of conductors. Interrupted lightning protectors.

§ 3. The distribution of sparks from Holtz’s machine and Ruhmkorff’s
coil over two conductors outwardly identical, but one of iron and the
other of copper. Comparative resistance to fusion and rupture for iron
and copper conductors. Identical damage produced by discharges in
several homogeneous and solid conductors.




                              APPENDIX G.

             CATALOGUE OF WORKS UPON LIGHTNING CONDUCTORS,
                            WITH A FEW UPON
       LIGHTNING, THUNDER, AND THE EFFECTS OF LIGHTNING STROKES,
 _Chiefly extracted from the_ RONALD’S CATALOGUE, _edited by Mr. Frost,
     but supplemented and brought down to 1880 by extracts from the
                             Catalogues of_
   R. ANDERSON, F.C.S.; LATIMER CLARK, C.E.; and G. J. SYMONS, F.R.S.

There are not many comments needed upon the following catalogue, but a
few are necessary.

The arrangement is, with one exception, strictly alphabetical under
author’s names; that exception being that all the Official Instructions
issued in France are placed together at the beginning of the catalogue.

The initials =R=, =C=, =A=, =S=, are those of the Catalogues or
Libraries in which the works are to be found; small type indicates that
the title of the work is given in the catalogue indicated; large type
that a copy of the book is in that Library. As Mr. Anderson does not
state distinctly whether he possesses the books or has merely their
titles, it has been thought safer to mark those taken from his catalogue
with the small ¤A¤. The existence of any specified work in a certain
library is absolute proof of the existence of the book, and hence the
larger type has a certain value, and, besides that, I purpose,
immediately after the publication of this Report, presenting to the
Society of Telegraph Engineers all the Electrical works which are in my
library but are not in the Ronald’s Library. It may therefore be assumed
that most of the works to which a large type initial is prefixed are, or
soon will be, in the splendid collections of the Society of Telegraph
Engineers and Electricians.

The small figures in the front column show the pages of Appendix F, upon
which abstracts of upwards of fifty of the following works will be
found—and thus it forms an index to the works abstracted.

                                                                G. J. S.


                     OFFICIAL INSTRUCTIONS, FRANCE.

       (_Abstracts of this series will be found on pages 51–69._)

 =R= =S=  │Instruction sur les Paratonnerres pour
          │  servir à l’Etablissement de ces Appareils
          │  au-dessus des Magasins à poudre, adoptée
          │  par le Comité des Fortifications dans sa
          │  Séance du 25 Août 1807: suivie des
          │  Rapports faits à ... l’Institut et à
          │  l’Académie des Sciences, sur cette
          │  Instruction et sur l’Etablissement des
          │  Paratonnerres en général. Fol. 39 pp. 1
          │  plate.                                      _Paris_, =1808=
          │    (This paper contains the reports by
          │      Franklin and others, dated 24th
          │      April, 1784; by Leroy and others,
          │      dated 27th December, 1799; and by La
          │      Place and others, dated 2nd November,
          │      1807.)
          │
 ¤R¤      │Instruction sur les Paratonnerres. Fol.       _Paris_, =1823=
          │
 =R=      │Instruction sur les Paratonnerres adoptée
          │  par l’Académie, 23 April, 1823, (Signé)
          │  Poisson, Lefevre-Gineau, Dulong, Fresnel,
          │  et Gay-Lussac rapporteur. 4to. 51 pp. 2
          │  plates.                                     _Paris_, =1824=
          │
       =S=│Instruction sur les Paratonnerres adoptée
          │  par l’Académie Royale des Sciences le 23
          │  Juin, 1823. 8vo. 51 pp. 2 plates.           _Paris_, =1824=
          │
 =R= =S=  │Supplément à l’Instruction sur les
          │  Paratonnerres, présenté par la section de
          │  physique. MM. Becquerel, Babinet,
          │  Duhamel, Despretz, Cagniard de Latour,
          │  Pouillet rapporteur. 4to. _Ext. des
          │  Comptes Rendus_, tom. xxxix. 112, and
          │  xl., Séance 18 Déc. 1854.                 _Paris_, =1854–5=
          │
 =R= ¤S¤  │Instruction sur les Paratonnerres adoptée
          │  par l’Acad. des Sciences. 12mo. 130 pp.
          │  Cuts.                                       _Paris_, =1855=
          │
 =R= ¤S¤  │Instruction sur les Paratonnerres des
          │  magasins à poudre. Rapport lu 14 Janv.,
          │  1867. Commissaires Becquerel, Babinet,
          │  Duhamel, Vaillant, Pouillet, Fizeau,
          │  Regnault. 4to. 1 plate. 15 pp. (_Ext. des
          │  Comptes Rendus_, tom. lxiv. Séance 21
          │  Janv. 1867.)                               _Paris_, =1867=.
          │
       =S=│Instruction sur les Paratonnerres du Louvre
          │  et des Tuileries. (_Ext. des Comptes
          │  Rendus_, tom. lxvii. Séance 20 Juillet,
          │  1868). 4to.                                 _Paris_, =1868=
          │
   ¤A¤ =S=│Instruction sur les Paratonnerres adoptée
          │  par l’Acad. des Sciences. Part I., 1823,
          │  M. Gay Lussac, rapporteur; Part II.,
          │  1854, and Part III., 1867, M. Pouillet,
          │  rapporteur. 12mo.                           _Paris_, =1874=
          │
 Met. Soc.│Analyse des Rapports de M. de Fonvielle, à
          │  la suite de la mission qui lui avait été
          │  confiée en 1872, par M. Jules Simon, pour
          │  faire en Angleterre une enquête sur la
          │  foudre et les Paratonnerres. Fcap. fol.     _Paris_, =1875=
          │
 Met. Soc.│Analyse des Rapports des Architectes sur
          │  l’Etat des Fcap. fol.                       _Paris_, =1875=
          │
 Met. Soc.│Instruction de la Commission chargée
          │  d’étudier l’établissement des
          │  paratonnerres des Edifices Municipaux de
          │  Paris, adoptée dans la Séance du 20 Mai,
          │  1875. Fcap. fol.                            _Paris_, =1875=
          │
 Met. Soc.│Résumé des expériences faites à
          │  l’Administration des Lignes
          │  Télégraphiques sur les parafoudres
          │  télégraphiques. Fcap. fol.                  _Paris_, =1875=


                               ANONYMOUS.

                     (_Arranged chronologically._)

