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                               LETTERS

                                  ON

                            NATURAL MAGIC,

                             ADDRESSED TO

                        SIR WALTER SCOTT, BART.

                                  BY

                   SIR DAVID BREWSTER, LL.D., F.R.S.

      [Illustration: Three figures on hill-top saluting sunrise]

                           SEVENTH EDITION.

                                LONDON:
                WILLIAM TEGG AND Co., 85, QUEEN STREET.
                              CHEAPSIDE.
                                 1856.




CONTENTS.


  LETTER I.

  Extent and interest of the subject--Science employed by
  ancient governments to deceive and enslave their subjects--Influence
  of the supernatural upon ignorant minds--Means
  employed by the ancient magicians to establish
  their authority--Derived from a knowledge of the phenomena
  of Nature--From the influence of narcotic drugs
  upon the victims of their delusion--From every branch of
  science--Acoustics--Hydrostatics--Mechanics--Optics--M.
  Salverte’s work on the occult sciences--Object of
  the following letters                                  Page 1


  LETTER II.

  The eye the most important of our organs--Popular description
  of it--The eye is the most fertile source of mental
  illusions--Disappearance of objects when their images fall
  upon the base of the optic nerve--Disappearance of objects
  when seen obliquely--Deceptions arising from viewing
  objects in a faint light--Luminous figures created by
  pressure on the eye, either from external causes or from
  the fulness of the blood-vessels--Ocular spectra or accidental
  colours--Remarkable effects produced by intense
  light--Influence of the imagination in viewing these
  spectra--Remarkable illusion produced by this affection
  of the eye--Duration of impressions of light on the
  eye--Thaumatrope--Improvements upon it suggested--Disappearance
  of halves of objects or of one of two persons--Insensibility
  of the eye to particular colours--Remarkable
  optical illusion described                                  8

  LETTER III.

  Subject of spectral illusions--Recent and interesting case
  of Mrs. A.--Her first illusion affecting the ear--Spectral
  apparition of her husband--Spectral apparition of a cat--Apparition
  of a near and living relation in grave-clothes,
  seen in a looking-glass--Other illusions, affecting
  the ear--Spectre of a deceased friend sitting in an
  easy-chair--Spectre of a coach-and-four filled with
  skeletons--Accuracy and value of the preceding cases--State of
  health under which they arose--Spectral apparitions are
  pictures on the retina--The ideas of memory and imagination
  are also pictures on the retina--General views of
  the subject--Approximate explanation of spectral apparitions  37


  LETTER IV.

  Science used as an instrument of imposture--Deceptions
  with plane and concave mirrors practised by the ancients--The
  magician’s mirror--Effects of concave mirrors--Aërial
  images--Images on smoke--Combination of
  mirrors for producing pictures from living objects--The
  mysterious dagger--Ancient miracles with concave
  mirrors--Modern necromancy with them, as seen by Cellini--Description
  and effects of the magic lantern--Improvements
  upon it--Phantasmagoric exhibitions of
  Philipstall and others--Dr. Young’s arrangement of
  lenses, &c., for the Phantasmagoria--Improvements
  suggested--Catadioptrical phantasmagoria for producing
  the pictures from living objects--Method of cutting off
  parts of the figures--Kircher’s mysterious hand-writing on
  the wall--His hollow cylindrical mirror for aërial images--Cylindrical
  mirror for re-forming distorted pictures--Mirrors
  of variable curvature for producing caricatures            56


  LETTER V.

  Miscellaneous optical illusions--Conversions of cameos into
  intaglios, or elevations into depressions, and the
  reverse--Explanation of this class of deceptions--Singular
  effects of illumination with light of one simple colour--Lamps
  for producing homogeneous yellow light--Methods
  of increasing the effects of this exhibition--Method of
  reading the inscription of coins in the dark--Art of
  deciphering the effaced inscription of coins--Explanation
  of these singular effects--Apparent motion of the eyes
  in portraits--Remarkable examples of this--Apparent
  motion of the features of a portrait, when the eyes are
  made to move--Remarkable experiment of breathing
  light and darkness                                         98


  LETTER VI.

  Natural phenomena marked with the marvellous--Spectre
  of the Brocken described--Analogous phenomena--Aërial
  spectres seen in Cumberland--Fata Morgana in
  the Straits of Messina--Objects below the horizon raised
  and magnified by refraction--Singular example seen at
  Hastings--Dover Castle seen through the hill on which it
  stands--Erect and inverted images of distant ships seen
  in the air--Similar phenomena seen in the Arctic regions--Enchanted
  coast--Mr. Scoresby recognizes his father’s
  ship by its aërial image--Images of cows seen in the air--Inverted
  images of horses seen in South America--Lateral
  images produced by refraction--Aërial spectres
  by reflexion--Explanation of the preceding phenomena      127


  LETTER VII.

  Illusions depending on the ear--Practised by the ancients--Speaking
  and singing heads of the ancients--Exhibition
  of the Invisible Girl described and explained--Illusions
  arising from the difficulty of determining the direction
  of sounds--Singular example of this illusion--Nature of
  ventriloquism--Exhibitions of some of the most celebrated
  ventriloquists--M. St. Gille--Louis Brabant--M.
  Alexandre--Capt. Lyon’s account of Esquimaux ventriloquists 157
  LETTER VIII.

  Musical and harmonic sounds explained--Power of breaking
  glasses with the voice--Musical sounds from the
  vibration of a column of air--and of solid
  bodies--Kaleidophone--Singular acoustic figures produced on
  sand laid on vibrating plates of glass--and on stretched
  membranes--Vibration of flat rulers and cylinders of
  glass--Production of silence from two sounds--Production
  of darkness from two lights--Explanation of these
  singular effects--Acoustic automaton--Droz’s bleating
  sheep--Maillardet’s singing-bird--Vaucanson’s flute-player--His
  pipe and tabor-player--Baron Kempelen’s
  talking-engine--Kratzenstein’s speaking-machine--Mr.
  Willis’s researches                                       179


  LETTER IX.

  Singular effects in nature depending on sound--Permanent
  character of speech--Influence of great elevations on the
  character of sounds, and on the powers of speech--Power
  of sound in throwing down buildings--Dog killed
  by sound--Sounds greatly changed under particular circumstances--Great
  audibility of sounds during the night
  explained--Sounds deadened in media of different
  densities--Illustrated in the case of a glass of champagne--and
  in that of new-fallen snow--Remarkable echoes--Reverberations
  of thunder--Subterranean noises--Remarkable
  one at the Solfaterra--Echo at the Menai suspension
  bridge--Temporary deafness produced in diving-bells--Inaudibility
  of particular sounds to particular ears--Vocal
  powers of the statue of Memnon--Sounds in
  granite rocks--Musical mountain of El-Nakous              212


  LETTER X.

  Mechanical inventions of the ancients few in number--Ancient
  and modern feats of strength--Feats of Eckeberg
  particularly described--General explanation of them--Real
  feats of strength performed by Thomas Topham--Remarkable
  power of lifting heavy persons when the
  lungs are inflated--Belzoni’s feat of sustaining pyramids
  of men--Deception of walking along the ceiling in an
  inverted position--Pneumatic apparatus in the foot of
  the house-fly for enabling it to walk in opposition to
  gravity--Description of the analogous apparatus employed
  by the gecko lizard for the same purpose--Apparatus used
  by the Echineis remora, or sucking-fish                   244


  LETTER XI.

  Mechanical automata of the ancients--Moving tripods--Automata
  of Dædalus--Wooden pigeon of Archytas--Automatic
  clock of Charlemagne--Automata made by
  Turrianus for Charles V.--Camus’s automatic carriage
  made for Louis XIV.--Degenne’s mechanical peacock--Vaucanson’s
  duck which ate and digested its food--Du
  Moulin’s automata--Baron Kempelen’s automaton chess-player--Drawing
  and writing automata--Maillardet’s
  conjurer--Benefits derived from the passion for automata--Examples
  of wonderful machinery for useful purposes--Duncan’s
  tambouring machinery--Watt’s statue-turning
  machinery--Babbage’s calculating machinery                264


  LETTER XII.

  Wonders of chemistry--Origin, progress, and objects of
  alchemy--Art of breathing fire--Employed by Barchochebas,
  Eunus, &c.--Modern method--Art of walking
  upon burning coals and red-hot iron, and of plunging the
  hands in melted lead and boiling water--Singular property
  of boiling tar--Workmen plunge their hands in
  melted copper--Trial of ordeal by fire--Aldini’s incombustible
  dresses--Examples of their wonderful power in
  resisting flame--Power of breathing and enduring air of
  high temperatures--Experiments made by Sir Joseph
  Banks, Sir Charles Blagden, and Mr. Chantrey              227

  LETTER XIII.

  Spontaneous combustion--In the absorption of air by
  powdered charcoal--and of hydrogen by spongy platinum--Dobereiner’s
  lamp--Spontaneous combustion in the
  bowels of the earth--Burning cliffs--Burning soil--Combustion
  without flame--Spontaneous combustion of human
  beings--Countess Zangari--Grace Pett--Natural fire-temples
  of the Guebres--Spontaneous fires in the Caspian
  Sea--Springs of inflammable gas near Glasgow--Natural
  light-house of Maracaybo--New elastic fluids in the
  cavities--of gems--Chemical operations going on in their
  cavities--Explosions produced in them by heat--Remarkable
  changes of colour from chemical causes--Effects
  of the nitrous oxide or Paradise gas when
  breathed--Remarkable cases described--Conclusion          313




                                LETTERS

                                  ON

                            NATURAL MAGIC;

                             ADDRESSED TO

                        SIR WALTER SCOTT, BART.




LETTER I.

 Extent and interest of the subject--Science employed by ancient
 governments to deceive and enslave their subjects--Influence
 of the supernatural upon ignorant minds--Means employed by the
 ancient magicians to establish their authority--Derived from a
 knowledge of the phenomena of Nature--From the influence of narcotic
 drugs upon the victims of their delusion--From every branch of
 science--Acoustics--Hydrostatics--Mechanics--Optics--M. Salverte’s
 work on the occult sciences--Object of the following letters.


  MY DEAR SIR WALTER,

As it was at your suggestion that I undertook to draw up a popular
account of those prodigies of the material world which have received
the appellation of _Natural Magic_, I have availed myself of the
privilege of introducing it under the shelter of your name. Although
I cannot hope to produce a volume at all approaching in interest
to that which you have contributed to the Family Library, yet the
popular character of some of the topics which belong to this branch of
Demonology may atone for the defects of the following Letters; and I
shall deem it no slight honour if they shall be considered as forming
an appropriate supplement to your valuable work.

The subject of Natural Magic is one of great extent as well as of
deep interest. In its widest range, it embraces the history of the
governments and the superstitions of ancient times,--of the means by
which they maintained their influence over the human mind,--of the
assistance which they derived from the arts and the sciences, and from
a knowledge of the powers and phenomena of nature. When the tyrants
of antiquity were unable or unwilling to found their sovereignty on
the affections and interests of their people, they sought to entrench
themselves in the strongholds of supernatural influence, and to rule
with the delegated authority of Heaven. The prince, the priest, and the
sage, were leagued in a dark conspiracy to deceive and enslave their
species; and man, who refused his submission to a being like himself,
became the obedient slave of a spiritual despotism, and willingly bound
himself in chains when they seemed to have been forged by the gods.

This system of imposture was greatly favoured by the ignorance of these
early ages. The human mind is at all times fond of the marvellous,
and the credulity of the individual may be often measured by his own
attachment to the truth. When knowledge was the property of only one
caste, it was by no means difficult to employ it in the subjugation
of the great mass of society. An acquaintance with the motions of the
heavenly bodies, and the variations in the state of the atmosphere,
enabled its possessor to predict astronomical and meteorological
phenomena with a frequency and an accuracy which could not fail to
invest him with a divine character. The power of bringing down fire
from the heavens, even at times when the electric influence was
itself in a state of repose, could be regarded only as a gift from
heaven. The power of rendering the human body insensible to fire was
an irresistible instrument of imposture; and in the combinations of
chemistry, and the influence of drugs and soporific embrocations on the
human frame, the ancient magicians found their most available resources.

The secret use which was thus made of scientific discoveries and
of remarkable inventions, has no doubt prevented many of them from
reaching the present times; but though we are very ill informed
respecting the progress of the ancients in various departments of the
physical sciences, yet we have sufficient evidence that almost every
branch of knowledge had contributed its wonders to the magician’s
budget, and we may even obtain some insight into the scientific
acquirements of former ages, by a diligent study of their fables and
their miracles.

The science of _Acoustics_ furnished the ancient sorcerers with some of
their best deceptions. The imitation of thunder in their subterranean
temples could not fail to indicate the presence of a supernatural
agent. The golden virgins whose ravishing voices resounded through the
temple of Delphos;--the stone from the river Pactolus, whose trumpet
notes scared the robber from the treasure which it guarded;--the
speaking head which uttered its oracular responses at Lesbos; and the
vocal statue of Memnon, which began at the break of day to accost the
rising sun,--were all deceptions derived from science, and from a
diligent observation of the phenomena of nature.

The principles of _Hydrostatics_ were equally available in the work of
deception. The marvellous fountain which Pliny describes in the island
of Andros as discharging wine for seven days, and water during the rest
of the year;--the spring of oil which broke out in Rome to welcome the
return of Augustus from the Sicilian war,--the three empty urns which
filled themselves with wine at the annual feast of Bacchus in the city
of Elis,--the glass tomb of Belus which was full of oil, and which when
once emptied by Xerxes could not again be filled,--the weeping-statues,
and the perpetual lamps of the ancients,--were all the obvious effects
of the equilibrium and pressure of fluids.

Although we have no direct evidence that the philosophers of antiquity
were skilled in _Mechanics_, yet there are indications of their
knowledge by no means equivocal in the erection of the Egyptian
obelisks, and in the transportation of huge masses of stone, and their
subsequent elevation to great heights in their temples. The powers
which they employed, and the mechanism by which they operated, have
been studiously concealed, but their existence may be inferred from
results otherwise inexplicable; and the inference derives additional
confirmation from the mechanical arrangements which seemed to have
formed a part of their religious impostures. When, in some of the
infamous mysteries of ancient Rome, the unfortunate victims were
carried off by the gods, there is reason to believe that they were
hurried away by the power of machinery; and when Apollonius, conducted
by the Indian sages to the temple of their god, felt the earth rising
and falling beneath his feet, like the agitated sea, he was no doubt
placed upon a moving floor capable of imitating the heavings of the
waves. The rapid descent of those who consulted the oracle in the
cave of Trophonius,--the moving tripods which Apollonius saw in the
Indian temples,--the walking statues at Antium, and in the temple of
Hierapolis,--and the wooden pigeon of Archytas, are specimens of the
mechanical resources of the ancient magic.

But of all the sciences _Optics_ is the most fertile in marvellous
expedients. The power of bringing the remotest objects within the very
grasp of the observer, and of swelling into gigantic magnitude the
almost invisible bodies of the material world, never fails to inspire
with astonishment even those who understand the means by which these
prodigies are accomplished. The ancients, indeed, were not acquainted
with those combinations of lenses and mirrors which constitute the
telescope and the microscope, but they must have been familiar with
the property of lenses and mirrors to form erect and inverted images
of objects. There is reason to think that they employed them to effect
the apparition of their gods; and in some of the descriptions of the
optical displays which hallowed their ancient temples, we recognize
all the transformations of the modern phantasmagoria.

It would be an interesting pursuit to embody the information which
history supplies respecting the fables and incantations of the ancient
superstitions, and to show how far they can be explained by the
scientific knowledge which then prevailed. This task has, to a certain
extent, been performed by M. Eusebe Salverte, in a work on the occult
sciences which has recently appeared; but notwithstanding the ingenuity
and learning which it displays, the individual facts are too scanty to
support the speculations of the author, and the descriptions are too
meagre to satisfy the curiosity of the reader.[1]

 [1] We must caution the young reader against some of the views given
 in M. Salverte’s work. In his anxiety to account for everything
 miraculous by natural causes, he has ascribed to the same origin some
 of these events in sacred history which Christians cannot but regard
 as the result of divine agency.

In the following letters I propose to take a wider range, and to enter
into more minute and popular details. The principal phenomena of
nature, and the leading combinations of arts, which bear the impress of
a supernatural character, will pass under our review, and our attention
will be particularly called to those singular illusions of sense, by
which the most perfect organs either cease to perform their functions,
or perform them faithlessly; and where the efforts and the creations of
the mind predominate over the direct perceptions of external nature.

In executing this plan, the task of selection is rendered extremely
difficult by the superabundance of materials, as well as from the
variety of judgments for which these materials must be prepared. Modern
science may be regarded as one vast miracle, whether we view it in
relation to the Almighty Being by whom its objects and its laws were
formed, or to the feeble intellect of man, by which its depths have
been sounded, and its mysteries explored; and if the philosopher who is
familiarized with its wonders, and who has studied them as necessary
results of general laws, never ceases to admire and adore their Author,
how great should be their effect upon less gifted minds, who must ever
view them in the light of inexplicable prodigies!--Man has in all ages
sought for a sign from heaven, and yet he has been habitually blind to
the millions of wonders with which he is surrounded. If the following
pages should contribute to abate this deplorable indifference to all
that is grand and sublime in the universe, and if they should inspire
the reader with a portion of that enthusiasm of love and gratitude
which can alone prepare the mind for its final triumph, the labours of
the author will not have been wholly fruitless.




LETTER II.

 The eye the most important of our organs--Popular description
 of it--The eye is the most fertile source of mental
 illusions--Disappearance of objects when their images fall
 upon the base of the optic nerve--Disappearance of objects
 when seen obliquely--Deceptions arising from viewing objects
 in a faint light--Luminous figures created by pressure on the
 eye, either from external causes or from the fulness of the
 blood-vessels--Ocular spectra or accidental colours--Remarkable
 effects produced by intense light--Influence of the imagination
 in viewing these spectra--Remarkable illusion produced by this
 affection of the eye--Duration of impressions of light on the
 eye--Thaumatrope--Improvements upon it suggested--Disappearance of
 halves of objects or of one of two persons--Insensibility of the eye
 to particular colours--Remarkable optical illusion described.


Of all the organs by which we acquire a knowledge of external nature,
the eye is the most remarkable and the most important. By our other
senses the information we obtain is comparatively limited. The touch
and the taste extend no farther than the surface of our own bodies.
The sense of smell is exercised within a very narrow sphere, and that
of recognizing sounds is limited to the distance at which we hear the
bursting of a meteor and the crash of a thunderbolt. But the eye enjoys
a boundless range of observation. It takes cognizance not only of
other worlds belonging to the solar system, but of other systems of
worlds infinitely removed into the immensity of space; and when aided
by the telescope, the invention of human wisdom, it is able to discover
the forms, the phenomena, and the movements of bodies whose distance is
as inexpressible in language as it is inconceivable in thought.

While the human eye has been admired by ordinary observers for the
beauty of its form, the power of its movements, and the variety of its
expression, it has excited the wonder of philosophers by the exquisite
mechanism of its interior, and its singular adaptation to the variety
of purposes which it has to serve. The eyeball is nearly globular,
and is about an inch in diameter. It is formed externally by a tough
opaque membrane called the _sclerotic_ coat, which forms the white of
the eye, with the exception of a small circular portion in front called
the _cornea_. This portion is perfectly transparent, and so tough in
its nature as to afford a powerful resistance to external injury.
Immediately within the cornea, and in contact with it, is the _aqueous_
humour, a clear fluid, which occupies only a small part of the front
of the eye. Within this humour is the iris, a circular membrane, with
a hole in its centre called the _pupil_. The colour of the eye resides
in this membrane, which has the curious property of contracting and
expanding so as to diminish or enlarge the pupil,--an effect which
human ingenuity has not been able even to imitate. Behind the iris is
suspended the _crystalline_ lens, in a fine transparent capsule or bag
of the same form with itself. It is then succeeded by the _vitreous
humour_, which resembles the transparent white of an egg, and fills
up the rest of the eye. Behind the vitreous humour, there is spread
out on the inside of the eyeball a fine delicate membrane, called the
_retina_, which is an expansion of the _optic nerve_, entering the back
of the eye and communicating with the brain.

A perspective view and horizontal section of the left eye, shown in the
annexed figure, will convey a popular idea of its structure. It is,
as it were, a small camera obscura, by means of which the pictures of
external objects are painted on the retina, and, in a way of which we
are ignorant, it conveys the impression of them to the brain.

[Illustration: Fig. 1.]

This wonderful organ may be considered as the sentinel which guards the
pass between the worlds of matter and of spirit, and through which all
their communications are interchanged. The optic nerve is the channel
by which the mind peruses the hand-writing of Nature on the retina,
and through which it transfers to that material tablet its decisions
and its creations. The eye is consequently the principal seat of the
supernatural. When the indications of the marvellous are addressed to
us through the ear, the mind may be startled without being deceived,
and reason may succeed in suggesting some probable source of the
illusion by which we have been alarmed: but when the eye in solitude
sees before it the forms of life, fresh in their colours and vivid in
their outline; when distant or departed friends are suddenly presented
to its view; when visible bodies disappear and reappear without any
intelligible cause; and when it beholds objects, whether real or
imaginary, for whose presence no cause can be assigned, the conviction
of supernatural agency becomes, under ordinary circumstances,
unavoidable.

Hence it is not only an amusing but a useful occupation to acquire a
knowledge of those causes which are capable of producing so strange a
belief, whether it arises from the delusions which the mind practises
upon itself, or from the dexterity and science of others. I shall
therefore proceed to explain those illusions which have their origin in
the eye, whether they are general, or only occasionally exhibited in
particular persons, and under particular circumstances.

There are few persons aware that when they look with one eye, there is
some particular object before them to which they are absolutely blind.
If we look with the right eye, this point is always about 15° to the
right of the object which we are viewing, or to the right of the axis
of the eye or the point of most distinct vision. If we look with the
left eye, the point is as far to the left. In order to be convinced
of this curious fact, which was discovered by M. Mariotte, place two
coloured wafers upon a sheet of white paper at the distance of three
inches, and look at the left-hand wafer with the right eye at the
distance of about 11 or 12 inches, taking care to keep the eye straight
above the wafer, and the line which joins the eyes parallel to the line
which joins the wafers. When this is done, and the left eye closed, the
right-hand wafer will no longer be visible. The same effect will be
produced if we close the right eye and look with the left eye at the
right-hand wafer. When we examine the retina to discover to what part
of it this insensibility to light belongs, we find that the image of
the invisible wafer has fallen on the base of the optic nerve, or the
place where this nerve enters the eye and expands itself to form the
retina. This point is shown in the preceding figure by a convexity at
the place where the nerve enters the eye.

But though light of ordinary intensity makes no impression upon this
part of the eye, a very strong light does, and even when we use candles
or highly luminous bodies in place of wafers, the body does not wholly
disappear, but leaves behind a faint cloudy light, without, however,
giving anything like an image of the object from which the light
proceeds.

When the objects are _white_ wafers upon a _black_ ground, the white
wafer absolutely disappears, and the space which it covers appears to
be completely black; and as the light which illuminates a landscape
is not much different from that of a white wafer, we should expect,
whether we use one or both eyes,[2] to see a black or a dark spot
upon every landscape, within 15° of the point which most particularly
attracts our notice. The Divine Artificer, however, has not left his
work thus imperfect. Though the base of the optic nerve is insensible
to light that falls directly upon it, yet it has been made susceptible
of receiving luminous impressions from the parts which surround it; and
the consequence of this is, that when the wafer disappears, the spot
which is occupied, in place of being black, has always the same colour
as the ground upon which the wafer is laid, being white when the wafer
is placed upon a white ground, and red when it is placed upon a red
ground. This curious effect may be rudely illustrated by comparing the
retina to a sheet of blotting-paper, and the base of the optic nerve to
a circular portion of it covered with a piece of sponge. If a shower
falls upon the paper, the protected part will not be wetted by the rain
which falls upon the sponge that covers it, but in a few seconds it
will be as effectually wetted by the moisture which it absorbs from the
wet paper with which it is surrounded. In like manner the insensible
spot on the retina is stimulated by a borrowed light, and the apparent
defect is so completely removed, that its existence can be determined
only by the experiment already described.

 [2] When both eyes are open, the object whose image falls upon the
 insensible spot of the one eye is seen by the other, so that, though
 it is not invisible, yet it will only be half as luminous and,
 therefore two dark spots ought to be seen.

Of the same character, but far more general in its effects, and
important in its consequences, is another illusion of the eye which
presented itself to me several years ago. When the eye is steadily
occupied in viewing any particular object, or when it takes a fixed
direction while the mind is occupied with any engrossing topic of
speculation or of grief, it suddenly loses sight of, or becomes blind
to, objects seen indirectly, or upon which it is not fully directed.
This takes place whether we use one or both eyes, and the object which
disappears will reappear without any change in the position of the
eye, while other objects will vanish and revive in succession without
any apparent cause. If a sportsman, for example, is watching with
intense interest the motions of one of his dogs, his companion, though
seen with perfect clearness by indirect vision, will vanish, and the
light of the heath or of the sky will close in upon the spot which he
occupied.

In order to witness this illusion, put a little bit of white paper on
a green cloth, and, within three or four inches of it, place a narrow
strip of white paper. At the distance of twelve or eighteen inches, fix
one eye steadily upon the little bit of white paper, and in a short
time a part or even the whole of the strip of paper will vanish as if
it had been removed from the green cloth. It will again reappear, and
again vanish, the effect depending greatly on the steadiness with which
the eye is kept fixed. This illusion takes place when both the eyes are
open, though it is easier to observe it when one of them is closed. The
same thing happens when the object is luminous. When a candle is thus
seen by indirect vision, it never wholly disappears, but it spreads
itself out into a cloudy mass, the centre of which is blue, encircled
with a bright ring of yellow light.

This inability of the eye to preserve a sustained vision of objects
seen obliquely, is curiously compensated by the greater sensibility of
those parts of the eye that have this defect. The eye has the power
of seeing objects with perfect distinctness only when it is directed
straight upon them; that is, all objects seen indirectly are seen
indistinctly: but it is a curious circumstance, that when we wish to
obtain a sight of a very faint star, such as one of the satellites of
Saturn, we can see it most distinctly _by looking away from it_, and
when the eye is turned full upon it it immediately disappears.

Effects still more remarkable are produced in the eye when it views
objects that are difficult to be seen from the small degree of light
with which they happen to be illuminated. The imperfect view which we
obtain of such objects forces us to fix the eye more steadily upon
them; but the more exertion we make to ascertain what they are, the
greater difficulties do we encounter to accomplish our object. The
eye is actually thrown into a state of the most painful agitation,
the object will swell and contract, and partly disappear, and it will
again become visible when the eye has recovered from the delirium into
which it has been thrown. This phenomenon may be most distinctly seen
when the objects in a room are illuminated with the feeble gleam of a
fire almost extinguished; but it may be observed in daylight by the
sportsman when he endeavours to mark upon the monotonous heath the
particular spot where moor-game has alighted. Availing himself of
the slightest difference of tint in the adjacent heath, he keeps his
eye steadily fixed on it as he advances, but whenever the contrast of
illumination is feeble, he will invariably lose sight of his mark,
and if the retina is capable of taking it up, it is only to lose it a
second time.

This illusion is likely to be most efficacious in the dark, when there
is just sufficient light to render white objects faintly visible, and
to persons who are either timid or credulous must prove a frequent
source of alarm. Its influence, too, is greatly aided by another
condition of the eye, into which it is thrown during partial darkness.
The pupil expands nearly to the whole width of the iris, in order to
collect the feeble light which prevails; but it is demonstrable that
in this state the eye cannot accommodate itself to see near objects
distinctly, so that the forms of persons and things actually become
more shadowy and confused when they come within the very distance at
which we count upon obtaining the best view of them. These affections
of the eye are, we are persuaded, very frequent causes of a particular
class of apparitions which are seen at night by the young and the
ignorant. The spectres which are conjured up are always _white_,
because no other colour can be seen, and they are either formed out of
inanimate objects which reflect more light than others around them,
or of animals or human beings whose colour or change of place renders
them more visible in the dark. When the eye dimly descries an inanimate
object whose different parts reflect different degrees of light, its
brighter parts may enable the spectator to keep up a continued view
of it; but the disappearance and reappearance of its fainter parts,
and the change of shape which ensues, will necessarily give it the
semblance of a living form, and if it occupies a position which is
unapproachable, and where animate objects cannot find their way, the
mind will soon transfer to it a supernatural existence. In like manner
a human figure shadowed forth in a feeble twilight may undergo similar
changes, and after being distinctly seen while it is in a situation
favourable for receiving and reflecting light, it may suddenly
disappear in a position fully before, and within the reach of, the
observer’s eye; and if this evanescence takes place in a path or road
where there was no side-way by which the figure could escape, it is
not easy for an ordinary mind to efface the impression which it cannot
fail to receive. Under such circumstances we never think of distrusting
an organ which we have never found to deceive us; and the truth of
the maxim that “seeing is believing” is too universally admitted, and
too deeply rooted in our nature, to admit on any occasion of a single
exception.

In these observations we have supposed that the spectator bears along
with him no fears or prejudices, and is a faithful interpreter of the
phenomena presented to his senses; but if he is himself a believer
in apparitions, and unwilling to receive an ocular demonstration of
their reality, it is not difficult to conceive the picture which will
be drawn when external objects are distorted and caricatured by the
imperfect indications of his senses, and coloured with all the vivid
hues of the imagination.

Another class of ocular deceptions have their origin in a property of
the eye which has been very imperfectly examined. The fine nervous
fabric which constitutes the retina, and which extends to the brain,
has the singular property of being _phosphorescent by pressure_. When
we press the eyeball outwards by applying the point of the finger
between it and the nose, a circle of light will be seen, which Sir
Isaac Newton describes as “a circle of colours like those in the
feather of a peacock’s tail.” He adds, that “if the eye and the
figure remain quiet, these colours vanish in a second of time; but
if the finger be moved with a quavering motion, they appear again.”
In the numerous observations which I have made on these luminous
circles, I have never been able to observe any colour but white, with
the exception of a general red tinge which is seen when the eyelids
are closed, and which is produced by the light which passes through
them. The luminous circles, too, always continue while the pressure
is applied, and they may be produced as readily after the eye has
been long in darkness as when it has been recently exposed to light.
When the pressure is very gently applied, so as to compress the fine
pulpy substance of the retina, light is immediately created when the
eye is in total darkness; and when in this state light is allowed to
fall upon it, the part compressed is more sensible to light than any
other part, and consequently appears more luminous. If we increase the
pressure, the eyeball, being filled with incompressible fluids, will
protrude all round the point of pressure, and consequently the retina
at the protruded part will be _compressed_ by the outward pressure
of the contained fluid, while the retina on each side, namely, under
the point of pressure and beyond the protruded part, will be drawn
towards the protruded part or _dilated_. Hence the part under the
finger which was originally compressed is now _dilated_, the adjacent
parts _compressed_, and the more remote parts immediately without this
_dilated_ also. Now we have observed, that when the eye is, under
these circumstances, exposed to light, there is a bright luminous
circle shading off externally and internally into total darkness.
We are led, therefore, to the important conclusions, that when the
retina is compressed in total darkness it gives out light; that when
it is compressed when exposed to light, its sensibility to light is
increased; and that when it is _dilated under exposure to light, it
becomes absolutely blind, or insensible to all luminous impressions_.

When the body is in a state of perfect health, this phosphorescence
of the eye shows itself on many occasions. When the eye or the head
receives a sudden blow, a bright flash of light shoots from the
eyeball. In the act of sneezing, gleams of light are emitted from each
eye both during the inhalation of the air, and during its subsequent
protrusion, and in blowing air violently through the nostrils, two
patches of light appear above the axis of the eye and in front of it,
while other two luminous spots unite into one, and appear as it were
about the point of the nose when the eyes are directed to it. When
we turn the eyeball by the action of its own muscles, the retina is
affected at the place where the muscles are inserted, and there may
be seen opposite each eye, and towards the nose, two semicircles of
light, and other two extremely faint towards the temples. At particular
times, when the retina is more phosphorescent than at others, these
semicircles are expanded into complete circles of light.

In a state of indisposition, the phosphorescence of the retina
appears in new and more alarming forms. When the stomach is under a
temporary derangement accompanied with headache, the pressure of the
blood-vessels upon the retina shows itself, in total darkness, by a
faint blue light floating before the eye, varying in its shape, and
passing away at one side. This blue light increases in intensity,
becomes _green_ and then _yellow_, and sometimes rises to _red_, all
these colours being frequently seen at once, or the mass of light
shades off into darkness. When we consider the variety of distinct
forms which in a state of perfect health the imagination can conjure
up when looking into a burning fire, or upon an irregularly shaded
surface,[3] it is easy to conceive how the masses of coloured light
which float before the eye may be moulded by the same power into those
fantastic and natural shapes, which so often haunt the couch of the
invalid, even when the mind retains its energy, and is conscious of the
illusion under which it labours. In other cases, temporary blindness
is produced by pressure upon the optic nerve, or upon the retina; and
under the excitation of fever or delirium, when the physical cause
which produces spectral forms is at its height, there is superadded a
powerful influence of the mind, which imparts a new character to the
phantasms of the senses.

 [3] A very curious example of the influence of the imagination in
 creating distinct forms out of an irregularly shaded surface, is
 mentioned in the life of Peter Heaman, a Swede, who was executed for
 piracy and murder at Leith in 1822. We give it in his own words:--

 “One remarkable thing was, one day as we mended a sail, it being a
 very thin one, after laying it upon deck in folds, I took the tar
 brush and tarred it over in the places which I thought needed to be
 strengthened. But when we hoisted it up, I was astonished to see that
 the tar I had put upon it represented a gallows and a man under it
 without a head. The head was lying beside him. He was complete, body,
 thighs, legs, arms, and in every shape like a man. Now, I oftentimes
 made remarks upon it, and repeated them to the others. I always said
 to them all, You may depend upon it that something will happen. I
 afterwards took down the sail on a calm day, and sewed a piece of
 canvas over the figure to cover it, for I could not bear to have it
 always before my eyes.”

In order to complete the history of the illusions which originate in
the eye, it will be necessary to give some account of the phenomena
called _ocular spectra_, or _accidental colours_. If we cut a figure
out of red paper, and, placing it on a sheet of white paper, view it
steadily for some seconds with one or both eyes fixed on a particular
part of it, we shall observe the red colour to become less brilliant.
If we then turn the eye from the red figure upon the white paper,
we shall see a distinct _green_ figure, which is the _spectrum_, or
accidental colour of the _red_ figure. With differently coloured
figures we shall observe differently coloured spectra, as in the
following table:--

   COLOUR OF THE              COLOUR OF THE
  ORIGINAL FIGURES.          SPECTRAL FIGURES.

    Red,                      Bluish-green.
    Orange,                   Blue.
    Yellow,                   Indigo.
    Green,                    Reddish-violet.
    Blue,                     Orange-red.
    Indigo,                   Orange-yellow.
    Violet,                   Yellow.
    White,                    Black.
    Black,                    White.

The two last of these experiments, viz., white and black figures, may
be satisfactorily made by using a white medallion on a dark ground, and
a black profile figure. The spectrum of the former will be found to be
black, and that of the latter white.

These ocular spectra often show themselves without any effort on
our part, and even without our knowledge. In a highly painted room,
illuminated by the sun, those parts of the furniture on which the sun
does not directly fall have always the opposite or accidental colour.
If the sun shines through a chink in a _red_ window-curtain, its light
will appear _green_, varying as in the above table, with the colour of
the curtain; and if we look at the image of a candle, reflected from
the water in a _blue_ finger-glass, it will appear _yellow_. Whenever,
in short, the eye is affected with one prevailing colour, it sees at
the same time the spectral or accidental colour, just as when a musical
string is vibrating, the ear hears at the same time its fundamental and
its harmonic sounds.