       ¤S¤│Petit traité du tonnerre, esclair, foudre,
          │  gresle et tremblement de terre. 12mo.      _Genève_, =1592=
          │
       ¤S¤│Death of V. Tyrrell by Lightning and
          │  Preservation of Sir J. Rous.                         =1661=
          │
       ¤S¤│Dreadful Storm of Thunder and Lightning,
          │  &c., at Bedford, August 19th. 4to.                   =1672=
          │
       ¤S¤│Extraordinary Thunder and Lightning in the
          │  N. of Ireland, with the sad effects of
          │  the Fall of a Cloud.                                 =1680=
          │
 =R=      │S——, Sir R. A Relation of the Effect of a
          │  Thunder-clap on the Compass of a Ship on
          │  the coast of New England. 3 pp. Also, a
          │  Letter concerning the former Relation. 2
          │  pp. (_Phil. Trans. for_ 1683, xiii. pp.
          │  520–21.)                                   _London_, =1683=
          │
       ¤S¤│Difesa della commune, ed antica sentenza
          │  che i fulmini discendano dalle nuvole
          │  contro l’opinione del S. Maffei, che si
          │  formino al basso, ed ascendano, etc. 4to. _Venezia_, =1749=
          │
 =R=      │Della maniera di preservare gli edificj dal
          │  Fulmine: Informazione al popolo, &c. 4to.
          │  38 pp. (_Vide_ Toaldo.) At p. 20 is
          │  inserted a translation of Saussure’s
          │  Manifeste, entitled _Manifesto ossia
          │  breve esposizione dell’ utilità dei
          │  Conduttori elettrici_.                    _Venezia_, =1772=
          │
 =R=      │Della maniera di preservare ... dal
          │  Fulmine. 8vo. 22 pp.                       _Milano_, =1776=
          │
 ¤R¤      │Neueste Versuche zur Bestimmung der
          │  zweckmässigsten Form der Gewitterstangen.
          │  (_Deutsch Mus._, Oct. 1778, pp. 351–62.)             =1778=
          │
 ¤R¤      │Encyclopædia Method. Arts. Article,
          │  Paratonnerre.                                        =1782=
          │
       ¤S¤│Accident by Lightning at Heckingham. 4to.,
          │  plates.                                              =1783=
          │
 =R=      │Nuovo metodo di costruire i Parafulmini
          │  praticato in Padova. 4to. 2 pp.
          │  (_Opuscoli Scelti_, vi. 380.)              _Milano_, =1783=
          │
 =R=      │Dell’ efficacità dei conduttori elettrici,
          │  Dubbj proposti ai Fisici moderni. 8vo.               =1784=
          │
 =R=      │Maniera pratica di fare li Conduttori 4to.
          │  (_Printed by order of the Magistrato
          │  della Sanità di Venezia._) (_Vide_
          │  Marzari.)                                 _Venezia_, =1787=
          │
 ¤R¤      │Einige gegen die Gewitterableiter gemachte       _Frankfort_,
          │  Einwürfe beantwörtet. 8vo.                           =1790=
          │
 =R=      │Dubbii sull’ Efficacia dei Conduttori. 8vo.
          │  122 pp. 1 plate (_Vide_ Bragadin.)        _Venezia_, =1795=
          │
 ¤R¤      │Nachricht und Zeichnung von einer im Jahre
          │  1778, am Schlossthurme, zu Dresden,
          │  angebrachten Ableitung. (_Schrift, d.
          │  Leipz. ökonomische Societät_, th. v. pp.
          │  222–32.)
          │
 =R=      │Risposta dell’ autore dei Dubbii sull’
          │  efficacia dei Conduttori, alla giunta al
          │  Giornale Astrometeorologico del Gr.
          │  Toaldo. (_Vide_ Bragadin.)
          │
 =R=      │Plain Directions for safe Lightning
          │  Conductors for Lightning. 8vo. 49 pp.
          │    _Note._—Part of a work. Begins at p. 33
          │
 ¤R¤      │Account of a mass of 7000 Bricks of a Wall
          │  displaced several feet by Lightning. 8vo.      _Manchester,
          │  (_Manchester Memoirs_, ii. 2.)                        n.d._
          │
 ¤R¤      │Relazione del Turbine scoppiato in Venezia
          │  nel Giorno 16 Giugno, 1805. Data Venezia,
          │  19 Giugno. 8vo. (_Da Rio Giornale_, ix.
          │  266.)                                      _Padova_, =1805=
          │
 ¤R¤      │(R. R.) Death by Lightning. Man killed at
          │  Colwall, near Ledbury, 1817. 8vo. (_Phil.
          │  Mag._ 1. 315.)                             _London_, =1817=
          │
 =R=      │On Lightning Conductors of Straw. (_See_
          │  Lapostolle.)                                         =1820=
          │
 =R=      │On the Cure of a case of Paralysis by
          │  Lightning. 8vo. 2 pp. (_Phil. Mag._ lix.
          │  287.)                                      _London_, =1822=
          │
 =R=      │Remarks upon Mosely’s article on Solar
          │  Spots of 1816 in _Phil. Mag._ xlix. 182.
          │  8vo. 3 pp. (_From New Monthly Mag. for
          │  January_, 1821. _At_ p. 72, _Chain Cables
          │  as Conductors_.)                           _London_, =1821=
          │
 =R=      │Anleitung zur Verfertigung und Benützung
          │  der Blizableiter. 8vo. 43 pp. 2 plates.
          │  (Translation of _French Official Report_      _Strasbourg_,
          │  of 1824, without name of Translator.)                =1824=
          │
 =R=      │Tubes formed by Lightning. 8vo. 1 p.
          │  (_Phil. Mag._ or _Annals_, iv. 228.)       _London_, =1828=
          │
 ¤R¤      │Memoir on Lightning Conductors—Reply to a
          │  Prize Question. Bordeaux, 1837. (_Vide_
          │  Bourges, Secretary of the Bordeaux              _Bordeaux_,
          │  Academy, Séance 1837, p. 83.)                        =1837=
          │
 ¤R¤      │On the knowledge of the Ancients concerning
          │  Lightning Conductors. 8vo. (_Fraser’s
          │  Magazine_, 1839?)                         _London_, =1839?=
          │
 ¤R¤      │Sur l’Histoire du Paratonnerre, 1843. (_Le
          │  Portique_, 1^{re} livraison, Jan. 1843,
          │  p. 51.)                                              =1843=
          │
 =R=      │Part of Bulletin des Mois de Mars, Avril.,
          │  Mai, Juin, Juillet, Août, 1854. 8vo.
          │  (_Toulouse Acad._ series 4, vol. iv. At
          │  p. 483, De Clos, _Effets de la Foudre sur       _Toulouse_,
          │  un Paratonnerre_.)                                   =1854=
          │
 ¤R¤      │De la Construction des Paratonnerres.
          │  Quelques Réflexions sur le Rapport de la
          │  Commission de l’Académie des Sciences du
          │  14 Janvier, 1867. 8vo. 29 pp.               _Paris_, =1868=
          │
          │
 =R= =S=  │=Abbadie=, A. D’. Sur le tonnerre en
          │  Ethiopie. 4to.                              _Paris_, =1858=
          │
 ¤R¤ ¤A¤  │=Achard=, F. K. Kurze Anleitung ländliche
          │  Gebäude vor Gewitterschäde sicher zu
          │  stellen. 8vo.                              _Berlin_, =1798=
          │
 =R=      │=Alden=, T., Jun. Effects of Lightning on
          │  the House of Captain Manning in
          │  Portsmouth, New Hampshire; in a letter to
          │  Dr. Eliot. 4to. 2 pp. (_Mem. Amer.              _Cambridge,
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          │
  =C= ¤A¤ │=Anderson=, R. Lightning Conductors: their
    =S=   │  history, nature, and mode of application.
   (120)  │  Large 8vo.                                 _London_, =1879=
          │
       =S=│ „   On the necessity for a regular
          │  Inspection of Lightning Conductors
          │  (_Brit. Ass. Rep._ 1880.) 8vo.             _London_, =1880=
          │
 =R=      │=Arago=, F. Notices scientifiques. Sur la
          │  Grêle et des Paragrêles, &c. 12mo.          _Paris_, =1827=
          │
 =R= =C=  │ „   Sur le Tonnerre. 12mo.
 ¤A¤ =S=  │                                              _Paris_, =1837=
          │
       =S=│ „   Ueber Gewitter. 12mo.                   _Weimar_, =1839=
          │
 =R= ¤A¤  │ „   Meteorological Essays. Translated by
 =S=      │  Sabine. 8vo.                               _London_, =1855=
          │
    ¤A¤   │=Arnold.= Blitzableiter zum Schutz der
          │  Wärterbuden. _Polyt. Centralblatt._ 650.             =1851=
          │
    ¤A¤   │=Arrowsmith=, J. On the Use of Black Paint
          │  in averting the effects of Lightning on
          │  Ships.                                               =1841=
          │
 ¤R¤      │=Astier=, C. B. Notice sur les Paragrèles à
          │  pointes; projet de paragrèles à flammes
          │  et expériences comparatives du pouvoir
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          │  8vo.                                                 =1829=
          │
  =R= =S= │=Ayrton=, W, E., and =Perry=, J. Lightning
   (132)  │  Conductors; an Answer to Prof. J. C.
          │  Maxwell’s suggestion to surround
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          │
          │
          │=Babinet.= (_See Official Instructions,
          │  France._)
          │
 ¤R¤      │=Baier=, J. W. De Fulmine, fulgure, et
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          │
 ¤R¤      │=Baldwin=, L. An Account of a very curious
          │  appearance of the Electric Fluid produced
          │  by raising a Kite in the time of a
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          │  4to. (_Mem. Amer. Acad._ i. part ii. 257,
          │  old series.)                               _Boston_, =1785=
          │
 =R=      │ „   Observations on Electricity, and an
          │  improved mode of constructing
          │  Lightning-rods; in a letter to J.
          │  Willard. 4to. (Letter dated January 25,
          │  1797.) (_Mem. Amer. Acad._ ii. part ii.       _Charlestown,
          │  96, old series.)                              U.S._, =1804=
          │
 =R= ¤A¤  │=Barberet=, D. Dissertation sur le Rapport
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 =R= ¤A¤  │=Barbier de Tinan.= Mémoires sur les
 =S=      │  Conducteurs pour préserver les édifices
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          │  traduits de l’Italien avec des Notes et
          │  des Additions, par M. Barbier de Tinan.       _Strasbourg_,
          │  8vo. 241 pp. 3 plates.                               =1779=
          │
 =R=      │ „   (Nuove) Considerazioni sopra i
          │  conduttori del Sig. Barbier di Tinan.
          │  Traduz. dal Francese. 4to. 43 pp.         _Venezia_, =1779=
          │    _Note_—This is a printer’s translation
          │      of Barbier’s Considerations sur les
          │      Conducteurs en général, appended to
          │      his translation of Toaldo’s Dei
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 =R=      │=Barletti=, C. Nuove Sperienze Elettriche,
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 ¤R¤      │=Bartletti=, C. Descrizione de’ fulmini di
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 ¤R¤      │ „   Dei Conduttori del fulmine.
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 ¤R¤      │=Bartaloni=, D. Lettera sopra il fulmine
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          │  also an English translation of the
          │  above_).                                    _Siena_, =1777=
          │
 =R=      │ „   Mem. sul conduttore Elettrico
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          │
 =R=      │ „   Relazione sopra un supposto Fulmine
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    ¤A¤   │=Beaufort=, Dr. A. de. Notice sur les          _Chateauroux_,
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 =R= ¤A¤  │=Beccaria=, G. B. Lettere dell’
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       ¤S¤│ „   Della elettricita terrestra
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          │
 =R= ¤A¤  │ „   A Treatise upon artificial
          │  electricity. 8vo.                          _London_, =1776=
          │
 ¤R¤      │=Beck=, D. Fassliche Unterredung, Gebäude
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 =R= =S=  │=Becquerel=, A. C. & E. Traité de                    _Paris_,
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          │
 ¤R¤ ¤S¤  │=Bennet=, A. New experiments on
          │  Electricity, Thunder, and Lightning. 8vo.   _Derby_, =1789=
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    ¤A¤   │=Bergman=, T. Tal on möjeligheten at
          │  förexomma askans skadeliga werkningar.         _Stockholm_,
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          │
 ¤R¤      │ „   Rede von der Möglichkeit des Donners        _Stockholm_,
          │  schädlichen Wirkungen vorzukommen. 4to.              =1764=
          │
 ¤R¤      │ „   Zusatz zu Vorhergehenden, _i.e._
          │  Wilcke, Bemerkungen bei einem den 30 May,
          │  1769.... Donnerschlage. 8vo. 5 pp. (_K.
          │  Akad. Schwed. Abh._ xxxii. 128.)          _Leipzig_, =1770=
          │
 ¤R¤      │=Bertholon=, de St. Lazare. Mémoire sur un
          │  nouveau moyen de se préserver contre la      _Montpellier_,
          │  Foudre. 4to.                                         =1777=
          │
 ¤R¤      │ „   Lettre à M. de la Tourette, sur les
          │  Paratonnerres ascendants et descendants
          │  de la Ville de Lyon. (_Samml. zu Phys._
          │  xix. _Mai_ 1782, p. 382.)                            =1782=
          │
 ¤R¤      │ „   Nouvelles Preuves de l’efficacité des     _Montpellier_,
          │  Paratonnerres. 4to. 28 pp. 3 plates.                 =1783=
          │
 =R= ¤A¤  │ „   De l’Électricité des Météores. 2 vols.
 =S=      │  8vo.                                        _Paris_, =1787=
          │
 ¤R¤ =S=  │ „   Die Electricität d. Lufterscheinungen.       _Leignitz_,
          │  2 vols. 8vo.                                         =1792=
          │
 =R=      │=Beyer.= On Lightning-conductors, &c. 8vo.
          │  2 editions.                               _Paris_, =1806–9=
          │
 =R=      │=Bianchini=, G. An Extract by Rolli, P., of
          │  an Italian Treatise, written by
          │  Bianchini, J., upon the Death of the
          │  Countess Cornelia Zangari ne’ Bandi, of
          │  Cesena. To which are subjoined Accounts
          │  of the Death of Hitchell, J. (see
          │  Hilliard, J.), who was burned to death by
          │  Lightning, and Grace Pitt at Ipswich,
          │  whose body was consumed to a coal. 4to.           _London_,
          │  19 pp. (_Phil. Trans._ xliii. 447.)               =1744–45=
          │
 ¤R¤      │=Bianchini=, G. F. On the Vertical Rod on
          │  the Château di Duino in the Friuli. 4to.
          │  (_Mémoires de l’ Acad. pour 1764_, edit.
          │  orig. p. 44.)                               _Paris_, =1764=
          │
 =R= ¤A¤  │=Bigot=, P. Anweisung zur Anlegung,
 =S=      │  Construction und Veranschlagung der
          │  Blitzableiter. 8vo.                        _Glogau_, =1834=
          │
    =C=   │=Biot.= (_See Official Instructions,
          │  France._)
          │
 ¤R¤      │=Bladth=, P. J. Bericht von zwei
          │  Blitz-Schlägen, welche das Schwedische
          │  Schiff Stockholms-Schloss in Ost-Indien,
          │  1777, getroffen haben. 8vo. 14 p.p.
          │  (_Neue Schwedische Akademie Abhandlung_,
          │  i. 1780, p. 97) Translation.              _Leipzig_, =1780=
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    =C=   │=Blagden & Nairne.= Proceedings relative to
          │  the Accident by Lightning at Heckingham.
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          │
    ¤A¤   │=Blesson.= Verbesserung an Blitzableitern.
          │  _Verhandl. des Vereins zur Beforderung
          │  des Gewerbefleisses in Preussen._ Jahrg.
          │  1831, 250.                                           =1831=
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 ¤R¤ ¤A¤  │=Böckmann=, J. L. Ueber Blitzableiter. Eine
 ¤S¤      │  Abhandlung auf höchsten Befehl                 _Carlsruhe_,
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          │
 ¤R¤      │ „   Ueber Blitzableiter. 3 Auflage von G.       _Carlsruhe_,
          │  F. Wucherer. 8vo.                                    =1839=
          │
 =R= ¤A¤  │=Bodde=, J. B. Grundzüge zur Theorie der
          │  Blitzableiter. 8vo. 84 p.p.               _Münster_, =1809=
          │   (Anderson says also “Munster, 1804.”)
          │
 ¤R¤      │=Boddington.= An accurate Statement of
          │  Facts relative to a Stroke of Lightning
          │  which happened on the 13th April, 1832.
          │  8vo.                                       _London_, =1832=
          │
          │=Bodino=, J. Universæ naturæ theatrum in
          │  quo rerum omnium Effectrices cause et
          │  fines quinques libris discutiuntur. 8vo.
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 =R= ¤A¤  │=Boeckmann=, J. L. Ueber die Blitzableiter.
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 ¤R¤      │=Bona e Corner.= Relazione dell’ andamento
          │  ed effetti del Fulmine che colpì il
          │  Campanile ... di S. Francesco della Vigna
          │  (in Venezia), l’anno, 1780, 24 Maggio.
          │  4to. 8 pp.                                _Venezia_, =1780=
          │  (This title is abridged from that of an
          │ official report made by Bona and Corner,
          │          officers of Artillery.)
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       ¤S¤│=Bonjean=, J. Météorologie; effets produits       _Chambéry_,
          │  par un coup de foudre. 8vo.                          =1848=
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 ¤R¤      │=Bottis=, G. Breve relazione degli effetti
          │  di un Fulmine che cadde in Napoli il mese
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 =R= =S=  │=Boudin=, M. Histoire physique et Médicale
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 =R=      │ „   De la Foudre considérée au point de
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          │  et de l’Hygiène publique. 8vo. 50 pp.       _Paris_, =1855=
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 =R=      │ „   Histoire de la Foudre et des
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          │  1837_, p. 83.)                                       =1837=
          │    _Note._—Contains notices of two
          │      memoirs, as replies to a prize
          │      question on Lightning-conductors. The
          │      first is an anonymous one, which
          │      speaks of the forms of roofs and of
          │      metallic masses spread over the
          │      edifice, &c. The second is by Mermet,
          │      of Pau, who received a gold medal,
          │      but not the prize.
          │
 =R=      │=Bragadin= (or Anonymous). Dubbii sull’
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 =R=      │ „   Risposta dell’ autore dei Dubbii sull’
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       ¤S¤│=Braun=, A. A. Ueber zwei am 26 Juli bei
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 ¤R¤      │=Breitinger=, D. Reflexionen ob es wohl
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 ¤R¤      │ „   Nachricht über das Einschlagen des
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 =R=      │=Breitinger=, D. Ragguaglio d’un Fulmine
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 ¤R¤      │ „   Instruction für diejenigen, welche
          │  sich mit der Verfertigung und Visitation
          │  der Blitzableiter beschäftigen.            _Zürich_, =1825=
          │
 ¤R¤ ¤A¤  │ „   Instruction über Blitzableiter im
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 =R=      │=Brewster=, Sir D. On the Life Boat, the
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    ¤A¤   │=Bright=, E. B. Lightning Conductors.
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 =R= =S=  │=Brook=, A. Miscellaneous experiments and
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    =C=   │=Brooks=, D. Facts and inferences relating
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          │  pp.                                                  =1872=
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    ¤A¤   │ „   Lightning and Lightning Rods.
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          │  lxvi. 4.                                             =1873=
          │
 (117) =S=│ „   Atmospheric electricity. 8vo.            _Philadelphia_,
          │                                                       =1878=
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 (132) =S=│=Brough=, R. S. Protection of Buildings          _Mussoorie_,
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 ¤R¤      │=Bucher.= Einige gegen die Gewitterableiter      _Frankfort_,
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  =R= ¤A¤ │=Buchner=, O. Die Construction und Anlegung
    =S=   │  der Blitzableiter. zum Schutze aller
   (128)  │  Arten von Gebäuden, Seeschiffen, and
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       =S=│ „   De bliksemafleiders, door C. J. v.
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 ¤R¤      │=Buissart.= Mémoire sur les divers
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 ¤R¤      │ „   Mémoire juridique sur les Conducteurs
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 =R=      │=Burnaby=, A. Voyages dans l’Amérique
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       ¤S¤│=Burt.= Miscellaneous Scientific papers.            =1861–65=
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 =R=      │=Busse=, F. G. von. Beruhigung über die
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 ¤R¤      │ „   Beschreibung einer wohlfeilen und
          │  sichern Blitzableitung, mit neuen Gründen
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 ¤R¤ ¤A¤  │=Butschany=, M. Dissertatio de Fulgure et
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          │
 ¤R¤ ¤A¤  │ „   Der Blitz entsteht nicht durch
          │  Entzündung einiger brennbaren Theilchen
          │  die in der Luft schweben, und ist auch
          │  kein Feuer. (_Beitrage zu Hannov.
          │  Magazin_, 1761.)                          _Hanover_, =1761=
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 ¤R¤      │ „   Eine Unvollkommenheit der
          │  Blitzableiter, nebst ihrer Verbesserung.
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          │
          │=Cagniard de Latour.= (_See Official
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 ¤R¤      │=Camerer=, J. W. Über das Einschlagen des
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 ¤R¤      │=Castelli=, C. Dissertazione sull’ origine
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 =R= A S  │=Cavallo=, T. A complete Treatise on         _London_, =1777,
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 ¤R¤      │=Cerini=, G. Impossibilità fisico-chimica
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  (70) =S=│=Chapman=, Sir F. E. Instructions as to the
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 ¤R¤      │=Chappe=, D’Auteroche. Observations sur
          │  l’orage du 6 Août, 1767, et d’un coup de
          │  foudre qui s’est élevé de la terrasse de
          │  l’Observatoire. 4to. (_Mém. de Paris_,
          │  1767, _Mém._ p. 344.)                       _Paris_, =1767=
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 =R=      │ „   Voyage en Californie pour
          │  l’Observation de Vénus sur le disque du
          │  Soleil le 3 Juin, 1767.... Redigé et
          │  publié par M. Cassini fils. 4to. 170 pp.
          │  4 plates.
    =S=   │(_On Lightning (as ascending)_, p. 31, _and
          │  reference to the same subject in his
          │  Voyage en Sibérie_).                        _Paris_, =1772=
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 ¤R¤      │ „   Voyage en Sibérie. (_Pogg._ i. 420,
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 ¤R¤      │=Chevallier=, J. G. Instruction sur les
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 ¤R¤      │=Chigi=, A. Lettera ad un amico sopra il
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 =R=      │=Chiminello=, V. Risposta ... al commento
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          │
 ¤R¤      │ „   Precauzione d’applicare il secondo
          │  conduttore ovvero l’Emissario per
          │  preservare gli edifizii dai Fulmini.
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          │
 =R=      │=Chinale= e Compa. Paragrandine.
          │  Istruzione. 8vo. 25 pp. 1 plate.
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 =R==C==S=│=Clark=, Latimer. On the Storms experienced
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 ¤R¤      │=Clerc.= Compte-rendu. 1er Sémestre de
          │  1819. 8vo. (_Lyon’s Acad.
          │  Comptes-rendus._)                            _Lyon_, =1819=
          │    =Note.=—Mention of a work received from
          │      le Comte de Lezai-Marnesia ... sur
          │      les Paratonnerres et les
          │      Paragrêles—N. D.
          │
 =R=      │=Close=, D. Passage d’une letter ... sur
          │  les effets de la Foudre sur la chaîne du
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          │  483.)                                                =1854=
          │
 =R=      │=Cohn=, F. Ein interessanter Blitzschlag
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          │ „   Die Einwirkung des Blitzes auf Bäume.
          │  4to. (_Acad. Leop.?_)
          │
       ¤S¤│=Colladon=, D. Mémoire sur les effets de la
          │  Foudre sur les arbres et les plantes
          │  ligneuses, et l’emploi des arbres comme
          │  parratonnerres. to.                        _Genève_, =1872=
          │
 (117) =S=│=Collin= et Fils. Paratonnerres. (_Extract
          │  from Catalogue._) 4to.
          │
 ¤R¤      │=Collinder=. De fulguribus. 4to. (_From
          │  Watts._)                                    _Upsal_, =1686=
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 =R=      │=Contessi=, M. Disquisizione sui
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 =R=      │=Costantini=, G. A. (?) Difesa della ...
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          │  pp.                                                 =1749=.
          │
 =R=      │=Cowper.= (Poet.) Letter to Tilloch, from
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          │  3rd vol. p. 178, in a letter to the Rev.
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          │  which burst “_on the steeple, or close to
          │  it_,” at Olney. 8vo. (_Phil. Mag._ xix.
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 ¤R¤      │=Crause= (Krause), R. W. De fulmine tactis.    _Jenæ_, =1694=
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 ¤R¤      │=Crœse=, G. De Fulmine. 4to. (_From              _Amsterdam_,
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 =R= =S=  │=Crosse=, A. Memorials of the late. 8vo.     _London_, =1857=
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          │
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    ¤A¤   │=Dalibard=, M. Histoire abrégée de
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          │=D’Auteroche.= (_See Chappe D’Auteroche._)
          │
 =R=      │=Davies=, E. An account of what happened
          │  from Thunder in Carmarthenshire; partly
          │  from the woman’s mouth that suffered by
          │  it, partly from what was observed by
          │  others; communicated to the Royal Society
          │  by Eames J., as he received it in a
          │  letter from Davies E., dated Pencarreg,
          │  Saturday, Dec. 6, 1729–30. 4to. 5 pp.             _London_,
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 =R=      │=Daviet de Foncenex=, F. Récit d’une foudre
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 =R=      │=Davy=, Sir H. Preservation from Lightning.
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          │=De Fonvielle.= (_See Fonvielle, De._)
          │
          │=De Fremery.= (_See Fremery, De._)
          │
          │=De La Pylaie.= (_See La Pylaie, De._)
          │
          │=De La Rive.= (_See La Rive, De._)
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 ¤R¤ ¤A¤  │=Delaval=, E. H. An account of the effects
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 ¤R¤      │=Della Bella=, G. Trattato sopra l’utilità
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 ¤R¤      │ „   Noticias historicas, e praticas à
          │  circa do modo de defender os edificios
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 =R=      │=Dell’Acqua=, C. Norme pratiche per ben
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 ¤R¤ ¤A¤  │=Dempp=, K. W. Vollständiger Unterricht in
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          │=Des Cartes Renati.= Principia philosophiæ.    _Amstelodami_,
          │  4to. 316 pp.                                         =1650=
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          │=Despretz.= (_See Official Instructions,
          │  France._)
          │
          │=De St. Lazare.= (_See Bertholon de St.
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 =R=      │=D’Hombre Firmas=, L. A. Effets de la
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 ¤R¤      │=Dietrich=, P. F. von. Sur les conducteurs
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 ¤R¤ ¤S¤  │=Dingley=. R. Vox Cœli, or Observations of
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 ¤R¤      │=Divisch=, P. “Erfand einen Wetterableiter.
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 =R= =S=  │=Dove=, H. W. Ueber Electricität. 8vo.       _Berlin_, =1848=
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 ¤R¤      │=Dralet.= On a Trombe, with thunder, &c.          _Toulouse_,
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          │=Drebble=, C. Einkurtzer Tractat von der
          │  Natur. Der Elementen und wie sie den Wind
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          │  25 pp.                                               =1628=
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          │=Duhamel.= (_See Official Instructions,
          │  France._)
          │
 =R=      │=Dujardin=, C. Traité élémentaire de
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          │  par M. Gay-Lussac. S.A. 12mo.                      _Paris._
          │
          │=Dulong.= (_See Official Instructions,
          │  France._)
          │
 =R=      │=Du Moncel=, T. Théorie des éclairs. 8vo.        _Cherbourg_,
          │  46 pp.                                               =1854=
          │
 =R=      │ „   Notice historique et théorique sur le
          │  tonnerre et les éclairs. 8vo. 54 pp.        _Paris_, =1857=
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       ¤S¤│ „   Exposé des applications de
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    ¤A¤   │=Dupin=, C. Observations au sujet du
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 =R=      │=Du Prez=, F. Mémoire en réponse ... sur         _Bruxelles_,
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 =R= =S=  │ „   Statistique des coups de foudre qui         _Bruxelles_,
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       =S=│=Edmonds=, R. On the two great
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 =R= ¤A¤  │=Eeles=, H. Letter concerning the cause of
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 ¤R¤ ¤A¤  │=Eisenlohr=, W. Anleitung z. Ausführung u.       _Carlsruhe_,
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       ¤S¤│ „   Second edition, with 3 plates.              _Carlsruhe_,
          │                                                       =1867=
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    ¤A¤   │=Eitelwein=, J. A. Kurze Anleitung auf
          │  welche Art Blitzableiter an den Gebäuden
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 ¤R¤      │=Elice=, F. Lettera sulla niuna influenza
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 =R=      │ „   Influenza delle campane sul fulmine.
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 =R=      │ „   Osservazioni sull’ Istruzione dei
          │  Parafulmini approvata dalla R. Acad.
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 =R=      │ „   Lettera del ... F. Elice ... al sig.
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          │      the tower of the lighthouse at Genoa,
          │      Jan. 4th, 1827.
          │
 ¤R¤      │ „   Istruzione sui Parafulmini. Lettera
          │  ... al P. C. Dentone. 8vo. 24 pp.          _Genova_, =1839=
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 ¤R¤      │ „   Istruzione sui Parafulmini; lettera
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 ¤R¤      │ „   Osservazioni sui Parafulmini. Luglio
          │  1843 e Nota sulla conducibilità di
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 ¤R¤      │=Ellinger=, A. Beiträge zur Erläuterung d.
          │  Vorstellung von Wetterwolken und Blitzen.        _Munchen_,
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 =R=      │=Englefield=, Sir H. C. Some particulars
          │  respecting the Thunderstorm at London and
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 ¤R¤      │=Esser=, Ferd. Abhandl. üb. Blitzableiter.
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    =C=   │=Falconer=, W. Observations on the
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 =R=      │=Felbiger=, J. I. von. Die Kunst Thuerme,
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 ¤R¤      │ „   Wie weit gewähren wohl
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 =R=      │=Ferri=, P. Riflessioni sopra gli Argomenti
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 ¤R¤      │=Fiedler=, K. G. Merkwürdige Blitzschlaege.
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 ¤R¤      │=Fischer=, D. Relatio de fulgure tonitru et
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 ¤R¤      │=Fischer=, J. B. De fœno sub combustione
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 =R=      │=Follini=, G. Sul passaggio del fulmine ...
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 =R= =C=  │=Fonveille=, W. de. Eclairs et Tonnere.
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       =S=│ „   Thunder and Lightning (translated by
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          │
   ¤A¤ ¤S¤│ „   Eclairs et Tonnerres. 8vo.               _Paris_, =1869=
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    ¤A¤   │ „   De l’Utilité, des Paratonnerres. 8vo.    _Paris_, =1874=
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 =R=      │=Forbes=, Eli. An account of the effects of
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 ¤R¤      │=Fowler=, T. A remarkable case of the
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    ¤A¤   │=Franklin=, B. Experiments and Observations
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       ¤S¤│ „   Expériences et Observations. 12mo.                =1752=
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 =R=      │ „   Letter from Dr. B. Franklin to D.
          │  Hume, Esq., on the method of securing
          │  houses from the effects of Lightning.          _Edinburgh_,
          │  8vo. 15 pp.                                          =1771=
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  =R= ¤C¤ │ „   Experiments and Observations. (_5th
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 =R= =S=  │ „   Mémoire sur la manière d’armer d’un
          │  conducteur la cathédrale de Strasbourg et
          │  sa tour. 8vo.                                        =1780=
          │    Entered in the Ronald’s Catalogue,
          │      under Barbiere de Tinan, but issigned
          │      by Franklin.
          │  (_See Official Instructions, France._)
          │
 ¤R¤      │=Frecksel.= Bemerkungen über Blitzschläge.             =1819=
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 =R=      │=Frost=, A. J. Catalogue of books and
 =C==S=   │  papers relating to Electricity, &c.,
          │  compiled by Sir Francis Ronalds, F.R.S.
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          │
 =R= =S=  │=Fremery=, N. C. De. Dissertatio philos,      _Lugd. Batav._,
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          │=Fresnel.= (_See Official Instructions,
          │  France._)
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 ¤R¤      │=Fuchs=, J. C. Von einem merkwürdigen
          │  Wetterschlage in Potsdam. (_Allerneueste
          │  Mannigfaltigkeiten_, 1782.)                          =1782=
          │
 ¤R¤      │ „   Zusätze und Ergänzungen der Nachricht
          │  von einem merkwürdigen Wetterschlage in
          │  Potsdam.... (_Allerneueste
          │  Mannigfaltigkeiten_, J. ii. Th. iii.)
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 =R=      │=Gallitzin=, D. A. F. Observations sur les
          │  conducteurs. Addressée à l’Acad. de
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          │
 ¤R¤      │=Garipuy.= Mémoire sur un coup de Tonnerre
          │  arrivé près la ville de Castres ...
          │  Réflexions sur les conducteurs
          │  électriques. (Lu 11 Avril, 1782.) 4to.
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 =R=      │=Gattoni=, G. C. Lettera all editore sui
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          │
 =R= ¤S¤  │=Gavarret=, J. Traité d’Electricité. 2               _Paris_,
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 =R= ¤S¤  │ „   Lehrbuch d. Electricität. (_Translated        _Leipzig_,
          │  by Arendt._) 2 bde.                               =1859–60=
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 =R=      │=Gay-Lussac.= (_See Official Instructions,
          │  France._)
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       ¤S¤│=Gersdorf=, —— v. Ueber die atmosphärische
          │  Electricität.                             _Görlitz_, =1802=
          │
 =R=      │=Gilbert=, I. A method of affording relief
          │  to persons injured by Lightning. In a
          │  letter from Mr. Isaiah Gilbert to the
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          │
 =R=      │=Gilii=, F. L. Memoria fisica sopra il
          │  Fulmine Caduto in Roma sulla casa dei P.
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          │  detta comunemente la chiesa nuova nel dì
          │  26 Novembre, 1781. 12mo. 28 pp.              _Roma_, =1782=
          │
 =R=      │ „   Breve ragionamento sopra il conduttore
          │  ... innalzato sulla Basilica di Sta.
          │  Maria degli Angioli. 8vo. 22 pp.             _Roma_, =1793=
          │
 ¤R¤      │=Gilly= und =Eytelwein=. Kurze Anleitung,
          │  auf welche Art Blitzableiter an d.
          │  Gebäuden anzubringen sind. 8vo. 3 plates.  _Berlin_, =1798=
          │
 ¤R¤      │ „   Kurze Anleit. &c. (Blitzableiter).
          │  8vo. 3 plates.                             _Berlin_, =1802=
          │
 ¤R¤      │ „   Kurze Anleit, &c. 3e Aufl. 8vo.         _Berlin_, =1819=
          │
          │=Gineau.= (_See Official Instructions,
          │  France._                                                  )
          │
 ¤R¤      │=Giorgi=, E. Ueber Blitzableiter. (_Vide
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       =S=│=Gray=, J. W. & Son. Lightning, its
          │  destructive action on buildings. 8vo.     _London_, =1875?=
          │
 ¤R¤      │=Green=, W. P. Selection of papers on the
          │  subject of fixed Lightning Conductors to
          │  the masts of H.M.’s Navy, constructed so
          │  as to pass from the truck to the keelson
          │  ... illustrated by engravings, &c. 8vo.    _London_, =1824=
          │
 ¤R¤      │ „   On Lightning Conductors for Ships.                =1828=
          │
       ¤S¤│ „   Precautions to avoid accidents by
          │  Lightning. 8vo.                                      =1837=
          │
 ¤R¤      │=Greimble.= Dissertatio physica de genu        _Agust. Vind._
          │  progressu et effectibus fulminis. 12mo.              =1759=
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    ¤A¤   │=Grenet=, E. Construction des
          │  Paratonnerres. 8vo.                         _Paris_, =1873=
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 ¤R¤      │=Grimm=, J. Über die Namen des Donners.
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          │
 =R= ¤A¤  │=Gross=, J. F. Grundsätze der
          │  Blitzableitungskunst geprüft, und durch
          │  einen merkerwürdigen Fall erläutert. Nach
          │  dem Tode des Verfassers herausgegeben von
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          │
 =R=      │=Guazzi=, A. Transunto del Ragguaglio d’un
          │  Fulmine caduto presso Casalmaggiore con
          │  danno di tre persone. 4to. 3 pp. (_Opusc.
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          │
 =R=      │=Guden=, P. P. Von der Sicherheit wider die      _Göttingen_,
          │  Donnerstrahlen. 8vo. 200 pp.                         =1774=
          │
 =R=      │=Gutle= und =Luz=. Unterricht vom Blitz und
          │  den Blitz-und-Wetter Ableitern, zur
          │  Errinerung und Beruhigung sonderlich der
          │  ungelehrten, und des gemeinen Mannes von
          │  F. Luz neu bearbeitet von J. K. Gutle.          _Nürnberg_,
          │  Erster Theil. 8vo. 222 pp. 1 plate.                  =1804=
          │
 =R=      │=Gutle=, J. C. Lehrbuch der praktischen
          │  Blitzableitungskunst ... als Fortsetzung
          │  der “Theoretischen Blitzableitungslehre.”       _Nürnberg_,
          │  8vo. 446 pp. 16 plates.                              =1804=
          │
 ¤R¤ ¤A¤  │ „   Algemeine Sicherheitsregeln für              _Nürnberg_,
          │  Jederman bey Gewitter. 8vo.                          =1805=
          │
 =R=      │ „   Fasslicher Unterricht wie man sich bei
          │  Gewittern vor den ... Wirkungen des
          │  Blitzes ohne Blitzableiter sicher ...           _Nürnberg_,
          │  verwahren kann. 8vo. 140 pp.                         =1805=
          │
 =R= ¤A¤  │ „   Neue Erfahrungen über die beste Art          _Nürnberg_,
          │  Blitzableiter anzulegen. 8vo.                        =1812=
          │
 ¤R¤      │ „   Neue wissenschaftliche Erfahrungen,
          │  Entdeckungen und Verbesserungen, &c. 8vo.
          │  272 pp. 4 plates.                         _München_, =1826=
          │
          │
 ¤R¤      │=Hachette=, J. N. P. Sur la formation des
          │  tubes fulminaires. 8vo. (_Ann. de Chim._
          │  xxxvii. 1828.)                              _Paris_, =1828=
          │
 =R=      │=Haidinger=, W. Ritter Von. Niedrigste
          │  Höhen von Gewitterwolken (Zwei Fälle in
          │  Erinnerung gebracht.) 8vo. 10 pp. (_Aus
          │  den Sitzungsberichten_ 1852, _der k.
          │  Akad. der Wissenschaften abgedruckt._
          │  Vol. ix. ii. Heft.)                          _Wien_, =1853=
          │
 =R= ¤S¤  │ „   Die südwestlichen Blitzkugeln am 20
          │  Octbr. 1868. Nachtrag zu der Mittheilg.
          │  am 5 Novbr. 8vo. 2 pp. (_Sitzb. d. k.
          │  Akad. d. Wiss._ Dec. Heft. 1868 lviii.
          │  Bde.)                                        _Wien_, =1868=
          │
 =R= ¤S¤  │ „   Ein kugelförmiger Blitz am 30 Aug.
          │  1865, gesehen zu Feistritz bei Peggau in
          │  Stiermark. 8vo. 4 pp. (_Sitzb. d. k.
          │  Akad. d. Wiss._ Dec. Heft. 1868, lviii.
          │  Bde.)                                        _Wien_, =1868=
          │
       =S=│=Hajingi=, B. ΚΕΡΑΥΝΟΛΟΓΙΑ ΦΥΣΙΚΗ, Seu                _Giessæ
          │  Disquisitio de Fulmine Naturalis. 4to.    Hassorum_, =1660=
          │
 =R=      │=Hallencreutz=, D. Beobachtung an
          │  Gewitterwolken welche Blitze gegen
          │  einander geben zu Pello innerhalb des
          │  Polarkreises. 8vo. 3 pp. 1 plate. (_K.
          │  Schwed. Akad. Abh._ xxxv. 85.)            _Leipzig_, =1773=
          │
 ¤R¤      │=Halley=, E. Observation sur les coups de
          │  Tonnerre multipliés et extraordinaires.
          │  4to. (_Mém. de Paris_, 1731. _Hist._ p.
          │  19.)                                        _Paris_, =1731=
          │
       =S=│=Hamberg=, H. E. Om den s. k.
          │  luftelektriciteten. 8vo.                   _Upsala_, =1872=
          │
 ¤R¤      │=Hannemann=, J. L. De fulminis effectu
          │  miro. (_Miscell. Acad. Nat. Cur._)                   =1685=
          │
    ¤A¤   │=Hare=, R. Ueber die Ursachen, warum
          │  Wetterableiter in einigen Fällen nicht
          │  schützen, und die Mittel dieselben
          │  vollkommen schützend zu machen nebst
          │  einer Widerlegung der herrschenden Idee
          │  dass Metalle die Elektricität vorzüglich
          │  anziehen. Aus. Gill’s Technological
          │  Repository, Nov., 1827, im _Polyt.
          │  Journ._, xxvii. 268.                                 =1828=
          │
 ¤R¤      │=Harris= (afterwards Sir), William Snow.
          │  Electrical Conductors for Ships.
          │  Experiment in Plymouth Harbour. 8vo. 7
          │  pp. (_Phil. Mag._ lx. 231.)                _London_, =1822=
          │
 =R= ¤C¤  │ „   Observations on the effects of
 ¤A¤ ¤S¤  │  Lightning on floating bodies, &c., with
          │  an account of a new method of applying
          │  fixed and continuous Conductors of
          │  Electricity to the Masts of Ships. Letter
          │  to Sir T. B. Martin. 4to. 89 pp. 5
          │  plates.                                    _London_, =1823=
          │    _Note._—The illustration accompanies
          │      plate i. The lines on the paper
          │      originally consisted of gold leaf....
          │      A discharge has been passed over the
          │      gold leaf to show by its deflagration
          │      the course of the electric matter.
          │
 =R=      │ „   On the relative powers of various
          │  metallic substances as Conductors of
          │  Electricity. Read Dec. 14, 1826. 4to. 7
          │  pp. 1 plate. (_Phil. Trans._)              _London_, =1827=
          │
 =R= ¤A¤  │ „   On the utility of fixing Lightning           _Plymouth_,
          │  Conductors on Ships. 8vo. 23 pp.                     =1830=
          │
 =R=      │ „   A series of papers on the defence of
          │  Ships and Buildings from Lightning. 8vo.
          │  46 pp. (_Nautical Magazine_, xxv.)         _London_, =1835=
          │
 =R= ¤S¤  │ „   Inquiries concerning the elementary
          │  laws of electricity. 4to.                  _London_, =1836=
          │
 ¤R¤      │ „   A series of three Papers, termed
          │  Illustrations of cases of damage by
          │  Lightning in the British Navy. (_Nautical
          │  Magazine_ for 1838.)                       _London_, =1838=
          │
    ¤A¤   │ „   On the Protection of Ships from
          │  Lightning. (_Annals of Electricity_, ii.
          │  81.)                                                 =1838=
          │
 =R= ¤S¤  │ „   State of the question relating to the
          │  protection of the British Navy from
          │  Lightning, by the method of fixed
          │  Conductors of Electricity, as proposed by       _Plymouth_,
          │  Mr. Snow Harris. With appendix. 8vo.                 =1838=
          │
   ¤C¤ ¤S¤│ „   History of 220 ships struck by
          │  Lightning.                                           =1839=
          │
 =R= ¤A¤  │ „   On Lightning Conductors, and on
          │  certain principles in Electrical science;
          │  being an investigation of Mr. Sturgeon’s
          │  experimental and theoretical researches
          │  in Electricity, published by him in the
          │  _Annals of Electricity_, &c. 8vo. 12 pp.
          │  1 plate. (_Phil. Mag._ for Dec., 1839, p.
          │  463.)                                      _London_, =1839=
          │
  =R= =S= │ „   Copy of the report and evidence from
   (83)   │  the Commission appointed to inquire into
          │  the plan of W. S. Harris, relating to the
          │  protection of Ships from the effects of
          │  Lightning. Ordered by the House of
          │  Commons to be printed, 11th Feb., 1840.
          │  Folio. 96 pp. 12 plates.                   _London_, =1840=
          │
       ¤S¤│ „   State of the question relating to the
          │  protection of the British Navy. 8vo.                 =1840=
          │
 ¤R¤      │ „   On the course of the Electrical
          │  discharge, and on the effects of
          │  Lightning on certain ships of the British
          │  Navy. 8vo. (_Edinb. and Lond. Phil.
          │  Mag._, Feb. and March, 1840.)              _London_, =1840=
          │
 =R=      │ „   On Lightning Conductors, and the
          │  effects of Lightning on H.M.’s ship
          │  “_Rodney_” and certain other ships of the
          │  British Navy; being a further examination
          │  of Mr. Sturgeon’s Memoir on Marine
          │  Lightning Conductors. 8vo. 12 pp. 1
          │  plate. (_Annals of Electricity_, iv.
          │  484.)                                      _London_, =1840=
          │
 ¤R¤      │ „   On the supposed Electro-magnetical
          │  effects of Marine Lightning Conductors.
          │  (_Nautical Magazine_, Enlarged Series,
          │  No. 2, vol. for 1841)                                =1841=
          │
 ¤R¤      │ „   Observations on the action of
          │  Lightning Conductors. (_Proc. London
          │  Elec. Soc._ for 1842.)                     _London_, =1842=
          │
 =R=      │ „   On the effects of Lightning on the
          │  British ship “_Underwood_,” 8vo. 8 pp.
          │  (_Nautical Mag._ for June, 1842.)          _London_, =1842=
          │
  =R= ¤C¤ │ „   On the nature of Thunderstorms, and
  ¤A¤ =S= │  the means of protecting Buildings and
   (85)   │  Shipping against ... Lightning. 8vo.       _London_, =1843=
          │
 ¤R¤      │=Harris=, W. S. A theoretical and practical
          │  view of Thunderstorms, and the protection
          │  of Buildings and Ships from Lightning.     _London_, =1843=
          │
 =R=      │ „   On Damage by Lightning in the British
          │  Navy. 8vo. 66 (pp. _Extract from the
          │  Nautical Magazine_, 1843.)                 _London_, =1843=
          │
       ¤S¤│ „   Brief history of 220 Ships. 8vo. 1844
          │
 =R= ¤S¤  │ „   Meteorology of Thunderstorms at Sea,
          │  with analytical deductions; and a history
          │  of the effects of Lightning on 210 ships
          │  of the Royal Navy. 8vo.                    _London_, =1844=
          │    _Note._—The first part was printed in
          │      the “Nautical Magazine” after the
          │      second part, containing the history
          │      of cases, had been completed. The
          │      first part has 18 pp.; the second
          │      part is entitled, “Damage by
          │      Lightning in the British Navy,” and
          │      has 66 pp.
          │
 =R=      │ „   Remarkable instances of the protection
          │  of certain Ships of H.M.’s Navy from the
          │  destructive effects of Lightning;
          │  collected from various authorities. 8vo.        _Plymouth_,
          │  18 pp.                                               =1844=
          │
 ¤R¤      │ „   Remarkable instances of defence of
          │  certain Ships of the Royal Navy from the
          │  destructive agency of Lightning, with
          │  practical and theoretical deductions.      _London_, =1846=
          │
 ¤R¤      │ „   Letter to the Secretary of the
          │  Incorporated Society for Building
          │  Churches, &c., on the Preservation of           _Plymouth_,
          │  Public Buildings from Lightning. 8vo.                =1847=
          │
 ¤R¤      │ „   A Public Official Letter to the India
          │  Board, dated June 21, 1847, relative to a
          │  Board Order requiring all Transports to
          │  be fitted with his Conductors.                       =1847=
          │
       ¤S¤│ „   History of 220 ships of the Royal
          │  Navy. 8vo.                                           =1847=
          │
 =R=      │ „   Remarkable instances of the protection
          │  of certain Ships ... from the destructive
          │  effects of Lightning. 8vo. 61 pp. 2
          │  plates.                                    _London_, =1847=
          │
 ¤R¤ ¤S¤  │ „   Instructions for the application of
          │  permanently fixed Conductors in H.M.’s
          │  ships, drawn up for the use of H.M.’s
          │  dockyards. Printed by order of the Lords
          │  Commissioners of the Admiralty.            _London_, =1848=
          │
 =R=      │ „   Letter to the Earl of Wilton on
          │  returns ... relative to ... fixed
          │  Metallic Conductors employed in H.M.’s          _Plymouth_,
          │  Navy. 8vo. 35 pp.                                    =1849=
          │
 =R=      │ „   Letter on the Preservation of Public
          │  Buildings from ... Lightning (revised)
          │  addressed to the ... Society for building
          │  Churches, &c., dated December, 1847. 8vo.
          │  12 pp.                                     _London_, =1850=
          │
 =R= ¤S¤  │ „   On the relative Cost and Efficiency of
          │  permanent and temporary forms of
          │  Lightning Conductors as applicable to the       _Plymouth_,
          │  defence of the Royal Navy. 8vo. 27 pp.               =1850=
          │
 =R=      │ „   Remarkable instances of the
          │  Preservation of certain Ships of the
          │  Royal Navy from Lightning. Abridged from
          │  Official and other authenticated Reports.       _Plymouth_,
          │  8vo. 19 pp.                                          =1850=
          │
 =R=      │ „   Destruction of Merchant Ships.
          │  Shipwreck by Lightning. 8vo. 6 pp.
          │  (_Nautical Magazine_ for November, 1852.)  _London_, =1852=
          │
 =R=      │ „   Papers relating to Harris’s Lightning
          │  Conductors and the destructive effects of
          │  Lightning on Ships. Fol. 11 pp. 2 plates.  _London_, =1852=
          │
 =R=      │ „   Papers relative to Harris’s Lightning
          │  Conductors, Appendix, with Addendum of 1
          │  sheet. Fol. 37 pp.                         _London_, =1852=
          │
 =R=      │ „   Review of the History and Progress of
          │  the general system of Lightning
          │  Conductors ... in the Royal Navy. 8vo. 10
          │  pp. (Reprinted from the _Nautical
          │  Magazine_ for March, 1853.)                          =1853=
          │
  =R= =S= │ „   Shipwrecks by Lightning. Copies of
   (90)   │  papers relative to Shipwrecks by
          │  Lightning as prepared by Sir Snow Harris,
          │  and presented by him to the Admiralty.
          │  Fol. 82 pp. 5 plates.                      _London_, =1854=
          │
       ¤S¤│=Harris=, W. S. On the relative cost and
          │  efficiency of Lightning Conductors. 8vo.             =1859=
          │
 =R= ¤A¤  │ „   A treatise on Frictional Electricity.
          │  (Edited by C. Tomlinson.) 8vo.             _London_, =1867=
          │
       ¤S¤│=Harting=, P. Notice sur un cas de
          │  formation de fulgurites et sur la
          │  présence d’autres fulgurites dans le sol       _Amsterdam_,
          │  de la Néerlande 4to.                                 =1874=
          │
 ¤R¤      │=Hartmann=, J. F. Verbesserter Versuch
          │  seines künstl. elektr. Blitzes. 8vo.
          │  (_Hamb. Mag._ xxiv. 1759.)                _Hamburg_, =1759=
          │
    ¤A¤   │ „   Gedanken über den Ursprunz der
          │  Luftelektricität bei Gewittern.                      =1763=
          │
 ¤R¤      │ „   Newen Erklarung der Entstehungsart der
          │  Donnerwetter. (_Göttingischen gemein,          _Göttingen_,
          │  Abhandl. von J._ 1775.)                              =1775=
          │
 ¤R¤ =S=  │=Harward=, S. A Discourse of the several
          │  Kinds and Causes of Lightnings, written
          │  by occasion of a fearefull Lightning
          │  which, on the 17th day of Nouember, Anno
          │  Dom. 1606, did in a very short time,
          │  burne vp the spire steeple of
          │  Bletchingley, in Surrey, and in the same
          │  melt into fragments a Goodly Ring of
          │  Bells. 4to.                                _London_, =1607=
          │
 ¤R¤      │=Hassencamp=, J. M. Wie ein Ort durch
          │  Wetterableiter su sichern.                _Rinteln_, =1782=
          │
 ¤R¤      │ „   Von den grossen Plätzen d.
          │  Strahlableiter, u. ihrer
          │  vortheilhaftesten Einrichtung zur
          │  Beschützung ganzer Städte.                _Rinteln_, =1784=
          │
 ¤R¤ ¤A¤  │=Hauch=, A. W. von. Von der Luftelekt.
          │  besonders mit Anwendung auf                   _Kopenhagen_,
          │  Gewitterableiter. 8vo.                               =1800=
          │
 =R= ¤A¤  │=Hehl.= Anleitung zur Errichtung und
          │  Untersuchung der Blitzableiter fur
          │  Bauverständige, Bau- und Feuerbeschauer        _Stuttgart_,
          │  und Gebäude-Inhaber. 8vo. 54 pp.                     =1827=
          │
 ¤R¤      │=Heinrich=, P. Ueber die Wirkung des
          │  Geschützes auf Gewitterwolken. 4to.
          │  (_Neue Abhandl. der Baierischen Akad.
          │  Philos._ v. p. i.)                        _München_, =1789=
          │
    ¤A¤   │=Helfenzreider=, J. E. Verbesserung der          _Eichstadt_,
          │  Blitzableiter. 8vo.                                  =1783=
          │
 =R=      │ „   Vorschlag ... die Blitzableiter zu           _Salzburg_,
          │  verbessern. 8vo. 15 pp.                              =1785=
          │
 ¤R¤      │ „   A new invention in Lightning
          │  Conductors. 8vo. (_Abhand. eine
          │  Privat-Gesellschaft_, vol. i. No. 12.)    _München_, =1792=
          │
 ¤R¤      │ „   Handgriffe bey Errichtung eines
          │  Blitzableiters von verbesserter Art. 8vo.
          │  (_Abhand. einer Privat-Ges. in
          │  Ober-Deutschland_, Th. i. p. 193.)        _München_, =1792=
          │
 ¤R¤      │=Helmuth=, J. H. Von d. wohlthätig.
          │  Erfindung d. Blitzableiters. (_Braunschw.
          │  Anzeig_, 17 7, S. 55.)                               =1777=
          │
 =R=      │=Helvig=, C. G. Bemerkungen über Blitz und
          │  Donner, nebst Vermuthungen über das
          │  Entstehen der Luft-Erscheinungen. 8vo. 32
          │  pp. 1 plate. (_Gilbert’s Ann. d. Physik_,
          │  li. S. 2, S. 10.)                         _Leipsig_, =1815=
          │
 ¤R¤      │=Hemmer=, J. J. Beschreibung einiger
          │  merkwürdiger Wetterschläge. 4to.
          │  (_Commentat. Acad. Theodoro-Palatinæ_ iv.       _Mannheim_,
          │  _Phys._ p. 87.)                                      =1780=
          │
 ¤R¤      │ „   Zergliederung des beständigen
          │  Elektrizitäts-Trägers. 4to. (_Commentat.
          │  Acad. Theodoro-Palatinæ_ iv. _Phys._ p.         _Mannheim_,
          │  94.)                                                 =1780=
          │
 ¤R¤      │ „   Kurzer Begriff u. Nutzen d.                _Düsseldorf_,
          │  Wetterableiter, u. s. w. 8vo.                        =1782=
          │
    ¤A¤   │ „   Kurzer Begriff und Nutzen der                _Mannheim_,
          │  Blitzableiter. 8vo.                                  =1783=
          │
 ¤R¤ ¤A¤  │ „   Kurze und deutliche Anweisung wie man,
          │  durch einen in jedem Orte wohnenden
          │  Schmied, oder andere in Metall arbeitende
          │  Handwerker, eine sichere Wetterableitung
          │  mit sehr geringen Kosten in allerhand     _Friedrichstadt_,
          │  Gebäuden anlegen lassen kann. 8vo.                   =1783=
          │
          │=Hemmer=, J. J. De fulminis ictibus in
          │  campanas, quæ pulsantur, ubi electricitas
          │  nubium ac fulminis theoria, nova et
          │  uberiore luce perfunduntur. 4to.
          │  (_Commentat. Acad. Theodoro-Palatinæ_ v.        _Mannheim_,
          │  _Phys._ p. 237.)                                     =1784=
          │
          │ „   Über d. Glockenläuten bey Gewittern.
          │  4to. (_Commentat. Acad.                         _Mannheim_,
          │  Theodoro-Palatinæ_ v. 1784.)                         =1784=
          │
   ¤A¤ ¤S¤│ „   Anleitung Wasserableiter an allen
          │  Gattungen von Gebäuden auf die sicherste       _Frankfurt_,
          │  Art anzulegen. 8vo.                                  =1786=
          │
 ¤R¤      │ „   Anleitung Wetterableiter ...                _Offenbach_,
          │  anzulegen. 8vo.                                      =1786=
          │
 =R=      │ „   Anleitung Wetterleiter ... anzulegen.        _Mannheim_,
          │  2nd edition. 8vo. 232 pp.                            =1788=
          │
 ¤R¤ =S=  │ „   Verhaltungsregeln wenn man sich zur
          │  gewitterzeit in keinem bewaffneten              _Mannheim_,
          │  gebäude befindet.                                    =1789=
          │
 ¤R¤      │ „   Unterr. z. sicherst Anleg. d.                _Mannheim_,
          │  Wetterableiter. 8vo.                                 =1808=
          │
 ¤R¤ ¤A¤  │ „   Rathgeber wie man sich vor Gewittern
          │  in unbewaffneten Gebäuden verwahren soll.       _Mannheim_,
          │  8vo. 1 plate.                                        =1809=
          │
 ¤R¤      │ „   Conductorum fulmineorum vim egregiam
          │  tribus recentioribus exemplis docet. 4to.
          │  (_Commentat. Acad. Theodoro-Palatinæ_ vi.       _Mannheim_,
          │  _Phys._ 516.)                                        =1790=
          │
 =R= ¤S¤  │ „   Nachricht von den in Kurpfalz
          │  angelegtern Wetterleiten. 4to.
          │  (_Commentat. Acad. Theodoro-Palatinæ_ iv.
          │  _Phys._ p. 21.)                                  _Mannheim_
          │
 ¤R¤      │ „   Enarrationes conductorum fulminis
          │  superiore quinquennio variis in locis a
          │  se positorum. 4to. (_Commentat. Acad.           _Mannheim_,
          │  Theodoro-Palatinæ_ v. _Phys._ p. 295.)               =1784=
          │
 =R= ¤S¤  │=Henley=, W. An account of the death of a
          │  person destroyed by Lightning in the
          │  Chapel in Tottenham Court Road, and its
          │  effects on the building; as observed by
          │  Mr. Wm. Henley, Mr. Edward Nairne, and
          │  Mr. Wm. Jones. 4to. 8 pp. 1 plate.
          │  (_Phil. Trans._ lxii. 133.)                _London_, =1773=
          │
 ¤R¤ ¤C¤  │ „   Experiments concerning the different
 ¤A¤ ¤S¤  │  efficacy of pointed and blunted rods in
          │  securing buildings against the stroke of
          │  Lightning. 4to. (_Phil. Trans._, 1774, p.
          │  133.)                                      _London_, =1774=
          │
 ¤R¤ ¤A¤  │=Henry=, J. Method of protecting from
          │  Lightning buildings covered with metallic
          │  roofs. 8vo. (_Proc. of Amer. Phil. Soc._
          │  iv. 179.)                                            =1845=
          │
 =R=      │ „   Report concerning a letter of S. D.
          │  Ingram to R. Patterson relative to the
          │  effect of Thunder on Telegraphic wires.
          │  8vo. 9 pp.                                           =1846=
          │
    =S=   │ „   Directions for constructing Lightning      _Washington_,
   (99)   │  Rods. 8vo.                                           =1871=
          │
    =C=   │ „   Instructions for observations of
          │  thunderstorms. 1 p. (Smithsonian
          │  Institution.)
          │
       =S=│=Hepburn=, J. S. Should Lightning
          │  Conductors terminate in a point or in a
          │  ball? (_Proc. Roy. Scot. Soc. Arts._)          _Edinburgh_,
          │  8vo.                                                 =1855=
          │
       ¤S¤│=Hericard de Thury.= De l’influence des
          │  arbres sur la foudre et ses effets. 8vo.             =1838=
          │
 ¤R¤      │=Herlicius=, D. (Herlich, &c.) Tractatus de
          │  fulmine et aliis impressionibus,
          │  prodigiis et miraculis. Vom Blitz, Donner
          │  und allerlei Feurzeichen, u.s.w. 4to.       _Starg_, =1604=
          │
   ¤C¤ ¤S¤│=Hervieu=, ——. Essai sur l’éléctricité
          │  Atmosphèrique. 8vo.                                  =1835=
          │
 ¤R¤ ¤S¤  │=Highton=, E. Effects of Atmospheric
          │  Electricity. 8vo.                                    =1847=
          │
          │=Hilliard=, J. Account of Fire from Heaven
          │  burning the body of J. Hitchell, of
          │  Christchurch, and fearfully burning the
          │  town of Dorchester. 4to.                   _London_, =1613=
          │
    ¤A¤   │=Holtz=, W. Uber die Theorie, die Anlage,       _Griefswald_,
          │  und die Prüfung der Blitzableiter. 8vo.              =1878=
          │
    =C=   │=Hooke=, R. The Posthumous works of,
          │  containing his Cutlerian Lectures, and
          │  other discoveries. Published by Richard
          │  Waller, R.S. Sec. Fol. 572 pp. 1 plate.    _London_, =1705=
          │
 =R=      │=Hoppe=, M. Über das Gewitter. 4to. 18 pp.
          │  (_Program des Fürstlich. Hedwigschen
          │  Gymnasium, in Neustettin ... 10 und 11        _Neustettin_,
          │  April_ 1865.)                                        =1865=
          │
 ¤R¤      │=Horner=, J. K. Bemerkung über
          │  Blitzableiter u.s.w.                       _Zürich_, =1816=
          │
  (99) =S=│=Hugueny=, F. Le coup de foudre de l’ile du     _Strasbourg_,
          │  Rhin. 4to.                                           =1869=
          │
          │
 =R= ¤A¤  │=Imhof=, M. Über das Schiessen gegen
          │  heranziehende Donner- und Hagel-Gewitter.
          │  (_Read 28th March, 1811._) 4to. 24 pp.    _München_, =1811=
          │
 ¤R¤ ¤A¤  │ „   Theoretisch prakt. Anweisung zur
          │  Anlegung der Blitzableitern. 8vo.         _München_, =1816=
          │
          │
       =S=│=James=, J. O. N. Memorandum on the
          │  Thunderstorm which passed over Calcutta
          │  8th June, 1871 (_Proc. Asiatic Soc.             _Calcutta_,
          │  Bengal._) 8vo.                                       =1871=
          │
 (111) =S=│=Jarriant.= Nouveau Paratonnerre accepté
          │  par l’Académie des Sciences. 8vo.           _Paris_, =1877=
          │
 (115) =S=│ „   Etude sur les Paratonnerres. 8vo.        _Paris_, =1878=
          │
 (117) =S=│=Johnston=, W. P. Report on the Lightning         _Calcutta_,
          │  Conductors at Dum Dum, Calcutta. 4to.                =1878=
          │
          │=Jungnitz=, L. A. Über d. Erfolg. d.
          │  Blitzfeuer auf d. Schneekoppe. 8vo.       _Breslau_, =1805=
          │
 ¤R¤      │ „   Darstell, d. Erfolgs d. auf d.
          │  Schneekoppe v. H. v. Lindener 1805
          │  angestellten u. an mehreren Orten
          │  beobachteten Blitzfeuer. 8vo.             _Breslau_, =1806=
          │
          │
 (114) =S=│=Karsten=, G. Ueber Blitzableiter und
          │  Blitzschläge in Gebäude welche mit
          │  Blitzableitern versehen waren. 8vo.          _Kiel_, =1877=
          │
       =S=│ „   Gemeinfatzliche Bemerkungen ueber die
          │  Elektricität des Gewitters und die
          │  Wirkung der Blitzableiter. 1st edition.
          │  8vo.                                         _Kiel_, =1879=
          │
 (119) =S=│ „   2nd Edition. 8vo.                         _Kiel_, =1879=
          │
       =S=│ „   3rd Edition. 8vo.                         _Kiel_, =1880=
          │
 ¤R¤      │=Kirchhoff=, N. A. J. Zurüstung, die
          │  Wirkung der Gewitterwolken darzustellen.
          │  8vo. (_Gött. Mag._ J. i. 1780, St. ii.         _Göttingen_,
          │  pp. 322–26).                                         =1780=
          │
 ¤R¤      │ „   Beschreibung einer Zurüstung, welche
          │  die anziehende Kraft der Erde gegen die
          │  Gewitterwolke, &c.... beweiset ... nebst  _Berlin, Nicolai,
          │  e. Beschreib. versch.... Maschin. 8vo. 56     and Hamburg_,
          │  pp. 1 plate.                                         =1781=
          │
 ¤R¤      │=Kirchmaier=, G. C. De fulmine et tonitru.        _Viteberg_,
          │                                                       =1659=
          │
 ¤R¤ ¤S¤  │=Kirchvogl=, A. B. De natura electr. aereæ.
          │  8vo.                                                 =1767=
          │
   =C= ¤S¤│=Klasen=, L. Die Blitzableiter in ihrer
          │  Construction und Anlage. 8vo. 74 pp.      _Leipzig_, =1879=
          │
    ¤A¤   │=Klein=, H. J. Das Gewitter und die
          │  dasselbe begleitenden Erscheinungen. 8vo.   _Gratz_, =1871=
          │
 =R=      │=Klugel=, G. S. Beschreib. d. Wirkung, ein.
          │  heftig. Gewitters d. 12 Juli 1789 zu
          │  Halle, nebst Erklärung d. Entstehung d.
          │  Gewitters. 8vo. 64 pp.                      _Halle_, =1789=
          │
       =S=│=Koenig=, J. G. De Fulmine, Fulgure, ac
          │  Tonitru Hiemali. 4to.                      _Norica_, =1706=
          │
       =S=│=Krayenhoff=, Baron. Handleiding tot het          _Nijmegen_,
          │  stellen van Bliksemafleiders. 8vo.                   =1836=
          │
    ¤A¤   │=Krull=, J. G. Versuche zur Bestätigung der
          │  Meinung, dass die elektrische Materie mit
          │  der Materie des Donners und Blitzes eine        _Hannover_,
          │  gross Aehnlichkeit habe.                             =1752=
          │
 ¤R¤      │=Kuhn=, K. G. Ueber Blitzableiter. “In d.
          │  Gelehrt Anzeigen d. Königl. bayer Acad.
          │  von. 1851 u. 1852;” _or_ in “Astronom
          │  Kalender 1850–52.”                                 =1851–2=
          │    _Note._—It seems uncertain to which
          │      this entry belongs.
          │
    ¤A¤   │=Kuhn=, K. G. Handbuch der angewandten
          │  Elektricitätslehre. Part I. Ueber
          │  Blitzableiter. 8vo.                       _Leipzig_, =1866=
          │
       =S=│ „   Bemerkungen ueber Blitzschläge. 8vo.   _Munchen_, =1867=
          │
       ¤S¤│ „   üb. d. Anordnung v. Blitzableitern, f.
          │  Pulvermagazine.                            _Münch._, =1867=
          │
 ¤R¤      │=Kyper= (Kieper), A. Disp. de fulmine quod
          │  a. 1636 ... turrim nitrariam aulicam
          │  Regiomonti percussit.                                =1637=
          │
          │
    ¤A¤   │=Lampadius=, W. A. Ueber die Electricität
          │  der Atmosphäre.                            _Berlin_, =1793=
          │
    ¤A¤   │ „   Versuche und Beobachtungen über
          │  Elektricität und Wärme der Atmosphäre.
          │  8vo.                                      _Leipzig_, =1805=
          │
    ¤A¤   │ „   Ein Schneegewitter und ein Vorschlag
          │  zur Vervollkommung der Blitzableiter.
          │  (_Gilberts Ann. der Physik_, xxix. 58.)              =1805=
          │
 ¤R¤      │=Lamy=, F. Conjectures physiques sur deux
          │  colomnes (sic) de Nuë qui ont parus
          │  depuis quelques années; et sur les plus
          │  extraordinaires effets du Tonnerre; avec
          │  une explication de ce qui s’est dit
          │  jusqu’icy des Trombes de mer; et une
          │  nouvelle addition, ou l’on verra de
          │  quelle manière le Tonnerre tombé
          │  nouvellement sur une Eglise de Lagni a
          │  imprimé sur une nappe d’autel une partie
          │  considérable du Canon de la Messe. 12mo.
          │  241 pp. 3 plates.                           _Paris_, =1689=
          │
          │ „   A German account of the extraordinary
          │  effects of Lightning at the Church of
          │  Lagni, printed in the _Hamburg Mag._ iii.
          │  226, and taken from Lamy’s French work,
          │  “Conjectures Phys.”, ... dated 1696,
          │  12mo. is given in Bauer, Abhandl. 1770,
          │  p. 161.
          │    _Note._—This German account contains a
          │      copy of “la partie considérable du
          │      Canon de la Messe,” which was found
          │      printed by lightning upon the
          │      altar-cloth, and also of certain
          │      parts in red ink not thus reprinted.
          │
 (134) =S=│=Lacoine=, E. Establissement de la formule
          │  relative au rayon d’Action des
          │  paratonnerres (_L’Electricité_, October,
          │  1880.)                                      _Paris_, =1880=
          │
 =R=      │=Landriani=, M. Gli effetti del Fulmine
          │  caduto la sera del 25 Agosto, 1780, nel
          │  campanile e Monastero di S. Vincenzo al
          │  Castello in Milano. 4to. 6 pp. (_Opus.
          │  Scelti_, iii. 328.)                        _Milano_, =1780=
          │
 =R=      │ „   Dell’ utilità dei Conduttori
          │  elettrici. 8vo. 304 pp.1 plate.            _Milano_, =1784=
          │
          │ „   Abhandlung vom Nutzen der
          │  Blitzableiter. Auf Befehl der Guberniss
          │  herausgegeben. Aus dem Italiänischen von
          │  G. Muller. 8vo.                              _Wien_, =1786=
          │
 =R=      │ „   Altra ricaduta del propagatore ...
          │  ossia ultima risposta contro la difesa
          │  dei Paragrandini. Lettera all’ Ateneo di
          │  Venezia. 8vo. 60 pp.                       _Milano_, =1826=
          │
 ¤R¤      │=Langenbucher=, J. Richtige Begriffe vom          _Augsburg_,
          │  Blitz und von Blitzableitern. 8vo.                   =1783=
          │
       =S=│=Langlois=, E. H. Notice sur l’incendie de
          │  la Cathédrale de Rouen occasionné par la
          │  foudre, le 15 Septembre, 1822. 8vo.         _Rouen_, =1823=
          │    (This Cathedral is reported to have
          │      been struck by Lightning in 1110,
          │      1117, 1284, 1351, 1625, 1627, 1642,
          │      1768 and 1822.)
          │
 ¤R¤      │=Lanteires=, J. Essai sur le Tonnerre
          │  considéré dans ses effets moraux sur les
          │  hommes, et sur un coup de foudre
          │  remarquable; suivis des notes
          │  communiquées à l’auteur par M. le               _Lausanne_,
          │  Professeur Saussure, à Genève. 8vo.                  =1789=
          │
          │=La Place.= (_See Official Instructions,
          │  France._)
          │
 =R= ¤A¤  │=Lapostolle.= Traité des Parafoudres et des
 =S=      │  Paragrêles en cordes de paille. 8vo. 320
          │  pp. &c., also 3 supplements.               _Amiens_, =1820=
          │
 =R=      │ „   Trattato sul modo di preservare le
          │  abitazioni dal Fulmine e le campagne
          │  dalla Grandine. Opera volgarizzata da
          │  Bodei. 8vo. 189 pp. 1 table.               _Milano_, =1821=
          │
    =C=   │ „   Ueber Blitz-und hagelableiter an        _Wiln. u. Prag_,
          │  Stroh-Seilen. 8vo. 54 pp.                            =1825=
          │
       ¤S¤│=La Pylaie=, De. Effets extraordinaires de
          │  la foudre. 8vo.                                      =1849=
          │
 =R= =S=  │=La Rive=, De. Traité de l’Electricité. 3            _Paris_,
          │  vols. 8vo.                                        =1854–58=
          │
 =R= ¤S¤  │ „   Treatise on Electricity (translated by         _London_,
          │  Walker.) 3 vols. 8vo.                             =1853–58=
          │
 =R=      │=Laroque.= Note sur des Eclairs de forme
          │  inusitée, observés à Toulouse pendant
          │  l’orage du 16 Juillet, 1850. 8vo. 3 pp.         _Toulouse_,
          │  (_Toulouse Acad._ 3e Série, vi. 349.)                =1850=
          │
 =R=      │=Lathrop=, Dr. J. Fatal effects of
          │  Lightning. In a letter to ... Joseph
          │  Willard. 4to. 7 pp. (_Mem. Amer. Acad._      _Charlestown_,
          │  Old Series, ii. pt. ii. p. 85.)                      =1804=
          │
 =R=      │ „   An account of the effects of Lightning
          │  on the house of Jn. Mason, in Boston, in
          │  a letter to Joseph Willard. 4to. 4 pp.
          │  (_Mem. Amer. Acad._, Old Series, ii. pt.     _Charlestown_,
          │  ii. p. 91.)                                          =1804=
          │
 =R=      │ „   Effects of Lightning on several
          │  persons in the house of Samuel Cary, of
          │  Chelsea, August 2, 1799, in a letter to
          │  John Davis. 4to. 4 pp. (_Mem. Amer.             _Cambridge,
          │  Acad._ Old Series, iii. pt. i. p. 82.)        U.S._, =1809=
          │
 =R=      │ „   Effects of Lightning on the house of
          │  Capt. D. Merry, and several other houses
          │  in the vicinity, on the evening of the
          │  11th May, 1805, in a letter to John
          │  Davis. 4to. 6 pp. (_Mem. Amer. Acad._ Old       _Cambridge,
          │  Series, iii. pt. i. p. 86.)                   U.S._, =1809=
          │
       =S=│=Laue=, J. G. De telo fulmineo. 4to.         _Lipsiæ_, =1706=
          │
 =R=      │=Lee=, A. An Account of the effect of
          │  Lightning on Two Houses in the city of
          │  Philadelphia, in a letter from A. Lee to
          │  James Bowdoin (dated July 29, 1781). 4to.
          │  6 pp. (_Mem. Amer. Acad._ Old Series, i.    _Boston, U.S._,
          │  247, part ii.)                                       =1785=
          │
 ¤R¤      │=Lehaitre.= Une instruction théor. et prat.
          │  sur les Paragrêles.                         _Bourg_, =1825=
          │
   =C= =S=│=Leigh=, J. Directions for ensuring
          │  personal safety during storms, and for
          │  the right application of Lightning
          │  Conductors. 6th Edition. 12mo.            _London_, =1835?=
          │
 =R= ¤S¤  │=Leithead=, W. Electricity, its nature,
          │  operation, and importance. 12mo.           _London_, =1837=
          │
 ¤R¤      │=Le Normand=, L. S. Sull’ utilità dei
          │  Parafulmini e Paragrandini per
          │  l’agricoltura. Seconda edizione. 8vo. 19
          │  pp.                                        _Milano_, =1823=
          │
    ¤A¤   │=Lenz.= Sur Combien de pieds carrés de la
          │  surface de la toiture doiton, en
          │  construisant un Paratonnerre, établir un
          │  Conducteur à terre? _Bullet. de la Classe
          │  phisico-mathématique de l’Acad. Impériale
          │  de St. Pétersbourg_, xv. 63.                         =1856=
          │
 =R=      │=Le Roy=, J. B. Lettera al Rozier su i
          │  Parafulmini. 4to. 2 pp. (_Scelta
          │  d’Opuscoli_, Nuova ed. ii. 222.
          │  _Translated by Fromond. It was printed in
          │  the_ 12_th in ed._ 1776, vol. xviii. _The
          │  original French version in the Journ. de
          │  Phys._, vol. ii.)                          _Milano_, =1782=
          │  (_See Official Instructions, France._)
          │
 ¤R¤      │=Leschevin.= Memoir upon a process employed
          │  in the ci-devant Maçonnais of France, to
          │  avert showers of Hail and to dissipate
          │  Storms. By M. Leschevin, Chief Commissary
          │  for Gunpowder and Saltpetre at Dijon.
          │  (_From Millin’s Magazin Encyclopédique
          │  for_ 1806, tom. ii. p. 5). 8vo. 7 pp.
          │  (_In Phil. Mag._ xxvi. 212.)               _London_, =1807=
          │
 ¤R¤      │=Leslie=, Sir J. On the Inefficacy of
          │  Lightning Conductors. (_From Arella, who
          │  says that this statement appears in
          │  Fernsac, Scienze fisiche matemat._ 1829,
          │  p. 130.)                                             =1829=
          │
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       ¤S¤│=Lichtenberg=, G. C. Verhaltungsregeln bey       _Göttingen_,
          │  nahen Donnerwettern.                                 =1778=
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 =R=      │ „   Über Gewitterfurcht und                     _Göttingen_,
          │  Blitzableitung. 8vo.                                 =1802=
          │
 =R= ¤A¤  │ „   Neueste Geschichte der Blitzableiter.       _Göttingen_,
          │  8vo.                                                 =1803=
          │
 =R= ¤A¤  │=Lichtenberg=, G. C. Vorschlag den Donner
          │  auf Noten zu se tzen 8vo. (_Lichtenberg’s
          │  Mathem. und Phys. Schriften, &c._, i.
          │  478.)
          │
 =R= ¤A¤  │ „   Versuche zur Bestimmung der
          │  zweckmässigsten Form der Gewitterstangen.      _Göttingen_,
          │  8vo.                                                 =1803=
          │
 =R= ¤A¤  │=Litchtenberg=, L. C. Verhaltungsmaass
          │  regeln bey nahen Donnerwetter nebst d.
          │  Mitteln sich gegen d. schädl Wirkungen d.
          │  Blitzes in Sicherheit zu setzen. 1 Aufl.
          │  8vo. 1 plate.                               _Gotha_, =1774=
          │
 ¤R¤      │ „   Verhaltungsregel bey nahen
          │  Donnerwetter; nebst d. Mitteln, sich
          │  gegen d. schädl. Wirkungen d. Blitzes in
          │  Sicherheit zu setzen. 2e Aufl. 1775. 8vo.
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          │
 ¤R¤      │=Limmer=, C. P. De Tonitru.
          │
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          │  experiments of electricity with a kite.
          │  4to.                                       _London_, =1754=
          │
 =R=      │=Linnæa=, E. C. Vom Blitzen der
          │  indianischen Kresse. 8vo. 3 pp. (Signed        _Hamburg and
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          │
 =R=      │=Litta=, A. A. Riflessioni sulla capacità
          │  de’ Conduttori elettrici esposte in una
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          │
          │ „   Lettera (al Toaldo) sui Parafulmini.
          │  Verona, 14 Mag. 1778. (On an insulated
          │  Conductor for safety and for
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          │  above, with the notice_ “19 Mag. rec.” 2
          │  pp.) (Toaldo, G.)                           _Padua_, =1840=
          │    (The above two articles are bound
          │      together with an Address to some
          │      friends (or Dedication), and signed
          │      Gaetano dott. Sorgata e Jacopo Prof.
          │      Cecconi (of 1 page). The whole forms
          │      a brochure, without any proper
          │      title-page. It is said in the
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          │      Seminario.)
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          │  Eclairs. Et Lettre de l’Auteur à M.
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          │  (_From Kuhn of 1866_, p. 279.)                       =1783=
          │
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          │  Blitzableitungslehre neu bearbeitet von
          │  Gutle, 1te Theil. 8vo.                               =1804=
          │
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          │  Wetter Ableitern ... neu bearbeitet von         _Nurnberg_,
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 ¤R¤      │=Lyon=, J. Account of several new and
          │  interesting phænomena discovered in
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          │  horses killed by Lightning near Dover.
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          │
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          │
 =R=      │ „   Sulla meteora che nella sera del 4
          │  Marzo, 1861, colpiva la cattedrale di
          │  Milano; e sulla riforma de’ suoi
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 ¤R¤      │=Mairan=, J. J. d’O. de. Sur les effets de
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  =C= =S= │=Majendie=, V. D. Report on the destruction
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 ¤R¤      │=Majocchi=, G. A. Istruzione teorica e
          │  pratica sui Parafulmini. 8vo. 114 pp. 1
          │  plate.                                     _Milano_, =1826=
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    =C=   │=Majoli Simonis=. Hoc est colloquia physica
          │  noua et admiranda tum lectu incunda et
          │  supra fidem recreabilia tum cognitu,
          │  insignia et penitus necessaria. Fol. 1428       _Moguntiæ_,
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          │
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          │  Eigenschaften des Donners, u. d. Mitteln
          │  wider das Einschlagen. Verfaszt von P.
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          │  Retzer aus d. latein Orig. das erst._
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  (131)=S=│ „   Remarks on some practical points
          │  connected with the construction of
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 =R=      │=Marini=, P. Relazione Memoria sul Fulmine
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          │  Dipartimento del Mella_, tom. i. _Elenco
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 ¤R¤      │=Marsault=, J. P. L. Electro-calorique, ou
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 =R=      │=Martin.= Mémoire sur un coup de Tonnerre
          │  qui a éclaté dans l’Eglise de St. Nicolas
          │  de Toulouse ... 17 March, 1787. 4to. 9
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   =C= =S=│=Martin=, T. H. La foudre, l’électricité et
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 ¤R¤ ¤A¤  │=Marum=, M. van. Verhandeling over het           _Groningen_,
          │  Electrizeeren. 8vo.                                  =1776=
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          │  conduttori ai campanili, alle chiese, ed
          │  alle case, descritta per uso dei fabbri,
          │  falegnami, e muratori, &c.... stampata
          │  per ordine del Magistrato Excell. Alla
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 =R=      │=Mawgridge=, R. A.... relation of the ...
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 =R=      │=Maxwell=, H. Observations on Trees as
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          │
 ¤R¤      │=May=, W. Verhall der uitwerkinge van eenen
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          │  Anh. über Hagel-Ableiter. Geprüft (2
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          │
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     (138)│  conducteurs et à raccordements terrestres      _Bruxelles_,
          │  multiples. Large 8vo.                                =1877=
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          │      in G. C. Lichtenberg’s Physikalische
          │      und Mathem. Schriften, tom. iii. p.
          │      251–301. Gœttingen, 1803, in 12mo.,
          │      (Vermischte Schriften, 1800–1805. 9
          │      vols. 12mo. _Gotha_.)
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       =S=│=Mittelstrass.= Die Blitzableiter nach den
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          │    The Pièces Justicatives contain
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          │
 =R=      │=Tietz=, J. Die Erfindung und erste
          │  Verbreitung d. Blitzableiters. 4to. 17
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          │
 =R=      │=Tilas=, D. Von einem Donnerschlage in
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          │
    ¤A¤   │=Toaldo=, G. Della Maniera di defendere gli
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          │
 =R=      │ „   Dell’ uso dei Conduttori metallici....
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          │  ... di Padova. 4to. 32 pp. 1 plate.       _Venezia_, =1774=
          │
 =R=      │ „   Del Conduttore elettrico posto nel
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          │  ed.) 4to. 37 pp. 1 plate.                 _Venezia_, =1776=
          │
 ¤R¤      │ „   Relazione del fulmine caduto nel
          │  Conduttore della Specola di Padova. (1st
          │  ed.) 4to.                                  _Padova_, =1777=
          │
 ¤R¤ ¤A¤  │ „   Dei Conduttori per preservare gli
          │  edifizj ... Memorie, in questa nuova ed.
          │  ritoccate ed accresciute di un’ Appendice
          │  ... 4to. 104 pp. 2 plates.                _Venezia_, =1778=
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          │      “Informazione al popolo” of 1772,
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          │      uso dei Conduttori ... Apologia ...
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          │      Padova.” His “Del Condutt.... di S.
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          │      Specola, Padova,” of 1777. His
          │      “Notizia del Fulmine ... nella Torre
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          │      which is a memoir appended to
          │      Barbier’s French translation of this
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          │      translation is by a printer, and not
          │      dated.
          │    _Note._—In his “Giornale
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          │      himself and others in the “Giornale
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          │
 =R=      │ „   Fenomeno singolare d’un Fulmine
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          │  fisici. 4to. 4 pp. (_Opus Scelti_, vii.
          │  35.)                                       _Milano_, =1784=
          │
 =R=      │ „   Appendice: Riflessioni sopra i colpi
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          │  ... Letta 8 Feb., 1787. 4to. (_Vide_
          │  Marzari.) _Saggi dell’ Accad. di Padova_,
          │  iii. 212, pt. i.                           _Padova_, =1794=
          │
 =R=      │ „   (or Anonym.) and =Saussure=. Della
          │  maniera di preservare gli edifizi dal
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          │      Saussure’s Exposition under the title
          │      “Manifesto ossia Breve esposizione;”
          │      the paging being continued from 20 to
          │      38. The date of Saussure’s work is
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          │      Tinan.)
          │
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          │
 ¤R¤      │ „   Nützliche Anmerkungen von den
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          │
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          │  Clocher neuf de N. Dame de Chartres.
          │  12mo. 215 pp.                               _Paris_, =1692=
          │
 ¤R¤      │=Vassalli-Eandi=, A. M. Conghietture sopra
          │  l’arte di tirare i Fulmini appo gli
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          │
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          │  preservare le case rustiche dal Fulmine.
          │  (_Calend. Georg._ 1814.)                             =1810=
          │
 =R=      │=Vauquelin=, C. On Stones supposed to have
          │  fallen from the Clouds, (and discussion
          │  thereon) in the French National Institut.
          │  vo. 2 pp. (_Phil. Mag._ xv. 187.)          _London_, =1803=
          │
 =R=      │ „   Memoir on the Stones said to have
          │  fallen from the Heavens. Read in the
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          │  (_Phil. Mag._ xv. 346.)                    _London_, =1803=
          │
 ¤R¤      │=Vauquelin=, L. N. Mémoire sur les pierres
          │  dites tombées du ciel. 8vo. (_Journ. des
          │  Mines_, xiii. 1802–3.)                    _Paris_, =1802–3=
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 =R=      │=Viacinna=, C. Del fulmine e della sicura
          │  maniera di evitarne gli effetti. Dialoghi
          │  Tre. 8vo. 156 pp.                          _Milano_, =1766=
          │
 =R=      │=Vismara=, G. Dei fulmini che hanno colpito
          │  il torrazzo di Cremona. Memoria. 8vo. 24
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 =R=      │=Volpicelli=, P. Sulla necessità di
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          │  metalliche, stabilite nella cima degli
          │  edifici. Nota. 4to. 5 pp. (_Atti dell’
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          │  i. del 3 Dicem. 1865, tom. xix. pp.
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          │  Construction der Blitzableiter.                      =1863=
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 =R= ¤S¤  │=Walker=, C. V. Transac. and Proc. of the
          │  London Electrical Soc. Edited by C. V. W.
          │  4to.                                       _London_, =1841=
          │
 =R= =S=  │ „   The effects of a Lightning-Flash on
 (84)     │  the Steeple of Brixton Church, and
          │  observations on Lightning Conductors
          │  generally. Large 8vo. 18 pp. 1 plate.
          │  (_Proceed. Lond. Elect. Soc._)             _London_, =1842=
          │
 =R=      │ „   On the Action of Lightning Conductors.
          │  La. 8vo. 15 pp. 1 plate. (_Proceed.
          │  London Elect. Soc._)                       _London_, =1842=
          │
  =R==C=  │ „   Memoir on the difference between
    =S=   │  Leyden Discharges and Lightning Flashes,
   (84)   │  &c. La. 8vo. 42 pp. (_Proceed. Lon.
          │  Elect. Soc._)                              _London_, =1842=
          │
 =R= ¤S¤  │ „   Proc. of the London Electrical Soc.
          │  8vo.                                       _London_, =1843=
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       ¤S¤│=Walker=, C. V. The Electrical Magazine.            _London_,
          │  Vols. i. & ii.                                    =1845–46=
          │
       ¤S¤│=Waltsgott=, J. F. De Fulgure, Tonitru ac
          │  Fulmine. 4to.                                        =1734=
          │
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          │  8vo.                                       _London_, =1746=
          │
 ¤R¤ ¤A¤  │=Weber=, F. A. Abhandlung von Gewittern u.        _Zurich und
          │  Gewitterableitern. 8vo.                    Leipzig_, =1792=
          │
 =R= ¤A¤  │=Weber=, J. Die Sicherung unserer Gebäude
          │  durch Blitzstrahlableiter theoretisch und
          │  praktisch beleuchtet und bewahrt, samt
          │  einer Beurtheilung der Ableiter aus Stroh
          │  von Lapostolle. Eine Vorlesung. 8vo. 46         _Landshut_,
          │  pp.                                                  =1822=
          │
 (127) =S=│=Weber=, L. Berichte ueber Blitzschläge in
          │  der Provinz Schleswig-Holstein. 8vo. 25
          │  pp. 2 plates.                                        =1880=
          │
       =S=│ „   Berichte ueber Blitschläge in der
          │  Provinz Schleswig-Holstein. Zweite Folge.
          │  8vo. 70 pp. 2 plates.                        _Kiel_, =1880=
          │
 ¤R¤ ¤A¤  │=Wenzel=, C. A. W. Adhandlung über die
          │  Blitzableiter aus d. Franz. 8vo.            _Wesel_, =1818=
          │
 ¤R¤      │ „   Adhandlung über die Blitzableiter; aus
          │  d. Franz, frei übers. f. angeh.                   _Berlin_,
          │  Ingenieur-Officire. 2 Abtheil. 8vo.                =1823–4=
          │
    ¤A¤   │=Wharton=, W. L. The effect of a Lightning
          │  Stroke. 8vo.                               _London_, =1841=
          │
 =R=      │=Wilcke=, J. K. Die Meynungen der
          │  Naturforscher von den Ursachen des
          │  Donners. 8vo. 19 pp. (_Schwedische Akad.       _Hamburg und
          │  Abhandl._ an. 1759, pp. 81 and 155.)       Leipzig_, =1759=
          │
       ¤S¤│ „   Von den Versuchen mit den eisernen
          │  Strangen, den Donnerschlag abzuwenden,
          │  und dem dabei beobachteten
          │  Merkwürdigoten.                                      =1759=
          │
 =R=      │ „   Bemerkungen bey einem d. 30 May in
          │  Stockholm geschehenen Donner-Schlage.
          │  8vo. 11 pp. 1 plate. (_Schwedische Akad.
          │  Abhandl._ an. 1770, vol. xxxii., p. 115.) _Leipzig_, =1770=
          │
 ¤R¤ ¤C¤  │=Wilson=, B. Observations on Lightning, and
 ¤A¤      │  the method of securing Buildings from its
          │  Effects. In a letter to Sir Charles
          │  Frederick. 4to. 68 pp. (_Phil. Trans._
          │  an. 1773, p. 49.)                          _London_, =1773=
          │
 =R=      │ „   Further Observations on Lightning.
          │  4to. 26 pp.                                _London_, =1774=
          │
 ¤R¤      │ „   New Experiments and Observations on
          │  the nature and use of Conductors. 4to.
          │  (_Phil. Trans._, pt. i. p. 245.)           _London_, =1777=
          │
 =R= ¤A¤  │ „   An account of Experiments made at the
          │  Pantheon, on the nature and use of
          │  Conductors; to which are added some new
          │  Experiments with the Leyden Phial. Read
          │  at the meetings of the Royal Society.
          │  4to. 100 pp. 4 plates.                     _London_, =1778=
          │
  ¤A¤ =S= │=Wilson=, R. Boiler and Factory Chimneys,
   (110)  │  and on Lightning Conductors. 8vo.          _London_, =1877=
          │
    ¤A¤   │=Winkler=, J. H. Abhandlung von dem
          │  elektrischen Ursprung des
          │  Wetterleuchtens.                                     =1746=
          │
    ¤A¤   │ „   De avertendi Fulminis Artificio
          │  secundum Electricitatis doctrinam
          │  Commentatio. 4to.                          _Lipsiæ_, =1753=
          │
 =R=      │=Wittiber.= Über atmosphär. Electricität
          │  und Gewitter, insbesondere die Gewitter
          │  der Grafschaft. 4to. 23 pp.                 _Glatz_, =1860=
          │
    ¤A¤   │=Wolff.= Versuche über Blitzableiter.                  =1801=
          │
 =R=      │=Woodcroft=, B. Patents for Inventions.
          │  Abridgments of Specifications relating to
          │  Electricity and Magnetism; their
          │  Generation and Applications. Printed by
          │  Order of the Commissioners of Patents.
          │  8vo. 769 pp.                               _London_, =1859=
          │
 ¤R¤      │ „   Patents for Inventions. Abridgments of
          │  Specifications relating to Electricity
          │  and Magnetism; their Generation and
          │  Applications. Part ii. A.D. 1858–1866.
          │  Printed by Order of the Commissioners of
          │  Patents. 8vo. 863 pp.                      _London_, =1870=
          │
 ¤R¤ ¤S¤  │=Wucherer=, G. F. Von Anlegung d.
          │  Blitzableiter auf Kirchen u. anderen           _Carlsruhe_,
          │  Hochgebäuden. 8vo.                                   =1839=
          │
          │
 ¤R¤ ¤A¤  │=Yelin=, J. K.v. Über d. Blitzableiter aus
 ¤S¤      │  Messingstricken u. üb. d. am 30 Ap. 1822,
          │  erfolgt. merkwürd. Blitzschlag auf d.
          │  Kirchthurm zu Rosstall. 8vo.              _München_, =1823=
          │
 ¤R¤ ¤A¤  │ „   Über die Blitzableiter aus
          │  Messingdrahtstricken. 2e Aufl. 8vo.       _München_, =1824=
          │
          │
  =C= =S= │=Zenger=, Prof. Symmetrische Blitzableiter.
   (104)  │  4to.
          │
    ¤A¤   │=Ziegler.= Blitzableiter von Platina.
          │  Allgem. Handlungszeit. v. Leuchs 175.
          │  _Ann. de l’Indust. nation. et étrang.,
          │  etc._ xviii. 320.                                    =1824=




                              APPENDIX H.

 APPLICATION TO AND REPLIES FROM THE LOCAL HONORARY SECRETARIES OF THE
 SOCIETY OF TELEGRAPH ENGINEERS AND CERTAIN OTHER DISTINGUISHED FOREIGN
                              AUTHORITIES.


In accordance with a resolution passed by the delegates at the meeting
on October 27, 1879, the following circular was prepared by the
Secretary, and issued to the gentlemen named in the appended table.

                              30, GREAT GEORGE STREET,
                                              WESTMINSTER, S.W.
                                                  _October 31st, 1879_

  Dear Sir,—At the invitation of the Meteorological Society, delegates
  have been nominated by the following societies:—Royal Institute of
  British Architects, Society of Telegraph Engineers, Physical
  Society, Meteorological Society, to consider the present modes of
  erecting lightning conductors, and improvements therein.

  At the last meeting I was instructed to ask you to have the kindness
  to furnish the conference with copies of such papers or reports as
  may be convenient, and as are generally accepted as authoritative in
  your country.

                                               Yours very truly,
                                                         G. J. SYMONS.

 ───────────────────────┬───────────────────────┬───────────────────────
 NAME.                  │COUNTRY.               │DATE OF REPLY.
 ───────────────────────┼───────────────────────┼───────────────────────
 Allen, J.              │Argentine Republic     │
 Aparicio, Don José     │Spain                  │
 Aylmer, J.             │France                 │
 Burton, C.             │Bolivia                │
 Cantoni, J.            │Italy                  │
 Collette, J. M.        │Netherlands            │Nov. 7th.
 Cracknell, E. C.       │New South Wales        │
 Dakers, J.             │Canada                 │
 D’Amico, E.            │Italy                  │Nov. 16, Dec. 8.
 Delarge, F.            │Belgium                │
 Field, S. D.           │W. America             │
 Jamieson, A.           │Mediterranean          │
 Karsten, G.            │Schleswig-Holstein     │Nov. 13.
 Madsen, C. L.          │Denmark                │Nov. 5, Dec. 7.
 Melsens, F.            │Belgium                │Nov. 6, Dec. 4.
 Michel, F.             │France                 │
 Morris, J.             │Japan                  │
 Myers, Gen.            │United States          │Dec. 13.
 Nielsen, C.            │Norway                 │Dec. 1.
 Preece, J. R.          │Persia                 │
 Siemens, W.            │Germany                │
 Teale, F. G.           │India                  │Dec. 12.
 Todd, C.               │South Australia        │
 Ward, G. G.            │United States          │Dec. 9.

The following are abstracts of the replies received:—

Nov. 5th, Copenhagen.—Mr. C. L. Madsen acknowledging receipt of letter
and promising further reply.

Nov. 6th, Belgium.—M. Melsens acknowledging receipt, and promising full
reply.

Nov. 7th, La Haye.—Mr. J. M. Collette acknowledging receipt of circular
and stating that lightning conductors are not in common use in Holland,
that there are no official and scarcely any other publications upon the
subject. Those who have to erect conductors upon public buildings
usually rely upon the rules adopted in countries where the use of
lightning conductors is more general.

Nov. 13th, Kiel, Schleswig-Holstein.—Dr. Karsten forwarding copy of the
latest edition of his work on lightning conductors (See Abstracts of
Printed Documents, pages (114) and (119).)

Nov. 16th, Rome.—Sig. E. D’Amico acknowledged receipt.

Dec. 1st, Christiana.—M. C. Nielsen acknowledging receipt, and
forwarding copy of paper by Prof. Mohn on “Lynildens Farlighed i Norgi.”
(See Abstracts, page (106) which he states is the only paper on the
subject printed in Norway.)

Dec 4th, Belgium.—Letter from M. Melsens, sending series of his works.
(See Appendix G.; Catalogue and Appendix F. pages (137) to (141).)

Dec. 7th, Copenhagen.—Mr. C. L. Madsen writes:

  “In continuation of my letter of 5th ult, I have great pleasure in
  forwarding a copy (enclosed) of ‘Regulations for the Arrangement and
  Construction of Lightning Conductors for Military and Public
  Buildings in Denmark, as adopted by the Royal Engineers, 1869,’
  which I have translated from the Danish original, and obtained the
  permission to place at the disposal of the Conference. The rules
  laid down in this paper are generally accepted as authoritative in
  Denmark, and have been followed in the erection of Lightning
  Conductors on the new Royal Theatre in Copenhagen.

  “I beg to add that in case a printed report is to be published by
  the Conference, I shall feel much obliged by having a few copies
  sent to me, and that I shall have great pleasure in continuing to
  have my attention directed to the subject.”


     REGULATIONS FOR THE ARRANGEMENT AND CONSTRUCTION OF LIGHTNING
 CONDUCTORS FOR MILITARY AND PUBLIC BUILDINGS IN DENMARK, AS ADOPTED BY
                       THE ROYAL ENGINEERS, 1869.

                      (_Translated from Danish._)

  To obtain a perfect system of lightning conductors it is necessary
  to observe:

  1. That the lightning conductor must be more exposed to the stroke
  of lightning than the building itself.

  2. That the lightning, after having struck the conductor, shall
  traverse the conducting wire to the earth more readily than through
  any other neighbouring object.

  3. That the lightning conductor is not destroyed by the stroke of
  lightning.

  A. _Arrangement._

  On the highest points of the building are placed _iron rods_, of
  such a length and number that no part of the building lies farther
  from the perpendicular line through the point of the rod, than twice
  the height of the point above the place of the rod. The lower ends
  of the rods are connected to a metallic conductor, _top conductor_,
  which follows the upper line of the building. From the top
  conductor, or from the rods, and at least from each three of these,
  _conducting wires_ are led down the roof and outer wall (best on the
  weather-side), and thence one foot under the earth, until about ten
  feet from the building. Here the wires are connected to the _earth
  plate_ in a well, the bottom of which well must reach a couple of
  feet under the lowest standing of the ground water. Each well, with
  its plate, ought at the utmost to serve three conducting wires. If
  necessary to employ more wells than one, the plates of these are
  joined up through a special conductor, the _earth conductor_, one
  foot under the surface of the earth. Great care must be taken that
  the earth plate is properly placed in ground water, that more or
  less communicates with the ocean—a condition which, in our country,
  will hardly present insurmountable difficulties.

[Illustration: Sketch of arrangements for Public Buildings in Denmark]

  Figure 1 shows a system of lightning conductors for a building 100
  feet long, with gable roof.

  NOTE 1.—If the roof is covered with metal, the conductors ought in
  several places to be connected to it; but, on the other hand, they
  must be kept, electrically, as distant from all other parts of the
  building as possible, especially from the metallic parts of it.

  NOTE 2.—If ground water is found at a considerable depth, under a
  dry layer of sand, a second plate, besides the general earth plate,
  ought to be placed just beneath the surface of the earth, the latter
  being made temporarily conductive by rain.

  NOTE 3.—As to powder magazines, which of course must be constructed
  of bricks or wood, the lightning conductors must not, without
  inevitable necessity, be placed on the building itself, but,
  retaining the above-mentioned dispositions in the main points (the
  top conductor excepted), they ought to be placed on masts, about ten
  feet from the magazine.

  Figure 2 shows a system of lightning conductor for a powder
  magazine, a hundred feet in length, with gable roof.

[Illustration:

  End and Side elevation.
]

[Illustration:

  Plan.
]

  B. _Construction._

  _The point_ ought to consist of a solid copper cylinder, ¾ inch
  diameter, 6 inches high, conically pointed, the top angle being
  about 30 degrees, and with gilt top. At the lower end a nut is
  applied, by which the point is screwed and afterwards soldered to
  the end of the rod. Most conveniently the rod is formed of round
  iron, which, like the rest of the conductor above earth, if
  constructed of iron, is painted over or galvanized. Under earth only
  galvanized iron is suitable. The upper diameter of the rod is ¾
  inch; 12 feet farther down, 1½ inch. The length is properly varying
  between 10 and 16 feet. It is to be preferred to use a greater
  number of low rods rather than fewer high ones. _The conductor_, as
  also the top and earth conductors, may consist of an iron bar, of ⅓
  square inch section, consequently 9/16 inch in the square side, or ⅝
  inch in diameter. Only for very great lengths will it be necessary,
  on account of the increased resistance of the conductor, to use
  thicker bars. In place of iron, copper may be used, the section of
  which need only to be ⅒ square inch. The conductors must be of as
  short a length, and with as few bends as possible; and the latter
  must be rounded at their angle points. They ought not to be bolted
  or spiked to the building, but, in view of changes of form
  occasioned by temperature or other reasons, they must rest in hooks,
  or be kept up by cramps that are fastened in wood or brick, far from
  the metallic parts of the building. It is of the utmost necessity
  that the conductor be continuous in its whole extent, from the point
  to the earth plate. Links of chains or cables are to be rejected.
  For this reason the number of joints must be limited, and a constant
  contact of the respective ends, extending over one or two square
  inches, procured by bolts or rivets and soldering. The metal should
  be filed on the contact sides, so as to clear it from oxide, this
  being an insulator, and the soldering made with tin. _The earth
  plate_ may consist of galvanized iron or copper. It ought to have at
  least a surface of 10 square feet in water, or 5 square feet area,
  if to serve one conductor; for each conductor in addition 50 per
  cent. must be added to the area. To diminish the circumference of
  the well, the plate may be given a cruciform transverse section; if
  then, for instance, the plate reaches 2½ feet down into the water,
  the wings need only have the length of 6 inches. _The well_ is
  constructed in the usual manner by digging or boring. In order to
  preserve the conductor from breaking, as the plate might press
  deeper into the ground, a beam is placed across the well’s upper
  part on which the horizontal part of the conductor rests.
  _Inspection_ of the lightning conductor must be effected once a
  year, and, besides, when circumstances demand it, for instance,
  after a stroke of lightning. The inspection must especially have the
  purpose:

  1. To examine whether the metallic continuity remains perfect; to
  verify this a galvanometer is inserted, and a galvanic current led
  through the conductor; and

  2. To examine whether the conductivity to ground water is in order.
  The earth plate being placed in a well, instead of being buried in
  the ground, will greatly facilitate this examination.

Dec. 8th, Rome.—Sig. D’Amico sent a copy of a letter received from
Professor Tacchini, Director of the Central Meteorological Office, in
answer to the communication made to him of the circular dated October
31st. The following translation has been kindly made by Professor T.
Hayter Lewis:—

                                METEOROLOGICAL CENTRAL OFFICE, ROME.
                                                _November 27th, 1879._

                    LIGHTNING RODS IN USE IN ITALY.

  Although I have not sufficient material for giving a complete answer
  to the request made in your letter, as noted in the margin, yet I
  think that the accompanying notice as to the system in use in Rome
  for fixing lightning rods may be useful to the Director General.

  1. The conductor of the lightning rod is constructed of iron, 17
  millimetres (c. ⅔rds. inch) diameter. The upper terminal or receiver
  is 4·5 metres (14 feet 9 inches) high, with a copper point 0·50 (c.
  1 foot 8 inches), gilt from 0·25 (c. 10 inches), fixed on a pilaster
  of masonry 2 metres (c. 6 feet 6 inches) high, and 60 centimetres
  (c. 2 feet) wide. Each terminal is intended to protect a horizontal
  superficies of radius double its height.

  2. In order to obtain a conductor as long as required, pieces of 5½
  metres (c. 18 feet) are united by a holdfast of brass. The fastening
  of the conductor to the walls and roofs is made by little pieces of
  marble of the annexed form, connected with the fabric.

[Illustration: Attachment and Earth Terminal used in Italy]

               A—Wall or roof.
               B—Little piece of marble.
               C—Hole through which the conductor passes.

  3. It is the custom to connect the conductor with masses of iron,
  and other metals in the building to be protected, avoiding the water
  pipes. (Referring probably to Terra Cotta pipes. T. H. Lewis.)

  4. In addition to the upper terminal and chief receiver, it is usual
  to fix secondary points according to the form of the building.

  5. The discharger or lower terminal (in contact with the earth) is
  made of copper rod, 12 millimetres (c. ½ inch) square, at least 6
  metres (c. 20 feet) long, in 3 strips with points of copper arranged
  in the manner shown—

[Illustration: Attachment and Earth Terminal used in Italy]

         D—Conductor.
         E—Lower terminal or discharger with points of copper.

  6. The discharger is introduced into a ditch or well excavated in
  moist ground, vertically or horizontally, according to the
  circumstances of the locality. The diameter of the well should be
  0·80 metres (c. 2 feet 8 inches), filled with carbon, and covered
  with earth.

  7. In an ordinary building we employ a discharger to each 3 points.

  8. In this manner were made all the lightning rods of P. Secchi, by
  Signor Lerigi Morea, maker of them in Rome.

  9. In some cases P. Secchi has made use, for the conductor, of the
  thicker wire used for the Telegraph.

  10. We may observe that, in other Italian cities, the same rules are
  adopted for the construction of lightning rods, as I myself have
  verified. Only, in some localities, in place of putting points of
  copper to the lower terminal the latter is terminated by a copper
  band.

                                                   P. TACCHINI,
                                                       _The Director_.

Dec. 9th, New York.—Mr. G. G. Ward acknowledges receipt, states that the
only papers of any value upon lightning conductors, published in America
and known to him are:—(A) a paper by Prof. Henry; (B) a treatise by
Prof. Phin; (C) a pamphlet by David Brooks; (D) a practical treatise by
H. Spang. The writer furnished copies of Nos. B and D, and all four will
be found noticed in the Abstracts of Printed Documents. See pages (99)
(102) (117) and (112.)

Dec. 12th, Calcutta.—Mr. F. G. Teale acknowledging receipt of circular
and forwarding copies of two papers accepted as authoritative in India,
viz:—(1) R. S. Brough on Protection of Buildings from Lightning, and (2)
W. P. Johnston on the Lightning Conductors at Dum Dum. (See Abstracts,
pages (117) and (132).)

Dec. 13th, Washington, U.S.A.—Lieut. Kilbourne acknowledges receipt on
behalf of Gen. Myers, enclosing copy of paper by Prof. Henry, and
stating that the works of Spang and Phin are considered authoritative.




                              APPENDIX I.

                        GENERAL CORRESPONDENCE.


                                          TRINITY HOUSE, LONDON, E.C.,
                                                _6th February, 1880_.

  SIR,

  I am directed by the board to transmit to you herewith, for the
  information of the Lightning Rod Conference, copies of reports made
  by Professor Faraday to this Corporation, one respecting a
  remarkable stroke of lightning which occurred at the Eddystone
  Lighthouse in January, 1853, and the other upon a similar accident
  experienced at the Nash Lights in August, 1852.

  The case to which Admiral Sullivan directed the attention of the
  Conference, as stated in your letter of the 30th October last, was
  probably one of these two.

  Should you desire any further details in connection with this
  subject, the Corporation desire me to assure you of the pleasure
  with which they will afford any information at their command.

                                          I am, Sir,
                                              Your obedient servant,
                                                          ROBIN ALLEN.

G. J. SYMONS, Esq.

[We have been favoured with copies of three separate reports by
Professor Faraday, and think that it is better to give them in
chronological order. There is only one other point in the correspondence
from the Trinity House which it seems necessary to mention, viz., that
the sections of the copper rods now used are as under.—ED.]

[Illustration:

  MAIN CONDUCTOR.

  1½ in.
]

[Illustration:

  CONNECTING BRANCHES.

  1¼ in.
]

REPORT ON THE LIGHTNING RODS OF LIGHTHOUSES, 1843.

DUNGENESS.—Dungeness Lighthouse stands about 14 feet above the sea and
measures 97 feet to the top of the lantern. The tower is of brick with
wood floors; the roof and frame of the lantern are of metal seated upon
a stone pedestal, to which it is secured. There is no conductor to the
building. The weathercock is fitted with a glass repeller, and a rod
similarly fitted is attached to the two copper flues which rise by the
side of the lantern.