If the prevailing light is _white_ and _very strong_, the spectra which
it produces are no longer black, but of various colours in succession.
If we look at the sun, for example, when near the horizon, or when
reflected from glass or water so as to moderate its brilliancy, and
keep the eye upon it steadily for a few seconds, we shall see, even for
hours afterwards, and whether the eyes are open or shut, a spectrum
of the sun varying in its colours. At first, with the eye open, it is
_brownish-red_ with a _sky-blue_ border, and when the eye is shut,
it is _green_ with a _red_ border. The _red_ becomes more brilliant,
and the _blue_ more vivid, till the impression is gradually worn off;
but even when they become very faint, they may be revived by a gentle
pressure on the eyeball.

Some eyes are more susceptible than others of these spectral
impressions, and Mr. Boyle mentions an individual who continued for
years to see the spectre of the sun when he looked upon bright objects.
This fact appeared to Locke so interesting and inexplicable, that he
consulted Sir Isaac Newton respecting its cause, and drew from him the
following interesting account of a similar effect upon himself:--“The
observation you mention in Mr. Boyle’s book of colours, I once made
upon myself with the hazard of my eyes. The manner was this: I looked
a very little while upon the sun in the looking-glass with my right
eye, and then turned my eyes into a dark corner of my chamber, and
winked, to observe the impression made, and the circles of colours
which encompassed it, and how they decayed by degrees, and at last
vanished. This I repeated a second and a third time. At the third time,
when the phantasm of light and colours about it were almost vanished,
intending my fancy upon them to see their last appearance, I found, to
my amazement, that they began to return, and by little and little to
become as lively and vivid as when I had newly looked upon the sun.
But when I ceased to intend my face upon them, they vanished again.
After this I found that as often as I went into the dark, and intended
my mind upon them, as when a man looks earnestly to see anything which
is difficult to be seen, I could make the phantasm return without
looking any more upon the sun; and the oftener I made it return, the
more easily I could make it return again. And at length, by repeating
this without looking any more upon the sun, I made such an impression
on my eye, that, if I looked upon the clouds, or a book, or any bright
object, I saw upon it a round bright spot of light like the sun, and,
which is still stranger, though I looked upon the sun with my right eye
only, and not with my left, yet my fancy began to make an impression
upon my left eye as well as upon my right. For if I shut my right eye,
and looked upon a book or the clouds with my left eye, I could see the
spectrum of the sun almost as plain as with my right eye, if I did
but intend my fancy a little while upon it: for at first, if I shut
my right eye, and looked with my left, the spectrum of the sun did
not appear till I intended my fancy upon it; but by repeating, this
appeared every time more easily. And now in a few hours’ time I had
brought my eyes to such a pass, that I could look upon no bright object
with either eye but I saw the sun before me, so that I durst neither
write nor read; but to recover the use of my eyes, shut myself up in
my chamber, made dark, for three days together, and used all means
in my power to direct my imagination from the sun. For if I thought
upon him, I presently saw his picture, though I was in the dark. But
by keeping in the dark; and employing my mind about other things, I
began, in three or four days, to have more use of my eyes again; and
by forbearing to look upon bright objects, recovered them pretty well;
though not so well but that, for some months after, the spectrums
of the sun began to return as often as I began to meditate upon the
phenomena, even though I lay in bed at midnight with my curtains drawn.
But now I have been well for many years, though I am apt to think, if
I durst venture my eyes, I could still make the phantasm return by
the power of my fancy. This story I tell you, to let you understand,
that in the observation related by Mr. Boyle, the man’s fancy probably
concurred with the impression made by the sun’s light to produce that
phantasm of the sun which he constantly saw in bright objects.”[4]

 [4] See the _Edinburgh Encyclopædia_, Art. ACCIDENTAL COLOURS.

I am not aware of any effects that had the character of supernatural
having been actually produced by the causes above described; but it
is obvious, that if a living figure had been projected against the
strong light which imprinted these durable spectra of the sun, which
might really happen when the solar rays are reflected from water, and
diffused by its ruffled surface, this figure would have necessarily
accompanied all the luminous spectres which the fancy created. Even in
ordinary lights, strange appearances may be produced by even transient
impressions; and if I am not greatly mistaken, the case which I am
about to mention is not only one which may occur, but which actually
happened. A figure dressed in _black_, and mounted upon a _white_
horse, was riding along, exposed to the bright rays of the sun,
which, through a small opening in the clouds, was throwing its light
only upon that part of the landscape. The _black_ figure was projected
against a white cloud, and the white horse shone with particular
brilliancy by its contrast with the dark soil against which it was
seen. A person interested in the arrival of such a stranger had been
for some time following his movements with intense anxiety, but, upon
his disappearance behind a wood, was surprised to observe the spectre
of the mounted stranger in the form of a _white_ rider upon a _black_
steed, and this spectre was seen for some time in the sky, or upon
any pale ground to which the eye was directed. Such an occurrence,
especially if accompanied with a suitable combination of events, might,
even in modern times, have formed a chapter in the history of the
marvellous.

It is a curious circumstance, that when the image of an object is
impressed upon the retina only for a few moments, the picture which
is left is exactly of the same colour with the object. If we look,
for example, at a window at some distance from the eye, and then
transfer the eye quickly to the wall, we shall see it distinctly, but
momentarily, with _light_ panes and _dark_ bars; but in a space of
time incalculably short, this picture is succeeded by the spectral
impression of the window, which will consist of _black_ panes and
_white_ bars. The similar spectrum, or that of the same colour as the
object, is finely seen in the experiment of forming luminous circles by
whirling round a burning stick, in which case the circles are always
red.

In virtue of this property of the eye, an object may be seen in
many places at once; and we may even exhibit at the same instant
the two opposite sides of the same object, or two pictures painted
on the opposite sides of a piece of card. It was found by a French
philosopher, M. D’Arcet, that the impression of light continued on the
retina about the eighth part of a second after the luminous body was
withdrawn, and upon this principle Dr. Paris has constructed the pretty
little instrument called the _Thaumatrope_, or the _Wonder-turner_. It
consists of a number of circular pieces of card, about two or three
inches broad, which may be twirled round with great velocity by the
application of the fore-finger and thumb of each hand to pieces of silk
string attached to opposite points of their circumference. On each
side of the circular piece of card is painted part of a picture, or
a part of a figure, in such a manner that the two parts would form a
group or a whole figure, if we could see both sides at once. Harlequin,
for example, is painted on one side, and Columbine on the other, so
that by twirling round the card the two are seen at the same time in
their usual mode of combination. The body of a Turk is drawn on one
side, and his head on the reverse, and by the rotation of the card the
head is replaced upon his shoulders. The principle of this illusion
may be extended to many other contrivances. Part of a sentence may be
written on one side of a card, and the rest on the reverse. Particular
letters may be given on one side, and others upon the other, or even
halves or parts of each letter may be put upon each side, or all these
contrivances may be combined, so that the sentiment which they express
can be understood only when all the scattered parts are united by the
revolution of the card.

As the revolving card is virtually transparent, so that bodies beyond
it can be seen through it, the power of the illusion might be greatly
extended by introducing into the picture other figures, either animate
or inanimate. The setting sun, for example, might be introduced into a
landscape; part of the flame of a fire might be seen to issue from the
crater of a volcano, and cattle grazing in a field might make part of
the revolutionary landscape. For such purposes, however, the form of
the instrument would require to be completely changed, and the rotation
should be effected round a standing axis by wheels and pinions, and a
screen placed in front of the revolving plane with open compartments
or apertures, through which the principal figures would appear. Had
the principle of this instrument been known to the ancients, it would
doubtless have formed a powerful engine of delusion in their temples,
and might have been more effective than the optical means which they
seem to have employed for producing the apparitions of their gods.

In certain diseased conditions of the eye, effects of a very remarkable
kind are produced. The faculty of seeing objects double is too common
to be noticed as remarkable; and though it may take place with only one
eye, yet, as it generally arises from a transient inability to direct
the axis of both eyes to the same point, it excites little notice.
That state of the eye, however, in which we lose sight of half of
every object at which we look, is more alarming and more likely to be
ascribed to the disappearance of part of the object than to a defect
of sight. Dr. Wollaston, who experienced this defect twice, informs us
that, after taking violent exercise, he “suddenly found that he could
see but half of a man whom he met, and that on attempting to read the
name of JOHNSON over a door, he saw only SON, the commencement of the
name being wholly obliterated from his view.” In this instance, the
part of the object which disappeared was towards his left; but on a
second occurrence of the same affection, the part which disappeared
was towards his right. There are many occasions on which this defect
of the eye might alarm the person who witnessed it for the first time.
At certain distances from the eye one of two persons would necessarily
disappear; and by a slight change of position either in the observer
or the person observed, the person that vanished would reappear, while
the other would disappear in his turn. The circumstances under which
these evanescences would take place could not be supposed to occur to
an ordinary observer, even if he should be aware that the cause had its
origin in himself. When a phenomenon so strange is seen by a person in
perfect health, as it generally is, and who has never had occasion to
distrust the testimony of his senses, he can scarcely refer it to any
other cause than a supernatural one.

Among the affections of the eye which not only deceive the person who
is subject to them, but those also who witness their operation, may be
enumerated the insensibility of the eye to particular colours. This
defect is not accompanied with any imperfection of vision, or connected
with any disease either of a local or a general nature, and it has
hitherto been observed in persons who possess a strong and a sharp
sight. Mr. Huddart has described the case of one Harris, a shoemaker
at Maryport in Cumberland, who was subject to this defect in a very
remarkable degree. He seems to have been insensible to every colour,
and to have been capable of recognizing only the two opposite tints
of _black_ and _white_. “His first suspicion of this defect arose
when he was about four years old. Having by accident found in the
street a child’s stocking, he carried it to a neighbouring house to
inquire for the owner. He observed the people call it a _red stocking_,
though he did not understand why they gave it that denomination, as he
himself thought it completely described by being called a stocking.
The circumstance, however, remained in his memory, and, with other
subsequent observations, led him to the knowledge of his defect. He
observed also, that when young, other children could discern cherries
on a tree by some pretended difference of colour, though he could only
distinguish them from the leaves by their difference of size and shape.
He observed also, that by means of this difference of colour, they
could see the cherries at a greater distance than he could, though he
could see other objects at as great a distance as they, that is, where
the sight was not assisted by the colour.” Harris had two brothers,
whose perception of colours was nearly as defective as his own. One of
these, whom Mr. Huddart examined, constantly mistook _light green_ for
_yellow_, and _orange_ for _grass green_.

Mr. Scott has described, in the Philosophical Transactions, his own
defect in perceiving colours. He states that he does not know any
_green_ in the world; that a _pink_ colour and a _pale blue_ are
perfectly alike; that he has often thought a _full red_ and a _full
green_ a good match; that he is sometimes baffled in distinguishing
a _full purple_ from a _deep blue_, but that he knows light, dark,
and middle _yellows_, and all degrees of _blue_ except _sky-blue_. “I
married my daughter to a genteel, worthy man, a few years ago; the
day before the marriage, he came to my house dressed in a new suit of
fine cloth clothes. I was much displeased that he should come, as I
supposed, in _black_, and said that he should go back to change his
colour. But my daughter said, No, no; the colour is very genteel; that
it was my eyes that deceived me. He was a gentleman of the law, in a
fine, rich, claret-coloured dress, which is as much black to my eyes as
any black that ever was dyed.” Mr. Scott’s father, his maternal uncle,
one of his sisters, and her two sons, had all the same imperfection.
Dr. Nichol has recorded a case where a naval officer purchased a
_blue_ uniform coat and waistcoat with _red_ breeches to match the
blue, and Mr. Harvey describes the case of a tailor at Plymouth, who
on one occasion repaired an article of dress with _crimson_ in place
of _black_ silk, and on another patched the elbow of a _blue_ coat
with a piece of _crimson_ cloth. It deserves to be remarked that our
celebrated countrymen, the late Mr. Dugald Stewart, Mr. Dalton, and
Mr. Troughton, have a similar difficulty in distinguishing colours.
Mr. Stewart discovered this defect when one of his family was admiring
the beauty of a Siberian crab-apple, which he could not distinguish
from the leaves but by its form and size. Mr. Dalton cannot distinguish
_blue_ from pink, and the solar spectrum consists only of two colours,
_yellow_ and _blue_. Mr. Troughton regards _red ruddy pinks_, and
brilliant _oranges_, as _yellows_, and _greens_ as _blues_, so that he
is capable only of appreciating _blue_ and _yellow_ colours.

In all those cases which have been carefully studied, at least in
three of them, in which I have had the advantage of making personal
observations, namely, those of Mr. Troughton, Mr. Dalton, and Mr.
Liston, the eye is capable of seeing the whole of the prismatic
spectrum, the red space appearing to be yellow. If the red space
consisted of homogeneous or simple red rays, we should be led to infer
that the eyes in question were not insensible to red light, but were
merely incapable of discriminating between the impressions of red and
yellow light. I have lately shown, however, that the prismatic spectrum
consists of three equal and coincident spectra of _red_, _yellow_, and
_blue_ light, and consequently, that much yellow and a small portion
of blue light exist in the red space; and hence it follows, that those
eyes which see only two colours, viz. _yellow_ and _blue_, in the
spectrum, are really insensible to the red light of the spectrum, and
see only the yellow with the small portion of blue with which the red
is mixed. The faintness of the yellow light which is thus seen in the
red space, confirms the opinion that the retina has not appreciated the
influence of the simple red rays.

If one of the two travellers who, in the fable of the chameleon, are
made to quarrel about the colour of that singular animal, had happened
to possess this defect of sight, they would have encountered at every
step of their journey, new grounds of dissension, without the chance
of finding an umpire who could pronounce a satisfactory decision.
Under certain circumstances, indeed, the arbiter might set aside the
opinions of both the disputants, and render it necessary to appeal to
some higher authority,

    ---- to beg he’d tell them if he knew
    Whether the thing was _red_ or _blue_.

[Illustration: _Fig. 2._]

In the course of writing the preceding observations an ocular illusion
occurred to myself of so extraordinary a nature, that I am convinced
it never was seen before, and I think it far from probable that it
will ever be seen again. Upon directing my eyes to the candles that
were standing before me, I was surprised to observe, apparently among
my hair, and nearly straight above my head, and far without the range
of vision, a distinct image of one of the candles inclined about 45°
to the horizon, as shown at A in Fig. 2. The image was as distinct and
perfect as if it had been formed by reflection from a piece of mirror
glass, though of course much less brilliant, and the position of the
image proved that it must be formed by reflection from a perfectly flat
and highly polished surface. But where such a surface could be placed,
and how, even if it were fixed, it could reflect the image of the
candle up through my head, were difficulties not a little perplexing.
Thinking that it might be something lodged in the eyebrow, I covered
it up from the light, but the image still retained its place. I then
examined the eyelashes with as little success, and was driven to the
extreme supposition that a crystallization was taking place in some
part of the aqueous humour of the eye, and that the image was formed by
the reflection of the light of the candle from one of the crystalline
faces. In this state of uncertainty, and, I may add, of anxiety, for
this last supposition was by no means an agreeable one, I set myself
down to examine the phenomenon experimentally. I found that the image
varied its place by the motion of the head and of the eyeball, which
proved that it was either attached to the eyeball or occupied a place
where it was affected by that motion. Upon inclining the candle at
different angles, the image suffered corresponding variations of
position. In order to determine the exact place of the reflecting
substance, I now took an opaque circular body and held it between
the eye and the candle till it eclipsed the mysterious image. By
bringing the body nearer and nearer the eyeball till its shadow became
sufficiently distinct to be seen, it was easy to determine the locality
of the reflector, because the shadow of the opaque body must fall
upon it whenever the image of the candle was eclipsed. In this way I
ascertained that the reflecting body was in the upper eyelash; and I
found, that, in consequence of being disturbed, it had twice changed
its inclination, so as to represent a vertical candle in the horizontal
position B, and afterwards in the inverted position C. Still, however,
I sought for it in vain, and even with the aid of a magnifier I
could not discover it. At last, however, Mrs. B., who possesses the
perfect vision of short-sighted persons, discovered, after repeated
examinations, between two eyelashes, a minute speck, which, upon being
removed with great difficulty, turned out to be a chip of red wax not
above the hundredth part of an inch in diameter, and having its surface
so perfectly flat and so highly polished that I could see in it the
same image of the candle, by placing it extremely near the eye. This
chip of wax had no doubt received its flatness and its polish from the
surface of a seal, and had started into my eye when breaking the seal
of a letter.

That this reflecting substance was the cause of the image of the
candle, cannot admit of a doubt; but the wonder still remains how the
images which it formed occupied so mysterious a place as to be seen
without the range of vision, and apparently through the head. In order
to explain this, let _m_ _n_, Fig. 2, be a lateral view of the eye. The
chip of wax was placed at _m_ at the root of the eyelashes, and being
nearly in contact with the outer surface of the cornea, the light of
the candle, which it reflected, passed very obliquely through the pupil
and fell upon the retina somewhere to the left of _n_, very near where
the retina terminates; but a ray thus falling obliquely on the retina
is seen, in virtue of the law of visible direction already explained,
in a line _n_ C perpendicular to the retina at the point near _n_,
where the ray fell. Hence the candle was necessarily seen through the
head as it were of the observer, and without the range of ordinary
vision. The comparative brightness of the reflected image still
surprises me; but even this, if the image really was brighter, may
be explained by the fact, that it was formed on a part of the retina
upon which light had never before fallen, and which may therefore
be supposed to be more sensible, than the parts of the membrane in
constant use, to luminous impressions.

Independent of its interest as an example of the marvellous in vision,
the preceding fact may be considered as a proof that the retina retains
its power to its very termination near the ciliary processes, and that
the law of visible direction holds true even without the range of
ordinary vision. It is therefore possible that a reflecting surface
favourably placed on the outside of the eye, or that a reflecting
surface in the inside of the eye, may cause a luminous image to fall
nearly on the extreme margin of the retina, the consequence of which
would be, that it would be seen in the back of the head, half way
between a vertical and a horizontal line.




LETTER III.

 Subject of spectral illusions--Recent and interesting case of Mrs.
 A.--Her first illusion affecting the ear--Spectral apparition of
 her husband--Spectral apparition of a cat--Apparition of a near and
 living relation in grave-clothes, seen in a looking-glass--Other
 illusions, affecting the ear--Spectre of a deceased friend
 sitting in an easy-chair--Spectre of a coach-and-four filled with
 skeletons--Accuracy and value of the preceding cases--State of health
 under which they arose--Spectral apparitions are pictures on the
 retina--The ideas of memory and imagination are also pictures on the
 retina--General views of the subject--Approximate explanation of
 spectral apparitions.


The preceding account of the different sources of illusion to which the
eye is subject is not only useful as indicating the probable cause of
any individual deception, but it has a special importance in preparing
the mind for understanding those more vivid and permanent spectral
illusions to which some individuals have been either occasionally or
habitually subject.

In these lesser phenomena, we find the retina so powerfully influenced
by external impressions, as to retain the view of visible objects
long after they are withdrawn: we observe it to be so excited by
local pressures of which we sometimes know neither the nature nor the
origin, as to see in total darkness moving and shapeless masses of
coloured light; and we find, as in the case of Sir Isaac Newton, and
others, that the imagination has the power of reviving the impressions
of highly luminous objects, months and even years after they were
first made. From such phenomena, the mind feels it to be no violent
transition to pass to those spectral illusions which, in particular
states of health, have haunted the most intelligent individuals, not
only in the broad light of day, but in the very heart of the social
circle.

This curious subject has been so ably and fully treated in your
Letters on Demonology, that it would be presumptuous in me to resume
any part of it on which you have even touched; but as it forms a
necessary branch of a Treatise on Natural Magic, and as one of the most
remarkable cases on record has come within my own knowledge, I shall
make no apology for giving a full account of the different spectral
appearances which it embraces, and of adding the results of a series of
observations and experiments on which I have been long occupied, with
the view of throwing some light on this remarkable class of phenomena.

A few years ago, I had occasion to spend some days under the same roof
with the lady to whose case I have above referred. At that time she
had seen no spectral illusions, and was acquainted with the subject
only from the interesting volume of Dr. Hibbert. In conversing with
her about the cause of these apparitions, I mentioned, that if she
should ever see such a thing, she might distinguish a genuine ghost,
existing externally, and seen as an external object, from one created
by the mind, by merely pressing one eye or straining them both, so
as to see objects double; for in this case the external object or
supposed apparition would invariably be doubled, while the impression
on the retina created by the mind would remain single. This observation
recurred to her mind when she unfortunately became subject to the same
illusions; but she was too well acquainted with their nature to require
any such evidence of their mental origin; and the state of agitation
which generally accompanies them seems to have prevented her from
making the experiment as a matter of curiosity.

1. The first illusion to which Mrs. A. was subject was one which
affected only the ear. On the 26th of December, 1830, about half-past
four in the afternoon, she was standing near the fire in the hall,
and on the point of going up stairs to dress, when she heard, as she
supposed, her husband’s voice calling her by name, “---- Come here!
come to me!” She imagined that he was calling at the door to have it
opened, but upon going there and opening the door she was surprised to
find no person there. Upon returning to the fire, she again heard the
same voice calling out very distinctly and loudly, “---- Come, come
here!” She then opened two doors of the same room, and upon seeing no
person she returned to the fire-place. After a few moments she heard
the same voice still calling, “---- ---- Come to me, come! come away!”
in a loud, plaintive, and somewhat impatient tone. She answered as
loudly, “Where are you? I don’t know where you are;” still imagining
that he was somewhere in search of her: but receiving no answer, she
shortly went up stairs. On Mr. A.’s return to the house, about half an
hour afterwards, she inquired why he called to her so often, and where
he was; and she was, of course, greatly surprised to learn that he had
not been near the house at the time. A similar illusion, which excited
no particular notice at the time, occurred to Mrs. A. when residing at
Florence about ten years before, and when she was in perfect health.
When she was undressing after a ball, she heard a voice call her
repeatedly by name, and she was at that time unable to account for it.

2. The next illusion which occurred to Mrs. A. was of a more alarming
character. On the 30th of December, about four o’clock in the
afternoon, Mrs. A. came down stairs into the drawing-room, which she
had quitted only a few minutes before, and on entering the room she
saw her husband, as she supposed, standing with his back to the fire.
As he had gone out to take a walk about half an hour before, she was
surprised to see him there, and asked him why he had returned so
soon. The figure looked fixedly at her with a serious and thoughtful
expression of countenance, but did not speak. Supposing that his mind
was absorbed in thought, she sat down in an arm-chair near the fire,
and within two feet at most of the figure, which she still saw standing
before her. As its eyes, however, still continued to be fixed upon her,
she said, after the lapse of a few minutes, “Why don’t you speak,----?”
The figure immediately moved off towards the window at the further end
of the room, with its eyes still gazing on her, and it passed so very
close to her in doing so, that she was struck by the circumstance of
hearing no step nor sound, nor feeling her clothes brushed against,
nor even any agitation in the air. Although she was now convinced that
the figure was not her husband, yet she never for a moment supposed
that it was anything supernatural, and was soon convinced that it was
a spectral illusion. As soon as this conviction had established itself
in her mind, she recollected the experiment which I had suggested, of
trying to double the object: but before she was able distinctly to do
this, the figure had retreated to the window, where it disappeared.
Mrs. A. immediately followed it, shook the curtains and examined the
window, the impression having been so distinct and forcible that she
was unwilling to believe that it was not a reality. Finding, however,
that the figure had no natural means of escape, she was convinced that
she had seen a spectral apparition like those recorded in Dr. Hibbert’s
work, and she consequently felt no alarm or agitation. The appearance
was seen in bright daylight, and lasted four or five minutes. When the
figure stood close to her it concealed the real objects behind it, and
the apparition was fully as vivid as the reality.

3. On these two occasions Mrs. A. was alone, but when the next phantasm
appeared her husband was present. This took place on the 4th of
January, 1830. About ten o’clock at night, when Mr. and Mrs. A. were
sitting in the drawing-room, Mr. A. took up the poker to stir the fire,
and when he was in the act of doing this, Mrs. A. exclaimed, “Why
there’s the cat in the room!” “Where?” asked Mr. A. “There, close to
you,” she replied. “Where?” he repeated. “Why on the rug, to be sure,
between yourself and the coal-scuttle.” Mr. A., who had still the
poker in his hand, pushed it in the direction mentioned: “Take care,”
cried Mrs. A., “take care, you are hitting her with the poker.” Mr.
A. again asked her to point out exactly where she saw the cat. She
replied, ”Why sitting up there close to your feet on the rug. She is
looking at me. It is Kitty--come here, Kitty!”--There were two cats
in the house, one of which went by this name, and they were rarely if
ever in the drawing-room. At this time Mrs. A. had no idea that the
sight of the cat was an illusion. When she was asked to touch it, she
got up for the purpose, and seemed as if she were pursuing something
which moved away. She followed a few steps, and then said, “It has gone
under the chair.” Mr. A. assured her it was an illusion, but she would
not believe it. He then lifted up the chair, and Mrs. A. saw nothing
more of it. The room was then searched all over, and nothing found in
it. There was a dog lying on the hearth, who would have betrayed great
uneasiness if a cat had been in the room, but he lay perfectly quiet.
In order to be quite certain, Mr. A. rang the bell, and sent for the
two cats, both of which were found in the housekeeper’s room.

4. About a month after this occurrence, Mrs. A., who had taken a
somewhat fatiguing drive during the day, was preparing to go to bed
about eleven o’clock at night, and, sitting before the dressing-glass,
was occupied in arranging her hair. She was in a listless and drowsy
state of mind, but fully awake. When her fingers were in active motion
among the papillotes, she was suddenly startled by seeing in the
mirror the figure of a near relation, who was then in Scotland and in
perfect health. The apparition appeared over her left shoulder, and
its eyes met hers in the glass. It was enveloped in grave-clothes,
closely pinned, as is usual with corpses, round the head, and under
the chin, and though the eyes were open, the features were solemn and
rigid. The dress was evidently a shroud, as Mrs. A. remarked even the
punctured pattern usually worked in a peculiar manner round the edges
of that garment. Mrs. A. described herself as at the time sensible of
a feeling like what we conceive of fascination, compelling her for a
time to gaze on this melancholy apparition, which was as distinct and
vivid as any reflected reality could be, the light of the candles upon
the dressing-table appearing to shine fully upon its face. After a few
minutes, she turned round to look for the reality of the form over her
shoulder; but it was not visible, and it had also disappeared from the
glass when she looked again in that direction.

5. In the beginning of March, when Mr. A. had been about a fortnight
from home, Mrs. A. frequently heard him moving near her. Nearly every
night, as she lay awake, she distinctly heard sounds like his breathing
hard on the pillow by her side, and other sounds such as he might make
while turning in bed.

6. On another occasion, during Mr. A.’s absence, while riding with
a neighbour, Mr.----, she heard his voice frequently as if he were
riding by his side. She heard also the tramp of his horse’s feet, and
was almost puzzled by hearing him address her at the same time with
the person really in company. His voice made remarks on the scenery,
improvements, &c., such as he probably should have done had he been
present. On this occasion, however, there was no visible apparition.

7. On the 17th March, Mrs. A. was preparing for bed. She had dismissed
her maid, and was sitting with her feet in hot water. Having an
excellent memory, she had been thinking upon and repeating to herself
a striking passage in the Edinburgh Review, when on raising her eyes,
she saw seated in a large easy-chair before her the figure of a
deceased friend, the sister of Mr. A. The figure was dressed as had
been usual with her, with great neatness, but in a gown of a peculiar
kind, such as Mrs. A. had never seen her wear, but exactly such as had
been described to her by a common friend as having been worn by Mr.
A.’s sister during her last visit to England. Mrs. A. paid particular
attention to the dress, air, and appearance of the figure, which sat
in an easy attitude in the chair, holding a handkerchief in one hand.
Mrs. A. tried to speak to it, but experienced a difficulty in doing
so; and in about three minutes the figure disappeared. About a minute
afterwards, Mr. A. came into the room, and found Mrs. A. slightly
nervous, but fully aware of the delusive nature of the apparition. She
described it as having all the vivid colouring and apparent reality
of life; and for some hours preceding this and other visions, she
experienced a peculiar sensation in her eyes, which seemed to be
relieved when the vision had ceased.

8. On the 5th October, between one and two o’clock in the morning, Mr.
A. was awoke by Mrs. A., who told him that she had just seen the figure
of his deceased mother draw aside the bedcurtains and appear between
them. The dress and the look of the apparition were precisely those in
which Mr. A.’s mother had been last seen by Mrs. A. at Paris, in 1824.

9. On the 11th October, when sitting in the drawing-room, on one side
of the fire-place, she saw the figure of another deceased friend
moving towards her from the window at the further end of the room. It
approached the fire-place, and sat down in the chair opposite. As there
were several persons in the room at the time, she describes the idea
uppermost in her mind to have been a fear lest they should be alarmed
at her staring, in the way she was conscious of doing, at vacancy, and
should fancy her intellect disordered. Under the influence of this
fear, and recollecting a story of a similar effect in your work on
Demonology, which she had lately read, she summoned up the requisite
resolution to enable her to cross the space before the fire-place, and
seat herself in the same chair with the figure. The apparition remained
perfectly distinct till she sat down, as it were, in its lap, when it
vanished.

10. On the 26th of the same month, about two P.M., Mrs.
A. was sitting in a chair by the window in the same room with her
husband. He heard her exclaim--”What have I seen?” And on looking at
her, he observed a strange expression in her eyes and countenance.
A carriage-and-four had appeared to her to be driving up the
entrance-road to the house. As it approached, she felt inclined to
go up stairs to prepare to receive company, but, as if spellbound,
she was unable to move or speak. The carriage approached, and as it
arrived within a few yards of the window, she saw the figures of
the postilions and the persons inside take the ghastly appearance of
skeletons and other hideous figures. The whole then vanished entirely,
when she uttered the above-mentioned exclamation.

11. On the morning of the 30th October, when Mrs. A. was sitting in her
own room with a favourite dog in her lap, she distinctly saw the same
dog moving about the room during the space of about a minute or rather
more.

12. On the 3rd December, about nine P.M., when Mr. and Mrs. A. were
sitting near each other in the drawing-room occupied in reading, Mr.
A. felt a pressure on his foot. On looking up he observed Mrs. A.’s
eyes fixed with a strong and unnatural stare on a chair about nine
or ten feet distant. Upon asking her what she saw, the expression of
her countenance changed, and upon recovering herself, she told Mr. A.
that she had seen his brother, who was alive and well at the moment in
London, seated in the opposite chair, but dressed in grave-clothes, and
with a ghastly countenance, as if scarcely alive.

Such is a brief account of the various spectral illusions observed by
Mrs. A. In describing them I have used the very words employed by her
husband in his communications to me on the subject;[5] and the reader
may be assured that the descriptions are neither heightened by fancy,
nor amplified by invention. The high character and intelligence of
the lady, and the station of her husband in society, and as a man of
learning and science, would authenticate the most marvellous narrative,
and satisfy the most scrupulous mind, that the case has been
philosophically as well as faithfully described. In narrating events
which we regard as of a supernatural character, the mind has a strong
tendency to give more prominence to what appears to itself the most
wonderful; but from the very same cause, when we describe extraordinary
and inexplicable phenomena which we believe to be the result of natural
causes, the mind is prone to strip them of their most marvellous
points, and bring them down to the level of ordinary events. From the
very commencement of the spectral illusions seen by Mrs. A., both she
and her husband were well aware of their nature and origin, and both
of them paid the most minute attention to the circumstances which
accompanied them, not only with the view of throwing light upon so
curious a subject, but for the purpose of ascertaining their connection
with the state of health under which they appeared.

 [5] _Edinburgh Journal of Science_, New Series, No. iv. pp. 218, 219,
 No. vi., p. 244, and No. viii., p. 261.

As the spectres seen by Nicolai and others had their origin in bodily
indisposition, it becomes interesting to learn the state of Mrs. A.’s
health when she was under the influence of these illusions. During the
six weeks within which the first three illusions took place, she had
been considerably reduced and weakened by a troublesome cough, and the
weakness which this occasioned was increased by her being prevented
from taking a daily tonic. Her general health had not been strong,
and long experience has put it beyond a doubt, that her indisposition
arises from a disordered state of the digestive organs. Mrs. A. has
naturally a morbidly sensitive imagination, which so painfully affects
her corporeal impressions, that the account of any person having
suffered severe pain by accident or otherwise, occasionally produces
acute twinges of pain in the corresponding parts of her person. The
account, for example, of the amputation of an arm will produce an
instantaneous and severe sense of pain in her own arm. She is subject
to talk in her sleep with great fluency, to repeat long passages of
poetry, particularly when she is unwell, and even to cap verses for
half an hour together, never failing to quote lines beginning with the
final letter of the preceding one till her memory is exhausted.

Although it is not probable that we shall ever be able to understand
the actual manner in which a person of sound mind beholds spectral
apparitions in the broad light of day, yet we may arrive at such a
degree of knowledge on the subject as to satisfy rational curiosity,
and to strip the phenomena of every attribute of the marvellous.
Even the vision of natural objects presents to us insurmountable
difficulties, if we seek to understand the precise part which the mind
performs in perceiving them; but the philosopher considers that he has
given a satisfactory explanation of vision, when he demonstrates that
distinct pictures of external objects are painted on the retina, and
that this membrane communicates with the brain by means of nerves of
the same substance as itself, and of which it is merely an expansion.
Here we reach the gulf which human intelligence cannot pass; and if the
presumptuous mind of man shall dare to extend its speculations farther,
it will do it only to evince its incapacity and mortify its pride.

In his admirable work on this subject, Dr. Hibbert has shown that
spectral apparitions are nothing more than ideas or the recollected
images of the mind, which, in certain states of bodily indisposition,
have been rendered more vivid than actual impression, or, to use other
words, that the pictures in the “mind’s eye” are more vivid than the
pictures in the body’s eye. This principle has been placed by Dr.
Hibbert beyond the reach of doubt; but I propose to go much farther,
and to show that the “mind’s eye” is actually the body’s eye, and that
the retina is the common tablet on which both classes of impressions
are painted, and by means of which they receive their visual existence
according to the same optical laws. Nor is this true merely in the
case of spectral illusions; it holds good of all ideas recalled by
the memory or created by the imagination, and may be regarded as a
fundamental law in the science of pneumatology.

It would be out of place in a work like this to adduce the experimental
evidence on which it rests, or even to explain the manner in which the
experiments themselves must be conducted: but I may state in general,
that the spectres conjured up by the memory or the fancy have always
a “local habitation,” and that they appear in front of the eye, and
partake in its movements exactly like the impressions of luminous
objects, after the objects themselves are withdrawn.

In the healthy state of the mind and body, the relative intensity of
these two classes of impressions on the retina is nicely adjusted. The
mental pictures are transient and comparatively feeble, and in ordinary
temperaments are never capable of disturbing or effacing the direct
images of visible objects. The affairs of life could not be carried on
if the memory were to intrude bright representations of the past into
the domestic scene, or scatter them over the external landscape. The
two opposite impressions, indeed, could not co-exist: the same nervous
fibre which is carrying from the brain to the retina the figures of
memory, could not at the same instant be carrying back the impressions
of external objects from the retina to the brain. The mind cannot
perform two different functions at the same instant, and the direction
of its attention to one of the two classes of impressions necessarily
produces the extinction of the other: but so rapid is the exercise
of mental power, that the alternate appearance and disappearance
of the two contending impressions are no more recognized than the
successive observations of external objects during the twinkling of
the eyelids. If we look for example at the façade of St. Paul’s, and
without changing our position call to mind the celebrated view of
Mont Blanc from Lyons, the picture of the cathedral, though actually
impressed upon the retina, is momentarily lost sight of by the mind,
exactly like an object seen by indirect vision; and during the instant
the recollected image of the mountain, towering over the subjacent
range, is distinctly seen, but in a tone of subdued colouring and
indistinct outline. When the purpose of its recall is answered, it
quickly disappears, and the picture of the cathedral again resumes the
ascendancy.