EDDYSTONE.—The height of the top of the lantern of the Eddystone above
the sea is about 95 feet. The roof and framing of the lantern are of
metal, secured through a stone plinth to the gallery of the tower by
metal fastenings. A conductor of copper rod, ¾ inch diameter, is
attached to the outside of the building; the rod rises 3 feet above the
top of the lantern and terminates in the sea at low water; it is fixed
to the tower and lantern by metal stays and fastenings and is isolated
by glass ferules. To give stability to the building eight wrought iron
ties are fixed in the interior of the house, extending downwards from
the underside of the lantern floor through the next two stories,
terminating by inserting the ends into the stone floor, the upper ends
are riveted into an iron ring round the manhole in the ceiling and
further secured by iron bolts passing through the stonework and
communicating indirectly with the metal work of the lantern.

[Illustration:

  Eddystone.
]

[Illustration:

  Spurn Point High Light.
]

SPURN POINT HIGH LIGHT.—The Spurn High Light stands about 16 feet above
the level of the sea, and measures 100 feet to the top of the lantern.
The tower is of brick with wood floors; the roof and framing of the
lantern are of metal, seated upon a stone plinth to which it is secured;
the weathercock is surmounted by a glass repeller. An isolated conductor
of copper rod, ¾ inch diameter, is attached to the outside of the tower
rising some feet above the lantern and passing down the side of the
tower below the surface of the ground.

SOUTH FORELAND.—The South Foreland High Light stands above 300 feet
above the sea, and measures from the ground to the top of the lantern 67
feet. The tower is of brick, the lantern roof and framing are of metal
with a cast iron pedestal; the weathercock is fitted with a glass
repeller. A conductor of copper rod, ¾ inch diameter, is attached to the
outside of the tower, of the same height as the weathercock. The rod is
fastened to the lantern and tower with metal stays and fastenings, and
passes into the ground, turning off at right angles to the tower a
little below the surface. A copper flue connected with a stove in the
base of the tower, passes up the centre of the tower through the roof of
the lantern, to the lower end of which a copper rod has been attached,
which is carried to the outside of the building into the ground.

[Illustration:

  South Foreland High Light.
]

The undersigned have, according to their instructions, met and
considered the circumstances under which lighthouses are placed as
respects lightning, and have arrived at the following conclusions:—

That lighthouses should be well defended from the top to the bottom.

That as respects the top, the metal of the lantern, and upwards, is
sufficient to meet every need, and satisfy every desire and fear.

That for the rest of the course down the tower, a copper rod ¾ of an
inch in diameter is quite, and more than, sufficient.

That at the bottom, where the rod enters the earth, it is desirable at
its termination to connect it metallically with a sheet of copper 3 or 4
feet long by 2 feet or more wide; the latter to be buried in the earth,
so as to give extensive contact with it.

That glass repellers are in every case useless.

That glass thimbles are not needed, but do no harm.

That if the repeller be removed, and the _point on the vane_ be
terminated as the lightning rods usually are, and then the metal of the
lantern be strongly attached to, and connected with, the upper end of
the copper rod, and the rod continued down the tower to the earth, and
the sheet of copper buried in it, such a system will be an effectual and
perfectly safe lightning conductor.

That then there need be no rod end rising by the side of, and above the
lantern.

That the rod may (if required on other accounts) come down on the inside
of the building, or in a groove in the wall; but should not be
unnecessarily removed from observation and inspection.

That all large metallic arrangements in the stonework, or other
non-metallic parts of the tower of the lighthouse, such as tying bars,
metal flues, &c., should be well connected, by copper, with the
conductor.

That the vicinity of two metallic masses without contact, or metallic
communication, is to be avoided.

That, as to the South Foreland High Light, the lantern, the central
stove, and the copper rod proceeding from it to the earth, connected as
they now are, form a perfect lightning conductor, even without the rod
that is there erected; but

That it is important casual arrangements should never be depended upon
for lightning conductors; but a copper rod be established for the
especial purpose: for, if the former be trusted to, the carelessness or
ignorance of workmen may, at after periods, upon occasions of repair or
cleansing, cause the necessary metallic connection to be left imperfect
or incomplete, and then the arrangement is not merely useless but
dangerous.

That, as to the Eddystone, it is desirable to connect the system of
wrought iron ties in it with the lightning conductor, by joining the
lower part of that iron rod which is nearest to the conductor with the
latter, by a copper rod or strap, equivalent to the conductor in
sectional area.

That the Dungeness Lighthouse is in a very anomalous condition; to
rectify which the two repellers should be removed, and also the
representative of the top of a lightning rod attached to the flue, and
that then a good copper conductor should be attached to the metal of the
lantern, upon the principles already expressed.

                                             (Signed.)       M. FARADAY.

 _25th September, 1843._

                  *       *       *       *       *

                                         23, GT. GEORGE STREET,
                                               _25th September, 1843_.

  SIR,

  The reference, on the important subject of lightning conductors, is
  to Mr. Faraday and to me. On receiving it I prepared drawings of the
  buildings to which our immediate attention was required, with an
  explanation of their present conductors.

  These were considered at a meeting with Mr. Faraday, when he
  explained the principles and their application to the several cases,
  deduced from his copious experiments and scientific observations.

  I have since received from him the accompanying Report for my
  signature along with his, but the report is altogether Mr. Faraday’s
  and therefore I prefer adding my approval of all it contains in this
  separate sheet, and recommending that authority be given to me to
  act upon it.

                                                 I am, Sir, &c.
                                             (Signed)       J. WALKER.

  JACOB HERBERT, Esq.
      _Trinity House._

                  *       *       *       *       *

                                         ROYAL INSTITUTION,
                                               _27th September, 1852_.

  MY DEAR SIR,

  I fortunately reached the Nash Low Lighthouse last Thursday, before
  any repairs were made of the injury caused by the discharge of
  lightning there, and found everything as it had been left: the
  repairs were to be commenced on the morrow.

  The night of Monday, 30th August, was exceedingly stormy, with
  thunder and lightning; the discharge upon the lighthouse was at six
  o’clock in the morning of the 31st, just after the keeper had gone
  to bed. At the same time, or at least in the same storm, the
  flag-staff between the upper and lower lights was struck, and some
  corn stacks were struck and fired in the neighbourhood. It is
  manifest that the discharge upon the tower was exceedingly powerful,
  but the lightning conductor has done duty well—has, I have no doubt,
  saved the building; and the injury is comparatively slight, and is
  referable almost entirely to circumstances which are guarded against
  in the report made by myself and Mr. Walker 22nd September, 1843.

  The conductor is made fast to the metal of the lantern, descends on
  the inside of the tower to the level of the ground, and passes
  through the wall and under the flag pavement which surrounds the
  tower. It is undisturbed everywhere, but there are signs of
  oxidation on the metal and the wall at a place where two lengths of
  copper are rivetted together, which show how great an amount of
  electricity it has carried.

  A water-butt stands in the gallery outside the lantern. A small
  copper pipe, 1 inch in diameter, brings the water from the roof of
  the lantern into this butt; it does not reach it, but terminates 10
  or 12 inches above it. A similar copper pipe conducts the surplus
  water from the butt to the ground, but it is not connected
  metallically with the other pipe, or with the metal of the
  conductor, or the lantern. Hence a part of the lightning which has
  fallen upon the lantern has passed as a flash, or, as we express it,
  by disruptive discharge from the outside of the lantern to this tub
  of water, throwing off a portion of the cement at the place, and has
  used this pipe as a lightning conductor in the rest of its course to
  the ground. The pipe has holes made in it in three places, but these
  are at the three joints, where, it being in different lengths, it is
  put together with tow and white lead, and where of course the
  metallic contact is again absent; and thus the injury there (which
  is very small) is accounted for. The pipe ends below at the level of
  the ground in a small drain, and at this end a disruptive discharge
  has (naturally) occurred, which has blown up a little of the cement
  that covered the place. Some earth is thrown up at the outer edge of
  the pavement round the tower over the same small drain, which tends
  to show how intense the discharge must have been over the whole of
  the place.

  Inside of the lantern there are traces of the lightning, occurring
  at places where pieces of metal came near together but did not
  touch, thus at the platform where a covering copper plate came near
  to the top of the stair railing, but the effects are very slight.
  All the lamps, ventilating tubes, &c., remained perfectly
  undisturbed, and there was no trace of injury or effect where the
  conductor and the lantern were united.

  Inside of the tower and the rooms through which the conductor passes
  there were and are no signs of anything (except at the rivetting
  above mentioned) until we reach the kitchen or living-room which is
  on a level with the ground, and here the chair was broken and the
  carpet and oil-cloth fired and torn. To understand this, it must be
  known that the separation between this room and the oil-cellar
  beneath is made by masonry consisting of large stones, the vertical
  joints of which are leaded throughout, so that the lead appears as a
  network upon the surface, both of the kitchen floor above, and the
  roof of the oil cellar beneath, varying in thickness in different
  places up to ⅓ or more of an inch, as in a piece that was thrown
  out. The nearest part of this lead to the conductor is about 9
  inches or a little more distant, and it was here that the skirting
  was thrown off, and the chair broken; here also that the fender was
  upset and the little cupboard against the skirting emptied of its
  articles. If this lead had been connected metallically with the
  conductor, these effects would not have happened.

  The electricity which in its tendency to pass to the earth took this
  course, naturally appeared in the oil-cellar beneath, and though the
  greater portion of it was dissipated through the building itself,
  yet a part appeared in its effects to have been directed by the oil
  cans, for though they were not at all injured or disturbed, the wash
  or colour in the wall above four or five of them was disturbed,
  showing that slight disruptive connections or sparks had occurred
  there.

  At the time of the shock, rain was descending in floods, and the
  side of the tower and the pavement was covered with a coat of water.
  This being a good conductor of electricity has shown its effects in
  connection with the intense force of the discharge. A part of the
  electricity leaving the conductor at the edge of the pavement and
  the tower, broke up the cement there, in its way to the water on the
  surface, which for the time acted to it as the sheet of copper—which
  I conclude is at the end of the conductor—does, _i.e._, as a final
  discharge to the earth. Also on different parts of the external
  surface of the tower near the ground, portions of cement, the size
  of half a hand, have been thrown off by the disruptive discharges
  from the body of the tower to this coat of water: all testifying to
  the intensity of the shock.

  I should state that the keeper says he was thrown out of bed by the
  shock. However, no trace of lightning appears in the bedroom, still
  there are evidences that powerful discharges passing at a distance,
  and on the other side of thick walls may affect bodies and living
  systems, especially by spasmodic action, and something of the kind
  may have occurred here. It may be as well for me to state that the
  upper floors are _leaded_ together like that of the kitchen. The
  reason why they did not produce like effect is evident in that they
  from their position could not serve as conductors to the earth as
  the lower course could.

  The keeper said he had told the coppersmith to make the necessary
  repairs in the pipe, and I instructed him to connect the waste pipe
  and the upper pipe by a flat strap of copper plate. I would
  recommend that the lead of the lower floor be connected metallically
  with the conductor to a plate of copper in the earth. I could not
  see the end of the present conductor, not being able by any tools at
  the lighthouse to raise the stonework, but I left instructions with
  the keeper to have it done, and report to me the state of matters.

                                                    I am, &c.,
                                            (Signed)       M. FARADAY.

                                                  THE SECRETARY,
                                                      _Trinity House_.


EDDYSTONE LIGHT.—REPORT _of_ PROFESSOR FARADAY _on Electrical Phenomenon
           which occurred thereat on the 11th January, 1853_.

                                           ROYAL INSTITUTION,
                                                 _24th January, 1853_.

  MY DEAR SIR,

  In reference to the remarkable stroke of lightning which occurred at
  the Eddystone Lighthouse, at midday on 11th January of this year,
  and made itself manifest by a partial flash discharge in the living
  rooms, I have to call your attention to the drawing herewith
  returned, and to the circumstances which appear (from it) to have
  accompanied and conduced to the discharge.

  In the body of the stone work above the store-room exist eight rings
  of metal; each going round the building, and each being four inches
  square of solid iron and lead. Also, latterly the bedroom and
  sitting-room have been lined with a framework of iron bars, situated
  vertically, and pinned by long bolts into the stonework.

  The part of the tower above the floor of the living-room is,
  therefore, filled with a metallic system, which, with the metal
  lantern, gives a very marked character to the upper half of the
  structure.

  The recent metallic arrangements (but not the rings) are connected
  with the lightning rod; and the copper part of this rod, beginning
  at the floor of the living-room, then proceeds downwards by the
  course which can be followed in the drawing, and terminates on the
  outside of the rock between high and low water marks.

  Considering all these circumstances, I was led to conclude that the
  conductor was in a very imperfect condition at the time of low
  water; and I had little doubt that I should find that the discharge
  had taken place when it was in this state, and very probably with a
  spring tide.

  The day of the stroke was the 11th January—a new moon occurred on
  the 9th, so that it was at a time of spring tide.

  The occurrence took place at midday; and, according to the tide
  tables, that was close upon the time of low water at Devonport. The
  end of the conductor would then be 6 feet from the water, if the
  latter were quiescent, and I cannot doubt that this circumstance
  gave rise to that diverted discharge which became so manifest to the
  keepers. Mr. Burges, with whom I have conversed about the matter,
  thinks it probable that, through the violence of the waves, the
  conductor does not now descend so much as is represented in the
  drawing.

  I think it essential that the lower end of the conductor be made
  more perfect in its action; and I should prefer this being done on
  the _outside_ of the tower and rock, if the rod can be rendered
  permanent in such a situation.

  If it be impossible to prolong and fix the lower end of the
  conductor where it now is, so that it shall have large contact with
  the sea at low water, then I would suggest, whether or no, on the
  more sloping part of the rock, about midway between high and low
  water, three or four holes could not be sunk to the depth of 3 feet,
  and about 3 or 4 feet apart, and that copper rods being placed in
  these, they should be connected together, and the lightning rod
  continued to them.

  If this _cannot_ be done, then it might be right to consider the
  propriety of the making a hole through the centre of the building
  and rock, about 2 or more inches in diameter, and 30 feet deep, and
  continuing the conductor to the bottom.

  A conversation with Mr. Burges regarding the present state of the
  Bishop’s Rock Lighthouse, now in course of construction, induces me
  also to suggest the propriety of making provision for the lightning
  conductor as the work proceeds.

  It would be easy now to fix terminal rods of copper, and to combine
  them upwards with the work. Considering the isolated and peculiarly
  exposed condition of a lighthouse on this site, I would propose that
  there be _two_ conducting rods from the lantern, down the outside on
  opposite sides of the tower, each terminating below in two or three
  prolongations, entering as proposed into the rock, or into fissures
  below low water mark, so as to be well and permanently fixed.

                                                    I am, &c.,
                                              (Signed)     M. FARADAY.

  THE SECRETARY,
      _Trinity House_.

[The present Eddystone Lighthouse, that is the stone one erected in
1757–59 from Smeaton’s designs, has a total height from low water level
to the top of the vane of 107 feet. The annexed engraving shows two
conductors, the old and defective one passing down the left hand side
and terminating half way between high and low water level, and the
proposed new one on the right terminating in holes in the rock.—ED.]

[Illustration:

  EDDYSTONE.
]

                  *       *       *       *       *

[The following letter would have been placed in Appendix A. along with
the replies from British Manufacturers of Lightning Conductors; but it
did not arrive until long after they had been printed off.—ED.]

Please find enclosed answer to your questions. In addition to
manufacturing rods, we have been protecting buildings with these rods
for thirty years. We sell in this way at retail from five to six hundred
thousand feet each year. We also issue a guarantee of $500 (£100) on
each building that we protect, which we hold ourselves ready to make
good in case of failure. Now, in this extensive business, we have only
had to pay one dollar damage done by lightning. We regard this as a
practical demonstration that our method of protecting buildings with
iron rods is as near perfect as it can be. There is more profit to be
made out of the copper rod, as it is made cheaply out of sheet copper,
and can be sold much higher than the iron rod. But knowing that iron for
all practical purposes is the best material for lightning rods, we feel
it to be our duty to do all we can to introduce it. We would most
respectfully ask the Conference to investigate this question as to what
kind of metal is best for rods for practical use, iron or copper. Our
own late Professor Joseph Henry pronounced in favour of iron. We have
many facts in relation to buildings being struck by lightning which we
could give at some future time if desired. We have gathered up a large
number of points that have been melted by lightning strokes. They are
melted down about ½ inch. They all look as if the same amount of heat
had been applied to each, showing very clearly that the quantity of
electricity in lightning strokes is quite uniform. We have never in any
instance known of the rod being melted, showing that the rod which we
use is of sufficient size.

                  *       *       *       *       *

1 & 2. We make spiral twisted iron rods weighing 45 lbs. to the hundred
feet [7¼ oz. per foot]. The rod is of the same sized material throughout
its length, except that a copper point, plated with silver and tipped
with platinum, is screwed on the upper terminal.

3. No proportion is observed between the length and sectional area.

4. Joints are made by means of copper nuts.

5. Attached to building by means of zinc strips, or a casting that fits
closely to the rod, which is screwed down.

6. The rod extends from 9 to 10 feet in the ground.

7. A circle twice the diameter of height of rod above roof.

8. All terminals on the roof are connected. There are never less than
two ground rods, and these are increased as the number of upper
terminals are increased.

We also manufacture copper rods, but do not use them where we protect
buildings, nor do we recommend them to other dealers from the fact that
our experience of thirty years has demonstrated that iron is the best
material for lightning rods.

                                                          COLE BROTHERS.

 MOUNT PLEASANT,
        IOWA, UNITED STATES.

                  *       *       *       *       *

A colliery chimney near Sunderland, 180 feet high, was struck by
Lightning, November 13th, 1878, and I was sent for to repair it. Upon
getting to the top, which was about 15 feet diameter, I found a great
many of the bricks displaced, and the upper terminal of the conductor
(which was a tube 0·50 in. internal, and about 0·62 in. external
diameter, and which had stood about 1 foot above the top of the chimney)
had been fused and was lying on the top of the chimney, it was quite
brittle, and easily broken by the hand. The upper 10 feet of ½ inch wire
rope was in a similar state; it seemed as if it had been passed through
an exceedingly hot furnace, and I rubbed it to dust in my hands. This 10
feet length was above the first holdfast, below the holdfast the wire
rope was perfectly good. The holdfast was one of those which are driven
into a wooden plug let into the wall and pinned tightly down on the
rope, which had been badly bruised in the fixing—in fact, knocked almost
flat. I believe that this was the cause of the accident, and that the
lightning travelled down as far as this holdfast, and there meeting
obstruction, returned destroying the wire and rod and shattering the
brickwork. The earth connection was good, the end was buried in a trench
2 feet deep and 15 feet long.

                                                          T. MASSINGHAM.

 NEWCASTLE-ON-TYNE.

                  *       *       *       *       *

I have been in communication with several of the principal brick
builders here by whom the great majority of the chimney stalks in
Glasgow and the west of Scotland are erected, and I believe the
following statements may be taken as correct:—

(1) Very few stalks under ninety feet in height have lightning
conductors, but, _as a rule_, the higher stalks have conductors. One of
my correspondents says that “this rule holds good in four cases out of
five.”

(2) A chimney being struck by lightning is an extremely rare occurrence
in this district. One builder of long experience (Mr. McDonald) says, “I
have known of several stalks that were struck by lightning, that had no
conductors. I cannot point to one that was struck by lightning and had a
conductor.” Another firm of old standing (Allan and Mann) say—“In our
experience we have not known of a chimney stalk, with lightning
conductor fixed, damaged by lightning.” Another firm (Bell, Hornsby and
Co.) say—“In our experience we have not known an ordinary stalk with or
without a conductor struck by lightning,” and Mr. Goldie says—“During
the last twenty years I can remember only one such case,” and he is not
sure whether the stalk had a conductor or not. There are three cases
known to have occurred in Glasgow, but I never heard of any others among
the hundreds—I may say thousands—of chimneys which are here. The great
stalk at St. Rollox was struck shortly after its erection. A stalk at
the works of Messrs. Alexander Paul and Co., was struck about nine years
ago. Mr. Goldie makes the remark—and I think it is well worthy of
notice—that in all these cases the accident happened shortly after the
completion of the stalk. In these circumstances the stalk would still,
no doubt, contain a large amount of moisture.

I think the St. Rollox stalk had a conductor fixed before it was struck,
but I am not aware whether either of the others had.

Mr. Higginbotham (Todd and Higginbotham) tells me that the stalk at
their works was struck before it was quite completed. It was _very
slightly_ injured. It was afterwards struck as mentioned in my letter.
On that occasion it had a lightning conductor.

The damage done was not very serious, but necessitated the binding of
the stalk with numerous iron hoops—as thus strengthened it still stands.
Mr. Higginbotham says that the opinion at the time was that the
conductor saved the stalk from complete destruction, but that it was too
small.

They, therefore, had it replaced by a much heavier one—copper rope ⅜th
of an inch diameter, kept 1½ inches from the brickwork by glass
insulators—which still remains.

                                                            J. HONEYMAN.

 140, BATH STREET, GLASGOW.

                  *       *       *       *       *

There was no lightning conductor of any kind at Wells Church. The
electric fluid struck the east side of the Tower just above the ridge of
the nave roof. The tower stands, or stood, at the west end. I enclose an
account of the fire from a local paper:—

WELLS.—TOTAL DESTRUCTION OF THE CHURCH.—“Near midnight of Saturday last,
August 2nd, 1879, a terrific thunderstorm burst over this town and a
large district around, causing most intense alarm and unfortunately
ending in sad disaster. The storm raged throughout the night, and was
accompanied in many places by a perfect deluge of rain. Between three
and four a.m. of Sunday, the 3rd, it appeared to reach its height, the
lightning being of a most vivid and alarming nature, and the thunder
reverberating in continuous peals. A lull then occurred, but between
five and six a.m. the storm again burst out with great fury, and at 5.50
the electric fluid struck the church on the eastern face of the tower
immediately above the apex of the roof, driving out a large portion of
the stone work, the flints flying hundreds of feet around. One large
stone fell upon the roof of a house, near the east window, and
penetrated to the room below, which was fortunately unoccupied; but the
tenant, Mr. R. Wharf, who slept in the next room, was aroused, and one
or two persons in the road seeing what had occurred, and observing smoke
directly after issuing from the roof of the church, raised an alarm of
fire, which quickly awakened the whole town.

                                                          R. M. PHIPSON.

 NORWICH.

                  *       *       *       *       *

The first visible injury to Wells Church was the “skinning” of a portion
of the tower (about 10 feet high by 5 feet broad) extending downwards
from the east window of the tower (_i.e._, the window which looked over
the roof of the nave,) to the point at which the lead-covered nave
joined the tower. The lightning is believed to have set fire to the roof
at this point, and also to have travelled along the lead roof to the
chancel, and in crossing the vestry to have ignited the surplices, as
the church was seen to be on fire at both ends before the middle was
touched. The “skinning” was accompanied by great disruptive force, as
the stones from the tower were not only shot the full length of the
church, but one large one fell on the roof of a house 60 feet beyond the
east end of the church.

                                                         WELLS, NORFOLK.

 F. LONG.

                  *       *       *       *       *

As your questions in the _Times_ of to-day allude only to protection to
_buildings_ from lightning, I need not say anything on the perfect
protection afforded to Her Majesty’s ships by the conductors of Sir Snow
Harris, from the time they were used in every ship in the service.

H.M.S. “Beagle,” Commander FitzRoy, was one of the first ships fitted
with them. At Monte Video a heavy shock of lightning passed down the
mainmast and through the ship without doing the slightest injury; but as
the vane staff which tapered to a fine point, was fused at the point, it
enables me to answer one of your questions. The copper was melted till
the diameter was about one eighth of an inch, but below that point the
conductor was not injured in any way.

You will like to know a case in which a copper wire acted as a perfect
conductor, _though fused throughout its length_. It was at Monte Video,
in the house of the English Consul, a flag-staff was struck, and
conducted the lightning through a flat roof, near the bell wire of a
suite of rooms (the wire ran in sight near the cornice) through a hole
in each dividing wall, and then down to the bell in the basement; the
wire was melted into drops like shot, which burnt a row of small holes
in the carpet of each room. A dark mark, on the cornice above, showed
where the wire had been. At the bell there was a slight explosion, and
some little damage, but I do not recollect whether anything acted
partially as a conductor from that point, and so carried off that part
of the charge.

This, I think, shows that even an ordinary bell wire will act as a
conductor for a rather strong stroke of lightning, as the large
flag-staff was shattered.

I am anxious to call the attention of your conference to a point that it
will be interesting to clear up. That is, whether a conductor should be
a _solid_ rod, or in a shape to give the largest amount of _surface_ in
the section? When I tell you that Faraday and Harris each told me that
the other “knew nothing about it,” because they differed entirely on
this point, I think you will see the importance of it. I had at the time
to approve of the conductors for lighthouses. I will, if you wish it,
give you more particulars on this point, as I believe it has never yet
been settled: lighthouses having been fitted with Faraday’s, and ships
and public buildings with Harris’ conductors. The one being a solid
bolt, the other a hollow tube or double thin plates.

If Harris was right there is an unnecessary amount of copper in
Faraday’s solid conductors; if Faraday is right, there is an unnecessary
outlay in putting a given amount of copper into the shape of a tube,
instead of using it as a solid rod.

                                               B. J. SULIVAN, _Admiral_.

P.S.—You should get from the Trinity House particulars of a case in
which, with a good solid conductor, the iron floor of a lighthouse,
aided by some lead in the wall, diverted the lightning from the
conductor, and caused damage inside. I think it was a Portland
lighthouse, but it is so many years since that I may not be right.

 TREGEN, BOURNEMOUTH.

                  *       *       *       *       *

Three or four years since, I was looking out of my office window in
Finsbury, when a flash of lightning struck the tower of the church of
St. Giles’, Cripplegate, towards which my sight happened at the time to
be directed. As a portion only of the flag-staff, placed at one corner
of the tower, was destroyed, I obtained permission to ascend the tower
and discover the reason. I found a substantial copper rope conductor
fixed in a somewhat careless fashion to the back of the tower, and
passing some distance into the earth. This copper rope was about an inch
in diameter, and was carried upwards, under and over several projections
and cornices, and across the roof of the tower to its centre—where it
stood erect, and evidently did its assigned work admirably. Clumsy and
unsatisfactory as the fixing of this bent copper rope seemed to me to
be, it is quite certain that it was most efficient; and had it not been
for the flag-staff, capped with lead, which was carried up considerably
higher than the copper rope, no evidence whatever of the lightning’s
path would have been revealed. As it was, the discharge of lightning
struck the leaden cap of the flag-staff, and descended down the wet,
wooden pole, until the summit of the copper-rope conductor in the centre
of the tower was reached, when the discharge flew across to the metallic
earth conductor, leaving the lower part of the flag-staff unhurt, but
shattering to splinters that portion which was higher than the summit of
the copper rope.

                                                        RICHARD HERRING.

 27, ST. MARY’S ROAD, HIGHBURY.

                  *       *       *       *       *

A small public-house of mine (the “Wheatsheaf”) stands at Trolley
Bottom, in the parish of Flamstead, between St. Albans and Dunstable. On
Wednesday, August 6th, 1879, about 2 p.m., during a storm, not otherwise
very severe, my tenant was seated by the tap-room window (A on the plan)
his wife being seated opposite to him, and having the window on her
left, whilst she held her child with her right hand; there were at the
same time in the room about five men besides. A sharp flash of lightning
occurred, and the poor woman (when the smoke cleared away) was observed
to have fallen backwards. She gasped twice, never spoke, and died
immediately, and bore no further mark of injury, I understand, than a
slight mark as of scorching on her neck, below the left ear. I fail to
recollect whether her clothing was scorched or not, the child’s shoe and
sock were both burnt, but she, herself, was unharmed. All present were
sensible of an atmosphere heavily laden with sulphurous fumes; but,
excepting as above, were absolutely unhurt.

On visiting the house about a week afterwards, with a view to its
repair, I found a small round hole as if made with a bullet in a pane of
the window (A) close to which the woman was sitting, but could discover
no further injury either to the other panes, the window-frame, the
floor, or anything in the room. In the parlour, B, the window-frame was
violently wrenched outwards two or three inches, several of the panes
were broken, one sash-line being scorched, as also the frame and linings
in places, especially in the neighbourhood of the sash-weights (iron).
The wooden chimney-piece E, was slightly moved from its position, the
various articles upon it were scattered, and a bottle of ink which stood
there, was thrown with some violence to the ceiling. The upper part of
the chimney to that room, G, and a portion of the wall, of which it was
a part, forming the gable end to the house were shattered, and at H a
stout post, contiguous to the house wall, and supporting the roof of a
lean-to, was split and wrenched from its position. The windows and
frames upstairs, C D, were in the same state as that at B. The chimney,
K, to the tap-room, was quite uninjured, and no harm was done to any
part of the back of the house.

[Illustration:

  ELEVATION. PLAN.
]

Flamstead is about four miles from Luton, and six from St. Albans, and
stands on high land. Trolley Bottom is a hamlet half-a-mile distant, and
is, as its name implies, low-lying. My house is, perhaps, the lowest in
position there. It faces the North-West.

I fear that my experiences will be found to have but little bearing upon
the main point you have in view, viz., the comparative merits of
different descriptions of Lightning Conductors. I venture to think,
however, that they are not altogether without interest as illustrating
the effects of lightning in a by no means exposed situation.

I am writing only from memory what was told me at the time, and should
you desire further information on any points, shall be happy to
endeavour to obtain it for you.

It would interest me very much to know how it is to be accounted for
that, whilst in the room in which the poor woman was struck, no further
damage was done, other parts of the house were, comparatively speaking,
wrecked.

                                                     JOHN EDWARD GROOME.

 KING’S LANGLEY.

                  *       *       *       *       *

I was in a house at Cannes (France) belonging to my late father on the
occasion of its being struck by lightning about five or six years ago.

The storm in which it occurred was a very short one, consisting of only
four explosions, _every one_ of which took effect on some building in
Cannes.

The rain was falling in torrents, and to this I consider we owed our
safety as the shoots and stack-pipes being full of water acted as
conductors. The villa stood high, but another building _very_ much
higher, and on higher ground, was within 100 yards. The lightning struck
the metal cowl of a brick chimney, which, being an addition, was led
down outside the walls of the house.

In the explosion the front of the grate of the room to which this
chimney belonged, together with fire-irons, &c., were all projected
across the room (a large one), about 30 feet; but no marks of lightning
having entered the room were apparent. In fact the lightning after
blowing up this chimney, together with much of the roof and wall of the
house (great portions of the solid masonry of which I found 50 and 60
yards off!) appears to have left the chimney and, taking the course of
the iron shoot round the house, to have divided into _three_ streams,
each of which ultimately found its way down a separate stack-pipe,
melting in its way all the soldering of the joints, but otherwise
leaving them uninjured.

One stream passed thus into a well, the door of which (locked the night
before) was burst open, I presume by the sudden expansion of the air,
another stream of the electric fluid passed into an underground drain,
which it burst up, hurling into the air the trees planted above it, the
third passing across a level asphalt roof, which it melted in spite of
the water lying on it, descended into the earth harmlessly.

You will see by this that the amount of electric fluid must have been
very great to require all these modes of dispersion, and it suggests the
question whether the diameter of the ordinary conductors would be
sufficient to carry off so great a stream. Of course, in this case,
there was no conductor, and therefore no means of testing it.

                                                   H. RADCLIFFE DUGMORE.

 THE LODGE,
     PARKSTONE, DORSET.

                  *       *       *       *       *

Thank you very much for the Pamphlet, which I have read with great
interest. Messrs. W. & W. (page 6) state that conductors in masts (like
Harris’s) are “most objectionable.” The best answer to that is: that
while ships were struck in the Navy, and lives lost every year before
they were introduced, no ship fitted with them ever received the
slightest damage; and since all ships were ordered to be fitted—now
about 30 to 35 years—I have never heard of the slightest damage, or the
loss of one life—that fact upsets all theories on the subject!

Then connections between the higher and lower masts, and especially at
right angles, are objected to on the ground that at a bend the conductor
may be fused; such a thing was never heard of in the thousands of
conductors that must have been fitted in the navy. Even if the movable
plate were turned back the lightning following the longest conductor
would leave one mast for the other, as the conductor went right over the
mastheads, and the two conductors nearly touched each other.

At Spring Grove, near Isleworth, the church had a high spire which was
fitted with a conductor, but the Vicarage was struck and some damage
done to it, though, I think, much nearer to the tower than its height. I
believe many are contented with one or two conductors to a building that
should have many more. My small house here is about 70 feet long by 38
feet wide, and I have seven conductors—one to each chimney.

If it is once decided beyond dispute, that copper conducts in proportion
to its _volume_; then a rod, or flat-plate, of about the proportions of
one to four or five, for the purpose of fitting closer round
projections, would be the cheapest and simplest form; but if it conducts
in proportion to _surface_ then of course a tube, _double_ plate, or
wire rope, would give the greatest protection at a given cost.

I firmly believe in the surface theory of Harris. I had been with him
often when he made experiments nearly fifty years since, and witnessed a
strip of tin foil of the thinnest kind, and about ¼ inch wide, protect a
model mast of about six inches in diameter from electric shock, that
without it split the mast to pieces, aided by a small hole through its
centre filled with gunpowder. And I always thought that the
surface-conducting theory of Harris was indisputable. But about 20 years
since, having to approve a proposal of the Trinity House for a new
conductor of a Lighthouse, which, like previous ones, was an inch in
diameter copper rod called “Faraday’s Plan,” I thought I would go up to
the Royal Institution and ask him why he did not use a copper tube
instead, giving much greater conducting power with less copper. I did
so, and he asserted positively that the conducting power depended
entirely on the volume of copper in the section of the conductor, no
matter whether it was in a bolt, plates, or tube; and that if Harris
said differently, “He knows nothing whatever about it;” of course, I
approved the rod conductor. But singularly enough, though I had not seen
Harris for years, he came to town a few days after, and came to the
Board of Trade to see me, and bring me a piece of his large tube
conductor, with a connection, that he was fitting to the Houses of
Parliament. When I told him what Faraday’s opinion was, he answered,
“Then he knows nothing about it.” I was still inclined to believe in
Harris; but a few years after, a young Indian R.E. Officer—Lieut.-Col.
Stewart—whose death not long after was a serious loss to the service,
was sent home to procure the electric cables for connecting different
Indian ports. I was asked by the Secretary of the Indian Office to give
him all the help I could. One day he came to me with a piece of the
cable he proposed using. Inside the iron wires was a single stout copper
wire about ⅒ of an inch in diameter. I asked him why he had not the
central wire of several strands as usual, as I believed it would greatly
increase the conductive power. He said that he had _carried out a number
of experiments on this point_ before deciding; and that he was satisfied
the conducting power depended on the _amount_ of _copper_ in the
conductor, and consequently a solid wire was better than one of the same
size made up by twisting small wires together.

This of course shook my confidence in Harris’ theory; but it is a point
that can be easily decided by experiments on a larger scale; and I hope
your Committee will be able to decide it finally.

Messrs. W. & W. prefer to a conductor on the masts a wire rope carried
down from the truck, stopped to a back stay. The following fact will
show its danger:—A French frigate, some fifty years since, had one so
fitted as an experiment; while striking T.G. masts the conductor formed
a large bight as the mast was lowered; a man standing on cap or
cross-trees—I forget which—formed a shorter conductor between two parts
of the wire rope and was killed without any other damage being done.

                                                          B. J. SULIVAN.

 BOURNEMOUTH.

                  *       *       *       *       *

With reference to your recent letter in the “Times,” I shall be glad if
you will inform me whether there has come under the consideration of the
Conference the question of lightning conductors on board iron ships with
_iron_ masts; for my part they would seem to be useless, and that if the
iron mast have sufficient metallic communication, through the bottom,
with the outside of the ship either by means of the screw shaft or in
some other way; no additional conductor, copper ribbon, or strip, down
the masts and along the decks over the ship’s side, or copper tube down
the shrouds and over the ship’s side could be of the slightest benefit.

In some ships one or other of these arrangements has been adopted, and
in others both have been applied at same time.

                                                       C. M. L. McHARDY.

 FERN HILL COTTAGE, WINDSOR FOREST.

                  *       *       *       *       *

I have observed your letter in “The Architect” of Saturday last. With
reference to the subject on which it treats, I chance to have noticed
since my residence here (a period of eight years) what I suppose to be
an unusual frequency of lightning striking objects immediately round
this spot, and the neighbourhood generally.

This inference is suggested by the fact that within the period mentioned
lightning has fallen within fifty yards of the same spot three
times—that this summer (one of those occasions) two other houses, both
(say) within 500 yards in a direct line from this spot, were also
struck—and generally, I believe, more objects are struck in this
neighbourhood than usually happens to be the case.

My idea may be a fallacy, for I have no sort of statistics by which to
test it; but if you suppose it is not so, and if such points come within
the scope of your inquiry, I should be glad to send you a map marked
with the spots where, and the dates when, lightning has fallen in or
near this town. The only local peculiarities I notice are: 1. An unusual
number of houses close to this have lightning conductors (a mere
coincidence, and not placed there on any impression like my own). 2. We
are at the bottom of a deep bay of parabolic plan which may influence
the movements of electrical disturbance. 3. A soil of sand and gravel
containing much oxide of iron.

                                                              A. BALDRY.

 ATHELNEY, BOURNEMOUTH, HANTS.

[Mr. Baldry kindly supplied the map, and we find that a half circle of
half a mile radius struck from the cliff-edge half a mile west of
Bournemouth Pier includes the churches of St. Peter, with one conductor,
and Holy Trinity with three; eight private houses with conductors, of
which four houses have one each, and the other four have two, five, six
and seven respectively, and within this area six objects are known to
have been struck—three in the year 1879, two in 1871, and one in 1870.
We do not know of any English locality where there are so many houses
with conductors; but there are many more remarkable cases of repeated
injury within small areas—_e.g._, in one storm in June, 1878, there were
at least eight separate buildings injured within a circle of half a mile
radius struck from the Metropolitan Cattle Market in the north of
London.—ED.]

                  *       *       *       *       *

It occurs to me that it is worth while for the delegates of the Royal
Institute of British Architects to raise the question, and, if possible
settle, whether or not the gas pipes which permeate many buildings might
or might not be utilized as lightning conductors; and whether any risk
of gas explosion would be incurred thereby.

In my own practice there occurred the case of a lofty building, with a
domed roof, and a sun-burner with a 1½ inch gas-pipe to supply it,
rising to the summit of the dome, and a large iron cowl over the
sun-burner.

The same circumstance occurs in most modern theatres. If the cowl were
struck by lightning there was perfect metallic connection thence to the
street gas mains—and one of larger sectional and superficial area than
an ordinary lightning conductor would give.

                                                            H. D. DAVIS.

 2, FINSBURY CIRCUS, CITY, E.C.