In darkness and solitude, when external objects no longer interfere
with the pictures of the mind, they become more vivid and distinct;
and in the state between waking and sleeping the intensity of the
impressions approaches to that of visible objects. With persons of
studious habits, who are much occupied with the operations of their
own minds, the mental pictures are much more distinct than in ordinary
persons; and in the midst of abstract thought, external objects even
cease to make any impression on the retina. A philosopher absorbed in
his contemplations experiences a temporary privation of the use of
his senses. His children or his servants will enter the room directly
before his eyes without being seen. They will speak to him without
being heard; and they will even try to rouse him from his reverie
without being felt; although his eyes, his ears, and his nerves
actually receive the impressions of light, sound, and touch. In such
cases, however, the philosopher is voluntarily pursuing a train of
thought on which his mind is deeply interested; but even ordinary
men, not much addicted to speculations of any kind, often perceive in
their mind’s eye the pictures of deceased or absent friends, or even
ludicrous creations of fancy, which have no connexion whatever with the
train of their thoughts. Like spectral apparitions they are entirely
involuntary, and though they may have sprung from a regular series of
associations, yet it is frequently impossible to discover a single link
in the chain.

If it be true, then, that the pictures of the mind and spectral
illusions are equally impressions upon the retina, the latter will
differ in no respect from the former, but in the degree of vividness
with which they are seen; and those frightful apparitions become
nothing more than our ordinary ideas, rendered more brilliant by some
accidental and temporary derangement of the vital functions. Their
very vividness, too, which is their only characteristic, is capable
of explanation. I have already shown that the retina is rendered
more sensible to light by voluntary local pressure, as well as by
the involuntary pressure of the blood-vessels behind it; and if, by
looking at the sun, we impress upon the retina a coloured image of that
luminary, which is seen even when the eye is shut, we may by pressure
alter the colour of that image, in consequence of having increased the
sensibility of that part of the retina on which it is impressed. Hence
we may readily understand how the vividness of the mental pictures must
be increased by analogous causes.

In the case both of Nicolai and Mrs. A. the immediate cause of the
spectres was a deranged action of the stomach. When such a derangement
is induced by poison, or by substances which act as poisons, the retina
is peculiarly affected, and the phenomena of vision are singularly
changed. Dr. Patouillet has described the case of a family of _nine_
persons who were all driven mad by eating the root of the _hyoscyamus
niger_, or black henbane. One of them leapt into a pond, another
exclaimed that his neighbour would lose a cow in a month, and a third
vociferated that the crown piece of sixty pence would in a short time
rise to five livres. On the following day they had all recovered their
senses, but recollected nothing of what had happened. On the same day
they all saw objects double, and, what is still more remarkable, on
the third day _every object appeared to them as red as scarlet_. Now
this red light was probably nothing more than the red phosphorescence
produced by the pressure of the blood-vessels on the retina, and
analogous to the masses of _blue_, _green_, _yellow_, and _red_ light,
which have been already mentioned as produced by a similar pressure in
headaches, arising from a disordered state of the digestive organs.

Were we to analyse the various phenomena of spectral illusions, we
should discover many circumstances favourable to these views. In those
seen by Nicolai, the individual figures were always somewhat paler than
natural objects. They sometimes grew more and more indistinct, and
became perfectly white; and, to use his own words, “he could always
distinguish with the greatest precision phantasms from phenomena.”
Nicolai sometimes saw the spectres when his eyes were shut, and
sometimes they were thus made to disappear,--effects perfectly
identical with those which arise from the impressions of very luminous
objects. Sometimes the figures vanished entirely, and at other times
only pieces of them disappeared, exactly conformable to what takes
place with objects seen by indirect vision, which most of those figures
must necessarily have been.

Among the peculiarities of spectral illusions, there is one which
merits particular attention, namely, that they seem to cover or conceal
objects immediately beyond them. It is this circumstance more than any
other which gives them the character of reality, and at first sight it
seems difficult of explanation. The distinctness of any impression on
the retina is entirely independent of the accommodation of the eye
to the distinct vision of external objects. When the eye is at rest,
and is not accommodated to objects at any particular distance, it is
in a state for seeing distant objects most perfectly. When a distinct
spectral impression, therefore, is before it, all other objects in its
vicinity will be seen indistinctly, for while the eye is engrossed with
the vision, it is not likely to accommodate itself to any other object
in the same direction. It is quite common, too, for the eye to see only
one of two objects actually presented to it. A sportsman who has been
in the practice of shooting with both his eyes open, actually sees a
double image of the muzzle of his fowling-piece, though it is only
with one of these images that he covers his game, having no perception
whatever of the other. But there is still another principle upon which
only one of two objects may be seen at a time. If we look very steadily
and continuously at a double pattern, such as those on a carpet
composed of two single patterns of different colours, suppose _red_ and
_yellow_; and if we direct the mind particularly to the contemplation
of the red one, the green pattern will sometimes vanish entirely,
leaving the red alone visible; and by the same process the red one may
be made to disappear. In this case, however, the two patterns, like
the two images, may be seen together; but if the very same portion of
the retina is excited by the direct rays of an external object, when
it is excited by a mental impression, it can no more see them both
at the same time, than a vibrating string can give out two different
fundamental sounds. It is quite possible, however, that the brightest
parts of a spectral figure may be distinctly seen along with the
brightest parts of an object immediately behind it, but then the bright
parts of each object will fall upon different parts of the retina.

These views are illustrated by a case mentioned by Dr. Abercrombie. A
gentleman, who was a patient of his, of an irritable habit, and liable
to a variety of uneasy sensations in his head, was sitting alone in his
dining-room in the twilight, when the door of the room was a little
open. He saw distinctly a female figure enter, wrapped in a mantle,
with the face concealed by a large black bonnet. She seemed to advance
a few steps towards him, and then stop. He had a full conviction that
the figure was an illusion of vision, and he amused himself for some
time by watching it; at the same time observing that he could see
through the figure so as to perceive the lock of the door, and other
objects behind it.[6]

 [6] Inquiries concerning the Intellectual Powers, and the
 Investigation of Truth. Edinburgh, 1830.

If these views be correct, the phenomena of spectral apparitions
are stripped of all their terror, whether we view them in their
supernatural character, or as indications of bodily indisposition.
Nicolai, even, in whose case they were accompanied with alarming
symptoms, derived pleasure from the contemplation of them, and he
not only recovered from the complaint in which they originated, but
survived them for many years.--Mrs. A., too, who sees them only at
distant intervals, and with whom they have but a fleeting existence,
will, we trust, soon lose her exclusive privilege, when the slight
indisposition which gives them birth has subsided.




LETTER IV.

 Science used as an instrument of imposture--Deceptions with plane
 and concave mirrors practised by the ancients--The magician’s
 mirror--Effects of concave mirrors--Aërial images--Images on
 smoke--Combination of mirrors for producing pictures from living
 objects--The mysterious dagger--Ancient miracles with concave
 mirrors--Modern necromancy with them, as seen by Cellini--Description
 and effects of the magic lantern--Improvements upon it--Phantasmagoric
 exhibitions of Philipstall and others--Dr. Young’s arrangement
 of lenses, &c., for the Phantasmagoria--Improvements
 suggested--Catadioptrical phantasmagoria for producing the
 pictures from living objects--Method of cutting off parts of the
 figures--Kircher’s mysterious hand-writing on the wall--His hollow
 cylindrical mirror for aërial images--Cylindrical mirror for
 re-forming distorted pictures--Mirrors of variable curvature for
 producing caricatures.


In the preceding observations man appears as the victim of his own
delusions--as the magician unable to exercise the spirits which he
has himself called into being. We shall now see him the dupe of
preconcerted imposture--the slave of his own ignorance--the prostrate
vassal of power and superstition. I have already stated that the
monarchs and priests of ancient times carried on a systematic plan
of imposing upon their subjects--a mode of government which was in
perfect accordance with their religious belief: but it will scarcely be
believed that the same delusions were practised after the establishment
of Christianity, and that even the Catholic sanctuary was often the
seat of these unhallowed machinations. Nor was it merely the low and
cunning priest who thus sought to extort money and respect from the
most ignorant of his flock: bishops and pontiffs themselves wielded
the magician’s wand over the diadem of kings and emperors, and, by
the pretended exhibition of supernatural power, made the mightiest
potentates of Europe tremble upon their thrones. It was the light of
science alone which dispelled this moral and intellectual darkness,
and it is entirely in consequence of its wide diffusion that we live
in times when sovereigns seek to reign only through the affections of
their people, and when the minister of religion asks no other reverence
but that which is inspired by the sanctity of his office and the purity
of his character.

It was fortunate for the human race that the scanty knowledge of former
ages afforded so few elements of deception. What a tremendous engine
would have been worked against our species by the varied and powerful
machinery of modern science! Man would still have worn the shackles
which it forged, and his noble spirit would still have groaned beneath
its fatal pressure.

There can be little doubt that the most common, as well as the most
successful, impositions of the ancients were of an optical nature,
and were practised by means of plane and concave mirrors. It has been
clearly shown by various writers that the ancients made use of mirrors
of steel, silver, and a composition of copper and tin, like those now
used for reflecting specula. It is also very probable, from a passage
in Pliny, that glass mirrors were made at Sidon; but it is evident,
that, unless the object presented to them was illuminated in a very
high degree, the images which they formed must have been very faint and
unsatisfactory. The silver mirrors, therefore, which were universally
used, and which are superior to those made of any other metal, are
likely to have been most generally employed by the ancient magicians.
They were made to give multiplied and inverted images of objects, that
is, they were plane, polygonal or many-sided, and concave. There is
one property, however, mentioned by Aulus Gellius, which has given
unnecessary perplexity to commentators. He states that there were
specula, which, when put in a particular place, gave no images of
objects, but when carried to another place, recovered their property
of reflection.[7] M. Salverte is of opinion that, in quoting Varro,
Aulus Gellius was not sufficiently acquainted with the subject, and
erred in supposing that the phenomenon depended on the _place_ instead
of the position of the mirror; but this criticism is obviously made
with the view of supporting an opinion of his own--that the property
in question may be analogous to the phenomenon of polarised light,
which, at a certain angle, refuses to suffer reflexion from particular
bodies. If this idea has any foundation, the mirror must have been of
glass or some other body not metallic, or, to speak more correctly,
there must have been _two_ such mirrors, so nicely adjusted not only
to one another, but to the light incident upon each, that the effect
could not possibly be produced but by a philosopher thoroughly
acquainted with the modern discovery of the polarisation of light
by reflexion. Without seeking for so profound an explanation of the
phenomenon, we may readily understand how a silver mirror may instantly
lose its reflecting power in a damp atmosphere, in consequence of the
precipitation of moisture upon its surface, and may immediately recover
it when transported into drier air.

 [7] _Ut speculum in loco certo positum nihil imaginet; aliorsum
 translatum faciat imagines._ Aul. Gel. Noct. Attic., lib. xvi., cap.
 18.

[Illustration: _Fig. 3._]

One of the simplest instruments of optical deception is the plane
mirror, and when two are combined for this purpose it has been called
the magician’s mirror. An observer in front of a plane mirror sees a
distinct image of himself; but if two persons take up a mirror, and
if the one person is as much to one side of a line perpendicular to
the middle of it as the other is to the other side, they will see each
other, but not themselves. If we now suppose MC, CD, NC, CD to be the
partitions of two adjacent apartments let square openings be made in
the partitions at A and B, above five feet above the floor, and let
them be filled with plate glass, and surrounded with a picture frame,
so as to have the appearance of two mirrors. Place two mirrors, E, F,
one behind each opening at A and B, inclined 45° to the partition MN,
and so large that a person looking into the plates of glass at A and
B will not see their edges. When this is done it is obvious that a
person looking into the mirror A will not see himself, but will see any
person or figure placed at B. If he believes that he is looking into a
common mirror at A, his astonishment will be great at seeing himself
transformed into another person, or into any living animal that may be
placed at B. The success of this deception would be greatly increased
if a plane mirror, suspended by a pulley, could be brought immediately
behind the plane glass at A, and drawn up from it at pleasure. The
spectator at A, having previously seen himself in this moveable mirror,
would be still more astonished when he afterwards perceived in the same
place a face different from his own. By drawing the moveable mirror
half up, the spectator at A might see half of his own face joined to
half of the face placed at B; but in the present day the most ignorant
persons are so familiar with the properties of a looking-glass, that
it would be very difficult to employ this kind of deception with the
same success which must have attended it in a more illiterate age. The
optical reader will easily see that the mirror F and the apartment NCD
are not absolutely necessary for carrying on this deception; for the
very same effects will be produced if the person at B is stationed at
G, and looks towards the mirror F in the direction GF. As the mirror
F, however, must be placed as near to A as possible, the person at G
would be too near the partition CN, unless the mirror F was extremely
large.

The effect of this and every similar deception is greatly increased
when the persons are illuminated with a strong light, and the rest of
the apartment as dark as possible; but whatever precautions are taken,
and however skilfully plane mirrors are combined, it is not easy to
produce with them any very successful illusions.

The concave mirror is the staple instrument of the magician’s cabinet,
and must always perform a principal part in all optical combinations.
In order to be quite perfect, every concave mirror should have its
surface elliptical, so that if any object is placed in one focus of the
ellipse, an inverted image of it will be formed in the other focus.
This image, to a spectator rightly placed, appears suspended in the
air, so that if the mirror and the object are hid from his view, the
effect must appear to him almost supernatural.

The method of exhibiting the effect of concave mirrors most
advantageously is shown in Fig. 4, where CD is the partition of a
room having in it a square opening EF, the centre of which is about
five feet above the floor. This opening might be surrounded with a
picture-frame, and a painting which exactly filled it might be so
connected with a pulley that it could be either slipped aside, or
raised so as to leave the frame empty. A large concave mirror MN is
then placed in another apartment, so that when any object is placed at
A, a distinct image of it may be formed in the centre of the opening
EF. Let us suppose this object to be a plaster cast of any object made
as white as possible, and placed in an _inverted_ position at A. A
strong light should then be thrown upon it by a powerful lamp, the rays
of which are prevented from reaching the opening EF. When this is done,
a spectator placed at O will see an erect image of the statue at B,
the centre of the opening, standing in the air, and differing from the
real statue only in being a little larger, while the apparition will
be wholly invisible to other spectators placed at a little distance on
each side of him.

[Illustration: _Fig. 4._]

If the opening EF is filled with smoke, rising either from a
chafing-dish, in which incense is burnt, or made to issue in clouds
from some opening below, the image will appear in the middle of the
smoke depicted upon it as upon a ground, and capable of being seen by
those spectators who could not see the image of the air. The rays of
light, in place of proceeding without obstruction to an eye at O, are
reflected as it were from those minute particles of which the smoke
is composed, in the same manner as a beam of light is rendered more
visible by passing through an apartment filled with dust or smoke.

It has long been a favourite experiment to place at A a white and
strongly illuminated human skull, and to exhibit an image of it amid
the smoke of a chafing-dish at B; but a more terrific effect would be
produced if a small skeleton suspended by invisible wires were placed
as an object at A. Its image suspended in the air at B, or painted upon
smoke, could not fail to astonish the spectator.

The difficulty of placing a living person in an inverted position,
as an object at A, has no doubt prevented the optical conjuror from
availing himself of so admirable a resource; but this difficulty may be
removed by employing a second concave mirror. The second mirror may be
so placed as to reflect towards MN the rays proceeding from an erect
living object, and to form an inverted image of this object at A. An
erect image of this inverted image will then be formed at B, either
suspended in the air, or depicted upon a wreath of smoke. This aërial
image will exhibit the precise form and colours and movements of the
living object, and it will maintain its character as an apparition if
any attempt is made by the spectator to grasp its unsubstantial fabric.

A deception of an alarming kind, called the _Mysterious dagger_,
has been long a favourite exhibition. If a person with a drawn and
highly polished dagger, illuminated by a strong light, stands a
little farther from a concave mirror than its principal focus, he
will perceive in the air between himself and the mirror an inverted
and diminished image of his own person, with the dagger similarly
brandished. If he aims the dagger at the centre of the mirrors
concavity, the two daggers will meet point to point, and, by pushing it
still farther from him towards the mirror, the imaginary dagger will
strike at his heart. In this case it is necessary that the direction of
the real dagger coincides with a diameter of the sphere of which the
mirror is a part; but if its direction is on one side of that diameter,
the direction of the imaginary dagger will be as far on the other side
of the diameter, and the latter will aim a blow at any person who is
placed in the proper position for receiving it. If the person who bears
the real dagger is therefore placed behind a screen, or otherwise
concealed from the view of the spectator, who is made to approach to
the place of the image, the thrust of the polished steel at his breast
will not fail to produce a powerful impression. The effect of this
experiment would no doubt be increased by covering with black cloth
the person who holds the dagger, so that the image of his hand only
should be seen, as the inverted picture of him would take away from the
reality of the appearance. By using two mirrors, indeed, this defect
might be remedied, and the spectator would witness an exact image of
the assassin aiming the dagger at his life.

The common way of making this experiment is to place a basket of fruit
above the dagger, so that a distinct aërial image of the fruit is
formed in the focus of the mirror. The spectator, having been desired
to take some fruit from the basket, approaches for that purpose, while
a person properly concealed withdraws the real basket of fruit with one
hand, and with the other advances the dagger, the image of which being
no longer covered by the fruit, strikes at the body of the astonished
spectator.

The powers of the concave mirror have been likewise displayed in
exhibiting the apparition of an absent or deceased friend. For this
purpose, a strongly illuminated bust or picture of the person is
placed before the concave mirror, and a distinct image of the picture
will be seen either in the air or among smoke, in the manner already
described. If the background of the picture is temporarily covered with
lamp-black, so that there is no light about the picture but what falls
upon the figure, the effect will be more complete.

As in all experiments with concave mirrors, the size of the aërial
image is to that of the real object as their distances from the mirror,
we may, by varying the distance of the object, increase or diminish the
size of the image. In doing this, however, the distance of the image
from the mirror is at the same time changed, so that it would quit the
place most suitable for its exhibition. This defect may be removed by
simultaneously changing the place both of the mirror and the object, so
that the image may remain stationary, expanding itself from a luminous
spot to a gigantic size, and again passing through all intermediate
magnitudes, till it vanishes in a cloud of light.

Those who have studied the effects of concave mirrors of a small
size, and without the precautions necessary to ensure deception,
cannot form any idea of the magical effect produced by this class of
optical apparitions. When the instruments of illusion are themselves
concealed,--when all extraneous lights but those which illuminate
the real object are excluded,--when the mirrors are large and
well-polished, and truly formed,--the effect of the representation on
ignorant minds is altogether overpowering; while even those who know
the deception, and perfectly understand its principles, are not a
little surprised at its effects. The inferiority in the effects of a
common concave mirror to that of a well-arranged exhibition is greater
even than that of a perspective picture, hanging in an apartment, to
the same picture exhibited under all the imposing accompaniments of a
dioramic representation.

It can scarcely be doubted, that a concave mirror was the principal
instrument by which the heathen gods were made to appear in the ancient
temples. In the imperfect accounts which have reached us of these
apparitions, we can trace all the elements of an optical illusion. In
the ancient temple of Hercules at Tyre, Pliny mentions that there was
a seat made of a consecrated stone, “from which the gods easily rose.”
Esculapius often exhibited himself to his worshippers in his temple
at Tarsus; and the temple of Enguinum in Sicily was celebrated as the
place where the goddesses exhibited themselves to mortals. Iamblichus
actually informs us, that the ancient magicians caused the gods to
appear among the vapours disengaged from fire; and when the conjuror
Maximus terrified his audience by making the statue of Hecate laugh,
while in the middle of the smoke of burning incense, he was obviously
dealing with the image of a living object dressed in the costume of the
sorceress.

The character of these exhibitions in the ancient temples is so
admirably depicted in the following passage of Damascius, quoted by M.
Salverte, that we recognise all the optical effects which have been
already described. “In a manifestation,” says he, “which ought not to
be revealed ... there appeared on the wall of the temple a mass of
light, which at first seemed to be very remote; it transformed itself,
in coming nearer, into a face evidently divine and supernatural, of
a severe aspect, but mixed with gentleness, and extremely beautiful.
According to the institutions of a mysterious religion, the
Alexandrians honoured it as Osiris and Adonis.”

Among more modern examples of this illusion, we may mention the case of
the Emperor Basil of Macedonia. Inconsolable at the loss of his son,
this sovereign had recourse to the prayers of the Pontiff Theodore
Santabaren, who was celebrated for his power of working miracles. The
ecclesiastical conjuror exhibited to him the image of his beloved
son, magnificently dressed and mounted upon a superb charger: the
youth rushed towards his father, threw himself into his arms, and
disappeared. M. Salverte judiciously observes, that this deception
could not have been performed by a real person who imitated the figure
of the young prince. The existence of this person, betrayed by so
remarkable a resemblance, and by the trick of the exhibition, could not
fail to have been discovered and denounced, even if we could explain
how the son could be so instantaneously disentangled from his father’s
embrace. The emperor, in short, saw the aërial image of a picture
of his son on horseback; and as the picture was brought nearer the
mirror, the image advanced into his arms, when it of course eluded his
affectionate grasp.

These and other allusions to the operations of the ancient magic,
though sufficiently indicative of the methods which were employed, are
too meagre to convey any idea of the splendid and imposing exhibitions
which must have been displayed. A national system of deception,
intended as an instrument of government, must have brought into
requisition not merely the scientific skill of the age, but a variety
of subsidiary contrivances calculated to astonish the beholder, to
confound his judgment, to dazzle his senses, and to give a predominant
influence to the peculiar imposture which it was thought desirable
to establish. The grandeur of the means may be inferred from their
efficacy, and from the extent of their influence.

This defect, however, is, to a certain degree, supplied by an account
of a modern necromancy, which has been left us by the celebrated
Benvenuto Cellini, and in which he himself performed an active part.

“It happened,” says he, “through a variety of odd accidents, that I
made acquaintance with a Sicilian priest, who was a man of genius, and
well versed in the Latin and Greek authors. Happening one day to have
some conversation with him when the subject turned upon the art of
necromancy, I, who had a great desire to know something of the matter,
told him, that I had all my life felt a curiosity to be acquainted with
the mysteries of this art.

“The priest made answer, ‘that the man must be of a resolute and
steady temper who enters upon that study.’ I replied, ‘that I had
fortitude and resolution enough, if I could but find an opportunity.’
The priest subjoined, ‘If you think you have the heart to venture, I
will give you all the satisfaction you can desire.’ Thus we agreed
to enter upon a plan of necromancy. The priest one evening prepared
to satisfy me, and desired me to look out for a companion or two. I
invited one Vincenzio Romoli, who was my intimate acquaintance: he
brought with him a native of Pistoia, who cultivated the black art
himself. We repaired to the Colosseo, and the priest, according to the
custom of necromancers, began to draw circles upon the ground, with
the most impressive ceremonies imaginable: he likewise brought hither
asafœtida, several precious perfumes, and fire, with some compositions
also, which diffused noisome odours. As soon as he was in readiness,
he made an opening to the circle, and having taken us by the hand,
ordered the other necromancer, his partner, to throw the perfumes
into the fire at a proper time, entrusting the care of the fire and
perfumes to the rest; and thus he began his incantations. This ceremony
lasted above an hour and a half, when there appeared several legions
of devils, insomuch that the amphitheatre was quite filled with them.
I was busy about the perfumes, when the priest, perceiving there was
a considerable number of infernal spirits, turned to me and said,
‘Benvenuto, ask them something.’ I answered, ‘Let them bring me into
the company of my Sicilian mistress Angelica.’ That night he obtained
no answer of any sort; but I had received great satisfaction in having
my curiosity so far indulged. The necromancer told me it was requisite
we should go a second time, assuring me that I should be satisfied in
whatever I asked; but that I must bring with me a pure, immaculate boy.

“I took with me a youth who was in my service, of about twelve years of
age, together with the same Vincenzio Romoli, who had been my companion
the first time, and one Agnolino Gaddi, an intimate acquaintance, whom
I likewise prevailed on to assist at the ceremony. When we came to the
place appointed, the priest having made his preparations as before,
with the same and even more striking ceremonies, placed us within the
circle, which he had likewise drawn with a more wonderful art and in a
more solemn manner than at our former meeting. Thus, having committed
the care of the perfumes and the fire to my friend Vincenzio, who was
assisted by Agnolino Gaddi, he put into my hand a pintaculo or magical
chart, and bid me turn it towards the places that he should direct me;
and under the pintaculo I held the boy. The necromancer, having begun
to make his tremendous invocations, called by their names a multitude
of demons who were the leaders of the several legions, and questioned
them, by the power of the eternal uncreated God, who lives for ever,
in the Hebrew language, as likewise in Latin and Greek; insomuch that
the amphitheatre was almost in an instant filled with demons more
numerous than at the former conjuration. Vincenzio Romoli was busied
in making a fire, with the assistance of Agnolino, and burning a great
quantity of precious perfumes. I, by the directions of the necromancer,
again desired to be in the company of my Angelica. The former thereupon
turning to me said,--’Know, they have declared that, in the space of a
month, you shall be in her company.’

“He thus requested me to stand resolutely by him, because the legions
were now above a thousand more in number than he had designed; and
besides, these were the most dangerous; so that, after they had
answered my question, it behoved him to be civil to them, and dismiss
them quietly. At the same time the boy under the pintaculo was in a
terrible fright, saying, that there were in that place a million of
fierce men, who threatened to destroy us; and that, moreover, four
armed giants of enormous stature were endeavouring to break into our
circle. During this time, whilst the necromancer, trembling with fear,
endeavoured by mild and gentle methods to dismiss them in the best way
he could, Vincenzio Romoli, who quivered like an aspen leaf, took care
of the perfumes. Though I was as much terrified as any of them, I did
my utmost to conceal the terror I felt; so that I greatly contributed
to inspire the rest with resolution; but the truth is, I gave myself
over for a dead man, seeing the horrid fright the necromancer was in.
The boy placed his head between his knees and said, ‘In this posture
will I die; for we shall all surely perish.’ I told him that all these
demons were under us, and what he saw was smoke and shadow; so bid
him hold up his head and take courage. No sooner did he look up than
he cried out, ‘The whole amphitheatre is burning, and the fire is
just falling upon us.’ So covering his eyes with his hands, he again
exclaimed, ‘that destruction was inevitable, and desired to see no
more.’ The necromancer entreated me to have a good heart, and take
care to burn proper perfumes; upon which I turned to Romoli, and bid
him burn all the most precious perfumes he had. At the same time I
cast my eye upon Agnolino Gaddi, who was terrified to such a degree
that he could scarce distinguish objects, and seemed to be half dead.
Seeing him in this condition, I said, ‘Agnolino, upon these occasions
a man should not yield to fear, but should stir about and give his
assistance, so come directly and put on some more of these.’ The
effects of poor Agnolino’s fear were overpowering. The boy, hearing
a crepitation, ventured once more to raise his head, when, seeing me
laugh, he began to take courage, and said ‘that the devils were flying
away with a vengeance.’

“In this condition we stayed, till the bell rang for morning prayers.
The boy again told us, that there remained but few devils, and these
were at a great distance. When the magician had performed the rest of
his ceremonies, he stripped off his gown, and took up a wallet full of
books which he had brought with him.

“We all went out of the circle together, keeping as close to each other
as we possibly could, especially the boy, who had placed himself in
the middle, holding the necromancer by the coat, and me by the cloak.
As we were going to our houses in the quarter of Banchi, the boy told
us that two of the demons whom we had seen at the amphitheatre went on
before us leaping and skipping, sometimes running upon the roofs of the
houses, and sometimes upon the ground. The priest declared, that though
he had often entered magic circles, nothing so extraordinary had ever
happened to him. As we went along, he would fain persuade me to assist
with him at consecrating a brook, from which, he said, we should derive
immense riches; we should then ask the demons to discover to us the
various treasures with which the earth abounds, which would raise us to
opulence and power; but that these love-affairs were mere follies, from
whence no good could be expected. I answered, ‘that I would readily
have accepted his proposal, if I understood Latin.’ He redoubled his
persuasions, assuring me, that the knowledge of the Latin language
was by no means material. He added, that he could have Latin scholars
enough, if he had thought it worth while to look out for them, but that
he could never have met with a partner of resolution and intrepidity
equal to mine, and that I should by all means follow his advice. Whilst
we were engaged in this conversation we arrived at our respective
houses, and all that night dreamt of nothing but devils.”

It is impossible to peruse the preceding description without being
satisfied that the legions of devils were not produced by any influence
upon the imaginations of the spectators, but were actual optical
phantasms, or the images of pictures or objects produced by one or
more concave mirrors or lenses. A fire is lighted, and perfumes and
incense are burnt, in order to create a ground for the images, and the
beholders are rigidly confined within the pale of the magic circle. The
concave mirror and the objects presented to it having been so placed
that the persons within the circle could not see the aërial image of
the objects by the rays deeply reflected from the mirror, the work of
deception was ready to begin. The attendance of the magician upon his
mirror was by no means necessary. He took his place along with the
spectators within the magic circle. The images of the devils were all
distinctly formed in the air immediately above the fire, but none of
them could be seen by those within the circle. The moment, however,
that perfumes were thrown into the fire to produce smoke, the first
wreath of smoke that rose through the place of one or more of the
images, would reflect them to the eyes of the spectator, and they could
again disappear if the wreath was not followed by another. More and
more images would be rendered visible as new wreaths of smoke arose,
and the whole group would appear at once when the smoke was uniformly
diffused over the place occupied by the images.

The “compositions which diffused noisome odours” were intended to
intoxicate or stupify the spectators, so as to increase their liability
to deception, or to add to the real phantasms which were before their
eyes, others which were the offspring only of their own imaginations.
It is not easy to gather from the description what parts of the
exhibition were actually presented to the eyes of the spectators, and
what parts of it were imagined by themselves. It is quite evident
that the boy, as well as Agnolino Gaddi, were so overpowered with
terror that they fancied many things which they did not see; but when
the boy declares that four armed giants, of an enormous stature, were
threatening to break into the circle, he gives an accurate description
of the effect that would be produced by pushing the figures nearer the
mirror, and then magnifying their images, and causing them to advance
towards the circle. Although Cellini declares that he was trembling
with fear, yet it is quite evident that he was not entirely ignorant of
the machinery which was at work; for in order to encourage the boy, who
was almost dead with fear, he assured them that the devils were under
their power, and that “what he saw was smoke and shadow.”

Mr. Roscoe, from whose Life of Cellini the preceding description is
taken, draws a similar conclusion from the consolatory words addressed
to the boy, and states that they “confirm him in the belief, that the
whole of these appearances, like a phantasmagoria, were merely the
effects of a magic lantern produced on volumes of smoke from various
kinds of burning wood.” In drawing this conclusion, Mr. Roscoe has
not adverted to the fact, that this exhibition took place about the
middle of the 16th century, while the magic lantern was not invented
by Kircher till towards the middle of the 17th century; Cellini
having died in 1570, and Kircher having been born in 1601. There
is no doubt that the effects described could be produced by this
instrument, but we are not entitled to have recourse to any other
means of explanation but those which were known to exist at the time
of Cellini. If we suppose, however, that the necromancer either had a
regular magic lantern, or that he had fitted up his concave mirror in
a box containing the figures of his devils, and that this box with its
lights was carried home with the party, we can easily account for the
declaration of the boy, “that as they were going home to their houses
in the quarter of Banchi, _two of the demons whom we had seen at the
amphitheatre went on before us leaping and skipping, sometimes running
upon the roofs of the houses, and sometimes upon the ground_.”

The introduction of the magic lantern as an optical instrument
supplied the magicians of the 17th century with one of their most
valuable tools. The use of the concave mirror, which does not appear
to have been even put up into the form of an instrument, required a
separate apartment, or at least that degree of concealment which it
was difficult on ordinary occasions to command; but the magic lantern,
containing in a small compass its lamp, its lenses, and its sliding
figures, was peculiarly fitted for the itinerant conjuror, who had
neither the means of providing a less portable and more extensive
apparatus, nor the power of transporting and erecting it.

The magic lantern shown in the annexed figure consists of a dark
lantern, AB, containing a lamp G, and a concave metallic mirror, MN,
and it is so constructed that when the lamp is lighted not a ray of
light is able to escape from it. Into the side of the lantern is fitted
a double tube, CD, the outer half of which D is capable of moving
within the other half. A large plano-convex lens C, is fixed at the
inner end of the double tube, and a small convex lens D, at the outer
end; and to the fixed tube CE, there is joined a groove EF, in which
the sliders containing the painted objects are placed, and through
which they can be moved. Each slider contains a series of figures or
pictures painted on glass with highly transparent colours. The direct
light of the lamp G, and the light reflected from the mirror MN,
falling upon the illuminating lens C, is concentrated by it so as to
throw a brilliant light upon the painting on the slider, and as this
painting is in the conjugate focus of the convex lens D, a magnified
image of it will be formed on a white wall or white cloth placed at PQ.
If the lens D is brought nearer to EF, or to the picture, the distinct
image will be more magnified, and will be formed at a greater distance
from D, so that if there is any particular distance of the image which
is more convenient than another, or any particular size of the object
which we wish, it can be obtained by varying the distance of the lens
D from EF.

[Illustration: _Fig. 5._]

When the image is received on an opaque ground, as is commonly the
case, the spectators are placed in the same room with the lantern;
but, for the purposes of deception, it would be necessary to place
the lantern in another apartment like the mirror in Fig. 4, and to
throw the magnified pictures on a large plate of ground glass, or a
transparent gauze screen, stretched across an opening EF, Fig. 4, made
in the partition which separates the spectators from the exhibitor.
The images might, like those of the concave mirror, be received upon
wreaths of smoke. These images are of course always inverted in
reference to the position of the painted objects; but in order to
render them really erect, we have only to invert the sliders. The
representations of the magic lantern never fail to excite a high degree
of interest, even when exhibited with the ordinary apparatus; but
by using double sliders, and varying their movements, very striking
effects may be produced. A smith, for example, is made to hammer
upon his anvil,--a figure is thrown into the attitude of terror by
the introduction of a spectral apparition, and a tempest at sea is
imitated, by having the sea on one slider, and the ships on other
sliders, to which an undulatory motion is communicated.

The magic lantern is susceptible of great improvement in the painting
of the figures, and in the mechanism and combination of the sliders.
A painted figure, which appears well executed to the unassisted eye,
becomes a mere daub when magnified 50 or 100 times; and when we
consider what kind of artists are employed in their execution, we need
not wonder that this optical instrument has degenerated into a mere
toy for the amusement of the young. Unless for public exhibition,
the expense of exceedingly minute and spirited drawings could not be
afforded; but I have no doubt that if such drawings were executed, a
great part of the expense might be saved by engraving them on wood, and
transferring their outline to the glass sliders.

A series of curious representations might be effected, by inserting
glass plates containing suitable figures in a trough having two of its
sides parallel, and made of plate glass. The trough must be introduced
at EF, so that the figure on the glass is at the proper distance from
the object lens D. When the trough is filled with water, or with
any transparent fluid, the picture at PQ will be seen with the same
distinctness as if the figure had been introduced by itself into the
groove EF; but if any transparent fluid of a different density from
water is mixed with it, so as to combine with it quickly or slowly, the
appearance of the figure displayed at PQ will undergo singular changes.
If spirits of wine, or any ardent spirit, are mixed with the water, so
as to produce throughout its mass partial variations of density, the
figure at PQ, will be as it were broken down into a thousand parts,
and will recover its continuity and distinctness when the two fluids
have combined. If a fluid of less density than water is laid gently
upon the water, so as to mix with it gradually, and produce a regular
diminution of density downwards--or if saline substances, soluble in
water, are laid at the bottom of the trough, the density will diminish
upwards, and the figure will undergo the most curious elongations and
contractions. Analogous effects may be produced by the application of
heat to the surface or sides of the trough, so that we may effect at
the same time both an increase and a diminution in the density of the
water, in consequence of which the magnified images will undergo the
most remarkable transformations. It is not necessary to place the glass
plate which contains the figure within the trough. It may be placed in
front of it, and by thus creating as it were an atmosphere with local
variations of density, we may exhibit the phenomena of the mirage and
of looming, in which the inverted images of ships and other objects are
seen in the air, as described in another letter.

The power of the magic lantern has been greatly extended by placing
it on one side of the transparent screen of taffeta which receives
the images, while the spectators are placed on the other side, and
by making every part of the glass sliders opaque, excepting the part
which forms the figures. Hence all the figures appear luminous on a
black ground, and produce a much greater effect with the same degree of
illumination. An exhibition depending on these principles was brought
out by M. Philipstall in 1802, under the name of the _Phantasmagoria_,
and when it was shown in London and Edinburgh, it produced the most
impressive effects upon the spectators. The small theatre of exhibition
was lighted only by one hanging lamp, the flame of which was drawn up
into an opaque chimney or shade when the performance began. In this
“darkness visible” the curtain rose and displayed a cave with skeletons
and other terrific figures in relief upon its walls. The flickering
light was then drawn up beneath its shroud, and the spectators in total
darkness found themselves in the middle of thunder and lightning.
A thin transparent screen had, unknown to the spectators, been let
down after the disappearance of the light, and upon it the flashes of
lightning and all the subsequent appearances were represented. This
screen being half-way between the spectators and the cave which was
first shown, and being itself invisible, prevented the observers from
having any idea of the real distance of the figures, and gave them the
entire character of aërial pictures. The thunder and lightning were
followed by the figures of ghosts, skeletons, and known individuals,
whose eyes and mouth were made to move by the shifting of combined
sliders. After the first figure had been exhibited for a short time,
it began to grow less and less, as if removed to a great distance, and
at last vanished in a small cloud of light. Out of this same cloud the
germ of another figure began to appear, and gradually grew larger and
larger, and approached the spectators, till it attained its perfect
development. In this manner the head of Dr. Franklin was transformed
into a skull; figures which retired with the freshness of life came
back in the form of skeletons, and the retiring skeletons returned in
the drapery of flesh and blood.

The exhibition of these transmutations was followed by spectres,
skeletons, and terrific figures, which, instead of receding and
vanishing as before, suddenly advanced upon the spectators, becoming
larger as they approached them, and finally vanished by appearing to
sink into the ground. The effect of this part of the exhibition was
naturally the most impressive. The spectators were not only surprised
but agitated, and many of them were of opinion that they could have
touched the figures. M. Robertson, at Paris, introduced along with his
pictures the direct shadows of living objects, which imitated coarsely
the appearance of those objects in a dark night or in moonlight.

All these phenomena were produced by varying the distance of the magic
lantern AB, Fig 5, from the screen PQ, which remained fixed, and at the
same time keeping the image upon the screen distinct, by increasing
the distance of the lens D from the sliders in EF. When the lantern
approached to PQ, the circle of light PQ, or the section of the cone
of rays PDQ, gradually diminished, and resembled a small bright cloud,
when D was close to the screen. At this time a new figure was put
in, so that when the lantern receded from the screen, the old figure
seemed to have been transformed into the new one. Although the figure
was always at the same distance from the spectators, yet, owing to its
gradual diminution in size, it necessarily appeared to be retiring to
a distance. When the magic lantern was withdrawn from PQ, and the lens
D at the same time brought nearer to EF, the image in PQ gradually
increased in size, and therefore seemed in the same proportion to be
approaching the spectators.

Superior as this exhibition was to any representation that had been
previously made by the magic lantern, it still laboured under several
imperfections. The figures were poorly drawn, and in other respects not
well executed, and no attempt whatever was made to remove the optical
incongruity of the figures becoming more luminous when they retired
from the observer, and more obscure when they approached to him. The
variation of the distance of the lens D from the sliders in EF was not
exactly adapted to the motion of the lantern to and from the screen, so
that the outline of the figures was not equally distinct during their
variations of magnitude.

Dr. Thomas Young suggested the arrangement shown in Fig. 6 for
exhibiting the phantasmagoria.

[Illustration: _Fig. 6._]

The magic lantern is mounted on a small car H, which runs on wheels
WW. The direct light of the lamp G, and that reflected from the mirror
M, is condensed by the illuminating lenses CC, upon the transparent
figures in the opaque sliders at E, and the image of these figures is
formed at PQ, by the object lens D. When the car H is drawn back on
its wheels, the rod IK brings down the point K, and by means of the rod
KL, pushes the lens D nearer to the sliders in EF, and when the car
advances to PQ, the point K is raised, and the rod KL draws out the
lens D from the slider, so that the image is always in the conjugate
focus of D, and therefore distinctly painted on the screen. The rod KN
must be equal in length to IK, and the point I must be twice the focal
length of the lens D before the object, L being immediately under the
focus of the lens. In order to diminish the brightness of the image
when it grows small and appears remote, Dr. Young contrived that the
support of the lens D should suffer a screen S to fall and intercept a
part of the light. This method, however, has many disadvantages, and we
are satisfied, that the only way of producing a variation in the light
corresponding to the variation in the size of the image, is to use a
single illuminating lens C, and to cause it to approach EF, and throw
less light upon the figures when D is removed from EF, and to make C
recede from EF when D approaches to it. The lens C should therefore
be placed in a mean position, corresponding to a mean distance of the
screen, and to the ordinary size of the figures, and should have the
power of being removed from the slider EF, when a greater intensity of
light is required for the images when they are rendered gigantic, and
of being brought close to EF when the images are made small. The size
of the lens C ought of course to be such that the section of its cone
of rays at EF is equal to the size of the figure on the slider when C
is at its greatest distance from the slider.

The method recommended by Dr. Young for pulling out and pushing in
the object lens D, according as the lantern approaches to or recedes
from the screen, is very ingenious and effective. It is, however,
clumsy in itself, and the connexion of the levers with the screen,
and their interposition between it and the lantern, must interfere
with the operations of the exhibitor. It is, besides, suited only to
short distances between the screen and the lantern; for when that
distance is considerable, as it must sometimes require to be, the
levers KL, KI, KT, would bend by the least strain, and become unfitted
for their purpose. For these reasons the mechanism which adjusts the
lens D should be moved by the axle of the front wheels, the tube which
contains the lens should be kept at its greatest distance from EF by
a slender spring, and should be pressed to its proper distance by the
action of a spiral cam suited to the optical relation between the two
conjugate focal distances of the lens.

Superior as the representations of the phantasmagoria are to those of
the magic lantern, they are still liable to the defect which we have
mentioned, namely, the necessary imperfection of the minute transparent
figures when magnified. This defect cannot be remedied by employing
the most skilful artists. Even Michael Angelo would have failed in
executing a figure an inch long with transparent varnishes, when all
its imperfections were to be magnified. In order, therefore, to perfect
the art of representing phantasms, the objects must be living ones, and
in place of chalky ill-drawn figures, mimicking humanity by the most
absurd gesticulations, we shall have phantasms of the most perfect
delineation, clothed in real drapery, and displaying all the movements
of life. The apparatus by which such objects may be used, may be called
the _catadioptrical phantasmagoria_, as it operates both by reflexion
and refraction.

[Illustration: _Fig. 7._]

The combination of mirrors and lenses which seems best adapted for this
purpose is shown in Fig. 7, where AB is a living figure placed before
a large concave mirror MN, by means of which a diminished and inverted
image of it is formed at _ab_. If PQ is the transparent screen upon
which the image is to be shown to the spectators on the right hand of
it, a large lens LL must be so placed before the image _ab_, as to
form a distinct and erect picture of it at A´B´ upon the screen. When
the image A´B´ is required to be the exact size of AB, the lens LL
must magnify the small image _ab_ as much as the mirror MN diminishes
the figure AB. The living object AB, the mirror MN, and the lens LL,
must all be placed in a moveable car for the purpose of producing the
variations in the size of the phantasms, and the transformations of
one figure into another. The contrivance for adjusting the lens LL, to
give a distinct picture at different distances of the screen, will, of
course, be required in the present apparatus. In order to give full
effect to the phantasms, the living objects at AB will require to be
illuminated in the strongest manner, and should always be dressed
either in white or in very luminous colours; and, in order to give them
relief, a black cloth should be stretched at some distance behind them.
Many interesting effects might also be produced by introducing at AB
fine paintings and busts.

It would lead us into too wide a field were we to detail the immense
variety of resources which the science of optics furnishes for such
exhibitions. One of these, however, is too useful to be passed without
notice. If we interpose a prism with a small refracting angle between
the image _ab_, Fig. 7, and the lens LL, the part of the figure
immediately opposite to the prism will be as it were detached from
the figure, and will be exhibited separately on the screen PQ. Let us
suppose that this part is the head of the figure. It may be detached
vertically, or lifted from the body as if it were cut off, or it may
be detached downwards and placed on the breast as if the figure were
deformed. In detaching the head vertically or laterally, an opaque
screen must be applied to prevent any part of the head from being
seen by rays which do not pass through the prism; but this and other
practical details will soon occur to those who put the method to an
experimental trial. The application of the prism is shown in Fig. 8,
where _ab_ is the inverted image formed by a concave mirror, ABC a
prism with a small refracting angle BCA, placed between _ab_ and the
lens LL, _s_ a small opaque screen, and AB the figure with its head
detached. A hand may be made to grasp the hair of the head, and the
aspect of death may be given to it, as if it had been newly cut off.
Such a representation could be easily made, and the effect upon the
spectators would be quite overpowering. The lifeless head might then be
made to recover its vitality, and be safely replaced upon the figure.
If the head A of the living object AB, Fig. 7, is covered with black
cloth, the head of a person or of an animal placed above A might be set
upon the shoulders of the figure AB by the refraction of a prism.

[Illustration: _Fig. 8._]

When the figure _ab_, Fig. 8, is of very small dimensions, as in the
magic lantern, a small prism of glass would answer the purpose required
of it; but in public exhibitions, where the image _ab_ must be of a
considerable size, if formed by a concave mirror, a very large prism
would be necessary. This, however, though impracticable with solid
glass, may be easily obtained by means of two large pieces of plate
glass made into a prismatic vessel and filled with water. Two of the
glasses of a carriage window would make a prism capable of doubling
the whole of the bust of a living person placed as an object at AB,
Fig. 7, so that two perfectly similar phantasms might be exhibited. In
those cases where the images before the lens LL are small, they may
be doubled and even tripled by interposing a well-prepared plate of
calcareous spar, that is, crossed by a thin film. These images would
possess the singular character of being oppositely coloured, and of
changing their distances and their colours, by slight variations in the
positions of the plate.[8]

 [8] See _Edin. Encyclopædia_, Art. OPTICS, Vol. xv., p. 611.

In order to render the images which are formed by the glass and
water prisms as perfect as possible, it would be easy to make them
achromatic, and the figures might be multiplied to any extent by using
several prisms, having their refracting edges parallel, for the purpose
of giving a similarity of position to all the images.

[Illustration: _Fig. 9._]

Among the instruments of natural magic which were in use at the revival
of science, there was one invented by Kircher for exhibiting the
mysterious hand-writing on the wall of an apartment, from which the
magician and his apparatus were excluded. The annexed figure represents
this apparatus as given by Schottus. The apartment in which the
spectators are placed is between LL and GH, and there is an open window
in the

side next LL, GH being the inside of the wall opposite to the window.
Upon the face of the plane speculum EF are written the words to be
introduced, and when a lens LL is placed at such a distance from the
speculum, and of such a focal length, that the letters and the place
of their representation are in its conjugate foci, a distinct image
of the writing will be exhibited on the wall at GH. The letters on
the speculum are of course inverted, as seen at EF, and when they are
illuminated by the sun’s rays S, as shown in the figure, a distinct
image, as Schottus assures us, may be formed at the distance of 500
feet. In this experiment, the speculum is by no means necessary. If the
letters are cut out of an opaque card, and illuminated by the light
of the sky in the day, or by a lamp during night, their delineation
on the wall would be equally distinct. In the daytime it would be
necessary to place the letters at one end of a tube or oblong box, and
the lens at the other end. As this deception is performed when the
spectators are unprepared for any such exhibition, the warning written
in luminous letters on the wall, or any word associated with the fate
of the individual observer, could not fail to produce a singular effect
upon his mind. The words might be magnified, diminished, multiplied,
coloured, and obliterated, in a cloud of light, from which they might
again reappear by the methods already described, as applicable to the
magic lantern.

The art of forming aërial representations was a great desideratum among
the opticians of the 17th century. Vitellio and others had made many
unsuccessful attempts to produce such images, and the speculations
of Lord Bacon on the subject are too curious to be withheld from the
reader.

“It would be well bolted out,” says he, “whether great refractions may
not be made upon reflexions, as well as upon direct beams. For example,
take an empty basin, put an angel or what you will into it; then go so
far from the basin till you cannot see the angel, because it is not in
a right line; then fill the basin with water, and you shall see it out
of its place, because of the refraction. To proceed, therefore, put a
looking-glass into a basin of water. I suppose you shall not see the
image in a right line or at equal angles, but wide. I know not whether
this experiment may not be extended, so as you might see the image and
not the glass, which, for beauty and strangeness, were a fine proof,
for then you should see the image like a spirit in the air. As, for
example, if there be a cistern or pool of water, you shall place over
against it the picture of the devil, or what you will, so as that you
do not see the water. Then put a looking-glass in the water; now if you
can see the devil’s picture aside, not seeing the water, it would look
like the devil indeed. They have an old tale in Oxford, that Friar
Bacon walked between two steeples, which was thought to be done by
glasses, when he walked upon the ground.”

[Illustration: _Fig. 10._]

Kircher also devoted himself to the production of such images, and he
has given in the annexed figure his method of producing them. At the
bottom of a polished cylindrical vessel AB, he placed a figure CD,
which we presume must have been highly illuminated from below, and
to the spectators who looked into the vessel in an oblique direction
there was exhibited an image placed vertically in the air as if it
were ascending at the mouth of the vessel. Kircher assures us that he
once exhibited in this manner a representation of the Ascension of our
Saviour, and that the images were so perfect that the spectators could
not be persuaded, till they had attempted to handle them, that they
were not real substances. Although Kircher does not mention it, yet
it is manifest that the original figure AB must have been a deformed
or anamorphous drawing, in order to give a reflected image of just
proportions. We doubt, indeed, if the representation or the figure was
ever exhibited. It is entirely incompatible with the laws of reflexion.

[Illustration: _Fig. 11._]

Among the ingenious and beautiful deceptions of the 17th century,
we must enumerate that of the re-formation of distorted pictures
by reflexion from cylindrical and conical mirrors. In these
representations, the original image from which a perfect picture
is produced is often so completely distorted, that the eye cannot
trace in it the resemblance to any regular figure, and the greatest
degree of wonder is of course excited, whether the original image is
concealed or exposed to view. These distorted pictures may be drawn
by strict geometrical rules; but I have shown in Fig. 11 a simple and
practical method of executing them. Let MN be an accurate cylinder made
of tin-plate or of thick pasteboard. Out of the farther side of it
cut a small aperture _abcd_; and out of the nearer side cut a larger
one ABCD, the size of the picture to be distorted. Having perforated
the outline of the picture with small holes, place it on the opening
ABCD, so that its surface may be cylindrical. Let a candle or a bright
luminous object, the smaller the better, be placed at S, as far behind
the picture ABCD as the eye is afterwards to be placed before it,
and the light passing through the small holes will represent on a
horizontal plane a distorted image of the picture A´B´C´D´, which,
when sketched in outline with a pencil, and shaded or coloured, will
be ready for use. If we now substitute a polished cylindrical mirror
of the same size in place of MN, then the distorted picture, when
laid horizontally at A´B´C´D´, will be restored to its original state
when seen by reflexion at ABCD in the polished mirror. It would be
an improvement on this method to place at ABCD a thin and flexible
plate of transparent mica, having drawn upon it with a sharp point,
or painted upon it, the figure required. The projected image of this
figure at A´B´C´D´ may then be accurately copied.

The effect of a cylindrical mirror is shown in Fig. 12, which is
copied from an old one which we have seen in use.

[Illustration: _Fig. 12._]

The method above described is equally applicable to concave cylindrical
mirrors, and to those of a conical form; and it may also be applied
to mirrors of variable curvature, which produce different kinds of
distortions from different parts of their surfaces.

[Illustration: _Fig. 13._]

By employing a mirror whose surface has a variable curvature like ABC,
Fig. 13, we obtain an instrument for producing an endless variety of
caricatures, all of which are characterised by their resemblance to
the original. If a figure MN is placed before such a mirror, it will
of course appear distorted and caricatured; but even if the figure
takes different distances and positions, the variations which the
image undergoes are neither sufficiently numerous nor remarkable to
afford much amusement. But if the figure MN is very near the mirror,
so that new distortions are produced by the different distances of
its different parts from the mirror, the most singular caricatures may
be exhibited. If the figure, for example, bends forwards his head and
the upper part of his body, they will swell in size, leaving his lower
extremities short and slender. If it draws back the upper part of the
body and advances the limbs, the opposite effect will take place. In
like manner different sides of the head, the right or the left side of
it, the brow or the chin, may be swelled and contracted at pleasure. By
stretching out the arms before the body they become like those of an
ourang-outang, and by drawing them back they dwindle into half their
regular size. All these effects, which depend chiefly on the agility
and skill of the performer, may be greatly increased by suitable
distortions in his own features and figure. The family likeness, which
is of course never lost in all the variety of figures which are thus
produced, adds greatly to the interest of the exhibition; and we have
seen individuals so annoyed at recognising their own likeness in the
hideous forms of humanity which were thus delineated, that they could
not be brought to contemplate them a second time. If the figure is
inanimate, like the small cast of a statue, the effect is very curious,
as the swelling and contracting of the parts and the sudden change
of expression give a sort of appearance of vitality to the image.
The inflexibility of such a figure, however, is unfavourable to its
transformation into caricatures.

Interesting as these metamorphoses are, they lose in the simplicity
of the experiment much of the wonder which they could not fail to
excite if exhibited on a great scale, where the performer is invisible,
and where it is practicable to give an aërial representation of the
caricatured figures. This may be done by means of the apparatus shown
in Fig. 7,[9] where we may suppose AB to be the reduced image seen in
the reflecting surface ABC, Fig. 13.[10] By bringing this image nearer
the mirror MM, Fig. 7, a magnified and inverted image of it may be
formed at _ab_, of such a magnitude as to give the last image in PQ the
same size as life. Owing to the loss of light by the two reflexions, a
very powerful illumination would be requisite for the original figure.
If such an exhibition were well got up, the effect of it would be very
striking.

 [9] Page 86.

 [10] Page 96.




LETTER V.

 Miscellaneous optical illusions--Conversion of cameos into intaglios,
 or elevations into depressions, and the reverse--Explanation of
 this class of deceptions--Singular effects of illumination with
 light of one simple colour--Lamps for producing homogeneous yellow
 light--Methods of increasing the effect of this exhibition--Method
 of reading the inscription of coins in the dark--Art of deciphering
 the effaced inscription of coins--Explanation of these singular
 effects--Apparent motion of the eyes in portraits--Remarkable examples
 of this--Apparent motion of the features of a portrait, when the
 eyes are made to move--Remarkable experiment of breathing light and
 darkness.


In the preceding letter I have given an account of the most important
instruments of Natural Magic which depend on optical principles: but
there still remain several miscellaneous phenomena on which the stamp
of the marvellous is deeply impressed, and the study of which is
pregnant with instruction and amusement.

One of the most curious of these is that false perception in vision
by which we conceive depressions to be elevations, and elevations
depressions, or by which intaglios are converted into cameos, and
cameos into intaglios. This curious fact seems to have been first
observed at one of the early meetings of the Royal Society of London,
when one of the members, in looking at a guinea through a compound
microscope of new construction, was surprised to see the head upon the
coin depressed, while other members could only see it embossed as it
really was.

While using telescopes and compound microscopes, Dr. Gmelin of
Wurtemburg observed the same fact. The protuberant parts of objects
appeared to him depressed, and the depressed parts protuberant: but
what perplexed him extremely, this illusion took place at some times
and not at others, in some experiments and not in others, and appeared
to some eyes and not to others.

After making a great number of experiments, Dr. Gmelin is said to
have constantly observed the following effects: Whenever he viewed
any object rising upon a plane of any colour whatever, provided it
was neither white nor shining, and provided the eye and the optical
tube were directly opposite to it, the elevated parts appeared
depressed, and the depressed parts elevated. This happened when he
was viewing a seal, and as often as he held the tube of the telescope
perpendicularly, and applied it in such a manner that its whole
surface almost covered the last glass of the tube. The same effect was
produced when a compound microscope was used. When the object hung
perpendicularly, from a plane, and the tube was supported horizontally
and directly opposite to it, the illusion also took place, and the
appearance was not altered when the object hung obliquely and even
horizontally. Dr. Gmelin is said to have at last discovered a method
of preventing this illusion, which was by looking, not towards the
centre of the convexity, but at first to the edges of it only, and then
gradually taking in the whole. “But why these things should so happen,
he did not pretend to determine.”

[Illustration: _Fig. 14._]

The best method of observing this deception is to view the engraved
seal of a watch with the eyepiece of an achromatic telescope, or with
a compound microscope, or any combination of lenses which inverts the
objects that are viewed through it.[11] The depression in the seal
will immediately appear an elevation, like the wax impression which
is taken from it; and though we know it to be hollow, and feel its
concavity with the point of our finger, the illusion is so strong
that it continues to appear a protuberance. The cause of this will be
understood from Fig. 14, where S is the window of the apartment, or
the light which illuminates the _hollow_ seal LR, whose shaded side
is of course on the same side L with the light. If we now invert the
seal, with one or more lenses, so that it may look in the opposite
direction, it will appear to the eye as in Fig. 15, with the shaded
side L farthest from the window. But as we know that the window is
still on our left hand, and that the light falls in the direction RL,
and as everybody with its shaded side farthest from the light must
necessarily be convex or protuberant, we immediately believe that the
hollow seal is now a cameo or bas-relief. The proof which the eye thus
receives of the seal being raised, overcomes the evidence of its being
hollow, derived from our actual knowledge, and from the sense of touch.
In this experiment the deception takes place from our knowing the real
direction of the light which falls upon the seal; for if the place of
the window, with respect to the seal, had been inverted as well as the
seal itself, the illusion could not have taken place.

 [11] A single convex lens will answer the purpose, provided we hold
 the eye six or eight inches behind the image of the seal formed in its
 conjugate focus.

[Illustration: _Fig. 15._]

[Illustration: _Fig. 16._]

In order to explain this better, let us suppose the seal LR, Fig. 14,
to be illuminated with a candle S, the place of which we can change at
pleasure. If we invert LR, it will rise into a cameo, as in Fig. 15;
and if we then place another candle S on the other side of it, as in
Fig. 16, the hollow seal will be equally illuminated on all sides, and
it will sink down into a cavity or intaglio. If the two candles do not
illuminate the seal equally, or if any accidental circumstance produces
a belief that the light is wholly or principally on one side, the mind
will entertain a corresponding opinion respecting the state of the
seal, regarding it as a hollow if it believes the light to come wholly
or principally from the right hand, and as a cameo if it believes the
light to come from the left hand.

If we use a small telescope to invert the seal, and if we cover up
all the candle but the flame, and arrange the experiment so that the
candle may be inverted along with the image, the seal will still retain
its concavity, because the shadow is still on the same side with the
illuminating body.

If we make the same experiments with the raised impression of the seal
taken upon wax, we shall observe the very same phenomena, the seal
being depressed when it alone is inverted, and retaining its convexity
when the light is inverted along with it.

The illusion, therefore, under our consideration is the result of an
operation of our own minds, whereby we judge of the forms of bodies by
the knowledge we have acquired of light and shadow. Hence the illusion
depends on the accuracy and extent of our knowledge on this subject;
and while some persons are under its influence, others are entirely
insensible to it. When the seal or hollow cavity is not polished, but
ground, and the surface round it of uniform colour and smoothness,
almost every person, whether young or old, learned or ignorant, will be
subject to the illusion; because the youngest and the most careless
observers cannot but know that the shadow of a hollow is always on
the side next the light, and the shadow of a protuberance on the side
opposite to the light; but if the object is the raised impression of a
seal upon wax, I have found that, when inverted, it still seemed raised
to the three youngest of six persons, while the three eldest were
subject to the deception.

[Illustration: _Fig. 17._]

This illusion may be dissipated by a process of reasoning arising from
the introduction of a new circumstance in the experiment. Thus, let RL,
Fig. 17, be the inverted seal, which consequently appears raised, and
let an opaque and unpolished pin, A, be placed on one side of the seal.
Its shadow will be of course opposite the candle as at B. In this case
the seal, which had become a cameo by its inversion, will now sink down
into a cavity by the introduction of the pin and its shadow; for as the
pin and its shadow are inverted, as shown in Fig. 18, while the candle
retains its place, the shadow of the pin falling in the direction AB
is a stronger proof to the eye that the light is coming from the right
hand, than the actual knowledge of the candle being on the left hand,
and therefore the cameo necessarily sinks into a cavity, or the shadow
is now on the same side as the light. This experiment will explain to
us why on some occasions an acute observer will elude the deception,
while every other person is subject to it. Let us suppose that a
particle of dust, or a little bit of wax, capable of giving a shadow,
is adhering to the surface of the seal, an ordinary observer will
take no notice of this, or if he does, he will probably not make it a
subject of consideration, and will therefore see the head on the seal
raised into a cameo; but the attentive observer, noticing the little
protuberance, and observing that its shadow lies to the left of it,
will instantly infer that the light comes in that direction, and will
still see the seal hollow.

[Illustration: _Fig. 18._]

I have already mentioned that in some cases even the sense of touch
does not correct the erroneous perception. We of course feel that the
part of the hollow on which the finger is placed is actually hollow;
but if we look at the other part of the hollow it will still appear
raised.

By using two candles yielding different degrees of light, and thus
giving an uncertainty to the direction of the light, we may weaken the
illusion in any degree we choose, so as to overpower it by touch, or by
a process of reasoning.

I have had occasion to observe a series of analogous phenomena arising
from the same cause, but produced without any instrument for inverting
the object. If AB, for example, is a plate of mother-of-pearl, and LR
a circular or any other cavity (Fig. 19) ground or turned in it, then
if this cavity is illuminated by a candle or a window at S, in place of
there being a shadow of the margin L of the hollow next the light, as
there would have been had the body been opaque, a quantity of bright
refracted light will appear where there would have been a shadow, and
the rest of the cavity will be comparatively obscure, as if it were
in shade. The necessary consequence of this is, that the cavity will
appear as an elevation when seen only by the naked eye, as it is only
an elevated surface that could have its most luminous side at L.

[Illustration: _Fig. 19._]

Similar illusions take place in certain pieces of polished wood,
chalcedony, and mother-of-pearl, where the surface is perfectly
smooth. This arises from there being at that place a knot or growth,
or nodule, of different transparency from the surrounding mass, and
the cause of it will be understood from Fig. 20. Let _m_ _o_ be the
surface of a mahogany table, _m_ A _o_ B a section of the table, and
_m_ _n_ _o_ a section of a knot more transparent than the rest of the
mass. Owing to the transparency of the thin edge at _o_, opposite to
the candle S, the side _o_ is illuminated, while the rest of the knot
is comparatively dark, so that, on the principles already explained,
the spot _m n o_ appears to be a hollow in the table. From this cause
arises the appearance of dimples in certain plates of chalcedony,
called hammered chalcedony, owing to its having the look of being
dimpled with a hammer. The surface on which these cavities are seen is
a section of small spherical aggregations of siliceous matter, which
exhibit the same phenomena as the cavities in wood. Mother-of-pearl
presents the very same phenomena, and it is indeed so common in this
substance, that it is nearly impossible to find a mother-of-pearl
button or counter which seems to have its surface flat, although they
are perfectly so when examined by the touch. Owing to the different
refraction of the incident light by the different growths of the shell
cut in different directions by the artificial surface, like the annual
growth of wood in a dressed plank, the surface has necessarily an
unequal and undulating appearance.

[Illustration: _Fig. 20._]

Among the wonders of science there are perhaps none more surprising
than the effects produced upon coloured objects by illuminating
them with homogeneous light, or light of one colour. The light which
emanates from the sun, and by which all the objects of the material
world are exhibited to us, is composed of three different colours,
_red_, _yellow_, and _blue_, by the mixture of which in different
proportions all the various hues of nature may be produced. These three
colours, when mixed in the proportion in which they occur in the sun’s
rays, compose a purely white light; but if any body on which this white
light falls shall absorb, or stop, or detain within its substance any
part of any one or more of these simple colours, it will appear to the
eye of that colour which arises from the mixture of all the rays which
it does not absorb, or of that colour which white light would have if
deprived of the colours which are absorbed. Scarlet cloth, for example,
absorbs most of the blue rays and many of the yellow, and hence appears
_red_. Yellow cloth absorbs most of the blue and many of the red rays,
and therefore appears yellow; and blue cloth absorbs most of the yellow
and red rays. If we were to illuminate the _scarlet_ cloth with pure
and unmixed _yellow_ light, it would appear _yellow_, because the
scarlet cloth does not absorb all the yellow rays, but reflects some
of them; and if we illuminate _blue_ cloth with yellow light, it will
appear nearly _black_, because it absorbs all the yellow light, and
reflects almost none of it. But whatever be the nature and colour of
the bodies on which the yellow light falls, the light which it reflects
must be yellow, for no other light falls upon them, and those which are
not capable of reflecting yellow light must appear absolutely black,
however brilliant be their colour in the light of day.

[Illustration: _Fig. 21._]

As the methods now discovered of producing yellow light in abundance
were not known to the ancient conjurors, nor even to those of later
times, they have never availed themselves of this valuable resource. It
has been long known that salt thrown into the wick of a flame produces
yellow light, but this light is mixed with blue and green rays, and is,
besides, so small in quantity, that it illuminates objects only that
are in the immediate vicinity of the flame. A method which I have found
capable of producing it in abundance is shown in Fig. 21, where AB is a
lamp, containing at A a large quantity of alcohol and water, or ardent
spirits, which gradually descends into a platina or metallic cup D.
This cup is strongly heated by a spirit-lamp L, inclosed in a dark
lantern, and when the diluted alcohol in D is inflamed, it will burn
with a fierce and powerful yellow flame. If the flame should not be
perfectly yellow, owing to an excess of alcohol, a proportion of salt
thrown into the cup will answer the same purpose as a further dilution
of the alcohol.[12]

 [12] See _Edinburgh Transactions_, vol. ix., p. 435.

A monochromatic lamp for producing yellow light may be constructed most
effectually, by employing a portable gas lamp, containing compressed
oil gas. If we allow the gas to escape in a copious stream, and set it
on fire, it will form an explosive mixture with the atmospheric air,
and will no longer burn with a white flame, but will emit a bluish
and reddish light. The force of the issuing gas, or any accidental
current of air, is capable of blowing out this flame, so that it is
necessary to have a contrivance for sustaining it. The method which I
used for this purpose is shown in Fig. 22. A small gas tube _a b c_,
arising from the main burner MN of the gas lamp PQ, terminates above
the burner, and has a short tube _d e_, moveable up and down within it,
so as to be gas-tight. This tube _d e_, closed at _e_, communicates
with the hollow ring _f g_, in the inside of which four apertures are
perforated in such a manner as to throw their jets of gas to the apex
of a cone, of which _f g_ is the base. When we cause the gas to flow
from the burner M, by opening the main cock A, it will rush into the
tube _a b c d_, and issue in small flames at the four holes in the
ring _f g_. The size of these flames is regulated by the cock _b_.
The inflammation, therefore, of the ignited gas will be sustained by
these four subsidiary flames through which it passes, independent of
any agitation of the air, or of the force with which it issues from
the burner. On a projecting arm _e h_, carrying a ring _h_, I fixed a
broad collar, made of coarse cotton wick, which had been previously
soaked in a saturated solution of common salt. When the gas was allowed
to escape at M, with such force as to produce a long and broad column
of an explosive mixture of gas and atmospheric air, the bluish flame
occasioned by the explosion passes through the salted collar, and is
converted by it into a mass of homogeneous yellow light. This collar
will last a long time without any fresh supply of salt, so that the gas
lamp will yield a permanent monochromatic yellow flame, which will
last as long as there is gas in the reservoir. In place of a collar
of cotton wick, a hollow cylinder of sponge, with numerous projecting
tufts, may be used, or a collar may be similarly constructed with
asbestos cloth, and, if thought necessary, it might be supplied with a
saline solution from a capillary fountain.

[Illustration: _Fig. 22._]

Having thus obtained the means of illuminating any apartment with
yellow light, let the exhibition be made in a room with furniture of
various bright colours, with oil or water-coloured paintings on the
wall. The party which is to witness the experiment should be dressed
in a diversity of the gayest colours; and the brightest-coloured
flowers and highly-coloured drawings should be placed on the tables.
The room being at first lighted with ordinary lights, the bright and
gay colours of everything that it contains will be finely displayed.
If the white lights are now suddenly extinguished, and the yellow
lamps lighted, the most appalling metamorphosis will be exhibited. The
astonished individuals will no longer be able to recognize each other.
All the furniture in the room, and all the objects which it contains,
will exhibit only one colour. The flowers will lose their hues. The
paintings and drawings will appear as if they were executed in China
ink; and the gayest dresses, the brightest scarlets, the purest lilacs,
the richest blues, and the most vivid greens, will all be converted
into one monotonous yellow. The complexions of the parties, too, will
suffer a corresponding change. One pallid, death-like yellow,

    ---- like the unnatural hue
    Which autumn paints upon the perished leaf,

will envelope the young and the old, and the sallow faces will alone
escape from the metamorphosis. Each individual derives merriment from
the cadaverous appearance of his neighbour, without being sensible that
he is himself one of the ghostly assemblage.

If, in the midst of the astonishment which is thus created, the white
lights are restored at one end of the room, while the yellow lights are
taken to the other end, one side of the dress of every person, namely,
that next the white light, will be restored to its original colours,
while the other side will retain its yellow hue. One cheek will appear
in a state of health and colour, while the other retains the paleness
of death; and, as the individuals change their position, they will
exhibit the most extraordinary transformations of colour.

If, when all the lights are yellow, beams of white light are
transmitted through a number of holes, like those in a sieve, each
luminous spot will restore the colour of the dress or furniture upon
which it falls, and the nankeen family will appear all mottled over
with every variety of tint. If a magic lantern is employed to throw
upon the walls or upon the dresses of the company luminous figures of
flowers or animals, the dresses will be painted with these figures
in the real colour of the dress itself. Those alone who appeared in
yellow, and with yellow complexions, will, to a great degree, escape
all these singular changes.

If red and blue light could be produced with the same facility and in
the same abundance as yellow light, the illumination of the apartment
with these lights in succession would add to the variety and wonder of
the exhibition. The red light might perhaps be procured in sufficient
quantity from the nitrate and other salts of strontian; but it would
be difficult to obtain a blue flame of sufficient intensity for the
suitable illumination of a large room. Brilliant white lights, however,
might be used, having for screens glass troughs containing a mass
one or two inches thick of a solution of the ammoniacal carbonate of
copper. This solution absorbs all the rays of the spectrum but the
blue, and the intensity of the blue light thus produced would increase
in the same proportion as the white light employed.

Amongst the numerous experiments with which science astonishes and
sometimes even strikes terror into the ignorant, there is none more
calculated to produce this effect than that of displaying to the eye in
absolute darkness the legend or inscription upon a coin. To do this,
take a silver coin (I have always used an old one), and after polishing
the surface as much as possible, make the parts of it which are raised
rough by the action of an acid, the parts not raised, or those which
are to be rendered darkest, retaining their polish. If the coin thus
prepared is placed upon a mass of red-hot iron, and removed into a dark
room, the inscription upon it will become less luminous than the rest,
so that it may be distinctly read by the spectator. The mass of red-hot
iron should be concealed from the observer’s eye, both for the purpose
of rendering the eye fitter for observing the effect, and of removing
all doubt that the inscription is really read in the dark, that is,
without receiving any light, direct or reflected, from any other body.
If, in place of polishing the depressed parts and roughening its raised
parts, we make the raised parts polished and roughen the depressed
parts, the inscription will now be less luminous than the depressed
parts, and we shall still be able to read it, from its being as it were
written in black letters on a white ground. The first time I made this
experiment, without being aware of what would be the result, I used
a French shilling of Louis XV., and I was not a little surprised to
observe upon its surface, in black letters, the inscription BENEDICTUM
SIT NOMEN DEI.