                  *       *       *       *       *

Lightning conductors have been a great hobby with me for many years, and
I have induced a great number of clergymen and others to fix them to
their towers and houses. During my time in the navy and merchant service
I witnessed many fearful effects of lightning, and for the last thirty
years I have been striving to persuade my friends to secure their houses
from these terrific visitations. On the 24th December, 1699, the upper
half of the fine steeple of this town was hurled to the ground, and a
large portion of the church broken in. Pinnacles were then substituted
for the upper portion of the steeple, to which I have had an efficient
conductor attached. As far as I can gather from records, and from the
abortions so frequently substituted for the original pinnacles of
towers, I have come to the conclusion that _nearly every tower in this
country_ has been struck by lightning during the last 400 years, when
nearly all the towers were built. Many years since, the Illustrated News
gave a sketch of a beautiful steeple (in Norfolk, I believe) destroyed
by lightning. It was stated that this was the second steeple which had
met with so sad a fate. After the destruction of the first, a second
steeple was built by subscription, at a cost of £1,000, and the
scaffolding had been removed only ten days when, during a terrific
thunderstorm, this second steeple was entirely destroyed! I wrote
immediately to the incumbent to ask about the _conductor_, and his
answer was that none had been fixed, but that it was quite decided that
an efficient one should be attached to _the third steeple_! This would
almost appear incredible, and I regret that I did not dot down the name
of the Parish and other data, but I think it was about 20 years since.

The conductors I recommend are simply copper rods of ¼ inch diameter,
attached to the highest chimney, and brought to the ground two or three
feet under the surface. When buildings are longer than they are high, I
always advise a conductor at each end. I generally place the conductor
four or five feet above the chimney, and bring it out from the base of
the building. Where a steeple or pinnacle has a vane it is only
necessary to fix the conductor to the base of the spindle. Sir W. Snow
Harris recommended much heavier copper conductors, but their great
expense has prevented their adoption. The old conductors in men-of-war
were composed of long copper links, of which nine feet went to the lb.,
and these were _always_ efficient _when in place_. Now of ¼ inch copper
rod there are only _five feet_ to a lb., so that I give a larger margin
for security.

                                                          JAMES LIDDELL.

 BODMIN.

                  *       *       *       *       *

I observed your notice that you required information in reference to
lightning and lightning conductors. A case was brought to my attention
last year which occurred in Middlesborough. I enclose you particulars of
the same extracted from my report, together with a tracing shewing the
elevation and plan of the chimney shaft which was struck with lightning.

                                                         BALDWIN LATHAM.

 7, WESTMINSTER CHAMBERS, VICTORIA STREET, S.W.

[Illustration: Plan and Elevation of washhouse of Middlesboro’ Fever
Hospital]

                    A. Wooden cover over boiler.
                    B. Boiler.
                    C. Iron disinfecting apparatus.
                    D. Iron flue into chimney.
                    E. Conductor.
                    *  Position of fracture.

  _Extract from a Letter from Mr. E. D. Latham, C.E., Borough Surveyor
    of Middlesborough, dated October 11th, 1878, with reference to the
    striking by lightning of the chimney in connection with the
    washhouse at the Middlesborough Fever Hospital at Linthorpe_:—

“The chimney, which is a brick one, is about 50 feet high and 5 feet
square at the base and stands at the north end of the washhouse, as
shown on the accompanying sketch. The conductor, a ⅜th inch copper rope,
is fixed on the south side of the chimney with holdfasts, no insulators,
and finishes in the usual manner, about 2 feet above the top. The
conductor is carried under the ground for a distance of about 9 feet
from the chimney, and terminates at a depth of about 4 feet in hard,
rather dry clay, the end being wrapped about three times round a common
brick buried in the ground. At a distance of about 9 feet above the
ground at the same side as the conductor, and only about one foot from
it there is a fracture in the brickwork where the electric fluid appears
to have penetrated the chimney and gone a short distance down the
inside, to the flue connected with the iron disinfecting apparatus,
which stands at the side of the clothes boiler, as shown on the plan.
The stone work of the top of the boiler was broken and other damage
done.”

_Extract from the reply of Mr. Baldwin Latham, C.E., to the above
communication_:—

“It is no uncommon thing for buildings provided with what are called
lightning conductors to be damaged by lightning, and the cause is due to
the inadequacy of the conductor to carry the electric fluid, which will
leave the conductor for a better or a larger conductor. Wire ropes are
found to be one of the worst forms, the same amount of metal when
applied in a solid rod or ribbon is far more efficient, as it offers
less resistance than the strands of a rope. You say your conductor is
perfect, but by examination of the drawings it will be seen that the
lightning descended the conductor to a certain point. At this point the
iron flue enters the shaft, but some distance from the conductor; the
mass of metal located there was a better conductor than the rope, so
that in leaving the rope for the better conductor, the electric fluid
passed through the brickwork and caused the damage. If the boiler and
flues did not join in metallic communication, damage would arise from
the fluid passing from the flue to the boiler, and if the boiler were
not in metallic communication with the earth, farther damage would arise
when the fluid left the boiler for the earth. It is well known that
electricity of high tension will leave small conductors for large ones,
and the knowledge of this fact is made use of in protecting the
telegraph system throughout the country. Many buildings and chimneys
have been struck that have been fitted with so-called lightning
conductors. A perfect system of protection against lightning consists in
linking together all the conductors about the buildings. Such was the
system introduced by Sir W. Snow Harris and adopted by the Government.”

                  *       *       *       *       *

_Reply of Dec. 12th, 1878, acknowledging receipt of Mr. Baldwin Latham’s
Letter._

“I am directed by the Town Council to tender you their thanks for the
trouble you have taken, and the valuable information you have given with
reference to the lightning conductor at the Middlesborough Fever
Hospital.

                                                       GEORGE BAMBRIDGE.
                                                           _Town Clerk._

 CORPORATION HALL, MIDDLESBOROUGH.

                  *       *       *       *       *

                          _Subsequent action._

At the suggestion of the Engineers of the Telegraphs in the district,
the earth portion of the rope has been imbedded in a mass of coke, and a
quantity of old iron has been placed at the bottom of it, to counteract
the influence of the boiler and disinfecting apparatus.

I beg to report an incident which occurred on board the barque “Southern
Queen,” from Pensacola, while coming up Channel on the morning of the
30th of December, 1879, the Eddystone Lighthouse bearing about north,
dist. 20 miles. At 6 a.m. of the above date, saw a terrific squall
rising in the W.N.W. point of the horizon, with vivid Lightning in it.

We immediately reduced sails down to lower topsails and foresail, and
about 7 a.m. the squall of wind and hailstones overtook us: it blew
furiously for about twenty minutes, and in the height of the squall a
thunderbolt broke on the ship, shattering the main royal mast-head,
thence the Lightning ran down the main royal stay to the fore topmast
head, and shattering that also. Thence it ran down the chain of the
fore-topsail haulyard and shattered about a fathom of the chain in bits.
When the bolt struck the ship it made a report like a hundred ton gun
fired off. The concussion on the ship threw every man off his feet. It
filled the cabin with smoke, and also the hold: the smoke had a sulphury
smell; also all the compasses in the ship were so magnetized that they
were flying right round.

And on arrival into the Commercial Docks we observed that a plank on
each side of the ship, in the wake of the main chains, had been blown
out by the Lightning. On the port side the oakum has been blown out of
the seams, and the edges of the planks shattered. Since the ship has
lightened up out of the water, we have discovered that the electric
fluid has passed out by a copper bolt, cut the copper sheathing in the
shape of a star, and turned it back.

Any further particulars I will be most happy to supply if required.

                                D. MORGAN, _Master_, “_Southern Queen_.”

 17, LIME STREET, LONDON.

[Two of the delegates visited the ship, but with the exception of
learning from the mate that he saw “a ball of fire descend from the
mizen and go over the port side” they had not been able to obtain any
additional particulars. They obtained some fragments of the broken
chain, a much rusted iron one, weighing however about two pounds per
foot.—ED.]

                  *       *       *       *       *

The patterns of lightning conductors obtained from Messrs. Hart, as
requested, are an improvement on the first “Spratt’s Patent” purchased
by the above-named firm; the original was a mixture of copper and zinc
wire, which, when it was exposed to a wet and smoky atmosphere, a
galvanic action took place and soon destroyed it.

About two months ago I engaged Messrs. Davis, of Derby and Newgate
Street, to test a rope of the above construction that had been fixed
about ten years at No. 1, Aberdeen Terrace, Blackheath, and I was
present at the time, and though we had a very powerful battery we could
not get a current through any part of it, as both the copper and zinc
had decayed: the copper wire is not stout enough to allow for corrosion
in this climate.

St. Michael’s Church, Blackheath Park, with the needle spire, as we call
it—built just fifty years ago—had a ½ inch iron rod; and as it now runs
through the new vestry just built I have advised the churchwardens to
have it tested, and they are going to have it done in the course of a
week or so.

St. Alphege Church, Greenwich, has a ribbon of copper about 1½ inches
wide by ¼ inch thick, and that has been up many years, and is as sound
as when it was fixed, for I examined it about two months ago.

I have advised the owner of No. 1 Aberdeen Terrace, to have a ribbon of
copper, as I am certain that wire ropes are not to be depended on in
this climate.

Hoping these few remarks will not be deemed out of place,

                                                      CHARLES J. HERYET.

 95, BLACKHEATH HILL, GREENWICH, S.E.

                  *       *       *       *       *

I have the honor to forward notes of an accident from lightning, which I
lately witnessed, having been informed that your Committee desires such
information.

The very rough sketch which I attach is, I believe, accurate; but I was
only allowed to look in at the door while a strong light was held
within, and to view the outside of the building. A native draughtsman
belonging to the office, however, was allowed to make some measurements,
which he communicated to me.

It seemed to me that the case was worthy of record, because the building
was so little injured.

                                            JOHN ASTED, Lieut.-Col. R.E.

 MASULIPATAM,
     MADRAS PRESIDENCY,
             _17th May, 1878_.

_May 8th, 1878._—Camped at Pedda Kondur, a village on the west bank of
the Kistna river, about 10 miles below Bezoarah anicut. All the morning
there was a southerly wind blowing unsteadily; by noon it fell calm, and
was very hot, clouds gathering in the east. Soon after midday thunder
was heard to the east, and a storm was evidently approaching. About 3
p.m. wind began to blow from the east, and soon rose to a gale, bringing
thick clouds of dust, and the thunder sounded very near. It rained
rather heavily, which laid the dust, and black clouds could then be seen
over-head, and nearly all round: the thunder, which was very loud,
sometimes sounding quite over-head. By half-past four the rain had
slackened, but thunder was almost incessant, and very loud. Just at this
time a stream of lightning descended within 80 yards of the tent, and
was accompanied by a tremendous explosion. The lightning struck a small
pagoda near the village, and some of the natives said that they observed
smoke rise from the summit when the lightning descended.

The accompanying rough sketch will show what the building is like. The
main part of it is a square pyramid, each side of the square, outside
measurement, being about 18 feet; height of apex above ground, 32 feet.
Built on to one side of the pyramid is an entrance chamber, with flat
roof, about 10 feet square, and the same in height. The apex of the
pyramid is surmounted by a metal (probably copper) finial, about 1 foot
in height; the ordinary attachment of such a finial to masonry is by
means of a small stake built into the masonry, on which the finial—which
is cast hollow—is fixed, and round which it is plastered with mortar.

[Illustration: Plan and Elevation of Indian Pagoda]

The interior of the pyramid forms one room, about 10 feet square, with a
domed ceiling, the thickness of the dome at crown being 2½ feet. In the
centre of this room is placed the idol, in this case a lingam, or
cylindrical stone pillar, 1 foot 4 inches high, and about 9 inches in
diameter, which stands on a square hollow stone tray (not cut out of one
stone, but fitted in two or more pieces) in which the offerings of ghee,
&c. are placed. This tray has a small spout on each face to carry off
the liquid ghee and water with which the priests’ ablutions are made.
The tray is raised on masonry, so that the height of the top of the
lingam is 3 feet 4 inches from the floor. The floor of the room is 1
foot above the surrounding ground; there is only one doorway leading
from the porch or entrance room above mentioned; and the sacred edifice
is closed by a substantial wooden door, with iron hinges and lock, on
the outer face of the entrance chamber. The whole building is of brick
in mortar, unplastered, and presents the appearance of being weather
worn.

The pagoda is at a distance of about 20 yards from some low native
houses, and stands in an open space, on two sides of which is the native
village; round the houses are some trees, mostly of small size, but
within 50 yards of the pagoda are two separate trees, which certainly
exceed it in height. The village is situated on the margin of the Kistna
river, and the surface of water in wells is at least 10 feet below the
surface of the ground.

The lightning struck the metal finial on the top of the pagoda, and
passed vertically through the dome, travelled along the east side of the
lingam without leaving any mark, and bored a small round hole in the
stone tray beneath it, passing into the ground below without disturbing
the idol or its foundation. The hole in the tray was not quite large
enough to admit the point of a little finger, and it was situated on a
joint of the stone, a place where moisture would probably linger. The
finial appeared undisturbed, but the masonry immediately round its base
was shattered, and a shower of pieces of brick and mortar was sent from
the top of the pyramid and scattered over the ground on the east side to
a distance of about 20 feet from the base. The masonry of the apex of
the pyramid was cracked in three places, and a small hole was bored in
it, on the east side of the finial, apparently about the same size as
that in the stone tray; but otherwise the masonry of the building
appeared totally uninjured—not a crack could be found anywhere.

The soil at this place is a clayey loam, rather lighter than the
ordinary delta alluvial soil.

When the building was struck a sulphurous smell was noticed.

                                            JOHN ASTED, Lieut.-Col. R.E.

                                                     MASULIPATAM,
                                                       _17th May, 1878_.

                  *       *       *       *       *

                                          IRISH LIGHTS OFFICE, DUBLIN,
                                                _13th March, 1880_.

  SIR,

  Adverting to your letter of the 13th ultimo, I have now the honour
  to forward herewith for the information of the Lightning Rod
  Conference copies of two Reports relating to the lighthouse at
  Berehaven being struck by lightning, in 1877, which, no doubt, is
  the Station alluded to by Professor Tyndall in his conversation with
  Mr. Inglis, of the Trinity House.

                                     I am, Sir,
                                         Your obedient Servant,
                                                 W. LEES, _Secretary_.

                  *       *       *       *       *

                                          IRISH LIGHTS OFFICE, DUBLIN,
                                                _February, 1877_.

  SIR,

  I most respectfully beg leave to state that, in accordance with your
  instructions I proceeded to Berehaven Lighthouse, and on my arrival
  at that station I made a very careful examination and found that the
  lightning was conveyed into the lantern by the iron stay bars that
  were connected to the lightning conductor at a collar about 5 feet
  over the gutter on the outside of the dome for the purpose of
  securing it, and bolted to the dome of lantern by iron bolts. After
  bursting off the several coats of paint at the heads of the bolts,
  it put out the lights, breaking the glasses, and knocking down both
  light keepers insensible; it having twisted off the lead voice-tube
  where it was secured to the side of the lightroom by a holdfast,
  bursting out the stone sheeting between the iron pillars supporting
  the marble top; it then passed through the voice tube to the
  principal keeper’s bedroom, where it burst out the studding and lath
  and plaster, and tearing away the voice-tube, the foot-board of the
  bed, and destroying the pictures that were hanging on the walls. It
  would appear that the current was interrupted in its course by the
  sudden bend of the voice-tube; for, after having dealt destruction
  in this apartment it was attracted by the iron holdfasts and spikes
  that secured the voice-tube and studding to the walls, and passed
  out through the external walls of dwelling to the out offices, where
  it passed along the eave gutters to the end of them; it then
  followed one of the iron holdfasts, and entered the wall, destroying
  it, and bursting out the cut-stone kneeler and barge course, it then
  passed down through the roof of the low buildings, destroying the
  slating, passing through the walls of the pantry, &c., tearing up
  portions of the 3 inch Yorkshire flagging of the floor and yard,
  dealing destruction to the shelving, doors, door frames, brickwork,
  glass, &c., and bursting up the seat of principal keeper’s w.c., it
  passed along the sewer to the assistant keeper’s w.c., breaking up
  the flags and seat and then passed out through the roof. Another
  current was attracted by the eave gutters at the east angle of the
  dwelling near the tower, and passed along them to the north east
  angle, splitting them through the centre. At this point its course
  was changed to the west, and passed into the assistant keeper’s yard
  and down the rain water pipe to the water tank, splintering it and
  the slating and brick wall, &c.; it also appears that the lightning
  struck the south-east side of the tower and entered it in several
  places at the base and near the lightning conductor, and apparently
  glanced off it where it was secured by holdfasts to the tower,
  rooting up the solid rock, but giving no indication that it had been
  conveyed to earth by the conductor as intended: the lightning also
  entered the assistant keeper’s kitchen through the chimney, knocking
  down a portion of the brickwork, &c.

  I may remark that the lightning conductor is formed by a copper rod,
  which stands about 10 feet over the gutter on the outside of the
  lantern, and is secured by three iron stays to the dome, as before
  described, and passes down through the centre of the gutter to the
  under side, where it is connected to a ½-inch copper-wire rope,
  which continues down the outside of the lantern close to the glass
  to the floor of the balcony, passing through the stone floor by
  means of a hole, jumped through it, then continues down the face of
  the tower closely pressed to it by the iron holdfasts and copper
  bands, which secure it until it reaches the rock at the base of the
  tower, where it terminates in a small hole 3 inches by 3 inches,
  jumped out of the rock about 6 inches under the surface.

  After having made a careful survey of the damage done, I deemed it
  advisable, and at the solicitation of the principal keeper, who
  seems to have been greatly shaken and nervous, to have the iron
  stay-bars disconnected from the dome of the lantern and the
  bolt-holes plugged up with timber, fearing a recurrence of the
  accident, as the weather was very stormy, and should lightning come
  on no person on the rock would enter the lantern. I also considered
  it prudent to have the loose gutters and cut-stone, also a part of
  the gable of the out offices, taken down, as it was in danger of
  falling into the narrow yard, which might cause a sad accident.

  Having provided workmen and materials and scaffolding for doing this
  work I again landed on the rock on Saturday last, with great
  difficulty, having been detained a day by the storm, and pointed out
  the temporary repairs that were necessary to be done for the
  protection of the people on the rock.

  The probable cost of repairing the damage done the buildings,
  independent of the lightning conductor, and which require to be done
  without delay, will be £120. Hoping the action I have taken in this
  matter will meet with your kind approval, I have the honour to be

                                   Your most obedient Servant,

                                           (Signed)      A. J. BERGIM.

[The other report is to the same effect as the above, and is therefore
omitted.—Ed.]

                  *       *       *       *       *

ACCIDENT BY LIGHTNING _at Upwood Gorse, Caterham, the residence of_ J.
TOMES, Esq., F.R.S. _28 May, 1879_.

As I happened to be visiting Mr. Tomes, in the autumn of 1879, I took
the opportunity of obtaining all the particulars I could with reference
to the accident which occurred on the night of the 28th May, 1879, when
his house was struck by lightning.

The house, a sketch plan and elevation of which are annexed, stands upon
a hill upwards of 700 feet above sea level, and is somewhat higher than
any other object in the vicinity. It is covered by a steep tiled roof,
that of the principal portion of the house being somewhat higher than
the rest, and upon the ridge of this roof stand two brick chimney stacks
of equal height. Upon the eastern stack, at its southern end, was fixed
a lightning conductor (shown by the line, A. B. C., on the south
elevation), the upper part consisting of a point and a length of copper
tube ½ an inch external and ⅜ inch internal diameter, which was screwed
into a collar connected to a woven band of one zinc and thirteen copper
wires carried through glass insulating rings along the slope of the
roof, over the rain-water gutters and down the side of the house into
the ground, going only 12 inches into dry chalk.

The electric fluid struck the lightning conductor, hurled the rod down
and shattered the chimney pots and some of the brickwork. The rod was
broken at the point marked A on the south elevation, where the sectional
area of the copper rod was reduced by the screw being cut into it for
the collar, which connected the rod with the woven band. This junction
and a portion of the band are forwarded for inspection, from which it
will be seen there are no rough broken surfaces, but that the thread of
the screw was partly melted. The copper wires composing the band were
bright and nodulated here and there throughout their length, showing
that it had been heated up to a sweating temperature. The zinc wire was
not continuous, having been wasted by oxidization. It showed no
indication of having been hot.

[Illustration:

  UPWOOD GORSE, CATERHAM. Scale—1 inch = 32 feet.
]

Having broken the conductor, the discharge appears to have divided at
the ridge of the roof, a portion passing down the southern and a portion
down the northern slope of the roof. That portion which passed down the
southern slope apparently followed the course of the conductor band as
far as the iron rain-water gutter, which it cracked, and perforated two
holes, about half an inch diameter, in two panes of glass at B. Here the
current apparently again divided, as shown by the dotted line from D to
E on the south elevation, some passing westwards and some eastwards
along the rain-water gutter round the eaves of the house, as traced by
the broken joints of the gutter. Westwards these joints (which were made
of red lead) were only broken from B to D, but eastwards they were
broken from B to E, and right round the eastern side of the house to F,
and along the northern side as far as G.

What seemed to be the greater portion of the discharge, however, passed
down the northern slope of the roof and along the course shown by the
dotted lines on the Plan and north elevation. The lightning first
followed the lead flashing H of the chimney stack, next broke some tiles
at I, and then without disturbing any of the rest of the tiling, leapt
across the roof, a distance of some 15 feet, to two galvanised iron
water cisterns in the roof at K, perforating a hole through the 9–inch
brick wall of the house in its course.

This hole, which was circular, was large enough to admit one’s finger
easily and was blackened on its interior; when first examined, eight or
ten minutes after the occurrence, it was still quite hot. One edge of
the lead flashing outside the wall was fused at G, close to the
rain-water gutter, from which it would seem that the current again
divided at the wall of the house. There are two galvanised iron cisterns
at K, connected by a pipe underneath (see adjoining sketch plan), and
the discharge appears to have passed from one cistern to the other and
then along the 1½ inch iron barrel rising main, from pumps, to the point
L^1 in the back kitchen, where the iron pipe separated into two branches
leading to the two pumps L^2 and M.

Probably a portion of the discharge passed down the iron suction pipe
from the pump L^2 into the rain-water tank P, but however this may have
been, a considerable portion passed from point L^1 along the 1½ inch
iron pipe LM to the pump M in the scullery, and thence along a ¾ inch
iron pipe to a water tap fixed over the iron sink N, but not in metallic
connection with it. Here the lightning broke the slate at the back of
the sink and sent it showering across the scullery, breaking the things
on the opposite side of the room. The iron sink was set on brick piers
and connected, by means of a 1½ inch iron pipe, with the self-acting
syphon “Flush Tank” O in the yard. This “Flush Tank” consisted of a
cylindrical cast-iron tank about 26 inches in diameter and 26 inches
deep, buried two-thirds in the ground, so that it formed a fair earth
connection.

There is an account of the accident in a letter by Mr. Charles S. Tomes
in _Nature_, of 12 June, 1879 (which has been made use of in the present
description), and there is also a letter about the accident by Mr.
Newall on the next page of _Nature_ to Mr. Tomes’ letter. The
description in this latter letter is, however, erroneous in several
particulars, especially where it speaks of the lightning passing round
the iron gutters to the iron water cisterns.

                                ROGERS FIELD,
                                    _B.A. Lond., M. Inst. C. E., F.M.S._

 CANNON ROW, WESTMINSTER.

[NOTE.—Mr. Tomes has most kindly sent the whole of the upper parts of
the conductor; and as the accident appears a very instructive one we
give full details, together with engravings of the more important
portions of the conductor.—ED.]

This conductor was of the pattern known as Spratt’s patent. The upper
terminal was what the vendors call a “reproducing point,” which they say
is “formed of two or more metals: the inner or core being steel, and the
outer of silver alloy, tipped with platinum;” the idea of the inventor
is said to have been that “should the outer coating become fused by an
extraordinary charge of electricity, the core will remain intact to
receive any further discharge.” In the present case the top is broken
and the iron centre is rusted and bent, but there is no indication on
the remaining portion of heat or fusion.

This point A was well screwed into a stout copper collar B.

[Illustration:

  D
]

[Illustration:

  F
]

Into the same collar was screwed the upper end of a copper tube C, 5 ft.
1 in. long, external diameter, 0·5 in., and internal diameter about 0·36
in., giving a thickness of only 0·07 in., or but little more than a
sixteenth of an inch. The mass of copper was therefore about equal to a
tape 1½ × 1/16, or ¾ × ⅛, or to a rod one-third of an inch in
diameter—the area being as nearly as possible 0·09 in. The tube weighs
29½ ounces, which corroborates the above measurements and shows that it
weighs rather less than 6 ounces per foot. This part of the conductor
was evidently greatly heated, as there are distinct marks of sweating in
several places. The lower part of this tube was screwed into the collar
D (which is drawn of its actual size in the annexed sketch) in order to
make connection with the short length of copper tube F, a portion of
which is also engraved, of its actual size. It was at E that the rupture
occurred. The charge passed the point A, then the top collar B, and
although it greatly heated the 5 ft. copper tube C, still no damage was
done, and so it passed into the second collar. Here, however, there seem
to have been two faults: the short copper tube F, was very slight,
weighing but little over 3½ ozs. to the foot, and this, which represents
but a very slight conductor, was greatly lessened by a deeply-cut thread
to the upper end, whereby the area was reduced to less than 1/20th of an
inch. As this was not screwed home, the total sectional area at E
immediately below the collar was reduced to the above small amount,
rupture and fusion occurred, and much of the charge left the conductor.
This short length of tube was, however, raised to a sweating temperature
in two places.

[Illustration: Sections of Rod at Upwood Gorse, Caterham]

The conductor consisted of 14 wires made into a flat plait, the wires
seem to have been of the following dimensions:—

                     Each of No.                        Total area.
     12 copper wires, 15 B.W.G., dia. of each ·072 in.:   0·048 in.
      1 copper wire,  18 B.W.G., dia. of each ·049 in.:   0·001 in.
      1  zinc wire,                   of each ·049 in.:   0·001 in.

Thus the total sectional area of the plait G would be about 0·050 in.,
or rather more than that of the short copper tube into the lower end of
which it was roughly thrust and riveted—but the joint was bad, there was
no solder at all, and the metallic contact was very imperfect.

As to the state of this plait (which was less than an inch wide, and
less than ⅒ in. thick), and as to the ridiculously imperfect earth
terminal, details are given in Mr. Field’s letter.

It may be well to recapitulate the dimensions:—

 ┌─────────────┬─────────────┬─────────────┬─────────────┬─────────────┐
 │DESCRIPTION. │   LENGTH.   │ DIMENSIONS. │  SECTIONAL  │HEAT EFFECTS.│
 │             │             │             │    AREA.    │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │“Reproducing │    9 in.    │0·45 × 0·45  │    0·20     │None visible.│
 │  point”     │             │  in.        │             │             │
 │Collar       │   1¼ in.    │0·75 in.     │    0·24     │None visible.│
 │             │             │  diam.      │             │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │             │             │External 0·5 │             │             │
 │             │             │  in. dia.   │             │{Sweated in  │
 │Copper tube  │ 5 ft. 1 in. │  Internal   │    0·09     │  places.    │
 │             │             │  0·36 in.   │             │             │
 │             │             │  dia. }     │             │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │             │             │External 0·75│             │             │
 │             │             │  in. dia.   │             │             │
 │Collar       │   1⅛ in.    │  Internal   │    0·24     │None visible.│
 │             │             │  0·50 in.   │             │             │
 │             │             │  dia.       │             │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │             │             │External 0·50│             │             │
 │             │             │  in. dia.   │             │{Sweated in  │
 │Short tube   │    7 in.    │  Internal   │    0·09     │  places.    │
 │             │             │  0·375 in.  │             │             │
 │             │             │  dia.       │             │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │             │             │External     │             │             │
 │Short tube   │             │  0·438 in.  │             │             │
 │  where      │    ¾ in.    │  dia.       │    0·04     │Fused.       │
 │  threaded   │             │  Internal   │             │             │
 │             │             │  0·375 in.  │             │             │
 │             │             │  dia.       │             │             │
 ├─────────────┼─────────────┼─────────────┼─────────────┼─────────────┤
 │Plait        │   53 ft.    │? 0·7 × 0·072│    0·05     │Sweated in   │
 │             │             │  in.        │             │  places.    │
 └─────────────┴─────────────┴─────────────┴─────────────┴─────────────┘

                                                                G. J. S.

                  *       *       *       *       *

We herewith hand you our circular, setting forth our ideas as to
lightning conductors. We claim that if one or more sharp edges or points
is so essential on the most elevated part or parts of a conductor, why
not establish this principle the entire length of the conductor? or why
not leave these most elevated part or parts blunt, or erect a small gilt
ball?

                                                      DAVID MUNSON & Co.

 INDIANAPOLIS, INDIANA, U.S.A.

[Illustration: Sections of Munson’s Rods]

  [The engravings are not drawn to scale, but are here reproduced; the
    shaded parts are galvanized iron, the lighter parts copper.—ED.]

                  *       *       *       *       *

I think that it would be very valuable if the Conference considered how
far iron ventilating pipes to drains will safely act as lightning
conductors. These pipes generally consist of iron jointed with red lead
or putty. Will not these joints interfere? Very often also a portion of
the pipe is wholly of lead. So many of these pipes are now carried up to
a very high level that the question is important.

                                               ROGERS FIELD, M.Inst.C.E.

 CANNON ROW, S.W.

                  *       *       *       *       *

Our opinion is that the drain to our Powder Magazine at Bruntcliffe (see
ante page 74) had no water in it at the time of the occurrence.

                                                      JOHN HAIGH & SONS.

                                                  VICTORIA COLLIERIES,
                                                             GILDERSOME.

                  *       *       *       *       *

We have the pleasure to send you a plated model of our new Conductor
Coupling, and hope you will be pleased with it.

When screwed up, the contact between the rod and the copper tape is
perfect. It is, of course, a very simple thing, but it overcomes the
difficulty of soldering, which is always more or less uncertain, and
rivetting up aloft is apt to be scamped.

And as to soldered connections, apart from the uncertainty of permanent
contact, it is very important to keep the soldering iron away from
roofs, it often damages the lead, and (as at Canterbury) the fire-pot is
a source of great danger to buildings.

[Illustration:

  FIG. 1.
]

[Illustration:

  FIG. 2.
]

[Illustration:

  FIG. 3.
]

A is the copper tape conductor. B is a screw plug, having two slots, _a
a_ (see fig. 3), and an intervening division _b_, all cast in one piece.
The tape or rope A is passed through one of the slots _a_, and bent over
the division piece _b_, the bent portion A1 is then returned through the
other slot. A screw socket forming the coupling C, bearing a collar to
rest in a ring bolt built into the structure to be protected, is then
screwed on to the plug B, and into this socket the rod or tube D is
screwed, it being suitably tapped for its reception, until the lower end
of the rod or tube is in firm contact with the tape or rope. These
latter are then firmly held together, and cannot by any possibility come
apart.

NOTE.—In fig. 2 the rod and tape are not shown in actual contact, the
drawing being intended to exhibit the separate parts.

                                                     R. C. CUTTING & Co.

 147, QUEEN VICTORIA STREET.

                  *       *       *       *       *

I have the pleasure of furnishing details of the recent damage to Christ
Church, at Carmarthen. The circumstances are these:

At the Eastern end of the church stands an ordinary square tower,
covered with a sloping slated roof; this roof is capped by an ornamental
open ironwork ridging, terminating at each end in a light open iron
pinnacle, and having in the centre another pinnacle similar to those at
the extremities. A is a view of this ironwork from the east end of the
church.

The conductor consisted of seven copper ropes stranded together, each
rope consisting of seven strands of No. 18 wire, the whole having a
diameter of about ½ an inch. It was fixed to the building by ordinary
copper staples; it ran up, and was attached to the southern portion of
the ornamental railing, and it terminated in a single point. There was
no special connection between the conductor and the iron guttering of
the church.

I could not ascertain in what manner the earth was made, but it was an
imperfect one, giving a resistance of 115 ohms, and this resistance
would have been greater but for an accidental circumstance mentioned
further on.

The lightning struck the central iron pinnacle of the ornamental ridge
and broke it off. In falling to the ground it was shattered into about
twenty pieces; but on the upper extremity, which was a solid cast-iron
spike, about ¾ inch square, there were marks of fusion across the whole
of the top to the depth of ⅛th of an inch.

I could not observe other marks of fusion at the point where the
pinnacle was broken off, but the lightning made its way to the
conductor, and on reaching the ground, at a distance of 4 feet from the
point where it entered, it burst out with explosive violence, blowing a
circular hole in the ground 2 feet in diameter and 8 inches deep (marked
B in plan). The earth from this hole was blown into the air, and fell in
a fine shower on objects standing 3 or 4 feet high and 14 or 15 feet
from the hole.

[Illustration:

  CHRIST CHURCH, CARMARTHEN.
]

A second flash struck the iron guttering at the south-western extremity
of the church (C), broke off a 2 feet length, and ran down the
waterspouts (D D). Opposite one of these a second hole, 9 inches deep
and a foot in diameter, was blown out of the ground, some 3 feet from
the base of the spout.

On examining more closely the surroundings of the lightning conductor, I
observed that the church gas-pipe, an iron one, about 1¼ inches in
diameter, passed through the wall of the building about 6 feet from the
conductor, and was carried in a direction corresponding with the hole
caused by the explosion (see plan). I immediately concluded that this
explosion was due to the current breaking across from the conductor to
the gas-pipe, and on opening up the hole I found this to be the fact.
The conductor crossed the gas-pipe at nearly a right angle, being about
a foot above it. The under portion of the conductor bore evident marks
of fusion, and, more interesting still, the gas-pipe was slightly coated
with a very thin deposit of copper, so thin that it perished in my
attempt to remove it; but still there was an undoubted coating at one
spot. But for the proximity of the conductor to the gas-pipe, the earth
resistance of the former would doubtless have been greater than it was,
and the damage would probably have been increased.

I was sorry that no means existed for examining the ornamental ridge,
but doubtless the metallic contact between the sections was very
imperfect, and to this cause was due the rupture of the pinnacle.

The fact, too, that the protector did not prevent the south-western
portion of the building being struck bears on the question of the area
made safe by a protector.

The tower stood 89 feet above the ground, the top of the iron pinnacle
99 feet, and the protector extended 1 foot 6 inches above the latter,
thus reaching a total height of 100 feet 6 inches. The total length of
the church was 123 feet.

The point C where the gutter was struck was 84 feet in a direct line
from the conductor, and stood 24 feet above the ground. This gives a
vertical height of the conductor of 76 feet 6 inches above the point
struck, the distance of the latter being a radius 8 feet greater than
the height of the former.

                                                               J. GAVEY.

                                             CARDIFF,
                                                   _January 10th, 1880_.


  ACCIDENT AT BOOTHAM BAR, YORK, COMPILED FROM NOTES AND MEASUREMENTS
                       TAKEN BY J. EDMUND CLARK.

The discharge occurred about 3 a.m., 22nd June, 1876. The principal
injury occurred to the bracket lamp at A. This lamp, which was an
ordinary street one, was supported by an iron bracket 2 ft. 6 in. long,
and 11 ft. 6 in. above the pavement. The gas was conveyed to it by 11
ft. 6 in. of vertical iron gas barrel, and thence to the burner by about
3 ft. of ordinary ½ in. composition pipe. The glass of the lamp was not
broken, but about 18 inches of the composition piping was twisted and
split open as with a sharp knife, and the other 18 inches was melted;
the gas was ignited and burning from the top of the iron barrel, thus
producing a large flame which ignited the house to which it was fixed.
That part of the lead pipe which was inside the lamp was uninjured,
whence it would appear that the point struck was at or near to the top
of the iron gas barrel; and this is supported by the fact that the lead
over the shop window and close to the bracket was turned up off the
wood-work.

The lamp, as will be seen by the plan, is attached to the corner of a
house, the eaves of which were 20 ft. above the lamp, while the ridge,
with a little lead flashing, was 24 ft., and the chimney pots were 31
ft. above the lamp, and not 15 ft. distant horizontally. This house was
slated and had wood gutters, and an iron rain-water pipe, but the latter
was 33 ft. horizontally from the point struck. The wooden gutters were
very old and rotten, and one of them was very slightly shifted; it is
not certain that this was done by the lightning, and there was no other
indication of its presence.

C is a lamp bracket extending 4 ft. from the wall of the house, and at D
are two old iron brackets.

At the distance of only 8 ft. from the lamp in the opposite direction
(N.W. of the lamp) rises Bootham Bar, a massive stone structure, of
which the four turrets rise to 44 ft. 3 in. above the pavement, and
therefore 33 ft. above the lamp. The whole roof, about 750 square feet,
is covered with thick sheet lead, and the building also contains the old
portcullis B heavily shod with iron.

The noteworthy feature of the case appears to be, that the only injury
is found at a spot surrounded by objects close to it, and greatly
exceeding it in height; in fact, that the lightning dipped into a sort
of cavity, instead of striking at the higher objects.

It is evident that in this case, although the composition pipe was
melted, the _iron_ one afforded ample conduction, and the city gas mains
a perfectly safe earth terminal.

[Illustration:

  SOUTH-EAST VIEW OF BOOTHAM BAR.
]

                     ACCIDENT AT BOOTHAM BAR, YORK.

[Illustration:

  VIEW OF HOUSE AND SECTION OF BAR.
]

[Illustration:

  GROUND PLAN OF HOUSES AND OF BAR.
]

                              REFERENCES.

                      A Gas bracket struck.
                      B Iron sheathed portcullis.
                      C Old gas bracket.
                      D Old Iron brackets.




                              APPENDIX J.

  DATA RESPECTING THE SECTIONAL AREA OF METAL REQUISITE FOR LIGHTNING
                              CONDUCTORS.


  (N.B.—In order to avoid confusion, all areas of iron have been reduced
      to ⅙th of their actual sizes, so that virtually tables I. and II.
      may be regarded as giving all details for _copper_—but the metal
      is specified in each case.)


                    TABLE I.—LIST OF METALS MELTED.

 ───────────────────┬────┬─────────────────┬────────────────────────────
      Material      │Form│      Size       │          REMARKS
 ───────────────────┼────┼─────────┬───────┼────────────────────────────
                    │    │Diameter.│Area of│
                    │    │         │Copper.│
 ───────────────────┼────┼─────────┼───────┼────────────────────────────
                    │    │   in.   │  in.  │
 COPPER             │Rod │·35      │·10    │Duprez, App., p. 92
 COPPER             │Rope│·31      │·075   │At Nantes, Callaud’s
                    │    │         │       │  _Traité_, p. 89
 [6]_Not Specified._│Rope│         │·07    │At Carcassone, Callaud’s
                    │    │         │       │  _Traité_, p. 89
 IRON               │Rod │         │·03    │Harris on Thunderstorms, p.
                    │    │         │       │  109
 BRASS              │Rod │·20      │·03    │Duprez, App., p. 92
 COPPER             │Rod │·13?     │·01?   │Sullivan, App., p. 195
 ───────────────────┴────┴─────────┴───────┴────────────────────────────

Footnote 6:

  Assumed to have been Iron, the dimension given is “18 mm.” = ·70 in.
  diam., or ·38 in. area.