The most surprising form of this experiment is when we use a coin
from which the inscription has been either wholly obliterated, or
obliterated in such a degree as to be illegible. When such a coin is
laid upon the red-hot iron, the letters and figures become oxidated,
and the film of oxide radiating more powerfully than the rest of the
coin, the illegible inscription may be now distinctly read, to the
great surprise of the observer, who had examined the blank surface of
the coin previous to its being placed upon the hot iron. The different
appearances of the same coin, according as the raised parts are
polished or roughened, are shown in Fig. 23 and 24.

In order to explain the cause of these remarkable effects, we must
notice a method which has been long known, though never explained, of
deciphering the inscriptions on worn-out coins. This is done by merely
placing the coin upon a hot iron; an oxidation takes place over the
whole surface of the coin, the film of oxide changing its tint with the
intensity or continuance of the heat. The parts, however, where the
letters of the inscription had existed, oxidate at a different rate
from the surrounding parts, so that these letters exhibit their shape,
and become legible in consequence of the film of oxide which covers
them having a different thickness, and therefore reflecting a different
tint from that of the adjacent parts. The tints thus developed
sometimes pass through many orders of brilliant colours, particularly
_pink_ and _green_, and settle in a bronze, and sometimes a black tint,
resting upon the inscription alone. In some cases the tint left on the
trace of the letters is so very faint that it can just be seen, and may
be entirely removed by a slight rub of the finger.

[Illustration: _Fig. 23._]

[Illustration: _Fig. 24._]

When the experiment is often repeated with the same coin, and the
oxidations successively removed after each experiment, the film of
oxide continues to diminish, and at last ceases to make its appearance.
It recovers the property, however, in the course of time. When the
coin is put upon the hot iron, and consequently when the oxidation
is the greatest, a considerable smoke arises from the coin, and this
diminishes like the film of oxide by frequent repetition. A coin
which had ceased to emit this smoke, smoked slightly after having been
exposed twelve hours to the air. I have found, from numerous trials,
that it is always the raised parts of the coin, and in modern coins the
elevated ledge round the inscription, that become first oxidated. In an
English shilling of 1816, this ledge exhibited a brilliant yellow tint
before it appeared on any other part of the coin.

If we use a uniform and homogeneous disc of silver that has never been
hammered or compressed, its surface will oxidate equally, provided all
its parts are equally heated. In the process of converting this disc
into a coin, the _sunk_ parts have obviously been _most compressed_
by the prominent parts of the die, and the _elevated_ parts _least
compressed_, the metal being in the latter left as it were in its
natural state. The raised letters and figures on a coin have therefore
less density than the other parts, and these parts oxidate sooner or
at a lower temperature. When the letters of the legend are worn off by
friction, the parts immediately below them have also less density than
the surrounding metal, and the site as it were of the letters therefore
receives from heat a degree of oxidation, and a colour different from
that of the surrounding surface. Hence we obtain an explanation of the
revival of the invisible letters by oxidation.

The same influence of difference of density may be observed in
the beautiful oxidations which are produced on the surface of
highly-polished steel, heated in contact with air, at temperatures
between 430° and 630° of Fahrenheit.[13] When the steel has hard
portions called pins by the workmen, the uniform tint of the film of
oxide stops near these hard portions, which always exhibit colours
different from those of the rest of the mass. These parts, on account
of their increased density, absorb the oxygen of atmospheric air less
copiously than the surrounding portions. Hence we see the cause why
steel expanded by heat absorbs oxygen, which when united with the
metal, forms the coloured superficial film. As the heat increases,
a greater quantity of oxygen is absorbed, and the film increases in
thickness.

 [13] See _Edinburgh Encyclopædia_, Art. STEEL, vol. xviii., p. 387.

These observations enable us to explain the legibility of inscriptions
in the dark, whether the coin is in a perfect state, or the letters
of it worn off. All _black_ or _rough_ surfaces radiate light more
copiously than _polished_ or _smooth_ surfaces, and hence the
inscription is _luminous_ when it is _rough_, and _obscure_ when it is
polished, and the letters covered with black oxide are more luminous
than the adjacent parts, on account of the superior radiation of light
by the black oxide which covers them.

By the means now described, invisible writing might be conveyed by
impressing it upon a metallic surface, and afterwards erasing it by
grinding and polishing that surface perfectly smooth. When exposed to
a proper degree of heat, the secret would display itself written in
oxidated letters. Many amusing experiments might be made upon the same
principle.

A series of curious and sometimes alarming deceptions, arises from the
representation of objects in perspective upon a plane surface. One of
the most interesting of these depends on the principles which regulate
the apparent direction of the eyes in a portrait. Dr. Wollaston has
thought this subject of sufficient importance to be treated at some
length in the Philosophical Transactions. When we look at any person
we direct to them both our face and our eyes, and in this position
the circular iris will be in the middle of the white of the eye ball,
or, what is the same thing, there will be the same quantity of white
on each side of the iris. If the eyes are now moved to either side,
while the head remains fixed, we shall readily judge of the change of
their direction by the greater or less quantity of white on each side
of the iris. This test, however, accurate as it is, enables us only to
estimate the extent to which the eyes deviate in direction from the
direction of the face to which they belong. But their direction in
reference to the person who views them is entirely a different matter;
and Dr. Wollaston is of opinion, that we are not guided by the eyes
alone, but are unconsciously aided by the concurrent position of the
entire face.

[Illustration: _Fig. 26._]

If a skilful painter draws a pair of eyes with great correctness
directed to the spectator, and deviating from the general position of
the face as much as is usual in good portraits, it is very difficult
to determine their direction, and they will appear to have different
directions to different persons. But what is very curious, Dr.
Wollaston has shown that the same pair of eyes may be made to direct
themselves either to or from the spectator by the addition of other
features in which the position of the face is changed. Thus, in Fig.
25, the pair of eyes are looking intently at the spectator, and the
face has a corresponding direction; but when we cover up the face in
Fig. 25 with the face in Fig. 26, which looks to the right, the eyes
change their direction, and look to the right also. In like manner,
eyes drawn originally to look a little to the right or the left of
the spectator, may be made to look directly at him by adding suitable
features.

[Illustration: _Fig. 25._]

The nose is obviously the principal feature which produces this
change of direction, as it is more subject to change of perspective
than any of the other features; but Dr. Wollaston has shown by a very
accurate experiment, that even a small portion of the nose introduced
with the features will carry the eyes along with it. He obtained four
exact copies of the same pair of eyes looking at the spectator, by
transferring them upon copper from a steel plate, and having added to
each of two pair of them a nose, in one case directed to the right,
and in the other to the left, and to each of the other two pair a very
small portion of the upper part of the nose, all the four pair of eyes
lost their front direction, and looked to the right or to the left,
according to the direction of the nose, or of the portion of it which
was added.

But the effect thus produced is not limited, as Dr. Wollaston
remarks, to the mere change in the direction of the eyes, “for a
total difference of character may be given to the same eyes by a due
representation of the other features. A lost look of devout abstraction
in an uplifted countenance, may be exchanged for an appearance of
inquisitive archness in the leer of a younger face turned downwards and
obliquely towards the opposite side,” as in Fig. 27, 28. This, however,
is perhaps not an exact expression of the fact. The new character
which is said to be given to the eyes is given only to the eyes in
combination with the new features, or, what is probably more correct,
the inquisitive archness is in the other features, and the eye does not
belie it.

Dr. Wollaston has not noticed the converse of these illusions, in which
a change of direction is given to fixed features by a change in the
direction of the eyes. This effect is finely seen in some magic lantern
sliders, where a pair of eyes is made to move in the head of a figure,
which invariably follows the motion of the eyeballs.

[Illustration: _Fig. 28._]

[Illustration: _Fig. 27._]

Having thus determined the influence which the general perspective of
the face has upon the apparent direction of the eyes in a portrait, Dr.
Wollaston applies it to the explanation of the well-known fact, that
when the eyes of a portrait look at a spectator in front of it they
will follow him, and appear to look at him in every other direction.
This curious fact, which has received less consideration than it
merits, has been often skilfully employed by the novelist, in alarming
the fears or exciting the courage of his hero. On returning to the
hall of his ancestors, his attention is powerfully fixed on the grim
portraits which surround him. The parts which they have respectively
performed in the family history rise to his mind: his own actions,
whether good or evil, are called up in contrast, and as the preserver
or the destroyer of his line, he stands, as it were, in judgment before
them. His imagination, thus excited by conflicting feelings, transfers
a sort of vitality to the canvas, and if the personages do not “start
from their frames,” they will at least bend upon him their frowns or
their approbation. It is in vain that he tries to evade their scrutiny.
Wherever he goes their eyes eagerly pursue him; they will seem even to
look at him over their shoulders, and he will find it impossible to
shun their gaze but by quitting the apartment.

As the spectator in this case changes his position in a horizontal
plane, the effect which we have described is accompanied by an apparent
diminution in the breadth of the human face, from only seven or eight
inches till it disappears at a great obliquity. In moving, therefore,
from a front view to the most oblique view of the face, the change in
its apparent breadth is so slow that the apparent motion of the head of
the figure is scarcely recognized as it follows the spectator. But if
the perspective figure has a great breadth in a horizontal plane, such
as a soldier firing his musket, an artilleryman his piece of ordnance,
a bowman drawing his bow, or a lancer pushing his spear, the apparent
breadth of the figure will vary from five to six feet or upwards till
it disappears, and therefore the change of apparent magnitude is
sufficiently rapid to give the figure the dreaded appearance of turning
round, and following the spectator. One of the best examples of this
must have been often observed in the foreshortened figure of a dead
body lying horizontally, which has the appearance of following the
observer with great rapidity, and turning round upon the head as the
centre of motion.

The cause of this phenomenon is easily explained. Let us suppose a
portrait with its face and its eyes directed straight in front, so as
to look at the spectator. Let a straight line be drawn through the
tip of the nose and half way between the eyes, which we shall call the
middle line. On each side of this middle line there will be the same
breadth of head, of cheek, of chin, and of neck, and each iris will be
in the middle of the white of the eye. If we now go to one side, the
apparent horizontal breadth of every part of the head and face will
be diminished, but the parts on each side of the middle line will be
diminished equally, and at any position, however oblique, there will be
the same breadth of face on each side of the middle line, and the iris
will be in the centre of the white of the eyeball, so that the portrait
preserves all the characters of a figure looking at the spectator, and
must necessarily do so wherever he stands.

This explanation might be illustrated by a picture which represents
three artillerymen, each firing a piece of ordnance in parallel
directions. Let the gun of the middle one be pointed accurately to the
eye of the spectator, so that he sees neither its right side nor its
left, nor its upper nor its under side, but directly down its muzzle,
so that if there was an opening in the breech he would see through
it. In like manner the spectator will see the left side of the gun on
his left hand, and the right side of the gun on his right hand. If
the spectator now changes his place, and takes ever such an oblique
position, either laterally or vertically, he must still see the same
thing; because nothing else is presented to his view. The gun of the
middle soldier must always point to his eye, and the other guns to the
right and left of him. They must therefore all three seem to move as
he moves, and follow his eye in all its changes of place. The same
observations are of course applicable to buildings and streets seen in
perspective.

In common portraits the apparent motion of the head is generally
rendered indistinct by the canvas being imperfectly stretched, as
the slightest concavity or convexity entirely deforms the face when
the obliquity is considerable. The deception is therefore best seen
when the painting is executed on a very flat board, and in colours
sufficiently vivid to represent every line in the face with tolerable
distinctness at great obliquities. This distinctness of outline is
indeed necessary to a satisfactory exhibition of this optical illusion.
The most perfect exhibition, indeed, that I ever saw of it was in the
case of a painting of a ship upon a sign-board executed in strongly
gilt lines. It contained a view of the stern and side of a ship in the
stocks, and, owing to the flatness of the board and the brightness of
the lines, the gradual development of the figure, from the most violent
foreshortening at great obliquities till it attained its perfect form,
was an effect which surprised every person that saw it.

[Illustration: _Fig. 29._]

The only other optical illusion which our limits will permit us to
explain, is the very remarkable experiment of what may be truly called
_breathing light or darkness_. Let S be a candle whose light falls at
an angle of 56° 45´ upon two glass plates A, B, placed close to each
other, and let the reflected rays AC, BD, fall at the same angle upon
two similar plates, C, D, but so placed that the plane of reflexion
from the latter is at right angles to the plane of reflexion from the
former. An eye placed at E, and looking at the same time into the two
plates C and D, will see very faint images of the candle S, which by a
slight adjustment of the plates, may be made to disappear almost wholly
allowing the plate C to remain as it is, change the position of D, till
its inclination to the ray BD is diminished about 3°, or made nearly
53° 11´. When this is done, the image that had disappeared on looking
into D will be restored, so that the spectator at E, upon looking into
the two mirrors C, D, will see no light in C, because the candle has
nearly disappeared, while the candle is distinctly seen in D. If, while
the spectator is looking into these two mirrors, either he or another
person breathes upon them gently and quickly, the breath will revive
the extinguished image in C, and will extinguish the visible image
in D. The following is the cause of this singular result. The light
AC, BD, is polarized by reflexion from the plates A, B, because it is
incident at the polarizing angle of 56° 45´ for glass. When we breathe
upon the plates C, D, we form upon their surface a thin film of water,
whose polarizing angle is 53° 11´, so that if the polarized rays AC,
BD, fell upon the plates C, D, at an angle of 53° 11´, the candle from
which they proceeded would not be visible, or they would not suffer
reflexion from the plates C, D. At all other angles the light would
be reflected and the candles visible. Now the plate D is placed at an
angle of 53° 11´ and C at an angle of 56° 45´, so that when a film
of water is breathed upon them the light will be reflected from the
latter, and none from the former; that is, the act of breathing upon
the plates will restore the invisible and extinguish the visible image.




LETTER VI.

 Natural phenomena marked with the marvellous--Spectre of the
 Brocken described--Analogous phenomena--Aërial spectres seen in
 Cumberland--Fata Morgana in the Straits of Messina--Objects below the
 horizon raised and magnified by refraction--Singular example seen at
 Hastings--Dover Castle seen through the hill on which it stands--Erect
 and inverted images of distant ships seen in the air--Similar
 phenomena seen in the Arctic regions--Enchanted coast--Mr.
 Scoresby recognizes his father’s ship by its aërial image--Images
 of cows seen in the air--Inverted image of horses seen in South
 America--Lateral images produced by refraction--Aërial spectres by
 reflexion--Explanation of the preceding phenomena.


Among the wonders of the natural world which are every day presented
to us, without either exciting our surprise or attracting our notice,
some are occasionally displayed which possess all the characters of
supernatural phenomena. In the names by which they are familiarly
known, we recognize the terror which they inspired, and even now,
when science has reduced them to the level of natural phenomena, and
developed the causes from which they arise, they still retain their
primitive importance, and are watched by the philosopher with as
intense an interest as when they were deemed the immediate effects
of Divine power. Among these phenomena we may enumerate the _Spectre
of the Brocken_, the _Fata Morgana_ of the Straits of Messina, the
_Spectre Ships_ which appear in the air, and the other extraordinary
effects of the _Mirage_.[14]

 [14] In the Sanscrit, says Baron Humboldt, the phenomenon of the
 Mirage is called _Mriga Trichna_, “thirst or desire of the antelope,”
 no doubt because this animal _Mriga_, compelled by thirst, _Trichna_,
 approaches those barren plains where, from the effect of unequal
 refraction, he thinks he perceives the undulating surface of the
 waters.--_Personal Narrative_, vol. iii., p. 554.

The Brocken is the name of the loftiest of the Hartz mountains, a
picturesque range which lies in the kingdom of Hanover. It is elevated
3,300 feet above the sea, and commands the view of a plain seventy
leagues in extent, occupying nearly the two-hundredth part of the
whole of Europe, and animated with a population of above five millions
of inhabitants. From the earliest periods of authentic history, the
Brocken has been the seat of the marvellous. On its summits are still
seen huge blocks of granite called the Sorcerer’s Chair and the Altar.
A spring of pure water is known by the name of the Magic Fountain,
and the Anemone of the Brocken is distinguished by the title of the
Sorcerer’s Flower. These names are supposed to have originated in the
rites of the great idol Cortho, whom the Saxons worshipped in secret
on the summit of the Brocken, when Christianity was extending her
benignant sway over the subjacent plains.

As the locality of these idolatrous rites, the Brocken must have been
much frequented, and we can scarcely doubt that the spectre which now
so often haunts it at sunrise must have been observed from the earliest
times; but it is nowhere mentioned that this phenomenon was in any
way associated with the objects of their idolatrous worship. One of
the best accounts of the spectre of the Brocken is that which is given
by M. Haue, who saw it on the 23rd of May, 1797. After having been on
the summit of the mountain no less than thirty times, he had at last
the good fortune of witnessing the object of his curiosity. The sun
rose about four o’clock in the morning through a serene atmosphere.
In the south-west, towards Achtermannshohe, a brisk west wind carried
before it the transparent vapours, which had not yet been condensed
into thick heavy clouds. About a quarter past four he went towards the
inn, and looked round to see whether the atmosphere would afford him a
free prospect towards the south-west, when he observed at a very great
distance, towards Achtermannshohe, a human figure of a monstrous size.
His hat having been almost carried away by a violent gust of wind,
he suddenly raised his hand to his head to protect his hat, and the
colossal figure did the same. He immediately made another movement by
bending his body,--an action which was repeated by the spectral figure.
M. Haue was desirous of making further experiments, but the figure
disappeared. He remained, however, in the same position, expecting
its return, and in a few minutes it again made its appearance on the
Achtermannshohe, when it mimicked his gestures as before. He then
called the landlord of the inn, and having both taken the same position
which he had before, they looked towards the Achtermannshohe, but saw
nothing. In a very short space of time, however, two colossal figures
were formed over the above eminence, and after bending their bodies
and imitating the gestures of the two spectators, they disappeared.
Retaining their position, and keeping their eyes still fixed upon the
same spot, the two gigantic spectres again stood before them, _and were
joined by a third_. Every movement that they made was imitated by the
three figures, but the effect varied in its intensity, being sometimes
weak and faint, and at other times strong and well defined.

[Illustration: _Fig. 30._]

In the year 1798, M. Jordan saw the same phenomenon at sunrise, and
under similar circumstances, but with less distinctness, and without
any duplication of the figures.[15]

 [15] See J. F. Gmelin’s _Gottingischen Journal der Wissenchaften_,
 vol. i., part iii., 1798.

Phenomena perfectly analogous to the preceding, though seen under less
imposing circumstances, have been often witnessed. When the spectator
sees his own shadow opposite to the sun upon a mass of thin fleecy
vapour passing near him, it not only imitates all his movements, but
its head is distinctly encircled with a halo of light. The aërial
figure is often not larger than life, its size and its apparent
distance depending, as we shall afterwards see, upon particular causes.
I have often seen a similar shadow when bathing in a bright summer’s
day in an extensive pool of deep water. When the fine mud deposited
at the bottom of the pool is disturbed by the feet of the bather, so
as to be disseminated through the mass of water in the direction of
his shadow, his shadow is no longer a shapeless mass formed upon the
bottom, but is a regular figure formed upon the floating particles of
mud, and having the head surrounded with a halo, not only luminous, but
consisting of distinct radiations.

One of the most interesting accounts of aërial spectres with which we
are acquainted has been given by Mr. James Clarke, in his Survey of the
Lakes of Cumberland, and the accuracy of this account was confirmed by
the attestations of two of the persons by whom the phenomena were first
seen. On a summer’s evening, in the year 1743, when Daniel Stricket,
servant to John Wren, of Wilton Hall, was sitting at the door along
with his master, they saw the figure of a man with a dog pursuing some
horses along Souterfell-side, a place so extremely steep, that a horse
could scarcely travel upon it at all. The figures appeared to run at
an amazing pace, till they got out of sight at the lower end of the
Fell. On the following morning, Stricket and his master ascended the
steep side of the mountain, in the full expectation of finding the man
dead, and of picking up some of the shoes of the horses, which they
thought must have been cast while galloping at such a furious rate.
Their expectations, however, were disappointed. No traces, either of
man or horse, could be found, and they could not even discover upon the
turf the single mark of a horse’s hoof. These strange appearances seen
at the same time by two different persons in perfect health, could not
fail to make a deep impression on their minds. They at first concealed
what they had seen, but they at length disclosed it, and were laughed
at for their credulity.

In the following year, on the 23rd June, 1744, Daniel Stricket, who
was then servant to Mr. Lancaster, of Blakehills, (a place near
Wilton Hall, and both of which places are only about half a mile
from Souterfell,) was walking, about seven o’clock in the evening,
a little above the house, when he saw a troop of horsemen riding
on Souterfell-side, in pretty close ranks, and at a brisk pace.
Recollecting the ridicule that had been cast upon him the preceding
year, he continued to observe the figures for some time in silence;
but being at last convinced that there could be no deception in the
matter, he went to the house, and informed his master that he had
something curious to show him. They accordingly went out together; but
before Stricket had pointed out the place, Mr. Lancaster’s son had
discovered the aërial figures. The family was then summoned to the
spot, and the phenomena were seen alike by them all. The equestrian
figures seemed to come from the lowest parts of Souterfell, and became
visible at a place called Knott. They then advanced in regular troops
along the side of the Fell, till they came opposite to Blakehills, when
they went over the mountain, after describing a kind of curvilineal
path. The pace at which the figures moved was a regular swift walk,
and they continued to be seen for upwards of two hours, the approach
of darkness alone preventing them from being visible. Many troops
were seen in succession; and frequently the last but one in a troop
quitted his position, galloped to the front, and took up the same pace
with the rest. The changes in the figures were seen equally by all
the spectators, and the view of them was not confined to the farm of
Blakehills only, but they were seen by every person at every cottage
within the distance of a mile, the number of persons who saw them
amounting to about twenty-six. The attestation of these facts, signed
by Lancaster and Stricket, bears the date of the 21st July, 1785.

These extraordinary sights were received not only with distrust, but
with absolute incredulity. They were not even honoured with a place in
the records of natural phenomena, and the philosophers of the day were
neither in possession of analogous facts, nor were they acquainted with
those principles of atmospherical refraction upon which they depend.
The strange phenomena, indeed, of the _Fata Morgana_, or the _Castles
of the Fairy Morgana_, had been long before observed, and had been
described by Kircher in the 17th century, but they presented nothing
so mysterious as the aërial troopers of Souterfell; and the general
characters of the two phenomena were so unlike, that even a philosopher
might have been excused for ascribing them to different causes.

This singular exhibition has been frequently seen in the straits of
Messina, between Sicily and the coast of Italy, and whenever it takes
place, the people, in a state of exultation, as if it were not only
a pleasing but a lucky phenomenon, hurry down to the sea, exclaiming
_Morgana, Morgana!_ When the rays of the rising sun form an angle
of 45° on the sea of Reggio, and when the surface of the water is
perfectly unruffled, either by the wind or the current, a spectator
placed upon an eminence in the city, and having his back to the sun
and his face to the sea, observes upon the surface of the water superb
palaces, with their balconies and windows, lofty towers, herds and
flocks grazing in wooded valleys and fertile plains; armies of men
on horseback and on foot, with multiplied fragments of buildings,
such as columns, pilasters, and arches. These objects pass rapidly in
succession along the surface of the sea during the brief period of
their appearance. The various objects thus enumerated are pictures
of palaces and buildings actually existing on shore, and the living
objects are of course only seen when they happen to form a part of the
general landscape.

If, at the time that these phenomena are visible, the atmosphere is
charged with vapour or dense exhalations, the same objects which are
depicted upon the sea will be seen also in the air, occupying a space
which extends from the surface to the height of twenty-five feet. These
images, however, are less distinctly delineated than the former.

If the air is in such a state as to deposit dew, and is capable of
forming the rainbow, the objects will be seen only on the surface of
the sea; but they all appear fringed with red, yellow, and blue light,
as if they were seen through a prism.

In our own country, and in our own times, facts still more
extraordinary have been witnessed. From Hastings, on the coast of
Sussex, the cliffs on the French coast are fifty miles distant,
and they are actually hid by the convexity of the earth; that is,
a straight line drawn from Hastings to the French coast would pass
through the sea. On Wednesday, the 26th of July, 1798, about five
o’clock in the afternoon, Mr. Latham, a Fellow of the Royal Society,
then residing at Hastings, was surprised to see a crowd of people
running to the sea-side. Upon inquiry into the cause of this, he
learned that the coast of France could be seen by the naked eye, and
he immediately went down to witness so singular a sight. He distinctly
saw the cliffs extending for some leagues along the French coast, and
they appeared as if they were only a few miles off. They gradually
appeared more and more elevated, and seemed to approach nearer to the
eye. The sailors with whom Mr. Latham walked along the waters edge were
at first unwilling to believe in the reality of the appearance; but
they soon became so thoroughly convinced of it, that they pointed out
and named to him the different places which they had been accustomed to
visit, and which they conceived to be as near as if they were sailing
at a small distance into the harbour. These appearances continued for
nearly an hour, the cliffs sometimes appearing brighter and nearer, and
at other times fainter and more remote. Mr. Latham then went upon the
eastern cliff or hill, which is of considerable height, when, as he
remarks, a most beautiful scene presented itself to his view. He beheld
at once Dungeness, Dover cliffs, and the French coast all along from
Calais, Boulogne, &c., to St. Vallery, and, as some of the fishermen
affirmed, as far west as Dieppe. With the help of a telescope, the
French fishing-boats were plainly seen at anchor, and the different
colours of the land upon the heights, together with the buildings, were
perfectly discernible. Mr. Latham likewise states that the cape of land
called Dungeness, which extends nearly two miles into the sea, and is
about sixteen miles in a straight line from Hastings, appeared as if
quite close to it, and the vessels and fishing-boats which were sailing
between the two places appeared equally near, and were magnified to
a high degree. These curious phenomena continued “in the highest
splendour” till past eight o’clock, although a black cloud had for some
time totally obscured the face of the sun.

A phenomenon no less marvellous was seen by Professor Vince, of
Cambridge, and another gentleman, on the 6th of August, 1806, at
Ramsgate. The summits _v w x y_ of the four turrets of Dover Castle
are usually seen over the hill AB, upon which it stands, lying between
Ramsgate and Dover; but on the day above-mentioned, at seven o’clock in
the evening, when the air was very still and a little hazy, not only
were the tops _v w x y_ of the four towers of Dover Castle seen over
the adjacent hill AB, _but the whole of the Castle, m n r s, appeared
as if it were situated on the side of the hill next Ramsgate_, and
rising above the hill as much as usual. This phenomenon was so very
singular and unexpected, that at first sight Dr. Vince thought it an
illusion; but upon continuing his observations, he became satisfied
that it was a real image of the Castle. Upon this he gave a telescope
to a person present, who, upon attentive examination, saw also a
very clear image of the Castle as the Doctor had described it. He
continued to observe it for about twenty minutes, during which time the
appearance remained precisely the same; but rain coming on, they were
prevented from making any further observations. Between the observers
and the land from which the hill rises there was about six miles of
sea, and from thence to the top of the hill there was about the same
distance. Their own height above the surface of the water was about
seventy feet.

[Illustration: _Fig. 31._]

This illusion derived great force from the remarkable circumstance,
that the hill itself did not appear through the image, as it might have
been expected to do. The image of the castle was very strong and well
defined, and though the rays from the hill behind it must undoubtedly
have come to the eye, yet the strength of the image of the castle so
far obscured the background, that it made no sensible impression on the
observers. Their attention was of course principally directed to the
image of the castle; but if the hill behind had been at all visible,
Dr. Vince conceives that it could not have escaped their observation,
as they continued to look at it for a considerable time with a good
telescope.

[Illustration: _Fig. 32._]

Hitherto our aërial visions have been seen only in their erect and
natural positions, either projected against the ground or elevated
in the air; but cases have occurred in which both erect and inverted
images of objects have been seen in the air, sometimes singly,
sometimes combined, sometimes when the real object was invisible, and
sometimes when a part of it had begun to show itself to the spectator.

In the year 1793, Mr. Huddart, when residing at Allonby, in Cumberland,
perceived the inverted image of a ship beneath the image, as shown
in Fig. 32; but Dr. Vince, who afterwards observed this phenomenon
under a greater variety of forms, found that the ship, which was here
considered the real one, was only an erect image of the real ship,
which was at that time beneath the horizon, and wholly invisible.

[Illustration: _Fig. 33._]

In August, 1798, Dr. Vince observed a great variety of these aërial
images of vessels approaching the horizon. Sometimes there was seen
only one inverted image above the real ship, and this was generally the
case when the real ship was full in view. But when the real ship was
just begin beginning to show its top-mast above the horizon, as at A,
Fig. 33, two aërial images of it were seen, one at B inverted, and the
other in its natural position at C. In this case the sea was distinctly
visible between the erect and inverted images, but in other cases the
hull of the one image was immediately in contact with the hull of the
other.

Analogous phenomena were seen by Captain Scoresby when navigating
with the ship Baffin the icy sea in the immediate neighbourhood of
West Greenland. On the 28th of June, 1820, he observed about eighteen
sail of ships at the distance of ten or fifteen miles. The sun had
shone during the day without the interposition of a cloud, and its
rays were peculiarly powerful. The intensity of its light occasioned a
painful sensation in the eyes, while its heat softened the tar in the
rigging of the ship, and melted the snow on the surrounding ice with
such rapidity that pools of fresh water were formed on almost every
place, and thousands of rills carried the excess into the sea. There
was scarcely a breath of wind: the sea was as smooth as a mirror. The
surrounding ice was crowded together, and exhibited every variety, from
the smallest lumps to the most magnificent sheets. Bears traversed the
fields and floes in unusual numbers, and many whales sported in the
recesses and openings among the drift ice. About six in the evening, a
light breeze at N.W. having sprung up, a thin stratus or “fog bank,”
at first considerably illuminated by the sun, appeared in the same
quarter, and gradually rose to the altitude of about a quarter of a
degree. At this time most of the ships navigating at the distance
of ten or fifteen miles began to change their form and magnitude,
and when examined by a telescope from the mast-head, exhibited some
extraordinary appearances, which differed at almost every point of the
compass. One ship had a perfect image, as dark and distinct as the
original, united to its mast-head in a reverse position. Two others
presented two distinct inverted images in the air, one of them a
perfect figure of the original, and the other wanting the hull. Two
or three more were strangely distorted, their masts appearing of at
least twice their proper height, the top-gallant mast forming one-half
of the total elevation; and other vessels exhibited an appearance
totally different from all the preceding, being as it were compressed,
in place of elongated. Their masts seemed to be scarcely one-half of
their proper altitude, in consequence of which one would have supposed
that they were greatly heeled-to one side, or in the position called
careening. Along with all the images of the ships a reflexion of the
ice, sometimes in two strata, also appeared in the air, and these
reflexions suggested the idea of cliffs composed of vertical columns of
alabaster.

On the 15th, 16th, and 17th of the same month, Mr. Scoresby observed
similar phenomena, sometimes extending continuously through half the
circumference of the horizon, and at other times appearing only in
detached spots in various quarters. The inverted images of distant
vessels were often seen in the air, _while the ships themselves were
far beyond the reach of vision_. Some ships were elevated to twice
their proper height, while others were compressed almost to a line.
Hummocks of ice were surprisingly enlarged, and every prominent object
in a proper position was either magnified or distorted.

But of all the phenomena witnessed by Mr. Scoresby, that of the
_Enchanted Coast_, as it may be called, must have been the most
remarkable. This singular effect was seen on the 18th of July, when
the sky was clear, and a tremulous and perfectly transparent vapour
was particularly sensible and profuse: at nine o’clock in the morning,
when the phenomenon was first seen, the thermometer stood at 42°
Fahr.; but in the preceding evening it must have been greatly lower,
as the sea was in many places covered with a considerable pellicle
of new ice,--a circumstance, which, in the very warmest time of the
year, must be considered as quite extraordinary, especially when it
is known that 10° farther to the north no freezing of the sea at
this season had ever before been observed. Having approached on this
occasion so near the unexplored shore of Greenland that the land
appeared distinct and bold, Mr. Scoresby was anxious to obtain a
drawing of it; but on making the attempt he found that the outline
was constantly changing, and he was induced to examine the coast with
a telescope, and to sketch the various appearances which presented
themselves. These are shown, without any regard to their proper order,
in Fig. 34, which we shall describe in Mr. Scoresby’s own words: “The
general telescopic appearance of the coast was that of an extensive
ancient city abounding with the ruins of castles, obelisks, churches,
and monuments, with other large and conspicuous buildings. Some of
the hills seemed to be surmounted by turrets, battlements, spires,
and pinnacles; while others, subjected to one or two reflexions,
exhibited large masses of rock, apparently suspended in the air, at a
considerable elevation above the actual termination of the mountains to
which they referred. The whole exhibition was a grand phantasmagoria.
Scarcely was any particular portion sketched before it changed its
appearance, and assumed the form of an object totally different. It
was perhaps alternately a castle, a cathedral, or an obelisk; then
expanding horizontally, and coalescing with the adjoining hills, united
the intermediate valleys, though some miles in width, by a bridge
of a single arch, of the most magnificent appearance and extent.
Notwithstanding these repeated changes, the various figures represented
in the drawing had all the distinctness of reality; and not only the
different strata, but also the veins of the rocks, with the wreaths of
snow occupying ravines and fissures, form sharp and distinct lines,
and exhibited every appearance of the most perfect solidity.”

[Illustration: _Fig. 34._]

One of the most remarkable facts respecting aërial images presented
itself to Mr. Scoresby in a later voyage which he performed to the
coast of Greenland in 1822. Having seen an inverted image of a ship
in the air, he directed to it his telescope; he was able to discover
it to be his father’s ship, which was at the time below the horizon.
“It was,” says he, “so well defined, that I could distinguish by a
telescope every sail, the general rig of the ship, and its particular
character; insomuch, that I confidently pronounced it to be my father’s
ship, the _Fame_, which it afterwards proved to be; though, on
comparing notes with my father, I found that our relative position, at
the time, gave a distance from one another very nearly thirty miles,
being about seventeen miles beyond the horizon, and some leagues beyond
the limit of direct vision. I was so struck with the peculiarity of
the circumstance, that I mentioned it to the officer of the watch,
stating my full conviction that the _Fame_ was then cruising in the
neighbouring inlet.”

Several curious effects of the mirage were observed by Baron Humboldt
during his travels in South America. When he was residing at Cumana,
he frequently saw the islands of Picuita and Boracha suspended in the
air, and sometimes with an inverted image. On one occasion he observed
small fishing-boats swimming in the air, during more than three or
four minutes, above the well-defined horizon of the sea; and when they
were viewed through a telescope, one of the boats had an inverted
image accompanying it in its movements. This distinguished traveller
observed similar phenomena in the barren steppes of the Caraccas, and
on the borders of the Orinoco, where the river is surrounded by sandy
plains. Little hills and chains of hills appeared suspended in the
air, when seen from the steppes, at three or four leagues’ distance.
Palm-trees standing single in the Llanos appeared to be cut off at
bottom, as if a stratum of air separated them from the ground; and, as
in the African desert, plains destitute of vegetation appeared to be
rivers or lakes. At the Mesa de Pavona M. Humboldt and M. Bonpland _saw
cows suspended in the air_ at the distance of 1000 toises, and having
their feet elevated 3’ 20” above the soil. In this case the images were
erect, but the travellers learned from good authority that _inverted
images of horses had been seen suspended in the air_ near Calabozo.