                TABLE II.—REMARKS RESPECTING DIMENSIONS.

 ───────────────────┬────┬─────────────────┬────────────────────────────
      Material      │Form│      Size       │          REMARKS
 ───────────────────┼────┼─────────┬───────┼────────────────────────────
                    │    │Diameter │Area of│
                    │    │         │Copper.│
 ───────────────────┼────┼─────────┼───────┼────────────────────────────
                    │    │   in.   │  in.  │
 COPPER             │Rod │         │·61    │Trinity House smallest,
                    │    │         │       │  App., p. 183
 COPPER             │Rod │·75      │·44    │Will carry any flash, Harris
                    │    │         │       │  on _Thunderstorms_, p. 115
 COPPER             │Rod │·50      │·20    │Never yet failed, Faraday,
                    │    │         │       │  App., p. 89
 COPPER             │Tube│         │·20    │War Office smallest, App.,
                    │    │         │       │  p. 70
 COPPER             │Tape│         │·19    │Gray & Son’s smallest, App.,
                    │    │         │       │  p.
 IRON               │Rod │         │·16    │Never affected, Franklin,
                    │    │         │       │  App., p. 52
 COPPER             │Any │         │·11    │Recommended by Phin, App.,
                    │form│         │       │  p. 103
 IRON               │Rod │         │·11    │More than sufficient, Gay
                    │    │         │       │  Lussac, App., p. 58
 COPPER             │Rope│·38      │·11    │Recommended by Callaud,
                    │    │         │       │  App., p. 104
 COPPER             │Tape│         │·09    │Freeman & Collier’s
                    │    │         │       │  smallest, App., p. 10
 IRON               │Rod │         │·08    │Never known to be melted,
                    │    │         │       │  Pouillet, App., p. 62
 IRON               │Rod │         │·08    │Should not be less, Henry,
                    │    │         │       │  App., p. 99
 COPPER             │Rope│·39      │·06    │Carried off heavy discharge,
                    │    │         │       │  Callaud _Traité_, p. 89
 IRON               │Rod │         │·06    │Recommended by Callaud,
                    │    │         │       │  App., p. 104
 IRON               │Rod │         │·06    │Recommended by Mohn, App.,
                    │    │         │       │  p. 107
 COPPER             │Rod │·25      │·05    │Recommended by Mohn, App.,
                    │    │         │       │  p. 107
 IRON               │Rod │         │·04    │Recommended by Phin, App.,
                    │    │         │       │  p. 103
 COPPER             │Rod │·20      │·03    │Recommended by Zenger, App.,
                    │    │         │       │  p. 106
 IRON               │Rope│         │·02    │Recommended by Mann, App.,
                    │    │         │       │  p. 108
 IRON               │Wire│         │·01    │Sufficient for any house,
                    │    │         │       │  Preece, App., p. 101
 ───────────────────┴────┴─────────┴───────┴────────────────────────────


                  DIMENSIONS OF LIGHTNING RODS—COPPER.

  _Partly extracted from the Appendix at the pages quoted, and partly
    compiled from specimens collected by the Conference, and from trade
    circulars._

 ────────────┬────────┬───────┬─────────┬───────────┬────┬──────┬────────────
             │        │       │         │           │    │Weight│Remarks, and
   Pattern   │Diameter│Breadth│Thickness│Superficies│Area│ per  │ References
             │        │       │         │           │    │ foot │     to
             │        │       │         │           │    │      │Appendices.
 ────────────┼────────┼───────┼─────────┼───────────┼────┼──────┼────────────
             │ Inches │Inches │  Inch   │  Inches   │Inch│ oz.  │
             │        │       │         │           │    │      │
             │Ext. 1½ │       │         │ Ext. 4·71 │    │      │Sir W. Snow
 TUBE        │ Int. 1 │       │    ¼    │ Int. 3·14 │ ·98│    60│  Harris
             │        │       │         │           │    │      │  (49)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Trinity
 HEMICYLINDER│   1½   │       │         │   3·86    │ ·88│    54│  House,
             │        │       │         │           │    │      │  Mains
             │        │       │         │           │    │      │  (183)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Trinity
 HEMICYLINDER│   1¼   │       │         │   3·21    │ ·61│    37│  House,
             │        │       │         │           │    │      │  Branches
             │        │       │         │           │    │      │  (183)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Freeman &
 TAPE        │        │   3   │  3/16   │   6·38    │ ·56│    34│  Collier’s
             │        │       │         │           │    │      │  largest
             │        │       │         │           │    │      │  (10)
             │        │       │         │           │    │      │
 TUBE        │Ext. 1½ │       │    ⅛    │ Ext. 4·71 │ ·54│    33│
             │Int. 1¼ │       │         │ Int. 3·93 │    │      │
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Faraday
             │        │       │         │           │    │      │  preferred
 ROD         │   ¾    │       │         │   2·35    │ ·44│    27│  this to
             │        │       │         │           │    │      │  smaller
             │        │       │         │           │    │      │  (89)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Gray & Son’s
 TAPE        │        │   3   │    ⅛    │   6·25    │ ·37│    23│  largest
             │        │       │         │           │    │      │  (7)
             │        │       │         │           │    │      │
 TUBE        │ Ext. 1 │       │    ⅛    │ Ext. 3·14 │ ·34│    21│
             │ Int. ¾ │       │         │ Int. 2·36 │    │      │
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Sanderson’s
 TAPE        │        │   2   │    ⅛    │   4·25    │ ·25│    15│  largest
             │        │       │         │           │    │      │  (23)
             │        │       │         │           │    │      │
 TAPE        │        │  1½   │   ·15   │   3·30    │ ·23│    14│
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │War Office
             │        │       │         │           │    │      │  (70)
 ROD         │   ½    │       │         │   1·57    │ ·20│    12│  Sir W.
             │        │       │         │           │    │      │  Snow
             │        │       │         │           │    │      │  Harris
             │        │       │         │           │    │      │  (49)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │War Office
             │        │       │         │           │    │      │  (70)
 TAPE        │        │  1½   │    ⅛    │   3·25    │ ·19│    12│  “Smallest
             │        │       │         │           │    │      │  desirable”
             │        │       │         │           │    │      │  Gray & Son
             │        │       │         │           │    │      │  (7)
             │        │       │         │           │    │      │
 TUBE        │ Ext. ⅝ │       │    ⅛    │ Ext. 1·96 │ ·20│    12│War Office
             │ Int. ⅜ │       │         │ Int. 1·18 │    │      │  (70)
             │        │       │         │           │    │      │
 TAPE        │        │  2½   │  1/16   │   5·12    │ ·15│     9│J. Davis &
             │        │       │         │           │    │      │  Son (14)
             │        │       │         │           │    │      │
 ROPE (49    │        │       │         │           │    │      │Pennycook &
   square    │   ⅔    │       │         │   10·78   │ ·15│     9│  Co.
   wires)    │        │       │         │           │    │      │
             │        │       │         │           │    │      │
 TAPE        │        │   2   │  1/16   │   4·12    │ ·13│     8│
             │        │       │         │           │    │      │
 TAPE        │        │   1   │    ⅛    │   2·25    │ ·13│     8│Phin, of New
             │        │       │         │           │    │      │  York (103)
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │{Massingham
 ROPE (49    │   ½    │       │         │   8·00?   │ ·10│     6│  (15)
   wires)    │        │       │         │           │    │      │  Newall’s
             │        │       │         │           │    │      │  Rope
             │        │       │         │           │    │      │
 TAPE        │        │  1½   │  1/16   │   3·12    │ ·09│     6│
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Freeman &
 TAPE        │        │   ¾   │    ⅛    │   1·75    │ ·09│     6│  Collier’s
             │        │       │         │           │    │      │  smallest
             │        │       │         │           │    │      │  (10)
             │        │       │         │           │    │      │
             │ Ext. ⅞ │       │         │ Ext. 2·75 │    │      │
 TUBE        │  Int.  │       │  1/32   │ Int. 2·55 │ ·08│     5│
             │ 13/16  │       │         │           │    │      │
             │        │       │         │           │    │      │
 ROPE (36    │        │       │         │           │    │      │
   wires &   │  7/16  │       │         │   5·00?   │ ·08│     5│J. Davis &
   hemp      │        │       │         │           │    │      │  Son (14)
   centre)   │        │       │         │           │    │      │
             │        │       │         │           │    │      │
 SPRATT’S    │        │       │         │           │    │      │
   PATENT    │        │  1⅓   │         │   4·52    │ ·08│     5│
   PLAIT (20 │        │       │         │           │    │      │
   wires)    │        │       │         │           │    │      │
             │        │       │         │           │    │      │
 TAPE        │        │   1   │  1/16   │   2·12    │ ·06│     4│
             │        │       │         │           │    │      │
 ROPE (49    │   ⅜    │       │         │   6·00?   │ ·06│     4│Newall’s
   wires)    │        │       │         │           │    │      │  Rope
             │        │       │         │           │    │      │
             │        │       │         │           │    │      │Sanderson’s
 TAPE        │        │   ⅝   │  1/12   │   1·42    │ ·05│     3│  smallest
             │        │       │         │           │    │      │  (23)
             │        │       │         │           │    │      │
 SPRATT’S    │        │       │         │           │    │      │
   PATENT    │        │   1   │         │   3·16    │ ·05│     3│
   PLAIT (14 │        │       │         │           │    │      │
   wires)    │        │       │         │           │    │      │
             │        │       │         │           │    │      │
 HART’S PLAIT│        │       │         │           │    │      │
   (13 copper│        │       │         │           │    │      │
   wires and │        │       │         │   3·08    │ ·05│     3│
   1 zinc    │        │       │         │           │    │      │
   one)      │        │       │         │           │    │      │
 ────────────┴────────┴───────┴─────────┴───────────┴────┴──────┴────────────




                              APPENDIX K.

NOTES RESPECTING LIGHTNING CONDUCTORS, COLLECTED IN PARIS IN MAY, 1881,
                      BY MESSRS. PREECE & SYMONS.


The information which we obtained may perhaps be most conveniently
grouped under the names, arranged in alphabetical order, of the
authorities whose opinions or whose practice we quote. These gentlemen
are M. Androuët, who, under the direction of M. Alphand, the City
Engineer, has charge of all the lightning conductors attached to the
municipal buildings of Paris, M. Borrel, of 47, rue des Petits Champs,
who has been making lightning conductors nearly all his life, M. le
Comte du Moncel, who is well known as perhaps the highest authority in
France upon the practical application of electricity, and lastly M.
Jarriant who is manufacturer to the municipality, and also, we believe,
to the War Department, besides having a large connection among
architects and engineers.

                  *       *       *       *       *

M. ANDROUËT accompanied us in a thorough examination of the conductors
as they are now fixed upon the south gallery of the Louvre, temporarily
occupied as the Hotel de Ville de Paris. They were stated to be only
temporarily fixed, because the offices of the Préfet of the Seine will
be removed to the new Hotel de Ville as soon as it is rebuilt, but they
were said nevertheless to be in almost all respects conformable to the
instructions issued by the municipality. The _tiges_ were iron rods, 10
m. (33 feet) high, with rather blunt terminals of gilded copper; they
were 35 m. (115 ft.) apart. All were united by a horizontal copper rope,
½ inch diameter (used instead of iron bars 0·8 in. square, because of
the temporary nature of the work), which was led along the roof through
iron holdfasts or crutches, which were carefully soldered to the metal
roof. All joints in the rope were spliced and heavily soldered. For
æsthetic reasons the main conductor is carried down _inside_ the
building, through various closets, &c., and finally, after a rather
circuitous course, it finds its earth terminal in a plate of copper 1 m.
(3 ft. 3 in.) square, immersed in the Seine. Although the roof is well
covered with metal no separate connections with earth are made. M.
Androuët tests the conductivity from every _tige_ in the spring of each
year, using a very portable apparatus, consisting of two Leclanché’s
cells and a trembling bell.

                  *       *       *       *       *

M. BORREL showed us various specimens of conductors, of earth terminals,
and also his portable testing apparatus. He also gave us a copy of the
_Instruction sur les Paratonnerres_, which he issues, and from which we
make a few extracts, especially as in several respects M. Borrel’s views
are expressed with unusual clearness, and although in holding some of
them he stands alone:

“A lightning conductor is a preventive agent destined to convey to moist
earth, or preferably to water, the electricity contained in a cloud.
When strong earth tension is produced by the passage of an oppositely
electrified cloud, the beneficial action of the conductor is indicated
by the luminous brush discharge from the top of the conductor.

“It is generally considered that a conductor protects a cone of
revolution, having for its base the height of the point above the roof
multiplied by 1·75, and for its summit the point. If, therefore, the
point be 6 m. (20 ft.) above the roof, it will protect a base 10½ m. (35
ft.) radius. M. Borrel supplies round upper terminals of galvanised
wrought iron about 10 m. (33 ft. high), and tapering from a diameter of
4 inches at the base to ¾ inch at the top.

“Having found that long exposure to the weather destroys iron wire
ropes, and even copper ones, if made of many small wires, he has adopted
where ropes are necessary, four or five rods nearly 0·20 in. diameter,
so slightly twisted as not to strain the metal. By this means the
numerous interstices of the ordinary ropes are avoided, and much greater
durability is insured.

“Where iron bars are used he employs galvanised wrought iron in square
bars, the sides ranging from 0·63 in. to 0·90 in.

“To allow for variations of length produced by changes of temperature,
he always inserts, in long roof conductors, a compensator, which is
merely a loop of copper tape.

“M. Borrel says that it is especially upon the earth connection that the
efficacy of a conductor largely depends; there must be a metallic mass,
with a large surface, and he describes his pattern of ‘_perd fluide_.’
It is composed of two sheets of galvanised wrought iron 3 ft. long, 6½
in. wide, and ½ an inch thick, hacked into sharp points in order to
facilitate the discharge of the electricity. He alludes to Callaud’s
basket of coke, but says that its efficiency has not been absolutely
demonstrated. M. Borrel insists upon the _perd fluide_ being immersed in
the water of a well, and one preferably not less than 2 ft. in diameter.
He strongly objects to insulators, and says that he always makes
metallic connection between the gutters, rain-water pipes, &c. and his
conductors. From the surface of the earth to 6 ft. above it, he encloses
his conductor in a wooden case in order that no one may touch it during
a storm.”

                  *       *       *       *       *

We had a long conversation with M. LE COMTE DU MONCEL, of whose remarks
the following is a _précis_:—

He objects to _square_ iron bars because their angles have a tendency to
facilitate lateral discharge.

He objects to conductors being painted, because he believes that the
surface of a conductor acts electro-statically. He knows that the brass
wire rope occasionally used for lighthouses is often destroyed, but
thinks that the theory enunciated in the Report of the Académie des
Sciences, 18th December, 1854 (see Appendix F., p. 62), can hardly be
maintained, and believes it to be more probable that the rope was in a
very bad state of oxidation.

Thinks that conductors should possess _both_ sectional area and surface.
Does not attach much importance to extremely sharp points, but thinks
that the suggestion of one stout central one to receive a disruptive
discharge, surrounded by three or four needles to facilitate silent
discharge, would be good.

The following statement was quoted from the Report of 20th May, 1875
(see Appendix F., page 68), that, “if a conductor cannot be led either
to the subterranean water or to a main water-pipe, no lightning rod
should be erected. It would do more harm than good.” Count du Moncel
said that the paragraph referred chiefly to buildings on large solid
rocks, but that obviously there is every degree of quality in the earth
contact which can be obtained; and that although it is easy to decide at
the two extremes, it is difficult to say how bad the earth must be in
order to render the erection of a conductor inadvisable.

                  *       *       *       *       *

M. JARRIANT, who is the manufacturer employed upon the Municipal
buildings of Paris (and author of two pamphlets, of which abstracts are
given in Appendix F, pages (111) and (115)), accompanied us through his
works, and afforded us all the information which we could desire.

He showed us a large collection of platinum points of various patterns,
ranging in cost from 12s. to 60s. each; he also showed us some which had
been employed by other makers, which were merely hollow sheaths of
platinum filled in with soft metal in order to reduce the cost.

He had also a large variety of upper terminals, including the patterns
used by the City of Paris, by the War Department for its military
establishments, and by civil engineers and architects.

We saw specimens of the ropes, rods, &c., usually supplied. The iron
ropes were galvanized and ¾ in. diameter. The copper ropes were made of
six twisted strands of copper wire enclosing a central core of hemp, the
total diameter being ½ an inch. The iron bars were square galvanized
wrought iron 0·80 in. square, in lengths of 16½ feet, rabbetted at the
ends with two holes for bolts. To make a joint a strip of foil is laid
between the two faces, the bolts are screwed up, and then the whole
joint is very heavily soldered.

Among various works in progress, we saw a highly decorated wrought iron
cross for the roof of a church, which cross would become the summit of
the conductor, its top and the extremity of each arm being furnished
with a short copper terminal tipped with a platinum point.

We were much struck by the fact that in France, where so much attention
has been given to lightning protection, there should be so much
diversity of practice. The Municipality adopt one system, the State
another, the War Department a third, and each individual manufacturer
has, as in England, his hobby.

We desire to record our thanks to Mr. J. Aylmer, C.E., for making the
various arrangements, by which we were able to see so much in the
comparatively short time at our disposal, and also for accompanying us
throughout.

                                                           W. H. PREECE.

                                                           G. J. SYMONS.

P.S.—A very convenient form of a rough testing apparatus has been made,
by the Silvertown Co., for one of the writers; it consists of one
Leclanché cell, a trembling bell, a key, and a pair of terminals to
attach insulated wires to the top and bottom of the lightning rod, all
fixed in a neat portable mahogany box, and with its aid any one can
readily examine the conductivity of his lightning rod.




                              APPENDIX L.

   ON THE LIGHTNING CONDUCTORS AT THE PARIS INTERNATIONAL ELECTRICAL
               EXHIBITION, BY MESSRS. DYMOND AND SYMONS.


It was hoped that at the Paris Electrical Exhibition would be found
examples of the various styles and patterns of lightning rods used in
the several countries of Europe and in the United States, and we
accordingly visited the Exhibition and inspected all the exhibits in any
way relating to the subject.

Those from France were naturally the most numerous (15), but there were
some very elaborate specimens of the system adopted in Belgium, in
accordance with the recommendations of M. Melsens; and there was also
sent by Dr. Weber, of Kiel, a very interesting collection of 12 points
which had been struck by lightning, all more or less fused and damaged.

The French exhibitors showed a great variety of points, but they were
for the most part referable to two or three types or classes, and only
varied in size. The favourite form appeared to be that shown by Fig. 1,
a rather finely tapering brass rod terminated by an acornshaped piece,
from the upper end of which projected a small needle. They were
constructed to be screwed to the top of the iron _tige_. They varied in
size from 1 ft. long and ¾ in. diameter at the base, tapering to ¼ in.
at the acorn, to 2 ft. 6 in. long and 1¼ in. diameter, tapering to ¼ in.
The acorns were generally about twice the diameter of the point to which
they were joined, and were about 1½ diameter long. The needles were
always made of platinum about 1½ in. long and ·1 in. diameter. Some
exhibitors showed a very similar pattern, but made in copper instead of
brass. There were also several specimens of blunt points in copper—the
_Point Municipal_, Fig. 2, tapering from 1 in. to ½ in. diameter and 1
ft. 8 in. long; tapering brass and iron rods, some of them having
platinum cones, were also exhibited. All these points were intended to
be mounted on exceedingly long upper terminals.

The conductors were generally made of wire rope, copper, brass, or
galvanized iron, and in the majority of cases composed of strands of
small wires, though there were a few specimens of ropes made of large
wires (say) ·1 in. in diameter; and there were also some specimens of
conductors made of iron bars with copper expansion bands. These last
specimens were about ·8 in. square, but almost all the ropes seemed to
us too small, generally about ·4 in. diameter, and we were surprised to
see that the iron ropes were no larger than the copper or brass ones.

[Illustration:

  4
]

[Illustration:

  3
]

[Illustration:

  2
]

[Illustration:

  1
]

The methods adopted for joining them to the upper terminals were either
to push the end into a socket and pin them across, or more frequently to
tie them more or less loosely round the base.

The practice as to insulation seemed to vary, some makers supplying
insulators and others not, but they almost all provided for carrying the
conductor from 6 to 9 in. away from the face of the building.

There were but few specimens of earth plates, they were in the form of
grapnels, and seemed very inadequate; not one would afford 3 superficial
feet of earth contact.

Some models and drawings showed that the French electricians assumed a
cone of protection whose radius was at least 1·75 of its height. (See
ante page (67).)

Excepting France the most numerous series of exhibits was that from
Belgium, which also contained a complete model of the monument erected
at Lacken in memory of Leopold I., showing the manner in which it had
been fitted with conductors under the superintendence, or according to
the system, of M. Melsens.

The monument referred to is a ten-sided Gothic building, with pinnacles
on two storeys and a spire. On the top of the spire, but below the
figure, is a considerable number of radiating points, and there is a
similar frill round the top of each of twenty pinnacles. Each aigrette
consists of seven copper points, each about 0·4 in. in diameter and 2
ft. long, tapering to a very sharp point; they are all leaded into a
collar or band encircling the stone work; and from them go the rods
about 0·4 in. in diameter, which are first taken into a cast iron box
about 8 in. × 5 in. × 2 in.; into this box are also taken rods which
lead to connections with (1) a well, (2) the water mains, and (3) the
gas mains. When these two series of rods are all in position in the box
it is filled with melted lead, and thus perfect connection is secured.
There were specimens of the aigrette, and also of the manner of joining
the rod to the gas and the water mains, and to the large iron pipe which
is sunk in the well. This is effected by bringing all the rods parallel
with the main, and arranging them, at equal distances from each other,
around it. They are then held tightly to it by two semicircular clamps
bolted together, and melted lead is poured in and caulked. The main, and
probably the inside of the clamps, was filed bright when the joint was
made.

The other exhibits—patterns of points and conductors—do not call for any
special mention, but we may notice that the Belgian makers were
generally much more careful than the French to make good electric
contact at the joints, and some conductors were exhibited cut through
the joints to show the care bestowed in this particular.

From Germany were sent some specimens of wire rope for conductors, made
of the usual strands of small wires. The iron ropes were slightly larger
and of slightly larger wires than the copper, but the former were not
more than 0·6 in. in diameter.

                  *       *       *       *       *

Dr. WEBER, of Kiel, exhibited a collection of 12 points, all which have
been struck by lightning—their length varies from 4 in. to 7 in., they
are of gilded copper, about 1 in. in diameter at the thickest point, and
vary in the acuteness of their extremities—some have platinum needles,
about 0·08 in. diameter, screwed into their points; these needles have,
in most cases, been wholly fused. In some cases the platinum is somewhat
thimble-shaped, and fitted over the copper—in these cases the platinum
is generally wholly melted, and the copper uninjured. Platinum of 0·12
in. diameter has been melted, but there is not one of these points of
which copper of that size has been fused. There is no indication that
these points have been fixed to tiges—on the contrary, they are all
hollow at the base, and have had soldered into them copper ropes, none
exceeding 0·33 in. diameter, and most of them consisting of three
strands of six wires each (=18 wires), the wires being about No. 18
B.W.G.

There were a few specimens of gilded copper points, sent from Austria,
such as Fig. 3; and our English makers also sent a few examples of
points, the crow foot, Fig. 4, for instance, of upper terminals, and of
rope and tape conductors.

                                                           E. E. DYMOND.

                                                           G. J. SYMONS.




                              APPENDIX M.

                             MISCELLANEOUS.


  MEANS TO BE ADOPTED FOR ENSURING PERSONAL SAFETY FROM THE EFFECTS OF
                               LIGHTNING.

            (_Abstracted by Prof. G. Carey Foster, F.R.S._)

WORKS CONSULTED:—

                                                   │Received from the
 _Correspondence_ addressed to Lightning Rod       │  Secretary of
   Conference.                                     │  Lightning Rod
                                                   │  Conference.
 Directions for Insuring Personal Safety during    │
   Storms of Thunder and Lightning; and for * * *  │
   By _John Leigh_, pp. 60. London (no date).      │

 _Benjamin Franklin._ Complete Works. 3 vols. 8vo. London, 1806.

 _Gehler._ Physikalisches Wörterbuch. Article “_Blitz_,” Leipzig, 1825.

 _François Arago._ Meteorological Essays, from the French by Sabine.
   London, 1855.

 _C. Kuhn._ Handb. d. angewandten Elektricitätslehre. Leipzig, 1866.

The danger to men and animals from the effects of lightning arises from
the fact that the bodies of living animals form comparatively good
conductors of electricity,—better, that is, than rain-water (probably
better even than sea-water), or than trees, walls of brick or stone,
hay-stacks, or in fact than almost any common objects consisting of
non-metallic materials. It may be assumed that the path of a
lightning-discharge striking the earth is determined by the line of
least inductive resistance between the thunder-cloud and the earth.[7]
Hence, a man standing on an open plain, or walking, or riding on
horseback, or in an open vehicle, across it, is liable to be struck by
lightning. There is no evidence that the motion of walking or riding
makes the liability either greater or less than it would be if he were
at rest. The danger is increased, other conditions being the same, by
nearness to water, or to large masses of metal, or other conducting
material, lying flat on the ground or rising only a little way from it.
An umbrella held over-head is probably dangerous, but I do not find
direct evidence that it is so among recorded cases.[8] Such small
metallic articles—money, keys, &c.,—as may be commonly carried in the
pocket, have probably no perceptible effect. In the open country, beyond
the reach of shelter, low-lying positions, if dry, are safer than those
which are more elevated and exposed; but, on the other hand,
water-courses are to be avoided. It is also safer to lie flat on the
ground than to stand or sit. If shelter is within reach, care should be
taken to get _completely under cover_. There is often much more danger
in standing under the lee of a house, or wall, or hay-stack, or thicket
of trees, than in remaining quite exposed. There is but little danger,
however, _inside_ a barn or outhouse, as far as possible from the walls,
or _underneath_ a wagon or the arch of a bridge. The inside of a wood is
also a tolerably safe situation if we keep clear of the branches of the
trees and as far as may be from their trunks. If isolated trees afford
the only shelter within reach, it is advisable to go _near_ them (within
two or three yards of their projecting branches) but not _under_ them.
Leaning against the trunk of an isolated tree during a thunderstorm is
very dangerous. In this case the danger arises from the fact that the
tree is a much better conductor than the air surrounding it, though a
worse conductor than the human body. Hence, if a man stands against a
tree, a line of least inductive resistance is likely to be determined
through his body and continued upwards through the tree. Like
considerations apply in the case of a person standing against a wall, or
other high object, consisting of very imperfectly conducting materials
and unprovided with efficient lightning conductors.

Footnote 7:

  The apparently capricious way in which lightning often strikes is not
  inconsistent with this statement. It proves, however, that the line of
  least inductive resistance is partly determined by atmospheric or
  terrestrial conditions which are not perceived by the eye.

Footnote 8:

  Is there any evidence to show that soldiers wearing spiked helmets, or
  marching with fixed bayonets, are specially liable to be struck by
  lightning? Various ancient writers—Cæsar, Seneca, Livy, Pliny, and
  others—mention luminous appearances (“Fire of St. Elmo”) presented by
  the javelins or pikes of soldiers during thunderstorms at night.

As to people indoors, we need only consider the case of those who are in
buildings which are either not at all or only imperfectly protected by
conductors; for, if a building is thoroughly protected, whatever is
inside it is protected also. Indoors, as out of doors, we have to avoid
forming part of a line of least inductive resistance. This consideration
leads to such rules as the following:—Keep to the lower rooms of a
house, rather than to the upper rooms; also keep as much as possible in
the middle of the room you are in, but avoid being under a metal
chandelier, or a lamp, or other object hung by a metal chain or wire;
keep away from a stove or fire-place, _especially when a fire is
burning_ in it; keep away from large metallic objects which are not in
electrical connection with the ground, especially if they are above the
level of the head (as mirrors, or pictures with gilt frames, hung
against the wall), or below the feet (as an iron pillar or beam
supporting the floor, or an iron staircase leading to a lower storey but
not continued to one above). Franklin recommends “sitting in one chair
and laying the feet up in another,” or as a further precaution “to bring
two or three mattresses or beds into the middle of the room, and,
folding them up double, [to] place the chair upon them.” But best of all
he says is, “where it can be had, a hammock, or swinging bed suspended
by silk cords equally distant from the walls on every side, and from the
ceiling and floor above and below.” Doors and windows are better shut
than open, but it does not seem that this condition is of much
importance.

It may be added for the comfort of the timid that Arago concludes that
the danger of being struck by lightning in a town (Paris) “is less than
the danger of being killed in passing along the street by the fall of a
chimney, or flower-pot, or of a workman engaged upon a roof; this latter
danger being [he imagines] one which occasions very little uneasiness.”
Also it seems to be the universal testimony of those who have been
restored after being struck by lightning that they had not been
conscious of either thunder or lightning. We may accordingly conclude
that all danger from a given discharge is over, not merely by the time
we hear the thunder, but as soon as ever we see the flash.

                                                                G. C. F.


              INJURY TO GAS AND WATER-PIPES BY LIGHTNING.

The city gas company of Berlin, having expressed the fear that gas-pipes
may be injured by lightning passing down a rod that is connected with
the pipes, Professor Kirchhoff has published the following reply:—

“As the erection of lightning-rods is older than the system of gas and
water-pipes as they now exist in nearly all large cities, we find
scarcely anything in early literature in regard to connecting the earth
end of lightning-rods with these metallic pipes, and in modern times
most manufacturers of lightning-rods, when putting them up, pay no
attention to pipes in or near the building that is to be protected.”
Kirchhoff is of the opinion, supported by the views of a series of
professional authorities, that the frequent recent cases of injury from
lightning to buildings that had been protected for years by their rods,
are due to a neglect of these large masses of metal. The Nicolai Church,
in Griefswald, has been frequently struck by lightning, but was
protected from injury by its rods. In 1876, however, lightning struck
the tower and set it on fire. A few weeks before, the church had had
gas-pipes put in it. No one seems to have thought that the new masses of
metal which had been brought into the church could have any effect on
the course of the lightning, otherwise the lightning-rods would have
been connected with the gas-pipes, or the earth connection been
prolonged to proximity with the pipe. A similar circumstance occurred in
the Nicolai Church in Stralsund. The lightning destroyed the rod in many
places, although it received several strokes in 1856, and conducted them
safely to the earth. Here, too, the cause of injury was in the neglect
of the gas-pipes, which were first laid in the neighbourhood of the
church in 1856, shortly before the lightning struck it. The injury done
to the school-house in Elmshorn, in 1876, and to the St. Lawrence’
Church, at Itzehoe, in 1877, both buildings being provided with rods,
could have been avoided if the rods had been connected with the adjacent
gas-pipes.

“If it were possible,” says Kirchhoff, “to make the earth connection so
large that the resistance which the electric current meets with when it
leaves the metallic conducting surface of the rod to enter the moist
earth, or earth water, would be zero, then it would be unnecessary to
connect the rods with the gas and water-pipes. We are not able, even at
immense expense, to make the earth connections so large as to compete
with the conducting power of metallic gas and water-pipes, the total
length of which is frequently many miles, and the surface in contact
with the moist earth is thousands of square miles. Hence the electric
current prefers for its discharge the extensive net of the system of
pipes to that of the earth connection of the rods, and this alone is the
cause of the lightning leaving its own conductor.”

Regarding the fear that gas and water-pipes could be injured, the author
says: “I know of no case where lightning has destroyed a gas or
water-pipe which was connected with the lightning-rod, but I do know
cases already in which the pipes were destroyed by lightning because
they were not connected with it. In May, 1809, lightning struck the rod
on Count Von Seefeld’s castle, and sprang from it to a small water-pipe,
which was about 80 metres from the end of the rod, and burst it. Another
case happened in Basel, July 9, 1849. In a violent shower one stroke of
lightning followed the rod on a house down into the earth, then jumped
from it to a city water-pipe, a metre distant, made of cast iron. It
destroyed several lengths of pipe, which were packed at the joints with
pitch and hemp. A third case, which was related to me by Professor
Helmholtz, occurred last year in Gratz. Then, too, the lightning left
the rod and sprang over to the city gas-pipes; even a gas explosion is
said to have resulted. In all three cases the rods were not connected
with the pipes. If they had been connected the mechanical effect of
lightning on the metallic pipes would have been null in the first and
third cases, and in the second the damage would have been slight. If the
water-pipes in Basel had been joined with lead instead of pitch, no
mechanical effect could have been produced. The mechanical effect of an
electrical discharge is greatest where the electric fluid springs from
one body to another. The wider this jump the more powerful is the
mechanical effect. The electrical discharge of a thunder cloud upon the
point of a lightning rod may melt or bend it, while the rod itself
remains uninjured. If the conductor, however, is insufficient to receive
and carry off the charge of electricity, it will leap from the conductor
to another body. Where the lightning leaves the conductor its mechanical
effect is again exerted, so that the rod is torn, melted, or bent. So,
too, is that spot of the body on which it leaps. In the examples above
given it was a lead pipe in the first place, a gas-pipe in the last
place, to which the lightning leaped when it left the rod, and which
were destroyed. Such injuries to water and gas-pipes near lightning-rods
must certainly be quite frequent. It would be desirable to bring them to
light, so as to obtain proof that it is more advantageous, both for the
rods and the building which it protects, as well as for the gas and
water-pipes, to have both intimately connected. Finally, I would mention
two cases of lightning striking rods closely united with the gas and
water-pipes. The first happened in Düsseldorf, July 23rd, 1878, on the
new Art Academy; the other August 19th, last year, at Steglitz. In both
cases the lightning-rod, the buildings, and the pipes were
uninjured.”—_Deutschen Bauzeitung._ Quoted in _The Building News_, Sept.
10, 1880.


                 COLLIERY WORKINGS STRUCK BY LIGHTNING.

                   THE INSTITUTE OF MINING ENGINEERS.

A meeting of the members of the North of England Institute of Mining and
Mechanical Engineers took place in the Wood Memorial Hall on Saturday,
Mr. G. C. Greenwell in the chair, when the secretary read an account of
an investigation which had been made into a statement that lightning had
entered Tanfield Moor Colliery on the 12th of July last, and traversed
the workings in several directions. Mr. Wm. Joicey kindly gave
permission to examine the witnesses of the occurrence, and the workings
of the colliery, so that a complete and accurate report could be drawn
up of the circumstance; and on the 30th of July, Mr. C. Berkley, Mr. J.
B. Simpson, Mr. W. H. Hedley, and the secretary went out to the
colliery, and were met by Mr. W. Joicey, one of the owners; Mr. Pringle,
the viewer; and Mr. Arkless, the resident viewer. The top of the working
shaft at the colliery is 34 fathoms from the Shield Row seam. An incline
bank leads northwards from the working shaft and ultimately reaches the
day by a drift, and a little to the south is an up-cast shaft. The
engine way leads south from the working shaft, and goes in-bye to a
goaf. Between the goaf and the working shaft are two down-cast shafts.
From what can be gathered the lightning passed down the working shaft
and struck the flat sheets, and then divided itself into two parts, one
of which went north up the incline way and probably passed out to the
day by the drift, where it was supposed to have left traces of its exit
in marks upon a bank near by. The other part went south along the engine
way; but after passing a point where it was noticed its further course
was not known. The thill of the seam is composed of soft sagger, and the
roof of strong post, both of which would offer great obstruction to the
absorption of the electric fluid; and the probability was that this
portion of the fluid had been dissipated in the goaf, or had forced an
exit by way of the down-cast shaft.

The evidence taken was appended.—Joseph Kirtley, back-overman, said a
light, distinct but not very bright, fell and struck the flat sheets,
and split up into several lights like a lot of lighted matches. He could
only see the light for a moment among the tub wheels. It struck the
puller-out, Wm. Watson, on the arm, and he complained that his arm was
numb, and when he got home it was yellow from the wrist to the elbow. A
heavy peal of thunder was heard very distinctly almost at the same
moment. No injury was done either in the shaft or on the road where the
lightning was said to have passed. He could liken it to nothing better
than a box of matches all struck at once.—James Offord, onsetter, said
he heard a crack like the report of a small pistol, and saw a light
close to his feet.—William Watson, puller-out at the bottom of the pit,
said he saw a flash of light come down and heard a noise like a gun: it
struck on the plate or flat sheet. He saw the light divide when it
struck. The light when it struck was very bright, but did not brighten
up the place to any distance.—Thomas Chrisp, a deputy, said he saw
something like a lot of fire flying, and thought the tram had cut the
point. It was as though a person had trodden upon matches and they had
gone off. The fire seemed a little larger than the light of a candle,
and to the best of his judgment came along the metals.—John Greener saw
a light on the rail about the size of a candle flickering, not steady.
It appeared to travel along the rail, and as it passed the tram made a
noise like the crack of a pistol, and he thought it was matches or
something on the way that was cracking.—John Hagan, a putter, said he
saw the lightning come along the plates. It caught him as it passed and
gave him a queer feeling in the legs. It made a sharp, cracking noise in
the plates like a gun.—George Chrisp, a siding minder, said he was about
50 yards from the shaft, and heard a cracking noise, and saw a bright
light and flash of fire against the big winding sheave, two feet
diameter, like five or six matches going off at once. There were no tubs
running by at the time.—Matthew Hardy, an engine flatter, who was about
100 yards along the shaft siding, said he saw a light like a spark from
a lamp, and there was a noise like a match being struck by a tub passing
over it. The light appeared to be close to him on the rope, which was
running.—It further appeared that the rails were fished; that it was not
noticed whether the lightning came down the rails or the rope; that it
was a self-acting incline; that a noise as of a pistol or gun shot was
heard when the light came to the tram; that a similar noise was heard as
the light left the tram; and that the metallic contact might have been
broken here by a fish-plate being off. The gentlemen who conducted the
inquiry had every reason to believe that the information thus obtained
forms a valuable record of the occurrence, and places beyond doubt the
possibility of lightning penetrating into the workings of collieries.—In
the course of the discussion which followed the reading of the paper,
Mr. A. L. Stevenson mentioned the occurrence of a similar circumstance
at Page Bank, about 10 years ago.—Professor Herschell said that in order
to produce an explosion the electric fluid must come in contact with a
highly explosive mixture; and the occurrence in question showed the
desirability of lightning conductors at collieries, and of the subject
being investigated by mining and electrical engineers.—Cordial votes of
thanks were given to the authors of the papers.—_Newcastle Daily
Journal._ October 5th, 1880.


  ACCIDENTS BY LIGHTNING AT THE SWAN COTTON MILL, CHADDERTON, OLDHAM.
                     REPORT BY J. DOHERTY, A.S.T.E.

  [On July 13th, 1880, during a thunderstorm, the large 400 light gas
    meter of this mill, though locked up in a cellar, and with no light
    near it, exploded, and the gas, which is supplied through a 4–inch
    main, was ignited. This was repaired, but on July 5th, 1881, during
    another thunderstorm, precisely the same accident occurred. At the
    request of Mr. Preece, F.R.S., Mr. Doherty, of H. M. Postal
    Telegraph Service, went and inspected the works, and forwarded the
    following report.—ED.]

                                                    _21st July, 1881._

  A very careful investigation of the Swan Mill premises has been
  made, with a view of arriving at some explanation of the recent
  injury to the gas meter, which was undoubtedly caused by lightning.
  The building is a large one, having for its internal supports a
  number of cast iron columns running from floor to basement, and on
  the top of the building, I am told, there are numerous iron gutters;
  round the various rooms are carried large iron gas pipes, and in
  numerous instances this gas piping is dead against the iron caps of
  the columns, thus the lightning may have struck any portion of the
  building, and the current have been conveyed, safely, by the gas
  piping to the large gas meter, where an imperfect joint
  (electrically imperfect) existed, viz., an india-rubber ring placed
  between the faces of the iron joint. It is to be regretted that the
  connecting pipes were not on the premises at the time of my visit,
  otherwise I could have spoken with a greater degree of certainty,
  but I have not the slightest doubt in my own mind as to the
  insulating ring between the joints being the cause of rupture.

  Tests were made, showing that the continuity of the present pipe is
  lessened by the existence of another india-rubber ring, and the
  oxidation of the connecting screws at another joint.

  I advised the Directors of the Spinning Company to connect the
  outlet and inlet main pipes by iron or copper wire straps. I feel
  convinced that if this had been done prior to 5th July the accident
  would not have occurred.

                                                           J. DOHERTY.


ESSAY ON THE EFFECTS OF HEAVY DISCHARGES OF ATMOSPHERIC ELECTRICITY, AS
 EXEMPLIFIED IN THE STORMS OF THE SUMMER OF 1846 * * * * AND REMARKS ON
 THE USE AND APPLICATION OF LIGHTNING CONDUCTORS. BY E. HIGHTON, ESQ.,
                                  C.E.

  (Transactions of the Society of Arts for 1846–47. London. Sm. 4to).

                 (_Abstracted by G. J. Symons, F.R.S._)

The author’s primary object in studying the subject was the discovery of
a method of protecting telegraphic apparatus from injury and danger.
That has long been accomplished, but some remarks in the Paper seem
worthy of extraction.

Mr. Highton went over St. George’s Church, Leicester, a few days after
it was wrecked by the lightning. He says that the sexton told him that
three minutes before the flash he had been tolling the curfew bell, and,
“while in the belfry, he noticed a kind of light on the clapper of the
bell, and heard also, as it were, a sort of hissing noise.”

[This seems to prove two things—(1) The fallacy of the old notion that
ringing the church bells sent away thunderstorms (see also ante, p.
(37);) and (2) that even very imperfect conductors, such as this
conductorless steeple, carry off much electricity by the silent or brush
discharge.—G. J. S.]

Mr. Highton found that the leaden flashings were frequently burst up,
the lead being sometimes forced up somewhat like a miniature volcano.
This he attributes to the explosion of confined atmospheric air, but
obviously water converted into superheated steam would yield a greater
expansive force.

The author quotes a case at Water Newton, Wansford, Northamptonshire,
where, although the Church had tower and spire, and the whole roof was
covered with lead, a tree 90 feet from the spire, and not one-third the
height of the spire, was struck, but the Church was not. This the author
attributes partly to the action of the leaves of the trees, and partly
to there being no iron or other vertical spouting to the Church.

Mr. Highton’s “Practical Rules” are _literatim et verbatim_:—

  1st. Where a building has any quantity of vertical metallic work, it
  is quite necessary, for its protection against Lightning, that it
  should have an artificial Lightning Conductor, (unless the materials
  of themselves form a natural one).

  2ndly. It is very desirable, that all metallic circuits, especially
  those in a vertical direction, should be metallically connected with
  the system of Lightning Conductors.

  3rdly. That, in many instances, a single insulated Lightning
  Conductor attached to a building may become positively injurious and
  dangerous; as it may cause many a cloud to discharge its electric
  force at that point, which would otherwise have passed over, and
  poured its power in some other channel.

  4thly. That, where Lightning Conductors are employed, they ought to
  be thoroughly well erected, and every course or channel that the
  Electric fluid has open to it carefully considered, and a division
  of the charge in those quarters provided against.

  5thly. That a Lightning Conductor, or a system of Lightning
  Conductors, where properly and scientifically erected, are perfect
  safeguards against the effects of heavy discharges of Atmospheric
  Electricity. But, if improperly applied, they may become a most
  dangerous addition to a building.

  6thly. That it is essentially necessary for the safety of the
  public, that all public buildings, and especially churches, should,
  if naturally deficient in safe and secure Lightning Conduction, have
  artificial Lightning Conductors erected for their protection.

  The above are given as a few general rules. It is difficult,
  however, and almost impossible, to lay down any fixed and definite
  rules for the erection of Lightning Conductors, to be applicable to
  _every_ building; as the very form, shape, and position of the
  building, and the _relative position_ of buildings in the immediate
  neighbourhood, so materially affect the data for the formation of
  those rules. In all cases, therefore, I consider it much better and
  safer for an Architect to call in a person of knowledge and
  experience in this branch of science, for directions for the proper
  erection of Lightning Conductors, than to trust to any printed rules
  whatever on the subject.

  That, as it is better in cases of illness where life is in danger to
  call in a medical man than to apply oneself the remedies set forth
  in works on medicine, so is it better, in the protection of
  buildings from the disastrous effects of Lightning, to trust only to
  the opinions and directions of those who have given to this
  difficult branch of science their study and attention.


                             THUNDERSTORMS.

                       BY PROFESSOR TAIT, F.R.S.

 [Delivered in the City Hall, Glasgow. Nature Aug. 12th, 19th, Sept. 2nd,
                               9th, 1880.]

           (_Abstracted by W. H. Preece, Esq., C.E., F.R.S._)

While a few years ago no qualified physicist would have ventured an
opinion as to the nature of electricity, now, thanks to Clerk-Maxwell,
electric and magnetic phenomena are regarded as mere stresses and
motions of the ether, and are brought within the resources of
mathematical analysis.

Thunderstorms are accompanied by darkness, the result of the intense
shadow of peculiar thick clouds charged with electricity, whose height
varies from 30 yards to 3 miles. The air is never free from electricity.
Snow, sleet, hail, and “luminous rain” are frequently indications of
great electrification. The atmospheric electric charge is usually
positive, and is probably the result of evaporation, but clouds
themselves are more generally negative.

Lightning, as a source of light, is very brilliant, comparable even with
the sun, but its duration is extremely short, hence its intensity is
about equal to that of full moon. The motion of a flash cannot be
detected; hence when people say they saw a flash going upwards or
downwards, they must be mistaken. It is an optical illusion. The
peculiar zigzag form, occasionally bifurcated, is that of a very large
electric spark, varied by local electrification and heat.

The motion of electricity is due to a difference of potential or
electrical pressure. The power of a machine is measured by the utmost
potential it can give to a conductor, and the _time_ required to charge
the conductor depends on its _capacity_. The damage which can be done by
a discharge is proportional to the square of the charge, and inversely
to the capacity of the receiver. Doubling a charge gives fourfold a
shock.

Electricity is entirely distributed on the surface of conductors. The
quantity per square inch of surface is _the density_, and the density
varies with the form of the conductor. On a very elongated body,
terminating in a point, the density becomes so exceedingly great that
the outward pressure of the electricity tending to escape forces a
passage through the surrounding air. Proper lightning rods must be
surrounded with a number of sharp points, lest one should be injured.
The proper function of a lightning rod is not to parry a dangerous flash
of lightning: it ought rather, by silent but continuous draining to
prevent any serious accumulation of electricity in a cloud near it.
Hence it must be thoroughly connected with the earth. At
Pietermaritzburgh, which is well covered with lightning conductors,
thunderstorms are frequent, but they cease to give lightning flashes
whenever they reach the town, and they begin to do so as soon as they
have passed over it.

The violent disruptive effects produced by lightning are principally due
to the sudden vaporization of moisture. Heated air conducts better than
cold air. Hence the killing of flocks and herds.

There is little or no danger inside a thunder-cloud. Thunder-bolts (so
called) are due to the vitrification of sand through which a discharge
has passed. The smell that accompanies lightning is due to ozone.

Sheet lightning and summer lightning are due to the lighting up of the
clouds by flashes of forked lightning not directly visible to the
spectator, sometimes even beneath the horizon.

Thunder corresponds to the snap of the electric spark, intensified and
re-echoed from clouds and surfaces. A longer zigzag flash acts
successively and intermittently from portions farther and farther from
the listener. Hence the crash, clap, rolling and pealing of thunder. The
extreme distance that it is heard is about ten miles, although guns have
been heard fifty miles.

Fireball or globe lightning undoubtedly exists and is probably due to a
species of natural Leyden jar, very highly charged, which no lightning
rod can destroy, except, perhaps, a close net work of stout copper
wires.

Water is the chief agent in thunderstorms. Copious rain and hail always
accompany them. Hot moist air precipitating its moisture as clouds as it
ascends, cooling by expansion but warmed by the latent heat of the
condensed vapour is the main spring. The condensation of aqueous vapour
is accompanied by an enormous development of energy. A fall of one-tenth
of an inch of rain over the whole of Britain gives heat equivalent to
the work of a million millions of horses for half an hour. The mere
contact of particles of aqueous vapour with those of air produces a
separation of the two electricities. Aqueous vapour condenses into cloud
particles, and the agglomeration of cloud particles into rain drops
would enormously increase the original potential of the electrified
vapour.

The column of smoke and vapour discharged by an active volcano gives out
flashes of lightning. Cloud caps on mountains frequently do the same.
Ascending currents of air mean change of density, difference of
pressure, heat condensation, and all the conditions required to produce
a thunderstorm, with its effects forming “one of the most exquisite of
the magnificent spectacles which nature from time to time so lavishly
provides.”


             ON THE PROTECTION OF BUILDINGS FROM LIGHTNING.

                    BY CAPTAIN J. P. BUCKNILL, R.E.

              (_Abstracted by W. H. Preece, C.E., F.R.S._)

In the first part of his paper the author popularly explains his own
views of electricity, the causes of thunderstorms, and the purpose
served by a lightning conductor. He urges the theory that lightning is
mostly to be feared by those who live on well conducting areas; and that
non-conducting areas, such as chalk hills, suffer the least, because
their inductive influence on charged clouds is less than in the former
case, even though they be on low ground. Points act as leaks, warding
off lightning by neutralising harmlessly the opposite electricities. The
trees of a forest act as a mass of points, silently discharging thunder
clouds. The potential of a thunder cloud is often a million and a-half
volts. The function of a lightning conductor is “(first) to attract the
lightning to another spot if possible, and (second) to arrange that even
if the building be struck, the work shall be given out at other portions
of the path of the stroke.”

He advocates strange views as to the space protected by a lightning
conductor, which, if true, would tend to show that there is no safety in
lightning conductors at all, for according to him, the safe area rule
may be upset in practice by all sorts of accidental circumstances. He
has, however, not grasped the meaning of the rule. He advocates the use
of iron as the best metal to use, specifying a weight of 2 lbs. per
foot. He thinks wire ropes are more easily applied than rods, ribbons,
or tubes, and prefers a rope 1·2 in. diam. of six strands of seven No.
11 B.W.G. wire, each round a hemp core—costing about 5d. per foot.
Conductors should be specified in terms of electrical units, viz.: ·3
ohms per 1000 yards, and be continuous. Every unavoidable joint should
be soldered. He has found in practice many bad joints, especially in
copper conductors. At Tipner one gave 10,000 ohms, and one in the Isle
of Wight 700 ohms. Each joint was apparently quite sound. He considers
that lofty conductors require no additional conductivity per unit of
length, and that high lightning rods are only required in exceptional
situations.

Several points are preferable to a single point, because the “gathering
power” is increased thereby, and the chance of lightning striking other
things in the immediate vicinity of the conductor is proportionately
diminished; the top of the rod is less likely to be fused when struck,
the stroke being divided between the various points; and also because
the brush discharge is thereby facilitated. He dwells with much emphasis
on the importance of the earth connection, which he regards as a joint,
and advocates greater surface than is usual at present. He illustrates
an excellent deep earth connection formed by a galvanised cast-iron
pipe, 10 feet long and 1 foot in diameter, sunk in a well below the
water level in the dryest season. He insists that both deep and shallow
surface earths are required.

Lastly he insists on periodical inspection, and the careful application
of electrical tests. In an appendix he describes his own testing
arrangements, with the results of nearly 500 tests made by him for the
War Department, from which he concludes “that _with the lightning
conductors erected as they are at present by the War Department_,
electrical testing is of small value.” Nevertheless, in spite of this
strong condemnation he asserts that the conductors now existing on our
magazines and fortifications have never yet failed.


  SPECIFICATION (No. 3925. September, 1880) of SAMUEL VYLE. LIGHTNING
                              CONDUCTORS.

                 (_Abstracted by G. J. Symons, F.R.S._)

The invention may be divided into two parts. In the first place, the
inventor proposes that in lieu, for instance, of the central strand of a
seven-strand copper wire rope, there shall be a central wire insulated
from the others, and only connected to them at the junction with the
upper terminal, while at the bottom this insulated wire is led up from
the earth to some place where it is easy of access.

Secondly, there is a differential galvanometer, resistance coil, and
other apparatus, which being connected with the conductor and with the
insulated wire, will enable the efficacy of the conductor to be read off
at any time.


                ON THE PARTIAL PROTECTION OF BUILDINGS.

                  (_By Prof. T. Hayter Lewis, F.S.A._)

The following are suggestions whereby the ordinary materials used in
building may, to some extent, be utilised as protectors against
lightning:—

(1) When the roofs and sides of a building are covered with galvanized
sheet iron on a framework of wood, if these coverings have good earth
contacts, either by themselves or through the ordinary iron rain-water
pipe, the building may be considered safe.

(2) Cottages and small houses have usually iron eaves gutters, slate or
tile hips and ridges, cement flashings, and iron rain-water pipes. If
the joints be sound, and the earth at the foot of the rain-water pipes
be moist, the houses will, to a considerable extent, be protected from
the level of the eaves gutters downwards. But as they will be quite
unprotected about that level, a wire rope or metal tape from the top of
the highest chimney to the gutters, which will very much diminish the
risk, is desirable.

(3) In larger buildings the gutters, rain-water pipes, hips, ridges, and
flashings of the roof are often made of lead. If the pipes have good
earth contacts, and conductors be fixed from the chimneys or other
projections to the lead-work, the buildings will be to some extent
protected.

(4) When the hips and ridges of roofs are of slate, terra cotta, or
other non-conducting materials, conductors along the ridges, connected
with the rain-water pipes, and with points along the ridge, and to the
chimneys, will be required.

                  *       *       *       *       *

But all the buildings above described would be exposed to the risk of
imperfect joints, bad workmanship, &c.; so that no structure can be
considered as secure unless it be protected by one or more conductors of
approved size and metal, and with carefully constructed connections and
earth contacts.




                                 INDEX
                                   TO
                            THE APPENDICES.


NOTE.—It must be distinctly understood that no responsibility for the
statements or views indicated by this index or set forth in the
appendices is assumed either by the delegates collectively or by the
Editor.

 Abel, Prof., on Mr. Preece’s Paper, 102

 Academy of Sciences, Report made to, 51 _et seq._

 Accident at Athelney, Bournemouth, 201

   „  at Carmarthen, 217

   „  at Caterham, 210

   „  Masulipatam, 206

   „  Trolley Bottom, Herts, 196

   „  in Belgium, 129

   „  in England, 38, 129

   „  in low-lying parts of France, 129

   „  in mountainous parts of France, 129

   „  to a French frigate, 200

   „  various, 126

   „  within small areas, 201

 Action, Mechanical, of lightning, 85

 Adams, Prof. W. G., Abstracts by, 76, 82

 Addiscombe, chimney of house struck, 38

 “Ætna,” Ship, struck at Corfu, 88

 Aigrettes or brushes of points, 139
       (_See_ POINTS MULTIPLE).

 Air in electric field in state of strain, 135

   „  terminals (_See_ POINTS).

 Alatri, Cathedral of, 126

 Allen, R., Letter from, 183

 All Saints’ Church, Nottingham, struck, 37

 Alphand, M., his Report, 67

 Alphington Church, near Exeter, struck, 37

 America, gutters and water pipes used, 125

 Analysis of Manufacturers’ Remarks, &c., 17

 Anderson, R., on Lightning Conductors, 120

   „  on testing, 111, 127

 Androuët, M., his assistance, 225

 Angle iron conductors, advantages of, 111

 Angles, Sharp, to be avoided, 11, 16, 28, 71, 94, 99, 178

   „  useful for discharging electricity, 111

 Arago, on bends in conductors, 94

   „  „  earth terminals, 95

 Architects, Royal Institute of British, Report of, 27

 Area protected (_See_ PROTECTION, AREA OF).

   „  Sectional, 15, 18, 22, 49, 110, 131, 132, 195, 223

   „  „  insufficiency of, 63

   „  „  varied with length, 7, 9, 12, 13, 14, 19, 20, 24, 131

   „  „  not varied with length, 4, 16, 243

 Asted, Col., Report of Accident, 206

 Atmospheric Electricity, 112, 119

   „  „  by D. Brooks, 117

   „  „  by R. Phillips, 98

   „  „  origin of, 117

 Attachment should always be of same metal as conductor, 21

   „  to building, 7, 8, 9, 11, 13, 14, 16, 21, 24, 31, 39, 81, 99, 103,
    115, 125, 130, 193

 Attraction, Conductors do not attract lightning, 71

   „  Specific, equal in all bodies, 73

 Attractive points, 127

 Austria, Accidents in, from Lightning, 126

 Aylmer, J., his assistance, 228

 Ayrton, Prof., Abstracts by, 43, 83, 85, 90

   „  „  on Clerk Maxwell’s Lightning Conductors, 132

   „  „  on Indian telegraphs, 102


 Babinet, M., his Report, 60, 66

 Backstroke of lightning dangerous, 85

 Baker, A. J., his Report, 34

 Ball, Hollow, with small points (_See_ POINTS MULTIPLE) 13, 23

   „  is a point when compared to a cloud, 73

   „  lightning, (_See_ LIGHTNING BALL.)

 Ballu, M., his Report, 67

 Band (_See_ TAPE and PLAIT).

 Barns full of new hay likely to be struck, 125

 Barque “Southern Queen” struck, 205

 Bar of iron, bad joints in, 116

   „  Melted by lightning, 61

   „  Rectangular flat, 74

   „  Small, become heated, 116

 Base of conductor should bifurcate, 65, 243

 Batteries, Casemated, 70

 Bayonne, Powder magazine at, 87

 “Beagle,” H.M.S., struck by lightning, 195

 Beams, how connected, 10

 Becquerel, M., his Report, 60, 66

   „  on discharge of lightning, 131

   „  on conducting power of metals, 124

 Belgrand, M., his Report, 67

 Bell, Hornsby & Co.’s experience, 193

 Bells in church steeple, 85

 Bell wire acts as a conductor, 39, 195

 Bends, Sharp, to be avoided (_See_ ANGLES).

 Berehaven lighthouse struck by lightning, 208

 Bisby, Mr., of Leeds, his conductor, 75

 Bishop’s Rock Lighthouse, 190

 Blitzableiter, Von G. Karsten, 114

 Blunt conductor (_See_ BALL _and_ POINTS).

 Boat, Packet, struck (_See_ SHIPS) 61

 Bolts, Iron, attracted lightning, 40

   „  to be connected with conductor, 11

 Books on Lightning Conductors, Catalogue of, 143

 Bootham Bar, York, 219

 Borrel, M., his views, 226

 Boy on pony, pony killed, boy escaped, 48

 Branches, Connecting, 183

 Brandon, D., his Report, 34

 Brass not a reliable metal, 62, 124, 227

   „  wire rope used in Bavaria, 124

 Break in conductor not fatal, 53

   „  „  „  to be avoided, 63

 Brescia powder magazine blown up, 76

 British Association Report, 1860, 46

 Brixton Church struck, 84

 Broek, R. Van der, Abstracts by, 114, 119, 137, 138, 140, 141

 Brook, Conductor to be carried to it, 14

 Brooks, D. 103, 181

 Brough, Mr., on Lightning Rods, 19, 49, 181

 Bruntcliffe, Yorkshire, Gunpowder store destroyed, 74, 216

 Brussels, Town Hall at, Lightning protector at, 138

 Brydone, Mr., Report of an accident, 85

 Buchanan, G., on gas works chimney, 89

 Bucknill, Capt., on the protection of buildings, 243

 Building, containing masses of metal, 61

   „  continually under attacks, 123

   „  injured, though protected, 27, 128

   „  Long, to have several conductors, 25, 202

   „  Metallic, safe, 72

   „  protected by cage of wires, 132

   „  struck from, 1589 to, 1879, 126

 Burges, Mr., 190


 Cable conductors (_See_ ROPE).

 Cagniard de Latour, M., his Report on Points, 60, 66

 Calcutta, Report on conductors at, 117

 Callaud, A., his Treatise, 103

   „  his grapnel in basket of coke, 131

 Canton, Mr., his experiments in London, 80

 Capacity of conductors, 127

 Caps, Cast-iron, to chimneys, 103

 Carbon in well, 180

 Carmarthen, Accident at, 217

 Casing of lead or wood for iron earth terminals, 125

 Catalogue of works upon lightning conductors, 143

 Caterham, accident at, 210

 Cathedral of Alatri, 126

 Cavendish, Hon. H., his Report, 76, 79

 Cemented water tank, iron conductor in it, 130

 Chain conductors melted, 61, 62

   „  though broken, still useful, 54

   „  objectionable, 9, 61, 62, 88, 123

   „  Early use of, as conductors, 122

   „  Old iron, for earth terminals, 74, 204

 Chapel, Rycroft, struck, 45, 46

 Chapman, Gen. Sir F. E., his Report, 72

 Charcoal for earth terminals, 12, 16, 58, 125, 126

 Charles, M., his Report on Instructions for erecting conductors, 57

 Cheapness of galvanized iron, 132

 Chimney, Accidents to, soon after erection, 194

   „  Granite, in Plymouth Dockyard, struck, 73

   „  Metal Caps to be joined to Conductors, 125

   „  New, contain much moisture, 194

   „  not struck that had conductors, 193

   „  of Edinburgh Gas-works, 89

   „  over, 90 feet have conductors, 193

   „  rod to be on, 100

   „  rope on, liable to corrosion, 125

   „  Shafts, copper band round top of, 9

   „  Stacks are Conductors, 7

   „  struck, 27, 28, 40, 45, 193, 194

   „  struck because of heated air, 113

   „  struck before completion, 94

   „  struck that had no conductors, 38, 193

   „  very rarely struck at Glasgow, 193

   „  with soot dangerous conductors, 106

   „  Zinc, struck, 37

 Church, Brixton, struck, 84

   „  Charles, at Plymouth, 86

   „  Christ, Carmarthen, 217

   „  Rosenberg, in Carinthia, destroyed, 1730, 123

   „  St. Bride, Fleet Street, damaged, 126

   „  Ste. Croix, Ixelles, struck by lightning, 140

   „  St. George, Leicester, damage to 126, 240

   „  St. Giles, Cripplegate’s truck, 196

   „  St. Mary, Genoa, 126

   „  Southampton, damage to, 126

   „  Steeple at Bodmin, destruction of, 202

   „  struck, 29, 37, 106, 126, 137, 199

   „  struck near Isleworth, 199

   „  tower, with pinnacles, 10, 29, 137

   „  towers struck in past, 400 years, 202

   „  with lightning conductor, 128

   „  without lightning rods damaged, 126

 Cinders with grating (_See_ EARTH TERMINALS).

 Circuit to be tested by galvanometer, 130, 244

 Cistern dangerous for base of conductor, 64

 Claire-Deville, M., his Report, 67

 Clamps, Iron, acted as conductors, 43

 Clark, J. E., Accident at Bootham Bar, York, 219

   „  Latimer, Abstracts by, 103, 106

 Clay, Conductor to be taken below surface of, 14

 Clevedon Church struck, 126

 Clifton, E. N., his Report, 41

 Clips, Gun-metal, 24

 Clouds are not perfect conductors, 101

 Cluster of points (_See_ POINTS MULTIPLE).

 Coke, broken, better than charcoal, 116

   „  prevents action of sulphur, 120

   „  round conductors, 9, 116, 118, 126, 131

 %center%(_See_ EARTH TERMINALS).

 Cole Brothers, 192

 Colliery Chimney near Sunderland struck, 193

   „  Workings, Lightning in, 237

 Colson, J., his Report, 28, 34

 Commission on damage by lightning, 127

 Comparative resistance to fusion, 141

   „  „  rupture, 141

 Conducting power depends on amount of copper in conductor, 200

   „  „  of metals, 74, 124, 131, 139

   „  „  of wires, 177

 Conduction, is it a question of surface or of mass? 15, 18, 49, 132

 Conductive capacity deficient in trees, 127

 Conductor at ends of buildings has radius of protection lessened, 134

   „  Construction of, 63, 107, 178, 179

   „  Cost of, for Houses of Parliament, £2314, 122

   „  damaged by holdfasts, 115, 193

   „  destroyed at ground line, 131

   „  partly destroyed, yet useful, 62

   „  deteriorate, 127

   „  dimensions of (_See_ SIZE OF).

   „  do not attract lightning, 88

 Conductor, every, should be complete in itself, 22

   „  Examination of, 9, 72, 102, 111, 124, 127, 130, 131, 132, 179, 244

   „  Expansion of, 11, 70, 125, 128, 226

   „  First, 121

   „  „  in England, 85, 121

   „  „  in Europe, 122, 129

   „  for lighthouses, 195, 199

   „  for iron ships, 122, 200

   „  for wooden ships, Snow Harris’s, 195, 199

   „  for steeples, with horizontal bands, 125

   „  how to be connected with metal portions of buildings, 65, 125,
    126, 128

   „  imperfect, Effect of, 21, 209

   „  in contact with metal in chimney, 111

   „  influenced by new water and gas mains, 127

   „  influenced by trees, 127

   „  is it to be a rope, rod, tube, or band?, 18, 132, 195

   „  joints in (_See_ JOINTS).

   „  laid in underground water, 128

   „  led into cemented water tank, 130

   „  „  water butt, 107

   „  Main, 183

   „  must protect ridge, gable ends, and eaves, 112

   „  not to be insulated (_See_ INSULATION).

   „  not to rise less than, 15ft. above chimney, 122

   „  now same as Franklin’s, 124

   „  number necessary, how determined, 51

   „  of copper, 107, 130

   „  „  and zinc wire, 205

   „  „  tape, 206

   „  „  rope, 196, 203

   „  „  the best, 125

   „  of hollow tube, 122, 196

   „  of Hotel de Ville, Brussels, 126

   „  of iron, 55, 107, 125, 131, 139, 140

   „  of large surface better than rod, 113

   „  of links of copper, 202

   „  of numerous thin wires, 139

   „  of solid bolt, 196

   „  of zinc wire melted, 107

 Conductor on buildings, to be linked together, 204

   „  on churches at Torquay defective, 130

   „  on ridge of roof, 125

   „  outside, 60, 126

   „  Points of (_See_ POINTS.)

   „  properly made, and properly fixed, insures safety, 12

   „  protects conical space (_See_ PROTECTION, AREA OF).

   „  reached water without earth plate, 128

   „  Ridge, 68, 177

   „  should extend above building, 106, 202

   „  should it present a large surface section? (_See_ AREA SECTIONAL).

   „  size of, 10, 12, 18, 19, 22, 86, 119, 125, 126, 129, 131, 192,
    194, 202, 214, 223, 225, 243

   „  spirally coiled up, 128

   „  struck by lightning, 128

   „  supposed perfect, proved defective, 131

   „  theory and action of, 106

   „  to be close to wall of building, 11, 15, 86

   „  to be continuous, 179

   „  to be fixed by iron staples, 125

   „  to be, 4 inches from walls and roofs, 118

   „  to be inside, 126, 225

   „  to be on side most exposed to weather, 60

   „  to be of metal of high conductivity, 131

   „  to be symmetrically arranged, 105

   „  to earth by shortest route, 126

   „  to gas and water mains (_See_ EARTH TERMINALS).

   „  to Middlesboro’ Hospital, 204

   „  to rest in hooks, 179

   „  to St. Alphege Church, Greenwich, 206

   „  to St. Michael’s Church, Blackheath, 205

 Cone of platinum (_See_ PLATINUM).

 Conic Terminals (_See_ POINTS).

 Conference Circulars by the Lightning Rod, 3, 175

 Conic Space, protected (_See_ PROTECTION, AREA OF).

 Connection (_See_ EARTH TERMINALS, _and also_ JOINTS).

   „  of metallic masses, 9, 10, 76, 77, 186

   „  „  not necessary, 126

 Contact between iron and copper to be avoided, 111

 Continuity between point and earth contact, 129

 Contraction to be provided for, 70, 125, 128

 Copper and iron form best conductors, 119

   „  and iron soldered, 107

   „  and zinc wire bad for conductors, 205

   „  Australian, 124

   „  better than silver, 139

   „  conducting power of, 19, 124, 131, 139

   „  conductors, 18, 70, 86, 117, 119, 125, 126, 130

   „  conductor too small, 126

   „  earth plate in dry sand, 128

   „  is it alone to be used?, 18

   „  less liable to oxidise, 131

   „  not to be in contact with galvanized iron, 102

   „  nuts, 192

   „  or iron conductors, 70, 192

   „  plates, bent, 125

   „  plate ending for conductors, 128

   „  plates to provide for expansion, 125

   „  points (_See_ POINTS).

   „  preferred to iron, 131

   „  purity of, 19, 124

   „  rarely used, 125

   „  tape recommended, 206

   „  rod conductor, 185, 186, 202

   „  rod, ½ in. diam. has never been fused, 125

   „  rod on Eddystone Lighthouse, 184

   „  rope conductor carelessly fixed, 196

   „  rope conductor insulated, 194

   „  rope to be used, 125,131

   „  „  of thick wires

   „  Russian, 124

   „  Spanish, 124

   „  tubing, 74, 122

   „  wire fused throughout its length, 195

   „  wires, deterioration of, 114

   „  wire rope applied to St. Paul’s Cathedral, 131

   „  wire rope, dimensions of, 8, 223

 Corn stacks fired by lightning, 187

 Coronal to be placed on chimneys, 132

 Corrosion of joints of rod, 126

 Cotton Mill, Explosion at, 239

 Coulomb, M., his Report, 51, 53

 Couplings, form of (_See_ JOINTS).

 Coutt’s Brewery, a rod at, 89

 Cramps, iron, stones held by, 29

 Cross, Metal, 53, 85, 227

 Croxton Park, trees struck, 48

 Cruickshank, A., his Report, 44

 Crutches on roof to carry rod, 52, 227

 Current, what it is, 100

 Cutting and Co., their conductor coupling, 216

 Cylinder in water (_See_ EARTH TERMINALS).

 Cylindrical rod or wire rope the best, 134


 D’Alibard, M., his experiments at Marly, 80

 Damage to building by alteration of position of safe, 127

 D’Amico, Sig., 179

 Damp air, a conductor, 48

 Dampness of new chimneys cause of being struck, 194

 Danger of explosion from use of gas pipes, 201

 Davioud, M., his report, 67

 Davis, H. D., suggestion about gas pipes, 201

   „  Jno. & Son, their answer, 14, 15, 17

 Davy on conducting power of metals, 124

 Deaths from lightning, 100, 126

 De la Place, M., his Report to French Academy, 51

 De la Rive says blunt points or balls equally effective, 106

 De la Rue’s (Dr. Warren) experiments, 133, 135

 Delaval, M., his Report, 76

 Delieul, Messrs., points made by, 66

 De Lor, M., his experiments in Paris, 80

 Denmark, lightning conductors in, 176

 Desains, M., his Report, 67

 De Saussure’s neighbours frightened at his conductors, 122

 De Senarmont, M., his Report on points, 66

 Designs for protecting private houses, 125

 Despretz, M., his Report on points, 66

 Destruction of conductors by use of iron wall eyes, 131

 Dimensions of conductors (_See_ CONDUCTORS, SIZES OF).

 Dimensions of upper terminals, 17, 18

 Discharge diverted from conductor by an anchor, 128

   „  from thunder cloud over plane surface would be vertical, 127

   „  of electricity by trees lessens energy of lightning, 127

   „  of electricity of high potential obeys laws of Ohm, 134

   „  of lightning—Earth contact, 131

   „  passes through conductor, Faraday, 132

 Discharging fork to be attached to lower end of conductor, 11, 231

 Doherty, J., on explosion at Swan Cotton Mill, 239

 Doors, copper, to magazines, 74

   „  iron, to powder store, 76

   „  lightning passed out of, 27, 48

 Drain, conductor to be led into, 14

 Duc, M., his Report, 67

 Dugmore, Mr., his evidence, 198

 Duhamel, M., his Report, 60, 66

 Dulong, M., his joint instructions, 59

 Dum Dum, accident at, 181

 Du Moncel, Comte, 67, 226

 Dungeness Lighthouse, 183, 186

 Duprez, M., his statistics of buildings and ships struck, 91

   „  on height of points, 96

 Dymond, E. E., Abstracts by, 51, 108


 Earth, “bad”, 110, 117, 126, 127, 209, 210, 218

   „  moist, better than a well for end of conductor, 74

   „  plate, pipe, or tube, 9, 24, 100, 114, 115, 118, 120, 128, 177,
    179, 186, 231

   „  plates at Torquay carried out to sea, 130

   „  „  unnecessary, 16

   „  Terminals, 11, 13, 14, 15, 21, 56, 95, 102, 106, 109, 116, 126,
    131, 140, 180

   „  „  at base of rain water pipe, 132

   „  „  bad, 110, 117, 126, 127, 209, 210, 218

   „  „  Borrell’s, 226

   „  „  Callaud’s, 104, 125, 131

   „  „  destroyed in moist earth, 116

   „  „  Discussion on, 131

   „  „  Duplicate, 65

   „  „  important, 11, 71, 126, 131, 243

 Earth Terminals of conductors in iron box, 126, 231

   „  „  of conductors, Stotherd, Lt.-Col., 130

   „  „  in wells, 15, 56, 60, 74, 77, 100, 118, 126, 139, 179, 180,
    231, 243

   „  „  iron should be galvanised, 120

   „  „  length of, 11

   „  „  multiple, 139, 243

   „  „  Oxidation of, 125, 131

   „  „  Rules for, 64, 72, 132

   „  „  to be accessible, 68

   „  „  to be carried away from building, 107

   „  „  to be connected, 120

   „  „  to be deep and wet, 107

   „  „  to be good, 126, 130

   „  „  to be in moist ground, 21, 52, 55, 56, 58, 74, 113, 118, 123,
    124, 125, 126, 131

   „  „  to be tested, 111, 131

   „  „  with charcoal cinders or coke, 9, 12, 16, 23, 24, 58, 104, 116,
    120, 125, 126, 131

   „  „  with coil of conductor, 9

   „  „  with galena, &c., 58

   „  „  with gas pipes (_See_ GAS).

   „  „  with iron forks or harrows, 11, 131

   „  „  with old iron, 74, 204

   „  „  with water, 52, 53, 67, 68, 126, 130, 140

   „  „  „  pipes, 9, 26, 46, 55, 56, 68, 118, 125, 126, 127, 128, 132,
    231, 235, 243

 Eddystone Lighthouse, 183, 184, 186, 189, 191

 Effects of climate on copper and zinc wire ropes, 205

 Electric current checked, 193

   „  discharge takes path with best conduction, 127

   „  fire not diverted from its path by rod, 125

 Electricity a terribly explosive power, 72

   „  Atmospheric, 98, 112, 117, 119

 Electricity, frictional and atmospheric the same, 82, 112

   „  carried off by water pipe, 126

   „  for telegraphic purposes follows Ohm’s laws, 133

   „  is force, not matter, 100

   „  of earth negative—atmosphere positive, 112

   „  Static, laws of, 132

   „  will leave small conductors for large ones, 204

 Electrodes, 110

 Elevated rods preferable to low conductors, 79

 End of conductor, lower, to be coiled up, 9

 Energy of lightning lessened by trees, 127

 England, accidents from lightning, 126

 Escurial, no conductor on, 100

 Examination of Conductors (_See_ CONDUCTORS, EXAMINATION OF).

 Expansion of conductor to be allowed for, 11, 70, 125, 128, 226, 229

 Experiment on wire across Thames, 121

   „  on plait of copper and zinc wire at Blackheath, 205

   „  with a very thin strip of tinfoil, 199

   „  with glass rods, 121

 Explosion of a gas meter, 239

 Explosions, electrical, their cause, 81

 Extent of surface does not favour lightning discharges, 134

 Eyes for fastening conductors, 99, 115 (_See_ ATTACHMENT).


 Faraday on conductors, 83, 84, 89, 102, 132, 183, 186, 187, 189, 190,
    195, 196, 199.

 Field, Rogers, C.E., on accident at Caterham, 210

   „  on ventilating pipes, 216

 Fire of inflammable materials, 127

 First conductor erected in England, 85, 121

 First conductor fixed in Europe at Hamburg, 122, 129

 Fixing conductors to ships, 87

 Fizeau, M., his report on powder magazines, 66, 67

 Flagstaff should have a conductor, 70

   „  struck, 44, 187, 196

 Flashing, Lead, how to connect wire rope with, 10, 11, 34

 Flash, lightning, effects of, 84

 Flow of electricity through conductors, 133

 Flues copper, 183, 185

   „  lightning passed down, 38, 39

   „  warm, and an iron grate, a dangerous conductor, 101

 Forest Hill, chimney of house struck, 38

 Forms of upper terminals (_See_ POINT).

 Formula for determining area protected (_See_ PROTECTION, AREA OF).