In all these cases of aërial spectres, the images were directly above
the real object; but a curious case was observed by Messrs. Jurine and
Soret on the 17th September, 1818, where the image of the vessel was
on one side of the real one. About 10 P.M. a barque at the distance
of about 4000 toises from Bellerive, on the lake of Geneva, was seen
approaching to Geneva by the _left_ bank of the lake, and at the same
time an image of the sails was observed above the water, which, instead
of following the direction of the barque, separated from it, and
appeared to approach Geneva by the right bank of the lake, the _image_
moving from _east_ to _west_, while the _barque_ moved from _north_ to
_south_. When the image first separated from the barque they had both
the same magnitude, but the image diminished as it receded from it,
and was reduced to one-half when the phenomenon disappeared.

A very unusual example of aërial spectres occurred to Dr. A. P. Buchan
while walking on the cliff about a mile to the east of Brighton, on the
morning of the 28th of November, 1804. “While watching the rising of
the sun,” says he, “I turned my eyes directly towards the sea, just as
the solar disk emerged from the surface of the water, and saw the face
of the cliff on which I was standing represented precisely opposite to
me at some distance on the ocean. Calling the attention of my companion
to this appearance, we discerned our own figures standing on the summit
of the apparent opposite cliff, as well as the representation of the
windmill near at hand.

“The reflected images were most distinct precisely opposite to where
we stood, and the false cliff seemed to fade away, and to draw near
to the real one, in proportion as it receded towards the west. This
phenomenon lasted about ten minutes, or till the sun had risen nearly
his own diameter above the surface of the ocean. The whole then seemed
to be elevated into the air, and successively disappeared, giving an
impression very similar to that which is produced by the drawing up of
a drop-scene in a theatre. The horizon was cloudy, or perhaps it might
with more propriety be said that the surface of the sea was covered
with a dense fog of many yards in height, and which gradually receded
before the rays of the sun.”

An illusion of a different kind, though not less interesting, is
described by the Rev. Mr. Hughes in his Travels in Greece, as seen
from the summit of Mount Ætna. “I must not forget to mention,” says
he, “one extraordinary phenomenon, which we observed, and for which I
have searched in vain for a satisfactory solution. At the extremity
of the vast shadow which Ætna projects across the island, appeared a
perfect and distinct image of the mountain itself elevated above the
horizon, and diminished as if viewed in a concave mirror. Where or what
the reflector could be which exhibited this image, I cannot conceive;
we could not be mistaken in its appearance, for all our party observed
it, and we had been prepared for it beforehand by our Catanian friends.
It remained visible about _ten_ minutes, and disappeared as the shadow
decreased. Mr. Jones observed the same phenomenon, as well as some
other friends with whom I conversed upon the subject in England.”

It is impossible to study the preceding phenomena without being
impressed with the conviction, that nature is full of the marvellous,
and that the progress of science and the diffusion of knowledge
are alone capable of dispelling the fears which her wonders must
necessarily excite even in enlightened minds. When a spectre haunts
the couch of the sick, or follows the susceptible vision of the
invalid, a consciousness of indisposition divests the apparition of
much of its terror, while its invisibility to surrounding friends
soon stamps it with the impress of a false perception. The spectres
of the conjuror, too, however skilfully they may be raised, quickly
lose their supernatural character; and even the most ignorant beholder
regards the modern magician as but an ordinary man, who borrows from
the sciences the best working implements of his art. But when, in the
midst of solitude, and in situations where the mind is undisturbed
by sublunary cares, we see our own image delineated in the air, and
mimicking in gigantic perspective the tiny movements of humanity;--when
we see troops in military array performing their evolutions on the very
face of an almost inaccessible precipice--when, in the eye of day, a
mountain seems to become transparent, and exhibits on one side of it a
castle which we know to exist only on the other; when distant objects,
concealed by the roundness of the earth, and beyond the cognisance of
the telescope, are actually transferred over the intervening convexity
and presented in distinct and magnified outline to our accurate
examination;--when such varied and striking phantasms are seen also by
all around us, and therefore appear in the character of real phenomena
of nature, our impressions of supernatural agency can only be removed
by a distinct and satisfactory knowledge of the causes which gave them
birth.

It is only within the last forty years that science has brought these
atmospherical spectres within the circle of her dominion; and not only
are all their phenomena susceptible of distinct explanation, but we can
even reproduce them on a small scale with the simplest elements of our
optical apparatus.

[Illustration: _Fig. 35._]

In order to convey a general idea of the causes of these phenomena, let
ABCD, Fig. 35, be a glass trough filled with water, and let a small
ship be placed at S. An eye situated about E, will see the top-mast
of the ship S, directly through the plate of glass BD. Fix a convex
lens _a_ of short focus upon the plate of glass BD, and a little above
a straight line SE joining the ship and the eye; and immediately above
the convex lens a place _a_ concave one _b_. The eye will now see,
through the convex lens _a_, an _inverted_ image of the ship at S´,
and through the concave lens _b_, an erect image of the ship at S´´,
representing in a general way the phenomena shown in Fig. 33. But it
will be asked, where are the lenses in nature to produce these effects?
This question is easily answered. If we take a tin tube with glass
plates at each end, and fill it with water, and if we cool it on the
outside with ice, it will act like a _concave_ lens when the cooling
effect has reached the axis; and, on the other hand, if we heat the
same tube filled with water, on the outside, it will act as a _convex_
glass. In the first case the density of the water diminishes towards
the centre, and in the second it increases towards the centre. The
very same effects are produced in the air, only a greater tract of air
is necessary for showing the effect produced, by heating and cooling it
unequally. If we now remove the lenses _a_, _b_, and hold a heated iron
horizontally above the water in the trough ABC, the heat will gradually
descend, expanding or rendering rarer the upper portions of the fluid.
If, when the heat has reached within a little of the bottom, we look
through the trough at the ship S in the direction ES´, we shall see
an inverted image at S´, and an erect one at S´´; and if we hide from
the eye at E all the ship S, excepting the top-mast, we shall have an
exact representation of the phenomenon in Fig. 33. The experiment will
succeed better with oil in place of water; and the same result may be
obtained without heat, by pouring clear syrup into the glass trough
till it is nearly one-third full, and then filling it up with water.
The water will gradually incorporate with the syrup, and produce, as
Dr. Wollaston has shown, a regular gradation of density, diminishing
from that of the pure syrup to that of the pure water. Similar effects
may be obtained by using masses of transparent solids, such as glass,
rock-salt, &c.

Now it is easy to conceive how the changes of density which we can
thus produce artificially may be produced in nature. If, in serene
weather, the surface of the sea is much colder than the air of the
atmosphere, as it frequently is, and as it was to a very great degree
during the phenomena described by Mr. Scoresby, the air next the sea
will gradually become colder and colder, by giving out its heat to
the water; and the air immediately above will give out its heat to
the cooler air immediately below it, so that the air from the surface
of the sea, to a considerable height upwards, will gradually diminish
in density, and therefore must produce the very phenomena we have
described.

[Illustration: _Fig. 36._]

The phenomenon of Dover Castle seen on the Ramsgate side of the hill,
was produced by the air being more dense near the ground and above the
sea than at greater heights, and hence the rays proceeding from the
castle reached the eye in curve lines, and the cause of its occupying
its natural position on the hill, and not being seen in the air, was
that the top of the hill itself, in consequence of being so near the
castle, suffered the same change from the varying density of the
air, and therefore the castle and the hill were equally elevated and
retained their relative positions. The reason why the image of the
castle and hill appeared erect was, that the rays from the top and
bottom of the castle had not crossed before they reached Ramsgate; but
as they met at Ramsgate, an eye at a greater distance from the castle,
and in the path of the rays, would have seen the image inverted. This
will be better understood from the preceding diagram, which represents
the actual progress of the rays, from a ship SP, concealed from the
observer at E by the convexity of the earth PQE. A ray proceeding from
the keel of the ship P is refracted into the curve line P _c x c_ E,
and a ray proceeding from the top-mast S, is refracted in the direction
S _d x d_ E, the two rays crossing at _x_, and proceeding to the eye
E with the ray from the keel P uppermost; hence the ship must appear
inverted as at _s p_. Now if the eye E of the observer had been placed
nearer the ship as at _x_, before the rays crossed, as was the case at
Ramsgate, it would have seen an erect image of the ship raised a little
above the real ship SP. Rays S _m_, S _n_, proceeding higher up in the
air, are refracted in the directions S _m m_ E, S _n n_ E, but do not
cross before they reach the eye, and therefore they afford the erect
image of the ship shown at _s´ p´_.

The aërial troopers seen at Souterfell were produced by the very
same process as the spectre of Dover Castle, having been brought by
unequal refraction from one side of the hill to the other. It is not
our business to discover how a troop of soldiers came to be performing
their evolutions on the other side of Souterfell; but if there was then
no road along which they could be marching, it is highly probable that
they were troops exercising among the hills in secret, previously to
the breaking out of the rebellion in 1745.

The image of the Genevese barque which was seen sailing at a distance
from the real one, arose from the same cause as the images of ships in
the air; with this difference only, that in this case the strata of
equal density were vertical or perpendicular to the water, whereas,
in the former cases they were horizontal or parallel to the water.
The state of the air which produced the lateral image may be produced
by a headland or island, or even rocks, near the surface, and covered
with water. These headlands, islands, or sunken rocks being powerfully
heated by the sun in the daytime, will heat the air immediately above
them, while the adjacent air over the sea will retain its former
coolness and density. Hence there will necessarily arise a gradation
of density varying in the same horizontal direction, or where the
lines of equal density are vertical. If we suppose the very same state
of the air to exist in a horizontal plane which exists in a vertical
plane, in Fig. 36, then the same images would be seen in a horizontal
line, viz., an inverted one at _s p_, and an erect one at _s´p´_. In
the case of the Genevese barque, the rays had not crossed before they
reached the eye, and therefore the image was an erect one. Had the
real Genevese barque been concealed by some promontory or other cause
from the observation of Messrs. Jurine and Soret, they might have
attached a supernatural character to the spectral image, especially if
they had seen it gradually decay, and finally disappear on the still
and unbroken surface of the lake. No similar fact had been previously
observed, and there were no circumstances in the case to have excited
the suspicion that it was the spectre of a real vessel produced by
unequal refraction.

The spectre of the Brocken and other phenomena of the same kind, have
essentially a different origin from those which arise from unequal
refraction. They are merely shadows of the observer projected on dense
vapour or thin fleecy clouds, which have the power of reflecting much
light. They are seen most frequently at sunrise, because it is at that
time that the vapours and clouds necessary for their production are
most likely to be generated; and they can be seen only when the sun
is throwing his rays horizontally, because the shadow of the observer
would otherwise be thrown either up in the air, or down upon the
ground. If there are two persons looking at the phenomenon, as when
M. Haue and the landlord saw it together, each observer will see his
own image most distinctly, and the head will be more distinct than the
rest of the figure, because the rays of the sun will be more copiously
reflected at a perpendicular incidence: and as, from this cause, the
light reflected from the vapour or cloud becomes fainter farther from
the shadow, the appearance of a halo round the head of the observer is
frequently visible. M. Haue mentions the extraordinary circumstance
of the two spectres of him and the landlord being joined by a _third
figure_, but he unfortunately does not inform us which of the two
figures was doubled, for it is impossible that a person could have
joined their party unobserved. It is very probable that the new spectre
forms a natural addition to the group, as we have represented it in
Fig. 30; and, if this was the case, it could only have been produced by
a duplication of one of the figures produced by unequal refraction.

The reflected spectre of Dr. Buchan standing upon the cliff at
Brighton, arose from a cause to which we have not yet adverted. It was
obviously no shadow, for it is certain, from the locality, that the
rays of the sun fell upon the face of the cliff and upon his person at
an angle of about 73° from the perpendicular, so as to illuminate them
strongly. Now, there are two ways in which such an image may have been
reflected, namely, either from strata of air of variable density, or
from a vertical stratum of vapour, consisting of exceedingly minute
globules of water. Whenever light suffers refraction, either in passing
at once from one medium into another, or from one part of the same
medium into another of different density, a portion of it suffers
reflexion. If an object, therefore, were strongly illuminated, a
sufficiently distinct image, or rather shadow of it, might be seen by
reflexion from strata of air of different density. As the temperature
at which moisture is deposited in the atmosphere varies with the
density of the air, then at the same temperature moisture might be
depositing in a stratum of one density, while no deposition is taking
place in the adjacent stratum of a different density. Hence there would
exist, as it were in the air, a vertical wall or stratum of minute
globules of water, from the surface of which a sufficiently distinct
image of a highly illuminated object might be reflected. That this
is possible may be proved by breathing upon glass. If the particles
deposited upon the glass are large, then no distinct reflection will
take place; but if the particles be very small, we shall see a distinct
image formed by the surface of the aqueous film.

The phenomena of the Fata Morgana have been too imperfectly described
to enable us to offer a satisfactory explanation of them. The aërial
images are obviously those formed by unequal refraction. The pictures
seen on the sea may be either the aërial images reflected from its
surface, or from a stratum of dense vapour, or they may be the direct
reflexions from the objects themselves. The coloured images, as
described by Minasi, have never been seen in any analogous phenomena,
and require to be better described before they can be submitted to
scientific examination.

The representation of ships in the air by unequal refraction has no
doubt given rise in early times to those superstitions which have
prevailed in different countries respecting “phantom ships,” as Mr.
Washington Irving calls them, which always sail in the eye of the
wind, and plough their way through the smooth sea, where there is
not a breath of wind upon its surface. In his beautiful story of the
storm ship, which makes its way up the Hudson against wind and tide,
this elegant writer has finely embodied one of the most interesting
superstitions of the early American colonists. The Flying Dutchman had,
in all probability, a similar origin; and the wizard beacon-keeper of
the Isle of France, who saw in the air the vessels bound to the island
long before they appeared in the offing, must have derived his power
from a diligent observation of the phenomena of nature.




LETTER VII.

 Illusions depending on the ear--Practised by the ancients--Speaking
 and singing heads of the ancients--Exhibition of the Invisible Girl
 described and explained--Illusions arising from the difficulty
 of determining the direction of sounds--Singular example of this
 illusion--Nature of ventriloquism--Exhibitions of some of the
 most celebrated ventriloquists--M. St. Gille--Louis Brabant--M.
 Alexandre--Capt. Lyon’s account of Esquimaux ventriloquists.


Next to the eye, the ear is the most fertile source of our illusions,
and the ancient magicians seem to have been very successful in turning
to their purposes the doctrines of sound. In the Labyrinth of Egypt,
which contained twelve palaces and 1500 subterraneous apartments, the
gods were made to speak in a voice of thunder; and Pliny, in whose
time this singular structure existed, informs us, that some of the
palaces were so constructed that their doors could not be opened
without permitting the peals of thunder to be heard in the interior.
When Darius Hystaspes ascended the throne, and allowed his subjects to
prostrate themselves before him as a god, the divinity of his character
was impressed upon his worshippers by the bursts of thunder and flashes
of lightning which accompanied their devotion. History has of course
not informed us how these effects were produced; but it is probable
that, in the subterraneous and vaulted apartments of the Egyptian
labyrinth, the reverberated sounds arising from the mere opening and
shutting of the doors themselves afforded a sufficient imitation of
ordinary thunder. In the palace of the Persian king, however, a more
artificial imitation is likely to have been employed, and it is not
improbable that the method used in our modern theatres was known to
the ancients. A thin sheet of iron, three or four feet long, such as
that used for German stoves, is held by one corner between the finger
and the thumb, and allowed to hang freely by its own weight. The hand
is then moved or shaken horizontally, so as to agitate the corner in a
direction at right angles to the surface of the sheet. By this simple
process a great variety of sounds may be produced, varying from the
deep growl of distant thunder to those loud and explosive bursts which
rattle in quick succession from clouds immediately over our heads.
The operator soon acquires great power over this instrument, so as
to be able to produce from it any intensity and character of sound
that may be required. The same effect may be produced by sheets of
tin-plate, and by thin plates of mica; but, on account of their small
size, the sound is shorter and more acute. In modern exhibitions an
admirable imitation of lightning is produced by throwing the powder of
rosin, or the dust of lycopodium, through a flame; and the rattling
showers of rain which accompany these meteors are well imitated by a
well-regulated shower of peas.

The principal pieces of acoustic mechanism used by the ancients were
_speaking_ or _singing heads_, which were constructed for the purpose
of representing the gods, or of uttering oracular responses. Among
these, the speaking head of Orpheus, which uttered its responses
at Lesbos, is one of the most famous. It was celebrated not only
throughout Greece, but even in Persia; and it had the credit of
predicting, in the equivocal language of the heathen oracles, the
bloody death which terminated the expedition of Cyrus the Great into
Scythia. Odin, the mighty magician of the North, who imported into
Scandinavia the magical arts of the East, possessed a speaking head,
said to be that of the sage Minos, which he had enchased in gold,
and which uttered responses that had all the authority of a divine
revelation. The celebrated mechanic Gerbert, who filled the papal chair
A.D. 1000, under the name of Sylvester II., constructed a speaking
head of brass. Albertus Magnus is said to have executed a head in
the thirteenth century, which not only moved but spoke. It was made
of earthenware, and Thomas Aquinas is said to have been so terrified
when he saw it, that he broke it in pieces; upon which the mechanist
exclaimed, “There goes the labour of thirty years!”

It has been supposed by some authors, that in the ancient
speaking-machines the deception is effected by means of ventriloquism,
the voice issuing from the juggler himself; but it is more probable
that the sound was conveyed by pipes from a person in another apartment
to the mouth of the figure. Lucian, indeed, expressly informs us,
that the impostor Alexander made his figure of Æsculapius speak, by
transmitting his voice through the gullet of a crane to the mouth of
the statue; and that this method was general appears from a passage in
Theodoretus, who assures us, that in the fourth century, when Bishop
Theophilus broke to pieces the statues at Alexandria, he found some
which were hollow, and which were so placed against a wall, that the
priest could conceal himself behind them; and address the ignorant
spectators through their mouths.

Even in modern times, speaking-machines have been constructed on this
principle. The figure is frequently a mere head placed upon a hollow
pedestal, which, in order to promote the deception, contains a pair of
bellows, a sounding-board, a cylinder and pipes supposed to represent
the organs of speech. In other cases these are dispensed with, and a
simple wooden head utters its sounds through a speaking trumpet. At the
court of Charles II., this deception was exhibited with great effect by
one Thomas Irson, an Englishman; and when the astonishment had become
very general, a popish priest was discovered by one of the pages in
an adjoining apartment. The questions had been proposed to the wooden
figure by whispering into its ear, and this learned personage had
answered them all with great ability, by speaking through a pipe in the
same language in which the questions were proposed. Professor Beckmann
informs us that children and women were generally concealed either in
the juggler’s box or in the adjacent apartment, and that the juggler
gave them every assistance by means of signs previously agreed upon.
When one of these exhibitions was shown at Göttingen, the Professor
was allowed, on the promise of secrecy, to witness the process of
deception. He saw the assistant in another room, standing before the
pipe with a card in his hand, upon which the signs agreed upon had
been marked, and he had been introduced so privately into the house
that even the landlady was ignorant of his being there.

An exhibition of the very same kind has been brought forward in our
own day, under the name of the _Invisible Girl_; and as the mechanism
employed was extremely ingenious, and is well fitted to convey an idea
of this class of deceptions, we shall give a detailed description of it.

[Illustration: _Fig. 37._]

The machinery, as constructed by M. Charles, is shown in fig. 37 in
perspective, and a plan of it in Fig. 38. The four upright posts A, A,
A, A, are united at top by a cross rail B, B, and by two similar rails
at bottom. Four bent wires a, _a_, _a_, _a_, proceeded from the top
of these posts, and terminated at _c_. A hollow copper ball M, about
a foot in diameter, was suspended from these wires by four slender
ribands _b_, _b_, _b_, _b_, and into the copper ball were fixed the
extremities of four trumpets T, T, T, T, with their mouths outwards.

[Illustration: _Fig. 38._]

The apparatus now described was all that was visible to the spectator;
and though fixed in one spot, yet it had the appearance of a piece of
separate machinery, which might have occupied any other part of the
room. When one of the spectators was requested by the exhibitor to
propose some question, he did it by speaking into one of the trumpets
at T. An appropriate answer was then returned from all the trumpets,
and the sound issued with sufficient intensity to be heard by an ear
applied to any of them, and yet it was so weak that it appeared to come
from a person of very diminutive size. Hence the sound was supposed to
come from an invisible girl, though the real speaker was a full-grown
woman. The invisible lady conversed in different languages, sang
beautifully, and made the most lively and appropriate remarks on the
persons in the room.

This exhibition was obviously far more wonderful than the speaking
heads which we have described, as the latter invariably communicated
with a wall, or with a pedestal through which pipes could be carried
into the next apartment. But the ball M and its trumpets communicated
with nothing through which sound could be conveyed. The spectator
satisfied himself by examination that the ribands _b_, _b_, were real
ribands, which concealed nothing, and which could convey no sound; and
as he never conceived that the ordinary piece of frame-work AB could
be of any other use than its apparent one of supporting the sphere M,
and defending it from the spectators, he was left in utter amazement
respecting the origin of the sound, and his surprise was increased
by the difference between the sounds which were uttered and those of
ordinary speech.

Though the spectators were thus deceived by their own reasoning,
yet the process of deception was a very simple one. In two of the
horizontal railings A, A, Fig. 38, opposite the trumpet mouths T,
there was an aperture communicating with a pipe or tube which went
to the vertical post B, and descending it, as shown at TAA, Fig. 39,
went beneath the floor _f f_, in the direction _p p_, and entered the
apartment N, where the invisible lady sat. On the side of the partition
about _h_, there was a small hole through which the lady saw what was
going on in the exhibition-room, and communications were no doubt made
to her by signals from the person who attended the machine. When one of
the spectators asked a question by speaking into one of the trumpets
T, the sound was reflected from the mouth of the trumpet back to the
aperture at A, in the horizontal rail, Fig. 38, and was distinctly
conveyed along the closed tube into the apartment N. In like manner the
answer issued from the aperture A, and being reflected back to the ear
of the spectator by the trumpet, he heard the sounds with that change
of character which they receive when transmitted through a tube and
then reflected to the ear.

[Illustration: _Fig. 39._]

The surprise of the auditors was greatly increased by the circumstance,
that an answer was returned to questions put in a whisper, and also
by the conviction that nobody but a person in the middle of the
audience could observe the circumstances to which the invisible figure
frequently adverted.

Although the performances of speaking heads were generally effected
by the methods now described, yet there is reason to think that the
ventriloquist sometimes presided at the exhibition, and deceived the
audience by his extraordinary powers of illusion. There is no species
of deception more irresistible in its effects than that which arises
from the uncertainty with which we judge of the direction and distance
of sounds. Every person must have noticed how a sound in their own ears
is often mistaken for some loud noise moderated by the distance from
which it is supposed to come; and the sportsman must have frequently
been surprised at the existence of musical sounds humming remotely in
the extended heath, when it was only the wind sounding in the barrel
of his gun. The great proportion of apparitions that haunt old castles
and apartments associated with death, exist only in the sounds which
accompany them. The imagination even of the boldest inmate of a place
hallowed by superstition, will transfer some trifling sound near his
own person to a direction and to a distance very different from the
truth, and the sound which otherwise might have no peculiar complexion
will derive another character from its new locality. Spurning the idea
of a supernatural origin, he determines to unmask the spectre, and
grapple with it in its den. All the inmates of the house are found
to be asleep--even the quadrupeds are in their lair--there is not a
breath of wind to ruffle the lake that reflects through the casement
the reclining crescent of the night; and the massive walls in which he
is enclosed forbid the idea that he has been disturbed by the warping
of panelling or the bending of partitions. His search is vain; and
he remains master of his own secret, till he has another opportunity
of investigation. The same sound again disturbs him, and, modified
probably by his own position at the time, it may perhaps appear to
come in a direction slightly different from the last. His searches are
resumed, and he is again disappointed. If this incident should recur
night after night with the same result--if the sound should appear to
depend upon his own motions, or be any how associated with himself,
with his present feelings, or with his past history, his personal
courage will give way; a superstitious dread, at which he himself
perhaps laughs, will seize his mind; and he will rather believe that
the sounds have a supernatural origin, than that they could continue to
issue from a spot where he knows there is no natural cause for their
production.

I have had occasion to have personal knowledge of a case much
stronger than that which has now been put. A gentleman, devoid of all
superstitious feelings, and living in a house free from any gloomy
associations, heard night after night in his bed-room a singular noise,
unlike any ordinary sound to which he was accustomed. He had slept in
the same room for years without hearing it, and he attributed it at
first to some change of circumstances in the roof or in the walls of
the room, but after the strictest examination no cause could be found
for it. It occurred only once in the night; it was heard almost every
night, with few interruptions. It was over in an instant, and it never
took place till after the gentleman had gone to bed. It was always
distinctly heard by his companion, to whose time of going to bed it had
no relation. It depended on the gentleman alone, and it followed him
into another apartment with another bed, on the opposite side of the
house. Accustomed to such investigations, he made the most diligent
but fruitless search into its cause. The consideration that the sound
had a special reference to him alone, operated upon his imagination,
and he did not scruple to acknowledge that the recurrence of the
mysterious sound produced a superstitious feeling at the moment. Many
months afterwards it was found that the sound arose from the partial
opening of the door of a wardrobe which was within a few feet of the
gentleman’s head, and which had been taken into the other apartment.
This wardrobe was almost always opened before he retired to bed, and
the door being a little too tight, it gradually forced itself open
with a sort of dull sound, resembling the note of a drum. As the door
had only started half an inch out of its place, its change of position
never attracted attention. The sound, indeed, seemed to come in a
different direction, and from a greater distance.

When sounds so mysterious in their origin are heard by persons
predisposed to a belief in the marvellous, their influence over the
mind must be very powerful. An inquiry into their origin, if it is made
at all, will be made more in the hope of confirming than of removing
the original impression, and the unfortunate victim of his own fears
will also be the willing dupe of his own judgment.

This uncertainty with respect to the direction of sound is the
foundation of the art of ventriloquism. If we place ten men in a row
at such a distance from us that they are included in the angle within
which we cannot judge of the direction of sound, and if in a calm day
each of them speaks in succession, we shall not be able with closed
eyes to determine from which of the ten men any of the sounds proceed,
and we shall be incapable of perceiving that there is any difference
in the direction of the sounds emitted by the two outermost. If a man
and a child are placed within the same angle, and if the man speaks
with the accent of a child without any corresponding motion in his
mouth or face, we shall necessarily believe that the voice comes from
the child; nay, if the child is so distant from the man that the voice
actually appears to us to come from the man, we shall still continue
in the belief that the child is the speaker; and this conviction would
acquire additional strength if the child favoured the deception, by
accommodating its features and gestures to the words spoken by the
man. So powerful, indeed, is the influence of this deception, that if
a jack-ass, placed near the man, were to open its mouth, and shake
its head responsive to the words uttered by his neighbour, we should
rather believe that the ass spoke than that the sounds proceeded from
a person whose mouth was shut, and the muscles of whose face were in
perfect repose. If our imagination were even directed to a marble
statue or a lump of inanimate matter, as the source from which we were
to expect the sounds to issue, we would still be deceived, and would
refer the sounds even to these lifeless objects. The illusion would be
greatly promoted, if the voice were totally different in its tone and
character from that of the man from whom it really comes; and if he
occasionally speaks in his own full and measured voice, the belief will
be irresistible that the assumed voice proceeds from the quadruped or
from the inanimate object.

When the sounds which are required to proceed from any given object
are such as they are actually calculated to yield, the process of
deception is extremely easy; and it may be successfully executed, even
if the angle between the real and the supposed direction of the sound
is much greater than the angle of uncertainty. Mr. Dugald Stewart
has stated some cases in which deceptions of this kind were very
perfect. He mentions his having seen a person who, by counterfeiting
the gesticulations of a performer on the violin, while he imitated the
music by his voice, riveted the eyes of his audience on the instrument,
though every sound they heard proceeded from his own mouth. The late
Savile Carey, who imitated the whistling of the wind through a narrow
chink, told Mr. Stewart that he had frequently practised this deception
in the corner of a coffee-house, and that he seldom failed to see some
of the company rise to examine the tightness of the windows, while
others, more intent on their newspapers, contented themselves with
putting on their hats and buttoning their coats. Mr. Stewart likewise
mentions an exhibition formerly common in some of the continental
theatres, where a performer on the stage displayed the dumb-show of
singing with his lips and eyes and gestures, while another person
unseen supplied the music with his voice. The deception in this case
he found to be at first so complete as to impose upon the nicest ear
and the quickest eye; but in the progress of the entertainment, he
became distinctly sensible of the imposition, and sometimes wondered
that it should have misled him for a moment. In this case there
can be no doubt that the deception was at first the work of the
imagination, and was not sustained by the acoustic principle. The real
and the mock singer were too distant, and when the influence of the
imagination subsided, the true direction of the sound was discovered.
This detection of the imposture, however, may have arisen from another
cause. If the mock singer happened to change the position of his head,
while the real singer made no corresponding change in his voice, the
attentive spectator would at once notice this incongruity, and discover
the imposition.

In many of the feats of ventriloquism the performer contrives, under
some pretence or other, to conceal his face, but ventriloquists of
great distinction, such as M. Alexandre, practise their art without any
such concealment.

Ventriloquism loses its distinctive character if its imitations are
not performed by a voice from the belly. The voice, indeed, does not
actually come from that region; but when the ventriloquist utters
sounds from the larynx without moving the muscles of his face, he
gives them strength by a powerful action of the abdominal muscles.
Hence he speaks by means of his belly, although the throat is the real
source from whence the sounds proceed. Mr. Dugald Stewart has doubted
the fact, that ventriloquists possess the power of fetching a voice
from within: he cannot conceive what aid could be derived from such
an extraordinary power; and he considers that the imagination, when
seconded by such powers of imitation as some mimics possess, is quite
sufficient to account for all the phenomena of ventriloquism which he
has heard. This opinion, however, is strongly opposed by the remark
made to Mr. Stewart himself by a ventriloquist, “that his art would
be perfect, if it were possible only to speak distinctly without any
movement of the lips at all.” But, independent of this admission, it is
a matter of absolute certainty, that this internal power is exercised
by the true ventriloquist. In the account which the Abbé Chapelle
has given of the performances of M. St. Gille and Louis Brabant, he
distinctly states that M. St. Gille appeared to be absolutely mute
while he was exercising his art, and that no change in his countenance
could be discovered.[16] He affirms, also, that the countenance of
Louis Brabant exhibited no change, and that his lips were close and
inactive. M. Richerand, who attentively watched the performances
of M. Fitz-James, assures us that during his exhibition there was
a distention in the epigastric region, and that he could not long
continue the exertion without fatigue.

 [16] Edinburgh Journal of Science, No. xviii., p. 254.

The influence over the human mind which the ventriloquist derives from
the skilful practice of his art is greater than that which is exercised
by any other species of conjuror. The ordinary magician requires his
theatre, his accomplices, and the instruments of his art, and he enjoys
but a local sovereignty within the precincts of his own magic circle.
The ventriloquist, on the contrary, has the supernatural always at
his command. In the open fields as well as in the crowded city, in
the private apartment as well as in the public hall, he can summon up
innumerable spirits; and though the persons of his fictitious dialogue
are not visible to the eye, yet they are unequivocally present to the
imagination of his auditors, as if they had been shadowed forth in
the silence of a spectral form. In order to convey some idea of the
influence of this illusion, I shall mention a few well-authenticated
cases of successful ventriloquism.

M. St. Gille, a grocer of St. Germain-en-Laye, whose performances have
been recorded by the Abbé de la Chapelle, had occasion to shelter
himself from a storm in a neighbouring convent, where the monks were
in deep mourning for a much-esteemed member of their community who had
been recently buried. While lamenting over the tomb of their deceased
brother the slight honours which had been paid to his memory, a voice
was suddenly heard to issue from the roof of the choir bewailing the
condition of the deceased in purgatory, and reproving the brotherhood
for their want of zeal. The tidings of this supernatural event brought
the whole brotherhood to the church. The voice from above repeated its
lamentations and reproaches, and the whole convent fell upon their
faces, and vowed to make a reparation of their error. They accordingly
chanted in full choir a _De Profundis_, during the intervals of
which the spirit of the departed monk expressed his satisfaction at
their pious exercises. The prior afterwards inveighed against modern
scepticism on the subject of apparitions, and M. St. Gille had great
difficulty in convincing the fraternity that the whole was a deception.

On another occasion, a commission of the Royal Academy of Sciences
at Paris, attended by several persons of the highest rank, met at St.
Germain-en-Laye to witness the performances of M. St. Gille. The real
object of their meeting was purposely withheld from a lady of the
party, who was informed that an aërial spirit had lately established
itself in the neighbourhood, and that the object of the assembly was
to investigate the matter. When the party had sat down to dinner in
the open air, the spirit addressed the lady in a voice which seemed to
come from above their heads, from the surface of the ground at a great
distance, or from a considerable depth under her feet. Having been thus
addressed at intervals during two hours, the lady was firmly convinced
of the existence of the spirit, and could with difficulty be undeceived.

Another ventriloquist, Louis Brabant, who had been valet-de-chambre
to Francis I., turned his powers to a more profitable account. Having
fallen in love with a rich and beautiful heiress, he was rejected by
her parents as an unsuitable match for their daughter. On the death
of her father, Louis paid a visit to the widow, and he had no sooner
entered the house than she heard the voice of her deceased husband
addressing her from above, “Give my daughter in marriage to Louis
Brabant, who is a man of large fortune and excellent character. I
endure the inexpressible torments of purgatory for having refused her
to him. Obey this admonition, and give everlasting repose to the soul
of your poor husband.” This awful command could not be resisted, and
the widow announced her compliance with it.

As our conjuror, however, required money for the completion of his
marriage, he resolved to work upon the fears of one Cornu, an old
banker at Lyons, who had amassed immense wealth by usury and extortion.
Having obtained an interview with the miser, he introduced the subjects
of demons and spectres, and the torments of purgatory; and, during an
interval of silence, the voice of the miser’s deceased father was heard
complaining of his dreadful situation in purgatory, and calling upon
his son to rescue him from his sufferings by enabling Louis Brabant to
redeem the Christians that were enslaved by the Turks. The awe-struck
miser was also threatened with eternal damnation if he did not thus
expiate his own sins; but such was the grasp that the banker took of
his gold, that the ventriloquist was obliged to pay him another visit.
On this occasion, not only his father but all his deceased relatives
appealed to him in behalf of his own soul and theirs; and such was
the loudness of their complaints, that the spirit of the banker was
subdued, and he gave the ventriloquist ten thousand crowns to liberate
the Christian captives. When the miser was afterwards undeceived, he is
said to have been so mortified that he died of vexation.

The ventriloquists of the nineteenth century made great additions to
their art, and the performances of M. Fitz-James and M. Alexandre,
which must have been seen by many of our countrymen, were far superior
to those of their predecessors. Besides the art of speaking by the
muscles of the throat and the abdomen, without moving those of the
face, these artists had not only studied with great diligence and
success the modifications which sounds of all kinds undergo from
distance, obstructions, and other causes, but had acquired the art
of imitating them in the highest perfection. The ventriloquist was
therefore able to carry on a dialogue in which the _dramatis voces_,
as they may be called, were numerous; and when on the outside of an
apartment, he could personate a mob with its infinite variety of
noise and vociferation. Their influence over an audience was still
further extended by a singular power over the muscles of the body. M.
Fitz-James actually succeeded in making the opposite or corresponding
muscles act differently from each other; and while one side of his face
was merry and laughing, the other was full of sorrow and in tears.
At one moment he was tall, thin, and melancholic, and after pausing
behind a screen, he came out “bloated with obesity and staggering with
fulness.” M. Alexandre possessed the same power over his face and
figure; and so striking was the contrast of two of these forms, that an
excellent sculptor, Mr. Joseph, has perpetuated them in marble.

This new acquirement of the ventriloquist enabled him, in his own
single person and with his own single voice, to represent upon the
stage a dramatic composition which would have required the assistance
of several actors. Although only one character in the piece could be
seen at the same time, yet they all appeared during its performance,
and the change of face and figure on the part of the ventriloquist was
so perfect, that his personal identity could not be recognized in the
_dramatis personæ_. This deception was rendered still more complete by
a particular construction of the dresses, which enabled the performer
to reappear in a new character after an interval so short that the
audience necessarily believed that it was another person.

It is a curious circumstance that Captain Lyon found among the
Esquimaux of Igloolik ventriloquists of no mean skill. There is much
rivalry among the professors of the art, who do not expose each
other’s secrets, and their exhibitions derive great importance from
the rarity of their occurrence. The following account of one of them
is so interesting that we shall give the whole of it in Captain Lyon’s
words:--

“Amongst our Igloolik acquaintances were two females and a few male
wizards, of whom the principal was Toolemak. This personage was cunning
and intelligent; and, whether professionally, or from his skill in
the chase, but perhaps from both reasons, was considered by all the
tribe as a man of importance. As I invariably paid great deference
to his opinion on all subjects connected with his calling, he freely
communicated to me his superior knowledge, and did not scruple to
allow of my being present at his interviews with Tornga, or his
patron spirit. In consequence of this, I took an early opportunity
of requesting my friend to exhibit his skill in my cabin. His old
wife was with him, and by much flattery and an accidental display
of a glittering knife and some beads, she assisted me in obtaining
my request. All light excluded, our sorcerer began chanting to his
wife with great vehemence, and she in return answered by singing
the Amna-aya, which was not discontinued during the whole ceremony.
As far as I could hear, he afterwards began turning himself rapidly
round, and in a loud, powerful voice vociferated for Tornga with great
impatience, at the same time blowing and snorting like a walrus. His
noise, impatience, and agitation increased every moment, and he at
length seated himself on the deck, varying his tones, and making a
rustling with his clothes. Suddenly the voice seemed smothered, and was
so managed as to sound as if retreating beneath the deck, each moment
becoming more distant, and ultimately giving the idea of being many
feet below the cabin, when it ceased entirely. His wife now, in answer
to my queries, informed me very seriously, that he had dived, and that
he would send up Tornga. Accordingly, in about half a minute, a distant
blowing was heard very slowly approaching, and a voice, which differed
from that at first heard, was at times mingled with the blowing, until
at length both sounds became distinct, and the old woman informed
me that Tornga was come to answer my questions. I accordingly asked
several questions of the sagacious spirit, to each of which inquiries I
received an answer by two loud claps on the deck, which I was given to
understand were favourable.

“A very hollow, yet powerful voice, certainly much different from the
tones of Toolemak, now chanted for some time, and a strange jumble of
hisses, groans, shouts, and gabblings like a turkey, succeeded in rapid
order. The old woman sang with increased energy; and as I took it for
granted that this was all intended to astonish the Kabloona, I cried
repeatedly that I was very much afraid. This, as I expected, added fuel
to the fire, until the poor immortal, exhausted by its own might, asked
leave to retire.

“The voice gradually sank from our hearing as at first, and a very
indistinct hissing succeeded; in its advance it sounded like the tone
produced by the wind on the brass chord of an Æolian harp. This was
soon changed to a rapid hiss like that of a rocket, and Toolemak with
a yell announced his return. I had held my breath at the first distant
hissing, and twice exhausted myself, yet our conjuror did not once
respire, and even his returning and powerful yell was uttered without a
previous stop or inspiration of air.

“Light being admitted, our wizard, as might be expected, was in a
profuse perspiration, and certainly much exhausted by his exertions,
which had continued for at least half an hour. We now observed a couple
of bunches, each consisting of two stripes of white deer-skin, and a
long piece of sinew, attached to the back of his coat. These we had not
seen before, and were informed that they had been sewn on by Tornga
while he was below.”[17]

 [17] _Private Journal of_ Captain G. F. Lyon. London, 1824, pp. 358,
 361.

Captain Lyon had the good fortune to witness another of Toolemak’s
exhibitions, and he was much struck with the wonderful steadiness of
the wizard throughout the whole performance, which lasted an hour and
a half. He did not once appear to move, for he was so close to the
skin behind which Captain Lyon sat, that if he had done so he must
have perceived it. Captain Lyon did not hear the least rustling of his
clothes, or even distinguish his breathing, although his outcries were
made with great exertion.[18]

 [18] Id. p. 366.




LETTER VIII.

 Musical and harmonic sounds explained--Power of breaking glasses
 with the voice--Musical sounds from the vibration of a column
 of air--and of solid bodies--Kaleidophone--Singular acoustic
 figures produced on sand laid on vibrating plates of glass--and
 on stretched membranes--Vibration of flat rulers and cylinders
 of glass--Production of silence from two sounds--Production
 of darkness from two lights--Explanation of these singular
 effects--Acoustic automaton--Droz’s bleating sheep--Maillardet’s
 singing-bird--Vaucanson’s flute-player--His pipe and
 tabor-player--Baron Kempelen’s talking-engine--Kratzenstein’s
 speaking-machine--Mr. Willis’s researches.


Among the discoveries of modern science, there are few more remarkable
than those which relate to the production of harmonic sounds. We
are all familiar with the effects of musical instruments, from the
deep-toned voice of the organ to the wiry shrill of the Jew’s harp.
We sit entranced under their magical influence, whether the ear is
charmed with the melody of their sounds, or the heart agitated by the
sympathies which they rouse. But though we may admire their external
form, and the skill of the artist who constructed them, we never think
of inquiring into the cause of such extraordinary combinations.

Sounds of all kinds are conveyed to the organ of hearing through the
air; and if this element were to be destroyed, all nature would be
buried in the deepest silence. Noises of every variety, whether they
are musical or discordant, high or low, move through the air of our
atmosphere at the surface of the earth with a velocity of 1090 feet
in a second, or 765 miles per hour; but in sulphurous acid gas sound
moves only through 751 feet in a second, while in hydrogen gas it moves
with the great velocity of 3000 feet. Along fluid and solid bodies,
its progress is still more rapid. Through water it moves at the rate
of 4708 feet in a second, through tin at the rate of 8175 feet, and
through iron, glass, and some kinds of wood, at the rate of 18,530 feet.

When a number of single and separate sounds follow each other in rapid
succession, they produce a continued sound, in the same manner as a
continuous circle of light is produced by whirling round a burning
stick before the eye. In order that the sound may appear a single one
to the ear, nearly sixteen separate sounds must follow one another
every second. When these sounds are exactly similar, and recur at equal
intervals, they form a musical sound. In order to produce such sounds
from the air, it must receive at least sixteen equally distant impulses
or strokes in a second. The most common way of producing this effect is
by a string or wire A B, Fig. 40, stretched between the fixed points A,
B. If this string is taken by the middle and pulled aside, or if it is
suddenly struck, it will vibrate between its two fixed points, as shown
in the figure, passing alternately on each side of its axis A B, the
vibrations gradually diminishing by the resistance of the air till the
string is brought to rest. Its vibrations, however, may be kept up, by
drawing a rosined fiddle-bow across it, and while it is vibrating it
will give out a sound corresponding to the rapidity of its vibrations,
and arising from the successive blows or impulses given to the air by
the string. This sound is called the fundamental sound of the string,
and its acuteness or sharpness increases with the number of vibrations
which the string performs in a second.

[Illustration: _Fig. 40._]

If we now touch the vibrating string A´ B lightly with the finger,
or with a feather at the middle point C, Fig. 40, it will give out a
more acute but fainter sound than before, and while the extent of its
vibrations is diminished, their frequency is doubled. In like manner,
if we touch the string A´´ B´´, Fig. 40, at a point C, so that A´´ C is
one-third of A´´ B´´, the note will be still more acute, and correspond
to thrice the number of vibrations. All this might have been expected;
but the wonderful part of the experiment is, that the vibrating string
A´ B´ divides itself at C into two parts A´ C, C B´, the part A´ C
vibrating round A and C as fixed points, and the part C B´ round C and
B´, but always so that the part A´ C is at the same distance on the
one side of the axis A´ B´ as at A _m_ C, while the part C B is on
the other side, as at C _n_ B. Hence the point C, being always pulled
by equal and opposite forces, remains at rest as if it were absolutely
fixed. This stationary point is called a _node_, and the vibrating
portions A´_m_ C, C _n_ B´ loops. The very same is true of the string
A´´ B´´, the points C and D being stationary points; and upon the
same principle a string may be divided into any number of vibrating
portions. In order to prove that the string is actually vibrating in
these equal subdivisions, we have only to place a piece of light paper
with a notch in it on different parts of the string. At the nodes C and
D it will remain perfectly at rest, while at _m_ or _n_ in the middle
of the loops it will be thrown off or violently agitated.

The acute sounds given out by each of the vibrating portions are called
_harmonic sounds_, and they accompany the fundamental sound of the
string in the very same manner as we have already seen that the eye
sees the accidental or harmonic colours while it is affected with the
fundamental colour.

The subdivision of the string, and consequently the production of
harmonic sounds, may be effected without touching the string at all,
and by means of a sympathetic action conveyed by the air. If a string
A B, for example, Fig. 40, is at rest, and if a shorter string A´´ C,
one third of its length, fixed at the two points A´´ and C, is set
vibrating in the same room, the string A B will be set vibrating in
three loops like A´´ B´´, giving out the same harmonic sounds as the
small string A´´ C.

It is owing to this property of sounding bodies that singers with great
power of voice are able to break into pieces a large tumbler glass, by
singing close to it its proper fundamental note; and it is from the
same sympathetic communication of vibrations that two pendulum clocks
fixed to the same wall, or two watches lying upon the same table, will
take the same rate of going, though they would not agree with one
another if placed in separate apartments. Mr. Ellicott even observed
that the pendulum of the one clock will stop that of the other, and
that the stopped pendulum will, after a certain time, resume its
vibrations, and in its turn stop the vibrations of the other pendulum.

The production of musical sounds by the vibrations of a column of air
in a pipe is familiar to every person, but the extraordinary mechanism
by which it is effected is known principally to philosophers. A column
of air in a pipe may be set vibrating by blowing over the open end of
it, as is done in Pan’s pipes; or by blowing over a hole in its side,
as in the flute; or by blowing through an aperture called a reed,
with a flexible tongue, as in the clarionet. In order to understand
the nature of this vibration, let AB, Fig. 41, be a pipe or tube, and
let us place in it a spiral spring AB, in which the coil or spire are
at equal distances, each end of the spiral being fixed to the end of
the tube. This elastic spring may be supposed to represent the air in
the pipe, which is of equal density throughout. If we take hold of
the spring at _m_, and push the point _m_ towards A and towards B in
succession, it will give us a good idea of the vibration of an elastic
column of air. When _m_ is pushed towards A, the spiral spring will
be compressed or condensed, as shown at _m_ A, No. 2, while at the
other end it will be dilated or rarefied, as shown at _m_ B, and in
the middle of the tube it will have the same degree of compression as
in No. 1. When the string is drawn to the other end of the tube B, the
spring will be, as in No. 3, condensed at the end B, and dilated at
the end A. Now when a column of air vibrates in a pipe AB, the whole
of it rushes alternately from B to A, as in No. 2, and from A to B as
in No. 3, being condensed at the end A, No. 2, and dilated or rarefied
at the end B, while in No. 3 it is rarefied at A and condensed at B,
preserving its natural density at the middle point between A and B. In
the case of the spring the ends AB are alternately pushed outwards and
pulled inwards by the spring, the end A being pushed outwards in No. 2,
and B pulled inwards, while in No. 3 A is pulled inwards and B pushed
outwards.

[Illustration: _Fig. 41._]

That the air vibrating in a pipe is actually in the state now
described, may be shown by boring small holes in the pipe, and putting
over them pieces of a fine membrane. The membrane opposite to the
middle part between A and B where the particles of the air have the
greatest motion, will be violently agitated, while at points nearer the
ends A and B it will be less and less affected.

[Illustration: _Fig. 42._]

Let us now suppose two pipes, AB, BC, to be joined together as in Fig.
42, and to be separated by a fixed partition at B; and let a spiral
spring be fixed in each. Let the spring AB be now pushed to the end
A, while the spring BC is pushed to C, as in No. 1, and back again,
as in No. 2, but always in opposite directions; then it is obvious
that the partition B is in No. 1 drawn in opposite directions towards
A and towards C, and always with forces equal to each other: that is,
when B is drawn slightly towards A, which it is at the beginning of
the motion, it is also drawn slightly towards C; and when it is drawn
forcibly towards A, as it is at the end of the motion of the spring,
it is also drawn forcibly towards C. If the partition B, therefore, is
moveable, it will still remain fixed during the opposite excursions
of the spiral springs; nay, if we remove the partition, and hook the
end of one spiral spring to the end of the other, the node or point of
junction will remain stationary during the movements of the springs,
because at every instant that point is drawn by equal and opposite
forces. If _three_, _four_, or _five_ spiral springs are joined in a
similar manner, we may conceive them all vibrating between their nodes
in the same manner.

Upon the very same principles we may conceive a long column of air
without partitions dividing itself into two, three, or four smaller
columns, each of which will vibrate between its nodes in the same
manner as the spiral spring. At the middle point of each small
vibrating column, the air will be of its natural density, like that
of the atmosphere; while at the nodes B, &c. it will be in a state of
condensation and rarefaction alternately.

If, when the air is vibrating in one column in the pipe AB, as in Fig.
41, No. 2, 3, we conceive a hole made in the middle, the atmospheric
air will not rush in to disturb the vibration, because the air within
the pipe and without it has exactly the same density. Nay, if, instead
of a single hole, we were to cut a ring out of the pipe at the middle
point, the column would vibrate as before. But if we bore a hole
between the middle and one of the ends, where the vibrating column
must be either in a state of condensation or rarefaction, the air must
either rush out or rush in, in order to establish the equilibrium.
The air opposite the hole will then be brought to the state of the
external air, like that in the middle of the pipe; it will become the
middle of a vibrating column: and the whole column of air, instead of
vibrating as one, will vibrate as two columns, each column vibrating
with twice the velocity, and yielding harmonic sounds along with the
fundamental sound of the whole columns, in the same manner as we have
already explained with regard to vibrating strings. By opening other
holes we may subdivide a vibrating column into any number of smaller
vibrating columns. The holes in flutes, clarionets, &c. are made for
this purpose. When they are all closed up, the air vibrates in one
column; and by opening and shutting the different holes in succession,
the number of vibrating columns is increased or diminished at pleasure,
and consequently the harmonic sounds will vary in a similar manner.

Curious as these phenomena are, they are still surpassed by those
which are exhibited during the vibration of solid bodies. A rod or
bar of metal or glass may be made to vibrate either longitudinally or
laterally.

An iron rod will vibrate longitudinally, like a column of air, if we
strike it at one end in the direction of its length; or rub it in
the same direction with a wetted finger, and it will admit the same
fundamental note as a column of air _ten_ or _eleven_ times as long,
because sound moves so much faster in iron than in air. When the
iron rod is thus vibrating along its length, the very same changes
which we have shown in Fig. 41, as produced in a spiral spring, or
in a column of air, take place in the solid metal. All its particles
move alternately towards A and towards B, the metal being in the one
case condensed at the end to which the particles move, and expanded
at the end from which they move, and retaining its natural density
in the middle of the rod. If we now hold this rod in the middle, by
the finger and thumb lightly applied, and rub it in the middle either
of AB or BC with a piece of cloth sprinkled with powdered rosin,
or with a well-rosined fiddle-bow drawn across the rod, it will
divide itself into two vibrating portions AB, BC, each of which will
vibrate, as shown in Fig. 42, like the two adjacent columns of air,
the section of the rod, or the particles which compose that section
at B, being at perfect rest. By holding the rod at any intermediate
point between A and B, so that the distance from A to the finger and
thumb is one-third, one-fourth, one-fifth, &c. of the whole length AC,
and rubbing one of the divisions in the middle, the rod will divide
itself into 3, 4, 5, &c. vibrating portions, and give out corresponding
harmonic sounds.

[Illustration: _Fig. 43._]

A rod of iron may be made to vibrate laterally or transversely, by
fixing one end of it firmly, as in a vice, and leaving the other free,
or by having both ends free or both fixed. When a rod, fixed at one
end and free at the other, is made to vibrate, its mode of vibrating
may be rendered evident to the eye; and for the purpose of doing
this, Mr. Wheatstone has contrived a curious instrument, called the
_Kaleidophone_, which is shown in Fig. 43. It consists of a circular
base of wood AB, about _nine_ inches in diameter and one inch thick,
and having four brass sockets firmly fixed into it at C, D, E, and F.
Into these sockets are screwed four vertical steel rods C, D, E, and
F, about thirteen or fourteen inches long; one being a square rod,
another a bent cylindrical one, and the other two cylindrical ones of
different diameters. On the extremities of these rods are fixed small
quicksilvered glass beads, either singly or in groups, so that when
the instrument is placed in the light of the sun or in that of a lamp,
bright images of the sun or flame are seen reflected on each bead. If
any of these rods is set vibrating, these luminous images will form
continuous and returning curve lines in a state of constant variation,
each different rod giving curves of different characters, as shown in
Fig. 44.

[Illustration: _Fig. 44._]

The Melodion, an instrument of great power, embracing five octaves,
operates by means of the vibrations of metallic rods of unequal
lengths, fixed at one end and free at the other.[19] A narrow and thin
plate of copper is screwed to the free extremity of each rod, and at
right angles to its length; and its surface is covered with a small
piece of felt, impregnated with rosin. This narrow band is placed near
the circumference of a revolving cylinder, and, by touching the key,
it is made to descend till it touches the revolving cylinder, and
gives out its sound. The sweetness and power of this instrument are
unrivalled; and such is the character of its tones, that persons of a
nervous temperament are often entirely overpowered by its effects.

 [19] See _Edinburgh Encyclopædia_, Art. SCIENCE, Curiosities in, Vol.
 xvii., p. 563.

The vibrations of plates of metal or glass of various forms exhibit
a series of the most extraordinary phenomena, which are capable of
being shown by very simple means. These phenomena are displayed in an
infinite variety of regular figures assumed by sand or fine lycopodium
powder, strewed over the surface of the glass plate. In order to
produce these figures, we must pinch or damp the plate at one or more
places, and when the sand is strewed upon its surface, it is thrown
into vibrations by drawing a fiddle-bow over different parts of its
circumference. The method of damping or pinching plates is shown in
Fig. 45. In No. 1, a square plate of glass AB, ground smooth at its
edges, is pinched by the finger and thumb. In No. 2, a circular plate
is held by the thumb against the top _c_ of a perpendicular rod, and
damped by the fingers at two different points of its circumference.
In No. 3 it is damped at three points of its circumference; _c_ and
_d_ by the thumb and finger, and at _e_ by pressing it against a fixed
obstacle _a b_. By means of a clamp like that at No. 4, it may be
damped at a greater number of points.

[Illustration: _Fig. 45._
  N^o 1    N^o 2
  N^o 3    N^o 4
]

[Illustration: _Fig. 46._
  N^o 1    N^o 2
  N^o 3    N^o 4
]

If we take a _square_ plate of glass, such as that shown in Fig. 46,
No. 1, and, pinching it at its centre, draw the fiddle-bow near one of
its angles, the sand will accumulate in the form of a cross, as shown
in the figure, being thrown off the parts of the plate that are in a
state of vibration, and settling in the nodes or parts which are at
rest. If the bow is drawn across the middle of one of the edges, the
sand will accumulate as in No. 2. If the plate is pinched at N, No. 3,
and the bow applied at F and perpendicular to AB, the sand will arrange
itself in three parallel lines, perpendicular to a fourth passing
through F and N. But if the point N, where it is pinched, is a little
farther from the edge than in No. 3, the parallel lines will change
into curves as in No. 4.

If the plate of glass is circular, and pinched at its centre, and also
at a point of its circumference, and if the bow is applied at a point
45° from the last point, the figure of the sand will be as in Fig. 47,
No. 1. If with the same plate, similarly pinched, the bow is drawn over
a part 30° from the pinched point of the circumference, the sand will
form six radii as in No. 2. When the centre of the plate is left free,
a different set of figures is produced, as shown in No. 3 and No. 4.
When the plate is pinched near its edge, and the bow applied 45° from
the point pinched, a circle of sand will pass through that point, and
two diameters of sand, at right angles to each other, will be formed as
in No. 3. When a point of the circumference is pressed against a fixed
obstacle, and the bow applied 30° from that point, the figure in No. 4
is produced.

[Illustration: _Fig. 47._

  No. 1.   No. 2.
  No. 3.   No. 4.]

If, in place of a solid plate, we strew the sand over a stretched
membrane, the sand will form itself into figures, even when the
vibrations are communicated to the membrane through the air. In order
to make these experiments, we must stretch a thin sheet of wet paper,
such as vegetable paper, over the mouth of a tumbler-glass with a
footstalk, and fix it to the edges with glue. When the paper is dry, a
thin layer of dry sand is strewed upon its surface. If we place this
membrane upon a table, and hold immediately above it, and parallel
to the membrane, a plate of glass vibrating so as to give any of the
figures shown in Fig. 47, the sand upon the membrane will imitate
exactly the figure upon the glass. If the glass plate, in place of
vibrating horizontally, is made to vibrate in an inclined position, the
figures on the membrane will change with the inclination, and the sand
will assume the most curious arrangements. The figures thus produced
vary with the size of the membrane, with its material, its tension, and
its shape. When the same figure occurs several times in succession, a
breath upon the paper will change its degree of tension, and produce
an entirely new figure, which, as the temporary moisture evaporates,
will return to the original figure, through a number of intermediate
ones. The pipe of an organ at the distance of a few feet, or the notes
of a flute at the distance of half a foot, will arrange the sand on the
membrane into figures which perpetually change with the sound that is
produced.

The manner in which flat rulers and cylinders of glass perform their
vibrations is very remarkable. If a glass plate about twenty-seven
inches long, six-tenths of an inch broad, and six hundredths of an
inch thick, is held by the edges between the finger and thumb, and has
its lower surface, near either end, rubbed with a piece of wet cloth,
sand laid upon its upper surface will arrange itself in parallel lines
at right angles to the length of the plate. If the place of these lines
is marked with a dot of ink, and the other side of the glass ruler is
turned upwards, and the ruler made to vibrate as before, the sand will
now accumulate in lines intermediate between the former lines, so that
the motions of one-half the thickness of the glass ruler are precisely
the reverse of those of the corresponding parts of the other half.

As these singular phenomena have not yet been made available by the
scientific conjuror, we must be satisfied with this brief notice of
them; but there is still one property of sound, which has its analogy
also in light, too remarkable to be passed without notice. This
property has more of the marvellous in it than any result within the
wide range of the sciences. _Two loud sounds may be made to produce
silence, and two strong lights may be made to produce darkness!_

If two equal and similar strings, or the columns of air in two equal
and similar pipes, perform exactly 100 vibrations in a second,
they will produce each equal waves of sound, and these waves will
conspire in generating an uninterrupted sound, double of either of
the sounds, heard separately. If the two strings or the two columns
of air are not in unison, but nearly so, as in the case where the
one vibrates 100 and the other 101 times in a second, then at the
first vibration the two sounds will form one of double the strength
of either; but the one will gradually gain upon the other, till at
the fiftieth vibration it has gained half a vibration on the other.
At this instant the two sounds will _destroy one another_, and an
interval of perfect silence will take place. The sound will instantly
commence, and gradually increase till it becomes loudest at the
hundredth vibration, where the two vibrations conspire in producing
a sound double of either. An interval of silence will again occur at
the 150th, 250th, 350th vibration, or every second, while a sound of
double the strength of either will be heard at the 200th, 300th, and
400th vibration. When the unison is very defective, or when there is
a great difference between the number of vibrations which the two
strings or columns of air perform in a second, the successive sounds
and intervals of silence resemble a rattle. With a powerful organ, the
effect of this experiment is very fine, the repetition of the sounds
_wow_--_wow_--_wow_--representing the double sound and the interval
of silence which arise from the total extinction of the two separate
sounds.

The phenomenon corresponding to this in the case of light is perhaps
still more surprising. If a beam of _red_ light issues from a luminous
point, and falls upon the retina, we shall see distinctly the luminous
object from which it proceeds; but if another pencil of red light
issues from another luminous point, anyhow situated, provided the
difference between its distance and that of the other luminous point
from the point of the retina, on which the first beam fell, is the
258th thousandth part of an inch, or exactly _twice_, _thrice_, _four_
times, &c., that distance; and if this second beam falls upon the
same point of the retina, the one light will increase the intensity
of the other, and the eye will see _twice_ as much light as when it
received only one of the beams separately. All this is nothing more
than what might be expected from our ordinary experience. But if
the difference in the distances of the two luminous points is only
_one-half_ of the 258th thousandth part of an inch, or 1½, 2½, 3½,
4½, times that distance, _the one light will extinguish the other and
produce absolute darkness_. If the two luminous points are so situated,
that the difference of their distances from the point of the retina is
intermediate between 1 and 1½, or 2 and 2½, above the 258th thousandth
part of an inch, the intensity of the effect which they produce will
vary from absolute darkness to double the intensity of either light. At
1¼, 2¼, 3¼ times, &c., the 258th thousandth of an inch, the intensity
of the two combined lights will be equal only to one of them acting
singly. If the lights, in place of falling upon the retina, fall upon
a sheet of white paper, the very same effect will be produced, a black
spot being produced in the one case, and a bright white one in the
other, and intermediate degrees of brightness in intermediate cases. If
the two lights are _violet_, the difference of distances at which the
preceding phenomena will be produced will be the 157th thousandth part
of an inch, and it will be intermediate between the 258th and the 157th
thousandth part of an inch for the intermediate colours. This curious
phenomenon may be easily shown to the eye, by admitting the sun’s light
into a dark room through a small hole about the 40th or 50th part of
an inch in diameter, and receiving the light on a sheet of paper. If
we hold a needle or piece of slender wire in this light, and examine
its shadow, we shall find that the shadow consists of bright and dark
stripes succeeding each other alternately, the stripe in the very
middle or axis of the shadow being a bright one. The rays of light
which are bent into the shadow, and which meet in the very middle of
the shadow, have exactly the same length of path, so that they form a
bright fringe of double the intensity of either; but the rays which
fall upon a point of the shadow at a certain distance from the middle,
have a difference in the length of their paths, corresponding to the
difference at which the lights destroy each other, so that a _black_
stripe is produced on each side of the middle bright one. At a greater
distance from the middle, the difference becomes such as to produce a
bright stripe, and so on, a bright and a dark stripe succeeding each
other to the margin of the shadow.

The explanation which philosophers have given of these strange
phenomena is very satisfactory, and may be easily understood. When a
wave is made on the surface of a still pool of water, by plunging a
stone into it, the wave advances along the surface, while the water
itself is never carried forward, but merely rises into a height and
falls into a hollow, each portion of the surface experiencing an
elevation and a depression in its turn. If we suppose two waves equal
and similar to be produced by two separate stones, and if they reach
the same spot at the same time, that is, if the two elevations should
exactly coincide, they would unite their effects, and produce a
wave twice the size of either; but if the one wave should be just so
far before the other, that the hollow of the one coincided with the
elevation of the other, and the elevation of the one with the hollow
of the other, the two waves would obliterate or destroy one another,
the elevation as it were of the one filling up half the hollow of the
other, and the hollow of the one taking away half the elevation of the
other, so as to reduce the surface to a level. These effects will be
actually exhibited by throwing two equal stones into a pool of water,
and it will be seen that there are certain lines of a hyperbolic form
where the water is quite smooth, in consequence of the equal waves
obliterating one another, while, in other adjacent parts, the water is
raised to a height corresponding to both the waves united.

In the tides of the ocean we have a fine example of the same principle.
The two immense waves arising from the action of the sun and moon upon
the ocean produce our spring-tides by their combination, or when the
elevations of each coincide; and our neap-tides, when the elevation of
the one wave coincides with the depression of the other. If the sun and
moon had exerted exactly the same force upon the ocean, or produced
tide waves of the same size, then our neap-tides would have disappeared
altogether, and the spring-tide would have been a wave double of the
wave produced by the sun and moon separately. An example of the effect
of the equality of the two waves occurs in the port of Batsha, where
the two waves arrive by channels of different lengths, and actually
obliterate each other.

Now, as sound is produced by undulations or waves in the air, and
as light is supposed to be produced by waves or undulations in an
ethereal medium, filling all nature, and occupying the pores of
transparent bodies, the successive production of sound and silence by
two loud sounds, or of light and darkness by two bright lights, may be
explained in the very same manner as we have explained the increase
and the obliteration of waves formed on the surface of water. If this
theory of light be correct, then the breadth of a wave of _red_ light
will be the 258th thousandth part of an inch, the breadth of a wave of
green light the 207th thousandth part of an inch, and the breadth of a
wave of violet light the 157th thousandth part of an inch.

Among the wonders of modern skill, we must enumerate those beautiful
automata by which the motions and actions of man and other animals have
been successfully imitated. I shall therefore describe at present some
of the most remarkable acoustic automata, in which the production of
musical and vocal sounds has been the principal object of the artist.

Many very ingenious pieces of acoustic mechanism have been from time to
time exhibited in Europe. The celebrated Swiss mechanist, M. le Droz,
constructed for the King of Spain the figure of a sheep, which imitated
in the most perfect manner the bleating of that animal; and likewise
the figure of a dog watching a basket of fruit, which, when any of the
fruit was taken away, never ceased barking till it was replaced.

The singing-bird of M. Maillardet, which he exhibited in Edinburgh
many years ago, is still more wonderful.[20] An oval box, about three
inches long, was set upon the table, and in an instant the lid flew up,
and a bird of the size of the humming-bird, and of the most beautiful
plumage, started from its nest. After fluttering its wings, it opened
its bill and performed four different kinds of the most beautiful
warbling. It then darted down into its nest, and the lid closed upon
it. The moving power in this piece of mechanism is said to have been
springs which continued their action only four minutes. As there was
no room within so small a figure for accommodating pipes to produce
the great variety of notes which were warbled, the artist used only
one tube, and produced all the variety of sounds by shortening and
lengthening it with a moveable piston.

 [20] A similar piece of mechanism had been previously made by M. le
 Droz.

Ingenious as these pieces of mechanism are, they sink into
insignificance when compared with the machinery of M. Vaucanson, which
had previously astonished all Europe. His two principal automata were
the flute-player, and the pipe and tabor-player. The flute-player
was completed in 1736, and wherever it was exhibited it produced the
greatest sensation. When it came to Paris it was received with great
suspicion. The French savants recollected the story of M. Raisin,
the organist of Troyes, who exhibited an automaton player upon the
harpsichord, which astonished the French court by the variety of
its powers. The curiosity of the king could not be restrained, and
in consequence of his insisting upon examining the mechanism, there
was found in the figure a pretty little musician five years of age.
It was natural, therefore, that a similar piece of mechanism should
be received with some distrust; but this feeling was soon removed
by M. Vaucanson, who exhibited and explained to a committee of the
Academy of Sciences the whole of the mechanism. This learned body
was astonished at the ingenuity which it displayed; and they did not
hesitate to state, that the machinery employed for producing the sounds
of the flute performed in the most exact manner the very operations
of the most expert flute-player, and that the artist had imitated the
effects produced, and the means employed by nature, with an accuracy
which exceeded all expectation. In 1738, M. Vaucanson published a
memoir, approved of by the Academy, in which he gave a full description
of the machinery employed, and of the principles of its construction.
Following this memoir, I shall therefore attempt to give as popular a
description of the automaton as can be done without lengthened details
and numerous figures.

The body of the flute-player was about 5½ feet high, and was placed
upon a piece of rock, surrounding a square pedestal 4½ feet high by 3½
feet wide. When the panel which formed the front of the pedestal was
opened, there was seen on the right a clock movement, which, by the
aid of several wheels, gave a rotatory motion to a steel axis about
2½ feet long, having cranks at six equidistant points of its length,
but lying in different directions. To each crank was attached a cord,
which descended and was fixed by its other end to the upper board of a
pair of bellows, 2½ feet long and 6 inches wide. Six pair of bellows
arranged along the bottom of the pedestal were then wrought, or made to
blow in succession, by turning the steel axis.

At the upper face of the pedestal, and upon each pair of bellows is a
double pulley, one of whose rims is 3 inches in diameter, and the other
1½. The cord which proceeds from the crank coils round the smaller
of these pulleys, and that which is fixed to the upper board of the
bellows goes round the larger pulley. By this means the upper board of
the bellows is made to rise higher than if the cords went directly from
them to the cranks.

Round the larger rims of three of these pulleys, viz. those on the
right hand, there are coiled three cords, which, by means of several
smaller pulleys, terminate in the upper boards of other three pair of
bellows placed on the top of the box.

The tension of each cord when it begins to raise the board of the
bellows to which it is attached, gives motion to a lever placed above
it between the axis and the double pulley in the middle and lower
region of the box. The other end of this lever keeps open the valve in
the lower board of the bellows, and allows the air to enter freely,
while the upper board is rising to increase the capacity of the
bellows. By this means there is not only power gained, in so far as the
air gains easier admission through the valve, but the fluttering noise
produced by the action of the air upon the valves is entirely avoided,
and the nine pair of bellows are wrought with great ease, and without
any concussion or noise.

These nine bellows discharge their wind into three different and
separate tubes. Each tube receives the wind of three bellows, the upper
boards of one of the three pair being loaded with a weight of four
pounds, those of the second three pair with a weight of two pounds,
and those of the other three pair with no weight at all. These three
tubes ascended through the body of the figure and terminated in three
small reservoirs placed in its trunk. These reservoirs were thus united
into one, which, ascending into the throat, formed by its enlargement
the cavity of the mouth terminated by two small lips, which rested
upon the whole of the flute. These lips had the power of opening more
or less, and by a particular mechanism, they could advance or recede
from the hole in the flute. Within the cavity of the mouth there is a
small moveable tongue for opening and shutting the passage for the wind
through the lips of the figure.

The motions of the fingers, lips, and tongue of the figure were
produced by means of a revolving cylinder, thirty inches long and
twenty-one in diameter. By means of pegs and brass staples fixed in
fifteen different divisions in its circumference, fifteen different
levers, similar to those in a barrel organ, were raised and depressed.
Seven of these regulated the motions of the seven fingers for stopping
the holes of the flute, which they did by means of steel chains rising
through the body, and directed by pulleys to the shoulder, elbow, and
fingers. Other three of the levers communicating with the valves of the
three reservoirs, regulated the ingress of the air, so as to produce a
stronger or a weaker tone. Another lever opened the lips so as to give
a free passage to the air, and another contracted them for the opposite
purpose. A third lever drew them backwards from the orifice of the
flute, and a fourth pushed them forward. The remaining lever enabled
the tongue to stop up the orifice of the flute.

Such is a very brief view of the general mechanism by which the
requisite motions of the flute-player were produced. The airs which it
played were probably equal to those executed by a living performer, and
its construction, as well as its performances, continued for many years
to delight and astonish the philosophers and musicians of Europe.

Encouraged by the success of this machine, M. Vaucanson exhibited in
1741 other automata, which were equally, if not more, admired. One of
these was the automaton duck, which performed all the motions of that
animal, and not only ate its food, but digested it;[21] and the other
was his pipe and tabor-player, a piece of mechanism which required
all the resources of his fertile genius. Having begun this machine
before he was aware of its peculiar difficulties, he was often about
to abandon it in despair, but his patience and his ingenuity combined,
enabled him not only to surmount every difficulty, but to construct an
automaton which performed complete airs, and greatly excelled the most
esteemed performers on the pipe and tabor.

 [21] See Letter XI.

The figure stands on a pedestal, and is dressed like a dancing
shepherd. He holds in one hand a flageolet, and in the other the stick
with which he beats the tambourine as an accompaniment to the airs of
the flageolet, about twenty of which it is capable of performing. The
flageolet has only three holes, and the variety of its tones depends
principally on a proper variation of the force of the wind, and on the
different degrees with which the orifices are covered. These variations
in the force of the wind required to be given with a rapidity which
the ear can scarcely follow, and the articulation of the tongue was
required for the quickest notes, otherwise the effect was far from
agreeable. As the human tongue is not capable of giving the requisite
articulations to a rapid succession of notes, and generally slurs
over one-half of them, the automaton was thus able to excel the best
performers, as it played complete airs with articulations of the tongue
at every note.