 Foster, Prof. G. Carey, on Personal safety, 233

 Fountains, Public, conductor lead away from, 56

 Franklin, Dr., and wet rat, 85

   „  discovered pointed metal best conductor, 121

   „  erected lightning rod to his house, 121

   „  experiments, 79, 84

   „  „  repeated by Buffon & Dalibar, 115

   „  first conductor was melted, 116

   „  his report to French Academy, 51

   „  on cold fusion, 102

   „  on connection of lightning rod, 54

   „  report on Purfleet, 76, 126

   „  round rod best, 114

   „  success in pushing use of conductors, 121

   „  tried his kite successfully, 121

 Freeman & Collier, their answer, 10, 17

 French instructions, 51

   „  „  on area protected, 22

 Fresnel, M., his instructions, 59

 Frost, A. J., Abstracts by, 99, 118

 Fusion, metals which resist, only to be used, 139

   „  of defective conductor, 215

   „  of rod, Wheatstone on, 83


 Gable near conductor struck by lightning, 28

 Galena, and melted sulphur, Bed of for end of conductor, 58

 Galvanic action between iron and copper, 111, 130

   „  of wet and smoke on conductors, 205

 Galvanised conductor painted, 139

   „  iron, 19, 67, 68, 72, 101, 120, 124, 125, 132, 139

   „  not to be in contact with copper, 102

 Galvanised iron best material for earth contact, 130

 Galvanometer for testing earth currents, 131

 Gas and water mains, 113

   „  „  „  utilisation of, 9, 28, 37, 39, 44, 72, 100, 102, 103, 108,
    114, 117, 125, 126, 128, 138, 201, 231, 235

 Gas coke for earth terminal, 23, 24

 Gases from chimney injure conductors, 111

 Gas ignited, 219

   „  meter exploded, 239

 Gasometer struck, 43

 Gas-pipes, Soft metal, not to be used as conductors, 108

 Gavarret’s, M., experiments, 139

 Gavey, J., on accident at Carmarthen, 217

 Gay Lussac’s iron conductor recommended, 104

 German “reception rod” of iron, 125

 Geneva cathedral, 103

 Genoa, St. Mary’s Church, 126

 Gilbert, Dr. (1600) magnetic and galvanic action one force, 120

 Gilt point (_See_ POINT GILDED.)

 Girard, M., his instructions, 59

 Girders, how connected, 10

 Glass, foundation of house insulated, 118

   „  insulators (_See_ INSULATORS.)

   „  repeller, 83, 185, 186

 Globular Lightning (_See_ LIGHTNING, BALL).

 Goldie’s, Mr., experience, 193

 Governments, French and English, size of rod sanctioned by, 12

 Grapnels and gratings for earth plates, 125, 126, 131

 Gray, J. W. and Son, their answer, 7–9, 17

 “Gridiron,” Termini of ribs pointed, 23, 24

 Groome’s, J. E., evidence, 196, 197, 198

 Ground connection (_See_ EARTH TERMINALS).

   „  containing ironstone, 48

 Guillemin’s, M., opinion, 132

 Gunpowder stores, conductor, how to be fixed, 82

 Gutters, Metallic, 40, 41, 45, 46, 47, 60, 125, 213

   „  must be connected with conductor, 60

   „  utilization of, 47, 125, 244

 Guyton, M., his practice with charcoal, 58


 Haigh & Son’s Colliery, 74, 216

 Harris, Sir William Snow, Crown adviser, 8

   „  combated the idea that rods attracted lightning, 122

   „  conductors to ships and buildings, 83, 122, 130, 196

   „  in conflict with Faraday, 195, 196, 200

   „  on Sectional Area, 110

   „  on copper conductors, 202

   „  on expense of conductors, 49

   „  on fusion, 86

   „  on hollow or solid conductors, 74

   „  on relative conductivity of metals, 71

   „  on shipwrecks by lightning, 90

   „  on thunderstorms, 85

   „  Principles adopted by, 70, 101

   „  regarding insulators, 15

   „  report on safety of conductors, 72, 110

   „  says discharges pass over surface, 132

   „  suggestions issued in army circulars, 122

 Hauksbee, F., F.R.S., similarity of electric flash and lightning, 121

 Hawksley, T., his report, 37

 Hay a bad conductor, 127

 Hay newly gathered, inflammable, 127

 Heated smoke from chimney, a conductor, 132

 Heckingham poorhouse struck, 87

 Height of rods, 120, 124, 125, 139, 177

 Hemispheres of brass, experiments with, 105

 Henly, W., his report, 78, 79

 Henry, Prof. Joseph, on construction of lightning rods, 99, 181

 Herring’s, Mr., evidence, 196

 Heryet, Chas. J., his opinion, 206

 Higginbotham’s, Mr., evidence, 194

 High buildings a source of safety to lower ones near, 12

 Highton, E., on lightning conductors, 239

 Hill, A., his Report, 37

 Hine, G. J., his Report, 37

 Hine, T. C., and Sons, Architects, ground plan of Nottingham Castle, 26

 Holborn Union Infirmary, Upper Holloway, struck, 39

 Holdfast, brass, 16

   „  copper, 7, 8, 13, 16, 21, 24, 39

   „  driven in too tight, 16, 193 (_See_ ATTACHMENT.)

 Hole in ship’s side, made by lightning, 62

 Honeyman’s, J., evidence, 194

 Hook and rings used as joints, 94

 Hoop iron in brickwork of chimneys struck, 46

 Hoops round chimney, 89

 Hopkins, Rev. G. H., his Report, 30

 Horizontal conductor, 71

   „  conductors for steeples, 125

 Horsley, Bishop, his Report, 79

 Hotel des Invalides, Paris, conductor on, 86

 Hotel de Ville, Brussels, conductors of, 126

 House at Bethnal Green cut in two by lightning, 41

   „  at Bournemouth with, 7 conductors, 199

   „  at Cannes (France) struck, 198

   „  near trees struck, 127

   „  of Parliament protected by Harris’s conductors, 122

   „  with two separate conductors, 128

 Hugueny, M. F., on “Le coup de foudre de l’ile du Rhin”, 99


 Ignition depends on retardation of discharge, 127

 Infirmary, how to be protected, 10

 Ingenhousz’s, Dr., experiments, 122

 Ingram, Mr., of Belvoir Castle, on trees struck, 47

 Inspection of conductors, 9, 72, 102, 111, 124, 127, 130, 131, 132,
    179, 244

 Instructions, 63, 99, 176, 181, 240

   „  British Army Circular, 70

   „  French Official, 59

   „  for formation of good earth, 64, 72, 132

 Instrument hut at Valencia, how protected, 105

 Insulation, shock decreased by, 118

 Insulators, 34, 37, 76, 99, 184, 186, 194

   „  approved, 13, 118

   „  objected to, 8, 11, 13, 14, 16, 21, 24, 68, 69, 73, 86, 89, 103,
    111, 118, 126, 139, 186, 226

 Iron a better conductor than formerly, 19

   „  and copper form best conductors, 119

   „  as a conductor, not objected to if galvanised, 19

   „  bar, 131, 226

   „  „  melted, 61

   „  bars on ridge for metallic connection, 125

   „  better than copper, 192, 243

   „  box for earth contact of conductors, 126

 Iron buildings covered with asphalte, 70

   „  built ship, metal-rigged, if protected, 122, 200

   „  cables, galvanized, sometimes used, 125

   „  conductors, 18, 69, 74, 116, 125

   „  „  bad, 9, 39, 192

   „  „  good, 81, 243

   „  „  cost of, 19, 70, 124, 132

   „  „  should weigh, 13 to, 37 oz. per foot, 119

   „  galvanized for conductor, 74, 116, 132, 139

   „  has greater specific heat than copper, 132

   „  its high temperature at fusion, 132

   „  in coke undergoes no change, 116

   „  Joints in defective, 116

   „  not to be used for rods, 123

   „  points, 88, 138

   „  pumps reaching to water act as attractive points, 127

   „  rain water pipes, good conductors, 102, 113

   „  “reception rod” used in Germany, 125

   „  rods on all sides best protection, 124

   „  safe in altered position caused damage to building, 127

   „  staples and wall eyes, 125, 130

   „  terminal rods, 124, 125

   „  underground, destruction of prevented, 125

   „  wires surrounding copper wire, 200

 Isolators (_See_ INSULATORS).

 Italy, Lightning rods used there, 179


 Jarriant, M., his books abstracted, 111, 115

   „  his manufactory, 227

 Jenkin, Professor, says point prevents discharge, 106

 Jerman, J., his report, 37

 Johnson, Clapham & Morris, their answer,13

 Johnston, W. P., 181

 Joints, avoided in wire cables, 132

   „  Cutting & Co., 216

   „  damaged, 69, 110, 126

   „  how avoided in upper terminals, 23

   „  how made, 7, 9, 10, 11, 13, 14, 16, 20, 24, 52, 55, 59, 63, 70,
    71, 103, 179, 192, 243

   „  must be perfect, 58, 131

   „  of bars always defective, 116

   „  of extra thickness, 74

   „  of rain water pipes, 132

 Joints should be metallically continuous, 20

   „  soldered, 9, 24, 66, 68, 70, 71, 102, 123, 125, 139, 140, 141, 243

   „  to be avoided, 10, 11, 16, 20, 63

 Journal of Society of Telegraph Engineers, May, 12, 1875, 130

 “Jupiter” ship struck, 62, 95


 Karsten, Prof. D. G., lightning conductors, by, 119

 Kew, experiments at, on atmospheric electricity, 112

 Kilbourne, Lieut., 181

 Kirchoff, Prof., on connection with gas mains, 235

 Kite, Silk, Franklin’s experiments with, 80

 Korte’s, Messrs., Paper, 105


 Lacoine, M., on area protected, 134

 Lane, T., his Report, 79

 Lantern on lighthouse, 184, 186

 La Place, M., his Reports, 53, 57

 Lateral discharge, 73, 83, 84, 85

 Latham, Baldwin, on conductors, 202

 Law, E. J., his Report, 37

 Laws of Static electricity, 132

 Lead a bad conductor, 123

   „  at joints, 94, 125

   „  casing for upper terminals, 131

   „  floors, 188, 189

   „  liked because of fitting sharp curves, 123

   „  pipe for earth connection, 77

   „  roofs and spouts, 51, 82, 102

   „  thin sheet of, covering ends of wire, very dangerous, 20

 Leaves of trees draw off electricity, 84

 Lefevre-Gineau, M., his instructions, 59

 Le Gentil, M., his observations, 84

 Length and sectional areas, proportion between, 14

   „  of conductor above top holdfast destroyed, 193

   „  of conductor determines amount of resistance, 131

 Lenz, M., on conducting power of metals, 124

 Leroy, M., his Report, 51, 53

 Lewis, Prof. T. Hayter, Abstracts by, 70, 79, 81, 84, 100, 110, 112,
    117, 120, 179

   „  his joint Report, 28, 37

 Leyden discharges and lightning flashes, 84

   „  Jar, 121

 Lichtenberg of Gottingen, his opinion, 129

 Liddell, J., on lightning conductors, 202

 Lighthouses and exposed buildings protected did not suffer, 106

 Lighthouse at Berehaven struck by lightning, 208

   „  damaged by lightning, 196

   „  lightning rods on, 183, 190

 Lightning an immense electric spark, 123

   „  Ball, 99, 101, 102, 108, 205, 242

   „  Bifurcated, 45

   „  conductor (_See_ CONDUCTOR).

   „  diffused, 108

   „  does it pass inside or outside conductor?, 15, 18, 49, 132

   „  Flash, 108

   „  follows line of least resistance, 108

   „  Force of, exemplified, 45

   „  Globular (_See supra_ BALL).

   „  going to earth without conductor, 128

   „  identical with electricity, 82

   „  incandescent matter, 100

   „  in colliery workings, 237

   „  leaves conductor and enters chimney, 203

   „  passed down mainmast and through ship, 195

   „  passed to iron supports, 128

   „  passing out of a ship by a copper bolt, 205

   „  Personal safety from, 233

   „  protectors (_See_ CONDUCTORS).

   „  ran along a bell wire, 195

   „  „  thatched roof of house, 128

   „  Rod Conference, their Circular, 28

   „  Rods (_See_ CONDUCTORS).

   „  Sheet, 108

   „  the cause of, 81

   „  various forms of, 108

 Lime, to prevent oxidation of cylinder, 140

 Line, conductor should run round building, 134

 Linked system of conductors introduced by Sir W. S. Harris, 204

 Links of chains, 179

 Llandaff Cathedral, conductor on, 102

 Lofty buildings require larger rods (_See_ AREA, SECTIONAL).

 Long conductors above buildings, their effect, 77

 Long’s, F., account of injury to Wells Church, 195

 Louvre, New Buildings of the, Special Report for, 64

   „  slightly injured by lightning, 123

 Low straggling buildings should have several conductors, 15

 Lucas, Mr., his Report, 67

 Lussac, Gay, M., his Report, 57, 59


 McDonald’s, Mr., experience, 193

 McGregor, W., protection from Lightning, 106

 Magazine, copper doors and windows to, 74, 216

   „  of metal, the safest, 73

   „  underground, 70

   „  well at each end of, 126

 (_See also_ POWDER MAGAZINES).

 Magne, Mr., his Report, 67

 Mahon, Lord, his Report, 79

 Mairie, of, 20th Arrondissement struck, 69

 Majendie, Major V. D., his Report, 74, 216

 Malcolm, Major, R. E., discussion on lightning conductors, 131

 Mann, Dr. R. J., Lecture at Society of Arts, 108

   „  discussion on earth connections, 131

   „  discussion on lightning conductors, 131

 Man might touch conductor in thunder storm, 126

 Marseilles, Powder Magazine at, how to be protected, 51, 52

 Massingham, T., evidence and letter, 15, 16, 17, 193

 Masses, metallic must be connected with conductor, 60, 94, 104, 126,
    132, 240

 Mass or surface, which conducts?, 13, 15, 18, 49, 74, 132, 227

 Masts of large vessels, each to have a conductor, 6

 Masulipatam, accident near, 206

 Materials, inflammable, not ignited, 127

 Maxwell, Hugh, on kind of trees struck, 47

 Maxwell’s, Clerk, Theory, 109, 126, 132, 133

 Mechanical action of lightning, 85

 Meiszner’s improvement, 130

 Melsens says discharge passes over surface, 132

   „  System of protection as applied to monument at Lacken, 230

   „  various works by, 124, 138, 140, 141

 Men-of-war, old conductors in, 202

 Merton College, Oxford, damaged, 126

 Metallic cap may assist protection of house, 132

   „  circuit, 126

   „  connection must be perfect, 130

   „  connections on ridge by iron bars, 125

   „  joints, 89

 Metals, contact of dissimilar, results in decay, 19, 21

 Metal cowl of chimney struck, 198

   „  for points must be good conductor, 139

   „  immaterial if sectional area be large, 131

   „  in buildings, contiguity with to be avoided, 5

   „  inside or out, to be connected with conductor, 125, 126

   „  melted, dimensions of, 61, 83, 223, 231

   „  of high conductivity for conductors, 131

   „  stays and fastenings, 184, 185

 Michel, M., Papers by, 67, 68, 111, 131

   „  on galvanised wire rope, 131

 Milne, D., his Report, 44

 Mining Engineers, Enquiry by, 237

 Mohn’s, H., Lynildens Farlighed I Norge, 106

 Moist earth destroys terminal, 116

   „  for lower terminal, essential, 21, 52, 56, 58, 125, 126

 %center%(_See_ EARTH TERMINALS).

 Moisture, Access of, to surfaces in contact, 71

 Moncel, Comte du, his Report, 67

   „  „  his opinions, 226

 Monte Video, English Consul’s house struck, 195

 Montgolfier, M., his Report, 57

 Monument, London, its immunity from injury by lightning, 103

 Morea, Signor Lerigi, 180

 Müller’s, Prof., conditions for lightning conductors, 129

 Müller’s, Dr. Hugo, experiments, 135

 Municipal buildings in Paris, lightning rods for, 67, 225

 Munson, D., & Co., their rods, 216

 Murgatroyd, J., his report, 39

 Murray, J., on Atmospheric Electricity, 82

 Musgrave, Dr., his report, 79

 Myers, Gen., 181


 Nails, copper, used in attaching conductor to building, 14
 %center%(_See also_ ATTACHMENT).

 Nairne, E., his report, 79

 Nash lights, 183, 187

 National Institute (of France) report made to, 53

 Nelson column, 90

 Newton, Sir I., machine of glass, 120

 “New York,” packet boat, struck, 61, 62

 Nickson, Mr., his report, 78

 Nottingham, Castle, how protected, 23, 24

 Nuts, copper, 192
 %center%(_See_ JOINTS).

 Number of persons killed by _one_ discharge, 129


 Objects on plains attract lightning, 127

 Odour, sulphurous, of lightning, 85

 Official instructions:

   „  Denmark, 176

   „  England, 70–74

   „  France, 51–69

   „  India, 181

   „  Italy, 179

   „  Norway, 106, 176

   „  United States, 181

 Ohm, his laws, 18, 133

   „  on conducting power of metals, 124

 Oldham, Explosion at, 239

 Oliver, T., his report, 39

 Oxidation, how to be avoided, 83

   „  of copper less than that of iron, 131

   „  of cylinder, 140

   „  „  earth terminals, 131

   „  „  surface of conductor unimportant, 73

   „  „  terminals leads to failures of conductors, 131


 Painted conductor, 69, 94, 99, 103, 113, 117

   „  galvanized conductor, 139

 Paint objected to, 67, 227

 Palais de l’Industrie, Paris, its construction, 61

 Paratonnerres, Traité des, 103

   „  A Collin et Fils, Paris, 117

   „  Nouveau par Jarriant, 111

   „  par Jarriant, 115

 Partial protection, 194, 244

 Passage of electricity of tension in bad conductors, 141

 Patterson, Mr., of Philadelphia, on good contact, 58

 Payneshill, site of first conductor, 85

 Pearson, J. L., his report, 39

 Pegwell Bay, tide receded, 48

 Pennycook & Co., their answer, 13, 14, 17

 Perfect lightning conductor, 131, 186

 Perforated iron pipe as earth terminal, 114

 Perrott’s, M., experiments, 139

   „  remarks on earth contacts, 140

 Perry, Prof., on conductors, 132

 Personal safety from Lightning, 233

 Persons killed by lightning in France, 129

 Perspiration from flock of sheep, a conductor, 48

 Phillips, R., on atmospherical electricity, 98

 Phin, John, on lightning rods, 102, 181

 Phipson, R.M., account of destruction of Wells Church, 194

 Pidgeon, Mr., discussion on earth connections, 131

 Pierron, M., his proposal, 52

 Pinnacles on church towers, 10, 29, 137

 Pipes, gas, (_See_ GAS, WATER, and EARTH TERMINALS).

   „  hard metal, as conductors, 108

   „  iron, easily made into protectors, 102

   „  of terra cotta, 180

   „  rain-water, 34, 74

   „  as earth terminal, 114

 Plait of copper wire, 5, 9, 205, 210, 215

 Planta, Mr., his report, 79

 Plate, Earth (_See_ EARTH PLATE).

 Platinum points, 37, 115, 140, 227

   „  „  approved of, 15, 54, 55, 59, 63, 66, 99, 104, 116, 120

   „  „  objected to, 67, 73, 103, 123, 139

   „  „  only half the conducting power of copper, 73

   „  „  blunted, 69

   „  „  fused, 128, 231

 Plymouth, Charles Church at, 86

 Point Aigrettes (_See infra_ MULTIPLE).

   „  attracts electricity, 82

   „  blunted, 53, 69

   „  breaks the force of lightning, 73

   „  coronal (_See infra_ MULTIPLE).

   „  dimensions of, 17, 18, 120, 130, 178

   „  Duhamel upon, 66

   „  Engravings of some modern ones, 230

   „  facilitate discharge, 131

 Point generally, 9, 17, 18, 76, 79, 81, 86, 92, 122, 125, 131, 139

   „  gilded, 9, 55, 59, 71, 120, 138

   „  „  needless, 73, 103, 113

   „  height of, 52, 138

   „  how to be fixed, 14, 52, 53, 55, 58, 130

   „  _in situ_, examination of necessary, 18

   „  melted, 53, 87, 92, 192, 195, 231

   „  multiple, 34, 231

   „  „  recommended, 10, 13, 14, 15, 23, 104, 108, 125, 132, 139, 243

   „  „  objected to, 18, 71

   „  not to be fusible, 93, 120

   „  of attraction, 127

   „  „  copper, 10, 13, 23, 66, 67, 107, 111, 117, 120, 123, 132, 139

   „  „  iron, 88, 138

   „  „  brass, 13

   „  „  pinnacles to be united to main conductors, 118

   „  „  platinum (_See_ PLATINUM).

   „  „  silver, 7, 120, 130, 139

   „  „  three kinds, 138

   „  „  vane, 186
 %center%(_See_ VANES).

   „  or blunt conductors, 77, 79, 106

   „  render lateral discharges less probable, 131

   „  Report upon, 60, 66

   „  sharp, 129, 130, 132, 138, 139

   „  „  not too, 92, 123, 129, 242

   „  „  experiments with, 51, 80

   „  should be kept clean, 130, 132

   „  „  of good conducting metal, 139

   „  should it be painted? (_See_ PAINTED).

   „  space protected by (_See_ PROTECTION, AREA OF).

   „  square tapering, 23

   „  used in Germany, fire gilded copper cone or sphere, 105, 111, 130

   „  useful, 102, 122

   „  useless, 77, 103, 113

   „  vertical, horizontal, or perpendicular, 58

 Poisson, M., his joint instructions, 59

 Polarity of ship’s compass reversed by lightning, 121

 Poles, Telegraphic, how protected, 101

 Pouillet, M., his joint Report, 60, 66

   „  on Conducting Powers of Metals, 124

   „  „  Discharge of Lightning, 131

 Powder magazines, 51, 52, 55, 56, 57, 66, 67, 70, 73, 74, 76, 81, 87,
    109, 118, 123, 126, 130, 177, 178, 216

 Preece’s, Mr. W. H., Abstract of Replies of Manufacturers, 22

   „  Discussion on Lightning Conductors, 131

   „  Discussion on Earth Connection, 131

   „  Abstracts by, 98, 102, 117, 130, 132, 241, 243

   „  on Conductors, 100

   „  „  Ball Lightning, 101, 102

   „  Paper Discussion on, 102

   „  Proper Form of Lightning Conductors, 132

   „  Space protected, 135

 Priestly, Dr., his Report, 79

 Pringle, Sir John, his Report, 79

   „  advocated use of points, 122

 Protector (_See_ CONDUCTOR).

 Protection, Area of, 6, 9, 13, 15, 16, 21, 22, 24, 57, 60, 64, 67, 71,
    73, 82, 87, 96, 102, 106, 111, 112, 117, 123, 125, 134, 135, 137,
    180, 192, 226, 230, 243

   „  of buildings from lightning, 195

   „  „  buildings from lightning, R. S. Brough, 132

   „  „  iron from decay by galvanizing, 132

   „  „  telegraph wires by lightning conductor, 130

   „  partial, 194, 244

 Prussia, accidents from lightning, 126

 Purfleet, Board House struck, 76, 78, 88, 122, 126

 Purity of copper essential, 124


 Quadrangular iron bar for conductor (_See_ IRON, BAR OF).

 Questions respecting damage by lightning, 28, 29


 Radius of Protection (_See_ PROTECTION, AREA OF).

 Railings to be joined to conductor, 125

 Railway Terminus at Antwerp struck, 137

   „  track makes capital earth, 117

 Rain-water pipe as conductor, 37, 38, 41, 132, 213

 Rat, Wet, indestructible by electricity, 85

 Ravel, M. de Puy Contal, his proposal, 52

 “Reception rod” of iron used in Germany, 125

 Regnault, M., his reports, 66

 Regnier’s system of lightning rods, 54, 57

 Regulations for lightning conductors in Denmark, 176

 Repellers, Glass, 186

 Resistance of conductor varies with its length (_See_ AREA, SECTIONAL).
    Retarding influence of electrostatic capacity, 133

 Return shock mechanical in effect, 129

 Ribbons and tubes still in use, 133

   „  or rods offer less resistance than ropes, 204

 %center%(_See also_ TAPE.)

 Richard & Co., their tall chimney struck, 44

 Richmann, Prof., killed, 1753, whilst experimenting, 121

 Ridges, metallic conductor covering, 68, 177

 Rittenhouse, Dr., of Philadelphia, his observations, 53

 Rivets, copper, used for joints, 24

 Robins, E. C., his report, 39

 Robertson, J., his report, 76

 Rochon, M., his report, 51, 57

 Rods better than ropes or chains, 96, 204

   „  solid copper, 10, 13, 14, 15, 73, 89, 117, 123, 184, 195

   „  copper not fusible, 125

   „  copper, their size, 70, 180

   „  Earth terminals of (_which see_).

   „  elevation, how coupled, 24

   „  horizontal, on roof, 52, 118

   „  how to be fastened to buildings, (_See_ ATTACHMENT).

   „  iron, conductor, 10, 46, 47, 77, 99, 117, 177

   „  „  tarred or galvanized, 104

   „  „  the size of, 52, 58, 70, 74, 130

   „  Joints in (_See_ JOINTS).

   „  Lightning, and how to construct them, 102

   „  Munson’s, 216

   „  must be thoroughly joined, 52

   „  not to be inside chimney, 111

   „  of greatest length gives most protection, 137

   „  of spirally twisted iron, 192

   „  Points of (_See_ POINTS).

   „  should be painted (_See_ PAINTED).

 Rods, size of (_See_ CONDUCTOR, Size of).

   „  Tie, must be connected with conductor, 60

   „  to be diameter of chimney above top, 111

   „  to be made of conical form, 129

   „  will not divert electric fire from its path, 125

 Rome, system of rods used there, 179

 Roof, all metals in, to be connected, 60, 72

   „  covered with metal, 37, 69, 177

   „  lead, easily made into protector, 102

   „  of wood or slate has conductor on ridge, 125

   „  with masses of metal, difficult to protect, 7

 Rope better than rod, 5, 10, 60, 111, 113, 131, 243

   „  brass wire, 60, 124

   „  conductor, how to fit to ship’s rigging, 6

   „  „  lower end of to be opened, 11, 15

   „  copper and zinc wire decayed, 205

   „  copper better than iron for towns, 19

   „  copper, its advantages and disadvantages, 8, 56, 63, 131, 134

   „  copper wire, 10, 13, 14, 34, 37, 39, 60, 75, 103, 125, 131, 225,
    226, 227

   „  „  dimensions of, 8, 9, 223

   „  „  has both surface and mass, 16

   „  „  too expensive, 58

   „  easily bent without angles, 19
   „  „  joined, diverted, or lengthened, 19

   „  hemp, for conductors, 56

   „  Iron wire, 19, 58, 68, 125, 227, 243

   „  „  „  smashed, 86

   „  liable to corrosion on factory chimneys, 125

   „  of thick copper wire, 226, 229

   „  or cable, fringed out at upper terminal, 14

   „  metallic, disadvantages of, 62, 63, 95, 204

   „  for connecting points with metal bars, 55

   „  with hemp strand in middle, 116, 227

   „  Wire, conductor, badly erected, 39

   „  damaged, 193

 Rosherville Church struck though provided with a conductor, 34

 Rounded and pointed conductors, 79
 %center%(_See_ POINT.)

 Route to earth for conductor, 126

 Royal Society, Committee of, 76, 78, 79

 Rules for erecting Conductors
 %center%(_See_ INSTRUCTIONS).

 Russell, F. & Co., their answers, 9, 17

 Rust increases electrical resistance, 70, 107


 Sacré’s, M. E., system, 140

 Safety from Lightning, Personal, 233

 St. Ann’s Hotel, Buxton, struck, 34

 St. Aubyn, J. P., 29

 St. Clotilde Church, Paris, struck, 69

 St. Eloi Church, Paris, struck, 69

 St. George’s, Leicester, 126, 240

 St. James’ Church, West-End, Hants, struck, 34

 St. Mary’s, Crumpsall, near Manchester, struck, 39

 St. Mark’s, Venice, 103

 St. Matthias’s Church, Brixton, struck, 39

 St. Michael’s Church, Stamford, struck, 43

 St. Paul’s Cathedral, Accident to, 78

   „  „  fitted with copper wire rope, 131

   „  „  its immunity from injury by lightning, 103

 St. Peter’s Church, Brighton, pinnacle struck, 48

 St. Sepulchre’s Church, Northampton, struck, 37

 St. Sulpice Church, Paris, struck, 69

 Sanderson & Co., their answers, 23, 24

 “Scientific American,” 118

 Screen, metallic, a protection, 85

 Secchi, P., 180

 Sectional Area (_See_ AREA, SECTIONAL).

 Sharp Points (_See_ POINTS).

 Sheets, Iron, struck, 53

 Sheet lightning is the reflection of forked, 101, 242

 Ships struck, 53, 61, 62, 88, 95, 195, 205

   „  conductors, 6, 90, 121, 122, 195, 199, 200

 Short terminal points to chimneys, 125

 Siemens, A., abstract by, 127

 Silver Points (_See_ POINTS OF SILVER).

 Simmons, J., his Essay, 81

 Size of conductor (_See_ CONDUCTOR, SIZE OF).
 Small conductor replaced by heavier one, 194

 Smoke discharged from chimney a conductor, 132

 Smoke often destroys brass, 124

 Snell, H. S., his report, 39

 Soil, change in nature of, its effect, 71

   „  dry, a non-conductor, 70

   „  metallic veins beneath, 61

   „  water beneath will attract lightning, 61

 Soldered joints (_See_ JOINTS).

 Solder, objectionable, 16

   „  the use of, imperative, 20

   „  „  not universal, 20

   „  with copper, 103

 Solid rods superseded by ropes of wire (_See_ ROPES), 131

 South Foreland Lighthouse, 185, 186

 Spagnoletti, Mr., discussion on lightning conductors, 131

 Spang, H. W., Treatise on Lightning Conductors, 112, 181

 Sparks from Holtz’s machine, 141

   „  „  Ruhmkorff’s coil, 141

 Space protected (_See_ PROTECTION, AREA OF).

 Specific attraction, equal in all bodies, 73

   „  heat of iron greater than copper, 132

 Sphere, Metal, on top of conductors, 111

 Spike of iron (_See_ POINT).

 Spiral twisted iron rods, 192

 Spires, Church, conductor for, how fixed, 23

 Spire, Church, conductors for without joints, 24

 Spires, connection from bottom of vane rod, 14

 Spout, Iron, entered by lightning, 43

 Spout split at joints, 45, 46, 47, 49

 Spratt’s patent conductors, 205, 210, 215

 Spurn Point High Light, 184

 Square building to have terminal at each end, 125

   „  wire, 13, 216

 Staples for attaching conductor (_See_ ATTACHMENT).

 Static discharges from conductors, 133

   „  electricity, laws of, 132

 Stays, Metal, 184,185

 Steeple of Jacobi Church, at Hamburg, 129

 Steeples to have horizontal conductors, 113, 125

 Steeple with lightning rod injured, 124, 125

 Steinheil’s lightning protector, 130

 Sterriker, John, his report, 45, 46

 Straps and nails (_See_ ATTACHMENT).

 Strasbourg, accident at, 99

 Straw conductors for country use, 104

 Strata, water bearing, connection to be made with (_See_ EARTH
    TERMINAL).

 Stream of fire in rigging of ship, 54

 Striking distance, 650 to, 6500 feet, 108

 Stroke, lightning, 9 or, 10 miles, 108

 Sullivan, Adml. 183, 195, 199

 Sulphur Paste made of galena and melted, for end of conductor, 58

 Sulphurous fumes destructive to terminals, 131

   „  odour of lightning, 85

 Sun burner to lofty building, 201

 Superficial conductors, advantages of, 86

 Supports of protector soldered with zinc, 140

 Supposed perfect conductor, 131

 Surface exposed to air considerable, 139

   „  or mass, which conducts?, 13, 15, 18, 49, 74, 89, 132

 Swan Cotton Mill, 239

 Sweden, accidents from lightning, 126

 Symons, G. J., 43, 46, 183

   „  abstracts by, 74, 89, 99, 102, 104, 111, 115, 131, 132, 134, 135


 Tacchini, Prof., 179, 180

 Tait, Prof., on thunderstorms, 241

 Tanks, 15, 71, 94, 107, 130

 Tape, joints, if any, should be rivetted and soldered, 7

   „  copper better than rope, 8, 204

   „  „  objections to, 5, 6, 16

   „  „  let into masts, 92

   „  lower end to have a discharging fork, 11

   „  Phin, upon, 103

   „  to be cut in strips for earth terminal, 15, 23

   „  copper, the sizes and lengths made, 7, 10, 14, 23, 70, 133

   „  cheaper than rope, 8, 9

 Tarred casing of wood to enclose iron, 125

   „  metallic rope, 60

 Taunton Church, large copper rope conductor, 8

 Teale, F. G., of Calcutta, 181

 Telegraph instruments injured, 100

   „  poles, how protected, 101

   „  wires affected underground, 101

 Temperature, variations of, affecting length of conductor, 68, 125, 226

 Terkelsen, C., abstract by, 106

 Terminal area protected by (_See_ PROTECTION, AREA OF).

 Terminals (_See_ POINTS).

 Terminal, earth (_See_ EARTH TERMINAL).

 Terminal for every, 20 ft. of roof, 125

   „  how fastened to roof, 52

   „  if numerous, should have proportionately thicker conductor (_See_
    AREA, SECTIONAL).

   „  long upper, 68, 77, 225, 229

   „  jar roof by vibration by wind, 116, 127

   „  not always pointed, 92, 125

   „  painted or tinned, 55

   „  rods, 17, 55, 66, 67, 72, 124

   „  „  to branch out at top
 %center%(_See_ POINTS).

   „  Upper, how attached to conductor, 60

   „  „  fused, 193

   „  „  should be cased in lead to protect from sulphurous fumes, 131

   „  „  to be a round rod, 125

   „  „  to be iron or copper, 82

   „  „  too small, 62

   „  „  what it is, 59

   „  „  what made of, 13

 Terra Cotta water pipes, 180

 Testing apparatus, 111, 225, 228, 243, 244

   „  of building as well as of conductor, 9

   „  of conductors with galvanometer, 9, 131

   „  to be periodical, 132, 244

 Theory of protection (_See_ PROTECTION, AREA OF).

 Thimbles, glass, 186

 Thomson, Prof. Sir W., on conductors, 47, 48, 49, 102, 133

 Thunderstorms dangerous where no woods are, 119

   „  in France, 1822, 123

   „  nature of, 85

 Ties, Metallic (_See_ ATTACHMENT).

 Tin and lead conductors tried, 123

 Tinfoil, experiments with, 199

 Tinned metallic wire, 95

 Tips (_See_ POINTS).

 Tomes, J., F.R.S,, accident to his house, 210

 Top conductor (_See_ CONDUCTOR RIDGE).

 Torquay, no good earth there, 130

 Tower of church struck, 29

   „  of house struck, 37

 Trees bad conductors, 127

 Trees, High, their protective action, 85, 127, 243

   „  injured while passing lightning to better conductor, 127

   „  on plains attract lightning, 127

   „  struck, 45, 47, 49

 Trenches, Connections in, 72

   „  filled with carbonaceous materials, 7, 12, 100, 125

   „  in rocky or dry soil, 72
   (_See also_ EARTH TERMINALS).

 Trough, Oaken, for lower terminals to pass through, 56

 Trinity House, 183

 Tube conductor for Houses of Parliament, 199

   „  Copper, 7, 10, 14, 70, 74, 133

   „  „  having copper cable passing through it, 13

   „  patent insertion joints, 7

   „  Iron, 86, 117

   „  conductors, why objectionable, 5

 Turrets, conductors for, how fixed, 23, 24

 Twyford Moors, near Winchester, 34


 Underground connection (_See_ EARTH TERMINAL).

 United States, accidents from lightning, 126

 University Coll., Chimney struck, 38

 University of Padua protected by conductors, 122

 Upper terminal (_See_ TERMINAL UPPER and POINTS).

 Upwood Gorse, Caterham, accident at, 210


 Vaillant, Le Maréchal, his Report, 66

 Vanes, how connected, &c., 10, 11, 14, 23, 39, 40, 52, 53, 104, 183,
    185, 186, 202

 Varley, C., quoted, 101

 Venetians decreed to use lightning rods in Republic, 122

 Ventilating pipes, 216

 Vitreous tubes (Fulgurites) formed by electricity, 112

 Vyle’s, S., rod & testing apparatus, 244


 Walker, C. V., on conductors, 84

   „  on Leyden discharges, 84

   „  J., 187

   „  Matthew, His knot, 16

 Wall eyes of iron, 130

 %center%(_See also_ ATTACHMENT).

 Wandsworth, chimney of house struck, 38

 Ward, G. G., of New York, 181

 Water mains and underground water generally (_See_ EARTH TERMINALS).

 Water spouts to be connected, 10, 226

 Watson’s, Dr., conductor at Payneshill, 85

   „  „  for ships, 121

   „  report, 76, 79

 Weathercock (_See_ VANES).

 Weber, Dr. L., on lightning discharges in Schleswig Holstein, 127, 231

 Week, St. Mary, the Church of, 29, 30

 Weight of conductors (_See_ CONDUCTORS, SIZE OF).

 Wells (_See_ EARTH TERMINALS).

 Wells Church, Norfolk, destruction of, by lightning, 194

 West side of house, rod to be on, 100

 Wheatstone quoted, on fusion of rod, 83

 Whichcord, J., his joint Report, 28

 White, W. H., Secretary R.I.B.A., circular signed by him, 28

 Wilkins & Weatherby, their answer, 4–6, 17

 Wilson, Mr., his report and views, 76, 79

 Wilson, R., on conductors on chimneys, 110

 Wind, action of on conductors, 116, 127

 Windmill with conductor struck, 128

 Windows, copper, to magazines, 74

 Winkler, Prof. J. H. (1746), electricity cause of thunderstorm, 129

 Wire cables (_See_ ROPE).

   „  cage as protection without use of earth, 132

   „  melted into drops like shot, 195

   „  of zinc melted, 107

   „  rusted in earth and was useless, 107

   „  square, 13, 216

 Withers, J. B. M., his report, 40

 Wood to be creosoted to form case for iron, 125

   „  coated with resin, as a conductor, 54

 Workhouse, how to be protected, 10

 Wrexham Church struck, 126

 Wrottesley, Col. G., R.E., his report, 40

 Wrought iron (_See_ IRON).

 Wyatt Papworth Church struck, 39


 York, accident at, 219


 Zenger’s, Prof. C., Symmetrische Blitzableiter, 104

 Zinc better conductor than iron, 74

   „  coating, 72

   „  chimney of house struck, 37

   „  cylinder, wire to pass through, 83

   „  strips, 192

   „  wire melted, 107

------------------------------------------------------------------------




                          TRANSCRIBER’S NOTES


 1. P. 170, changed “Annals of Electricity. 10 vols. 8vo. 18363–4” to
      “Annals of Electricity. 10 vols. 8vo. 1836”.
 2. Silently corrected typographical errors and also variations in
      spelling.
 3. Retained anachronistic, non-standard, and uncertain spellings as
      printed.
 4. Enclosed italics font in _underscores_.
 5. Enclosed bold font in =equals=.
 6. Enclosed small font in ¤currency signs¤.
 7. Superscripts are denoted by a caret before a single superscript
      character or a series of superscripted characters enclosed in
      curly braces, e.g. M^r. or M^{ister}.
 8. Subscripts are denoted by an underscore before a series of
      subscripted characters enclosed in curly braces, e.g. H_{2}O.