In constructing this machine, M. Vaucanson observed that the flageolet
must be a most fatiguing instrument for the human lungs, as the muscles
of the chest must make an effort equal to fifty-six pounds in order to
produce the highest notes. A single ounce was sufficient for the lowest
notes: so that we may, from this circumstance, form an idea of the
variety of intermediate effects required to be produced.

While M. Vaucanson was engaged in the construction of these wonderful
machines, his mind was filled with the strange idea of constructing
an automaton containing the whole mechanism of the circulation of
the blood. From some birds which he made, he was satisfied of its
practicability; but as the whole vascular system required to be made
of elastic gum or caoutchouc, it was supposed that it could only be
executed in the country where the caoutchouc tree was indigenous.
Louis XVI. took a deep interest in the execution of this machine.
It was agreed that a skilful anatomist should proceed to Guiana to
superintend the construction of the blood-vessels, and the king
had not only approved of, but had given orders for, the voyage.
Difficulties, however, were thrown in the way, Vaucanson became
disgusted, and the scheme was abandoned.

The two automata which we have described were purchased by Professor
Bayreuss of Helmstadt; but we have not been able to learn whether or
not they still exist.

[Illustration: _Fig. 48._]

Towards the end of the eighteenth century a bold and almost successful
attempt was made to construct a _talking automaton_. In the year 1779,
the Imperial Academy of Sciences at St. Petersburgh proposed, as the
subject of one of their annual prizes, an inquiry into the nature
of the vowel sounds, A, E, I, O, and U, and the construction of an
instrument for artificially imitating them. This prize was gained by
M. Kratzenstein, who showed that all the vowels could be distinctly
pronounced by blowing through a reed into the lower ends of the pipes
of the annexed figures, as shown in Fig. 48, where the corresponding
vowels are marked on the different pipes. The vowel I is pronounced by
merely blowing into the pipe _a b_, of the pipe marked I, without the
use of a reed.

[Illustration: _Fig. 49._]

About the same time that Kratzenstein was engaged in these researches,
M. Kempelen of Vienna, a celebrated mechanician, was occupied with the
same subject. In his first attempt he produced the vowel sounds, by
adapting a reed R, Fig. 49, to the bottom of a funnel-shaped cavity
A B, and placing his hand in various positions within the funnel.
This contrivance, however, was not fitted for his purpose, but after
long study, and a diligent examination of the organs of speech, he
contrived a hollow oval box, divided into two portions attached by a
hinge so as to resemble jaws. This box received the sound which issued
from the tube connected with the reed, and by opening and closing the
jaws, he produced the sounds, A, O, OU, and an imperfect E, but no
indications of an I. After two years’ labour he succeeded in obtaining
from different jaws the sounds of the consonants P, M, L, and by means
of these vowels and consonants, he could compose syllables and words,
such as _mama_, _papa_, _aula_, _lama_, _mulo_. The sounds of two
adjacent letters, however, ran into each other, and an aspiration
followed some of the consonants; so that, instead of _papa_, the word
sounded _phaa-ph-a_; these difficulties he contrived with much labour
to surmount, and he found it necessary to imitate the human organs of
speech by having only one mouth and one glottis. The mouth consisted
of a funnel, or bell-shaped piece of elastic gum, which approximated,
by its physical properties, to the softness and flexibility of the
human organs.[22] To the mouth-piece was added a nose made of two tin
tubes, which communicated with the mouth. When both these tubes were
open, and the mouth-piece closed, a perfect M was produced; and when
one was closed and the other open, an N was sounded. M. Kempelen could
have succeeded in obtaining the four letters D, G, K, T, but, by using
a P instead of them, and modifying the sound in a particular manner,
he contrived to deceive the ear by a tolerable resemblance of these
letters.

 [22] Had M. Kempelen known the modern discovery of giving glue any
 degree of softness, by mixing it with molasses or sugar, which is
 always absorbing moisture from the atmosphere, he might have obtained
 a still more perfect imitation of the human organs.

There seems to be no doubt that he at last was able to produce entire
words and sentences, such as _opera_, _astronomy_, _Constantinopolis_,
_Vous êtes mon ami, Je vous aime de tout mon cœur, Venez avec moi à
Paris, Leopoldus secundus, Romanorum imperator semper Augustus_, &c.,
but he never fitted up a speaking figure; and probably, from being
dissatisfied with the general result of his labours, he exhibited only
to his private friends the effects of the apparatus, which was fitted
up in the form of a box.

This box was rectangular, and about three feet long, and was placed
upon a table, and covered with a cloth. When any particular word was
mentioned by the company, M. Kempelen caused the machine to pronounce
it, by introducing his hands beneath the cloth, and apparently giving
motion to some parts of the apparatus. Mr. Thomas Collinson, who had
seen this machine in London, mentions, in a letter to Dr. Hutton, that
he afterwards saw it at M. Kempelen’s own house in Vienna, and that he
then gave it the same word to be pronounced which he gave it in London,
viz. the word _Exploitation_, which, he assures us, it again distinctly
pronounced with the French accent.

M. Kratzenstein seems to have been equally unsuccessful; for though he
assured M. de Lalande, when he saw him in Paris, in 1786, that he had
made a machine which could speak pretty well, and though he showed him
some of the apparatus by which it could sound the vowels, and even such
syllables as _papa_ and _mama_, yet there is no reason to believe that
he had accomplished more than this.

The labours of Kratzenstein and Kempelen have been recently pursued
with great success by our ingenious countryman, Mr. Willis, of
Cambridge. In repeating Kempelen’s experiment, shown in Fig. 49, he
used a shallower cavity, such as that in Fig. 50, and found that he
could entirely dispense with the introduction of the hand, and could
obtain the whole series of vowels by sliding a flat board C D over the
mouth of the cavity. Mr. Willis then conceived the idea of adapting to
the reed cylindrical tubes, whose length could be varied by sliding
joints. When the tube was greatly less than the length of a stopped
pipe in unison with the reed, it sounded I, and by increasing the
length of the tube, it gave E, A, O, and U, in succession. But what was
very unexpected, when the tube was so much lengthened as to be 1½ times
the length of a stopped pipe in unison with the reed, the vowels began
to be again sounded in an inverted order, viz. U, O, A, E, and then
again in a direct order, I, E, A, O, U, when the length of the tube was
equal to twice that of a stopped pipe, in unison with the reed.

[Illustration: _Fig. 50._]

Some important discoveries have been recently made by M. Savart
respecting the mechanism of the human voice;[23] and we have no doubt
that, before another century is completed, a _Talking_ and a _Singing
machine_ will be numbered among the conquests of Science.

 [23] See _Edinburgh Journal of Science_, No. viii., p. 200.




LETTER IX.

 Singular effects in nature depending on sound--Permanent character
 of speech--Influence of great elevations on the character of
 sounds, and on the powers of speech--Power of sound in throwing
 down buildings--Dog killed by sound--Sounds greatly changed under
 particular circumstances--Great audibility of sounds during
 the night explained--Sounds deadened in media of different
 densities--Illustrated in the case of a glass of champagne--and
 in that of new-fallen snow--Remarkable echoes--Reverberations of
 thunder--Subterranean noises--Remarkable one at the Solfaterra--Echo
 at the Menai suspension bridge--Temporary deafness produced in
 diving-bells--Inaudibility of particular sounds to particular
 ears--Vocal powers of the statue of Memnon--Sounds in granite
 rocks--Musical mountain of El-Nakous.


Although, among the phenomena of the material world, there is scarcely
one which, when well considered, is not an object of wonder, yet those
which we have been accustomed to witness from our infancy lose all
their interest from the frequency of their occurrence, while to the
natives of other countries they are unceasing objects of astonishment
and delight. The inhabitant of a tropical climate is confounded at
the sight of falling snow, and he almost discredits the evidence of
his senses when he sees a frozen river carrying loaded waggons on its
surface. The diffusion of knowledge by books, as well as by frequent
communication between the natives of different quarters of the globe,
has deprived this class of local wonders of their influence, and the
Indian and the Scandinavian can visit each other’s lands without any
violent excitement of surprise. Still, however, there are phenomena
of rare occurrence, of which no description can convey the idea, and
which continue to be as deeply marked with the marvellous as if they
had been previously unknown. Among these we may rank the remarkable
modifications which sound undergoes in particular situations and under
particular circumstances.

In the ordinary intercourse of life, we recognize individuals as
much by their voice as by the features of their face and the form of
their body. A friend who has been long absent will often stand before
us as a stranger, till his voice supplies us with the full power of
recognition. The brand imprinted by time on his outer form may have
effaced the youthful image which the memory had cherished, but the
original character of his voice and its yet remembered tones will
remain unimpaired.

An old friend with a new face is not more common in its moral than in
its physical acceptation; and though the sagacity of proverbial wisdom
has not supplied us with the counterpart in relation to the human
voice, yet the influence of its immutability over the mind has been
recorded by the poet in some of his most powerful conceptions. When
Manfred was unable to recognize in the hectic phantom of Astarte the
endeared lineaments of the being whom he loved, the mere utterance of
his name recalled “the voice which was his music,” and invested her
with the desired reality.

                      Say on, say on--
    I live but in the sound--It is thy voice!

    BYRON.

The permanence of character thus impressed upon speech exists only in
those regions to whose atmosphere our vocal organs are adapted. If
either the speaker or the hearer is placed in air differing greatly in
density from that to which they are accustomed, the voice of the one
will emit different sounds, or the same sounds will produce a different
impression on the ear of the other. But if both parties are placed in
this new atmosphere, their tones of communication will suffer the most
remarkable change. The two extreme positions, where such effects become
sufficiently striking, are in the compressed air of the diving-bell,
when it is immersed to a great depth in the sea, or in the rarefied
atmosphere which prevails on the summit of the Himalaya or the Andes.

In the region of common life, and even at the stillest hour of night,
the ear seldom rests from its toils. When the voice of man and the
bustle of his labours have ceased, the sounds of insect life are
redoubled; the night breeze awakens among the rustling leaves, and the
swell of the distant ocean, and the sounds of the falling cataract or
of the murmuring brook, fill the air with their pure and solemn music.
The sublimity of deep silence is not to be found even in the steppes
of the Volga, or in the forests of the Orinoco. It can be felt only in
those lofty regions

    Where the tops of the Andes,
      Shoot soaringly forth.

As the traveller rises above the limit of life and motion, and enters
the region of habitual solitude, the death-like silence which prevails
around him is rendered still more striking by the diminished density
of the air which he breathes. The voice of his fellow traveller ceases
to be heard even at a moderate distance, and sounds which would stun
the ear at a lower level make but a feeble impression. The report of
a pistol on the top of Mont Blanc is no louder than that of an Indian
cracker. But while the thinness of the air thus subdues the loudest
sounds, the voice itself undergoes a singular change: the muscular
energy by which we speak experiences a great diminution, and our powers
of utterance, as well as our power of hearing, are thus singularly
modified. Were the magician, therefore, who is desirous to impress upon
his victim or upon his pupil the conviction of his supernatural power,
to carry him, under the injunction of silence,

    ----------------------------- to breathe
    The difficult air of the iced mountain’s top,
    Where the birds dare not build, nor insect’s wing
    Flit o’er the herbless granite,

he would experience little difficulty in asserting his power over
the elements, and still less in subsequently communicating the same
influence to his companion.

But though the air at the tops of our highest mountains is scarcely
capable of transmitting sounds of ordinary intensity, yet sounds of
extraordinary power force their way through its most attenuated strata.
At elevations where the air is three thousand times more rare than
that which we breathe, the explosion of meteors is heard like the
sound of cannon on the surface of the earth, and the whole air is often
violently agitated by the sound. This fact alone may give us some idea
of the tremendous nature of the forces which such explosions create,
and it is fortunate for our species that they are confined to the upper
regions of the atmosphere. If the same explosions were to take place in
the dense air which rests upon the earth, our habitations and our lives
would be exposed to the most imminent peril.

Buildings have often been thrown down by violent concussions of the
air, occasioned either by the sound of great guns or by loud thunder,
and the most serious effects upon human and animal life have been
produced by the same cause. Most persons have experienced the stunning
pain produced in the ear, when placed near a cannon that is discharged.
Deafness has frequently been the result of such sudden concussions,
and, if we may reason from analogy, death itself must often have
been the consequence. When peace was proclaimed in London, in 1697,
two troops of horse were dismounted and drawn up in line in order to
fire their volleys. Opposite the centre of the line was the door of a
butcher’s shop, where there was a large mastiff dog of great courage.
This dog was sleeping by the fire, but when the first volley was fired,
it immediately started up, ran into another room, and hid itself under
a bed. On the firing of the second volley, the dog rose, ran several
times about the room trembling violently, and apparently in great
agony. When the third volley was fired, the dog ran about once or twice
with great violence and instantly fell down dead, throwing up blood
from his mouth and nose.

Sounds of known character and intensity are often singularly changed
even at the surface of the earth, according to the state of the ground
and the conditions of the clouds. On the extended heath, where there
are no solid objects capable of reflecting or modifying sound, the
sportsman must frequently have noticed the unaccountable variety of
sounds which are produced by the report of his fowling-piece. Sometimes
they are flat and prolonged, at other times short and sharp, and
sometimes the noise is so strange that it is referred to some mistake
in the loading of the gun. These variations, however, arise entirely
from the state of the air, and from the nature and proximity of the
superjacent clouds. In pure air of uniform density the sound is sharp
and soon over, as the undulations of the air advance without any
interrupting obstacles. In a foggy atmosphere, or where the vapours
produced by heat are seen dancing as it were in the air, the sound is
dull and prolonged; and when these clouds are immediately over-head, a
succession of echoes from them produces a continued or reverberating
sound. When the French astronomers were determining the velocity of
sound by firing great guns, they observed that the report was always
single and sharp under a perfectly clear sky, but indistinct, and
attended by a long-continued roll like thunder, when a cloud covered
a considerable part of the horizon. It is no doubt owing to the same
cause, namely, the reflexion from the clouds, that the thunder rolls
through the heavens, as if it were produced by a succession of electric
explosions.

The great audibility of sounds during the night is a phenomenon of
considerable interest, and one which had been observed even by the
ancients. In crowded cities or in their vicinity, the effect was
generally ascribed to the rest of animated beings; while in localities
where such an explanation was inapplicable, it was supposed to arise
from a favourable direction of the prevailing wind. Baron Humboldt
was particularly struck with this phenomenon when he first heard the
rushing of the great cataracts of the Orinoco in the plain which
surrounds the Mission of the Apures. These sounds he regarded as
three times louder during the night than during the day. Some authors
ascribed this fact to the cessation of the humming of insects, the
singing of birds, and the action of the wind on the leaves of the
trees, but M. Humboldt justly maintains that this cannot be the cause
of it on the Orinoco, where the buzz of insects is much louder in the
night than in the day, and where the breeze never rises till after
sunset. Hence he was led to ascribe the phenomenon to the perfect
transparency and uniform density of the air, which can exist only at
night after the heat of the ground has been uniformly diffused through
the atmosphere. When the rays of the sun have been beating on the
ground during the day, currents of hot air of different temperatures,
and consequently of different densities, are constantly ascending from
the ground and mixing with the cold air above. The air thus ceases
to be a homogeneous medium, and every person must have observed the
effects of it upon objects seen through it which are very indistinctly
visible, and have a tremulous motion, as if they were “dancing in
the air.” The very same effect is perceived when we look at objects
through spirits and water that are not perfectly mixed, or when we view
distant objects over a red-hot poker or over a flame. In all these
cases the light suffers refraction in passing from a medium of one
density into a medium of a different density, and the refracted rays
are constantly changing their direction as the different currents rise
in succession. Analogous effects are produced when sound passes through
a mixed medium, whether it consists of two different mediums or of one
medium where portions of it have different densities. As sound moves
with different velocities through media of different densities, the
wave which produces the sound will be partly reflected in passing from
one medium to the other, and the direction of the transmission wave
changed: and hence in passing through such media different portions of
the wave will reach the ear at different times, and thus destroy the
sharpness and distinctness of the sound. This may be proved by many
striking facts. If we put a bell in a receiver containing a mixture of
hydrogen gas and atmospheric air, the sound of the bell can scarcely be
heard. During a shower of rain or of snow, noises are greatly deadened;
and when sound is transmitted along an iron wire or an iron pipe of
sufficient length, we actually hear two sounds, one transmitted more
rapidly through the solid, and the other more slowly through the air.
The same property is well illustrated by an elegant and easily repeated
experiment of Chladni’s. When sparkling champagne is poured into a tall
glass till it is half full, the glass loses its power of ringing by a
stroke upon its edge, and emits only a disagreeable and puffy sound.
This effect will continue while the wine is filled with bubbles of
air, or as long as the effervescence lasts; but when the effervescence
begins to subside the sound becomes clearer and clearer, and the glass
rings as usual when the air-bubbles have vanished. If we reproduce
the effervescence by stirring the champagne with a piece of bread, the
glass will again cease to ring. The same experiment will succeed with
other effervescing fluids.

The difference in the audibility of sounds that pass over homogeneous
and over mixed media is sometimes so remarkable as to astonish those
who witness it. The following fact is given on the evidence of an
officer who observed it:--When the British and the American forces
were encamped on each side of a river, the outposts were so near, that
the form of individuals could be easily distinguished. An American
drummer made his appearance, and began to beat his drum; but though
the motion of his arms was distinctly seen, not a single sound reached
the ear of the observer. A coating of snow that had newly fallen upon
the ground, and the thickness of the atmosphere, had conspired to
obstruct the sound. An effect the very reverse of this is produced by
a coating of glazed or hardened snow, or by an extended surface of ice
or water. Lieutenant Foster was able to carry on a conversation with
a sailor across Port Bowen Harbour, a distance of no less than a mile
and a quarter, and the sound of great guns has been heard at distances
varying from 120 to 200 miles. Over hard and dry ground of a uniform
character, or where a thin soil rests upon a continuous stratum of
rock, the sound is heard at a great distance, and hence it is the
practice among many Eastern tribes to ascertain the approach of an
enemy by applying the ear to the ground.

Many remarkable phenomena in the natural world are produced by the
reflexion and concentration of sound. Every person is familiar with
the ordinary _echo_ which arises from the reflexion of sound from an
even surface, such as the face of a wall, of a house, of a rock, of
a hill, or of a cloud. As sound moves at the rate of 1090 feet in a
second, and as the sound which returns to the person who emits it has
travelled over a space equal to twice his distance from the reflecting
surface, the distance in feet of the body which occasions the echo may
be readily found by multiplying 545 by the number of seconds which
elapse between the emission of the sound and its return in the form of
an echo. This kind of echo, where the same person is the speaker and
the hearer, never takes place, unless when the observer is immediately
in front of the reflecting surface, or when a line drawn from his mouth
to the flat surface is nearly perpendicular to it, because in this
case alone the wave of sound is reflected in the very same direction
from the wall in which it reaches it. If the speaker places himself
on one side of this line, then the echo will be heard most distinctly
by another person as far on the other side of it, because the waves
of sound are reflected like light, so that the angle of incidence or
the inclination at which the sound falls upon the reflected surface
is equal to the angle of reflexion, or the inclination at which the
sound is returned from the wall. If two persons, therefore, are placed
before the reflecting wall, the one will hear the echo of the sound
emitted by the other, and obstacles may intervene between these two
persons, so that neither of them hears the direct sound emitted by the
other; in the same manner as the same persons similarly placed before
a looking-glass would see each other distinctly by reflexion, though
objects might obstruct their direct view of each other.

Hitherto we have supposed that there is only one reflecting surface,
in which case there will be only one echo; but if there are several
reflecting surfaces, as in the case in an amphitheatre of mountains,
or during a thunder-storm, where there are several strata or masses
of clouds; or if there are two parallel or inclined surfaces between
which the sound can be repeatedly reflected, or if the surface is
curved, so that the sound reflected from one part falls upon another
part, like the sides of a polygon inscribed in a circle,--in all these
cases there will be numerous echoes, which produce a very singular
effect. Nothing can be more grand and sublime than the primary and
secondary echoes of a piece of ordnance discharged in an amphitheatre
of precipitous mountains. The direct or primary echoes from each
reflecting surface reach the ear in succession, according to their
different distances, and these are either blended with or succeeded
by the secondary echoes, which terminate in a prolonged growl, ending
in absolute silence. Of the same character are the reverberated claps
of a thunderbolt reflected from the surrounding clouds, and dying
away in the distance. The echo which is produced by parallel walls
is finely illustrated at the Marquis of Simonetta’s villa near Milan,
which has been described by Addison and Keysler, and which we believe
is that described by Mr. Southwell in the Philosophical Transactions
for 1746. Perpendicular to the main body of this villa there extend two
parallel wings about fifty-eight paces distant from each other, and the
surfaces of which are unbroken either with doors or windows. The sound
of the human voice, or rather a word quickly pronounced, is repeated
above forty times, and the report of a pistol from fifty-six to sixty
times. The repetitions, however, follow in such rapid succession that
it is difficult to reckon them, unless early in the morning before the
equal temperature of the atmosphere is disturbed, or in a calm, still
evening. The echoes appear to be best heard from a window in the main
building between the two projecting walls, from which the pistol also
is fired. Dr. Plot mentions an echo in Woodstock Park which repeats
seventeen syllables by day and twenty by night. An echo on the north
side of Shipley church, in Sussex, repeats twenty-one syllables. Sir
John Herschel mentions an echo in the Manfroni palace at Venice, where
a person standing in the centre of a square room about twenty-five
feet high, with a concave roof, hears the stamp of his foot repeated
a great many times; but as his position deviates from the centre, the
echoes become feebler, and at a short distance entirely cease. The
same phenomenon, he remarks, occurs in the large room of the library
of the museum at Naples. M. Genefay has described, as existing near
Rouen, a curious oblique echo which is not heard by the person who
emits the sound. A person who sings hears only his own voice, while
those who listen hear only the echo, which sometimes seems to approach,
and at other times seems to recede from the ear; one person hears a
single sound, another several sounds, and one hears it on the right,
and another on the left, the effect always changing as the hearer
changes his position. Dr. Birch has described an extraordinary echo at
Roseneath, in Argyleshire, which certainly does not now exist. When
eight or ten notes were played upon a trumpet, they were correctly
repeated, but on a key a third lower. After a short pause, another
repetition of the notes was heard in a still lower tone, and after
another short interval they were repeated in a still lower tone.

In the same manner as light is always lost by reflexion, so the
waves of sound are enfeebled by reflexion from ordinary surfaces,
and the echo is in such cases fainter than the original sound. If
the reflecting surface, however, is circular, sound may be condensed
and rendered stronger in the same manner as light. I have seen a
fine example of this, in the circular turn of a garden wall nearly
a mile distant from a weir across a river. When the air is pure and
homogeneous, the rushing sound of the water is reflected from the
hollow surface of the wall, and concentrated in a focus, the place of
which the ear can easily discover from the intensity of the sound being
there a maximum. A person not acquainted with the locality conceives
that the rushing noise is on the other side of the wall.

In whispering galleries, or places where the lowest whispers are
carried to distances at which the direct sound is inaudible, the sound
may be conveyed in two ways, either by repeated reflexions from a
curved surface in the direction of the sides of a polygon inscribed
in a circle, or where the whisperer is in the focus of one reflecting
surface, and the hearer in the focus of another reflecting surface,
which is placed so as to receive the reflected sounds. The first of
these ways is exemplified in the whispering gallery of St. Paul’s,
and in the octagonal gallery of Gloucester cathedral, which conveys
a whisper seventy-five feet across the nave; and the second in the
baptistery of a church in Pisa, where the architect, Giovanni Pisano,
is said to have constructed the cupola on purpose. The cupola has an
elliptical form, and when one person whispers in one focus, it is
distinctly heard by the person placed in the other focus, but not by
those who are placed between them. The sound first reflected passes
across the cupola, and enters the ears of the intermediate persons,
but it is too feeble to be heard till it has been condensed by a
second reflexion to the other focus of ellipse. A naval officer,
who travelled through Sicily in the year 1824, gives an account of
a powerful whispering place in the cathedral of Girgenti, where the
slightest whisper is carried with perfect distinctness through a
distance of two hundred and fifty feet, from the great western door to
the cornice behind the high altar. By an unfortunate coincidence, the
focus of one of the reflecting surfaces was chosen for the place of the
confessional; and when this was accidentally discovered, the lovers
of secrets resorted to the other focus, and thus became acquainted
with confessions of the gravest import. This divulgence of scandal
continued for a considerable time, till the eager curiosity of one
of the dilettanti was punished, by hearing his wife’s avowal of her
own infidelity. This circumstance gave publicity to the whispering
peculiarity of the cathedral, and the confessional was removed to a
place of greater secrecy.

[Illustration: _Fig. 51._]

An echo of a very peculiar character has been described by Sir John
Herschell in his Treatise on Sound, as produced by the suspension
bridge across the Menai strait in Wales. “The sound of a blow with a
hammer,” says he, “on one of the main piers, is returned in succession
from each of the cross-beams which support the road-way, and from the
opposite pier at a distance of five hundred and seventy-six feet; and
in addition to this, the sound is many times repeated between the
water and the road-way. The effect is a series of sounds which may be
thus written: the first return is sharp and strong from the road-way
over-head; the rattling which succeeds dies away rapidly, but the
single repercussion from the opposite pier is very strong, and is
succeeded by a faint palpitation, repeating the sound at the rate of
twenty-eight times in five seconds, and which, therefore corresponds to
a distance of a hundred and eighty-four feet, or very nearly the double
interval from the road-way to the water. Thus it appears that in the
repercussion between the water and road-way, that from the latter only
affects the ear, the line drawn from the auditor to the water being
too oblique for the sound to diverge sufficiently in that direction.
Another peculiarity deserves especial notice, namely, that the echo
from the opposite pier is best heard when the auditor stands precisely
opposite to the middle of the breadth of the pier, and strikes just
on that point. As it deviates to one or the other side, the return is
proportionally fainter, and is scarcely heard by him when his station
is a little beyond the extreme edge of the pier, though another person,
stationed (on the same side of the water) at an equal distance from the
central point, so as to have the pier between them, hears it well.”

A remarkable subterranean echo is often heard when the hoofs of a horse
or the wheels of a carriage pass over particular spots of ground. This
sound is frequently very similar to that which is produced in passing
over an arch or vault, and is commonly attributed to the existence of
natural or artificial caves beneath. As such caves have often been
constructed in times of war as places of security for persons and
property, many unavailing attempts have been made to discover hidden
treasures where their locality seemed to be indicated by subterraneous
sounds. But though these sounds are sometimes produced by excavations
in the ground, yet they generally arise from the nature of the
materials of which the ground is composed, and from their manner of
combination. If the hollow of a road has been filled up with broken
rock, or with large waterworn stones, having hollows either left
entirely empty, or filled up with materials of different density, then
the sound will be reflected in passing from the loose to the dense
materials, and there will arise a great number of echoes reaching the
ear in rapid succession, and forming by their union a hollow rumbling
sound. This principle has been very successfully applied by Sir John
Herschell to explain the subterranean sounds with which every traveller
is familiar who has visited the Solfaterra, near Naples. When the
ground at a particular place is struck violently by throwing a large
stone against it, a peculiar hollow sound is distinctly heard. This
sound has been ascribed by some geologists to the existence of a great
vault communicating with the ancient seat of the volcano, by other
writers to a reverberation from the surrounding hills with which it
is nearly concentric, and by others to the porosity of the ground.
Dr. Daubeny, who says that the hollow sound is heard when any part
of the Solfaterra is struck, accounts for it by supposing that the
hill is not made up of one entire rock, but of a number of detached
blocks, which, hanging as it were by each other, form a sort of vault
over the abyss within which the volcanic operations are going on.[24]
Mr. Forbes, who has given the latest and most interesting description
of this singular volcano,[25] agrees in opinion with Dr. Daubeny;
while Mr. Scrope[26] and Sir John Herschell concur in opinion that
no such cavities exist. “It seems most probable,” says the latter,
“that the hollow reverberation is nothing more than an assemblage
of partial echoes arising from the reflexion of successive portions
of the original sound, in its progress through the soil at the
innumerable half-coherent surfaces composing it: were the whole soil
a mass of sand, these reflexions would be so strong and frequent as
to destroy the whole impulse in too short an interval to allow of a
distinguishable after-sound. It is a case analogous to that of a strong
light thrown into a milky medium or smoky atmosphere; the whole medium
appears to shine with a nebulous undefined light. This is to the eye
what such a hollow sound is to the ear.”[27]

 [24] Description of Volcanoes, p. 170.

 [25] _Edinburgh Journal of Science_, New Series, No. i., p. 124.

 [26] Considerations on Volcanoes, and _Edinburgh Journal of Science_,
 No. xx., p. 261, and No. xiv., p. 265.

 [27] Art. SOUND, _Encycl. Metrop._, § 110.

It has been recently shown by M. Savart, that the human ear is so
extremely sensible as to be capable of appreciating sounds which
arise from about _twenty-four thousand_ vibrations in a second, and
consequently that it can hear a sound which lasts only the twenty-four
thousandth part of a second. Vibrations of such frequency afford only
a shrill squeak or chirp; and Dr. Wollaston has shown that there are
many individuals with their sense of hearing entire, who are altogether
insensible to such acute sounds, though others are painfully affected
by them. Nothing, as Sir John Herschell remarks, can be more surprising
than to see two persons, neither of them deaf, the one complaining of
the penetrating shrillness of a sound, while the other maintains there
is no sound at all. Dr. Wollaston has also shown that this is true also
of very grave sounds; so that the hearing or not hearing of musical
notes at both extremities of the scale seems to depend wholly on the
pitch or frequency of vibration constituting the note, and not upon the
intensity or loudness of the noise. This affection of the ear sometimes
appears in cases of common deafness, where a shrill tone of voice, such
as that of women and children, is often better heard than the loud and
deeper tone of men.

Dr. Wollaston remarked, that when the mouth and nose are shut, the
tympanum or drum of the ear may be so exhausted by a forcible attempt
to take breath by the expansion of the chest, the pressure of the
external air upon the membrane gives it such a tension, that the ear
becomes insensible to grave tones, without losing in any degree the
perception of sharper sounds. Dr. Wollaston found, that after he had
got into the habit of making the experiment, so as to be able to
produce a great degree of exhaustion, his ears were insensible to
all sounds below F, marked by the bass clef. “If I strike the table
before me,” says he, “with the end of my finger, the whole board sounds
with a deep dull note. If I strike it with my nail, there is also at
the same time a sharp sound produced by quicker vibrations of parts
around the point of contact. When the ear is exhausted, it hears only
the latter sound, without perceiving in any degree the deeper note of
the whole table. In the same manner, in listening to the sound of a
carriage, the deeper rumbling noise of the body is no longer heard by
an exhausted ear; but the rattle of a chain or loose screw remains at
least as audible as before exhaustion.” Dr. Wollaston supposes that
this excessive tension of the drum of the ear, when produced by the
compressed air in the diving-bell, will also produce a corresponding
_deafness to low tones_. This curious experiment has been since made
by Dr. Colladon, when descending in the diving-bell at Howth, in 1820.
“We descended,” says he, “so slowly that we did not notice the motion
of the bell; but as soon as the bell was immersed in water, we felt
about the ears and the forehead a sense of pressure, which continued
increasing during some minutes. I did not, however, experience any pain
in the ears; but my companion suffered so much that we were obliged
to stop our descent for a short time. To remedy that inconvenience,
the workmen instructed us, after having closed our nostrils and mouth,
to endeavour to swallow, and to restrain our respiration for some
moments, in order that, by this exertion, the internal air might act
on the Eustachian tube. My companion, however, having tried it, found
himself very little relieved by this remedy. After some minutes, we
resumed our descent. My friend suffered considerably; he was pale; his
lips were totally discoloured; his appearance was that of a man on the
point of fainting; he was in involuntary low spirits, owing, perhaps,
to the violence of the pain, added to that kind of apprehension which
our situation unavoidably inspired. This appeared to me the more
remarkable, as my case was totally the reverse. I was in a state of
excitement resembling the effect of some spirituous liquor. I suffered
no pain; I experienced only a strong pressure round my head, as if an
iron circle had been bound about it. I spoke with the workmen, and had
some difficulty in hearing them. This difficulty of hearing rose to
such a height, that during three or four minutes I could not hear them
speak. I could not, indeed, hear myself speak, though I spoke as loudly
as possible; nor did even the great noise caused by the violence of the
current against the sides of the bell reach my ears.”

The effect thus described by Dr. Colladon is different from that
anticipated by Dr. Wollaston. He was not merely deaf to low tones, but
to all sounds whatever; and I have found, by repeated experiment, that
my own ears become perfectly insensible even to the shrill tones of the
female voice, and of the voice of a child, when the drum of the ear is
thrown into a state of tension by yawning.

With regard to sounds of high pitch at the other extremity of the
scale, Dr. Wollaston has met with persons, whose hearing was in
other respects perfect, who never heard the chirping of the _Gryllus
campestris_, which commonly occurs in hedges during a summer’s evening,
or that of the house-cricket, or the squeak of the bat, or the chirping
of the common house-sparrow. The note of the bat is a full octave
higher than that of the sparrow; and Dr. Wollaston believes that the
note of some insects may reach one octave more, as there are sounds
decidedly higher than that of a small pipe, one-fourth of an inch in
length, which he conceives cannot be far from six octaves above the
middle E of the pianoforte. “The suddenness of the transition,” says
Dr. Wollaston, “from perfect hearing to total want of perception,
occasions a degree of surprise, which renders an experiment on this
subject with a series of small pipes among several persons rather
amusing. It is curious to observe the change of feeling manifested
by various individuals of the party, in succession, as the sounds
approach and pass the limits of their hearing. Those who enjoy a
temporary triumph are often compelled in their turn to acknowledge to
how short a distance their little superiority extends.” In concluding
his interesting paper on this subject, Dr. Wollaston conjectures that
animals, like the grylli (whose powers of hearing appear to commence
nearly where ours terminate), may have the power of hearing still
sharper sounds which at present we do not know to exist, and that there
may be other insects having nothing in common with us, but who are
endowed with a power of exciting, and a sense of perceiving, vibrations
which make no impression upon our organs, while their organs are
equally insensible to the slower vibrations to which we are accustomed.

With the view of studying the class of sounds inaudible to certain
ears, we would recommend it to the young naturalist to examine the
sounds emitted by the insect tribe, both in relation to their effect
upon the human ear, and to the mechanism by which they are produced.
The Cicadæ or locusts in North America appear, from the observations
of Dr. Hildreth,[28] to be furnished with a bagpipe on which they play
a variety of notes. “When any one passes,” says he, “they make a great
noise and screaming with their air bladder or bagpipes. These bags are
placed under, and rather behind, the wings in the axilla, something in
the manner of using the bagpipes with the bags under the arms--I could
compare them to nothing else; and, indeed, I suspect the first inventor
of the instrument borrowed his ideas from some insect of this kind.
They play a variety of notes and sounds, one of which nearly imitates
the scream of the tree toad.”

 [28] _Edinburgh Journal of Science_, No. xvii., p. 158.

Among the acoustic wonders of the natural world may be ranked the
vocal powers of the statue of Memnon, the son of Aurora, which modern
discoveries have withdrawn from among the fables of ancient Egypt.
The history of this remarkable statue is involved in much obscurity.
Although Strabo affirms that it was overturned by an earthquake, yet as
Egypt exhibits no traces of such a convulsion, it has been generally
believed that the statue was mutilated by Cambyses. Ph. Casselius,
in his dissertation on vocal or speaking stones, quotes the remark
of the scholiast in Juvenal, “that, when mutilated by Cambyses, the
statue, which saluted both the sun and the king, afterwards saluted
only the sun.” Philostratus, in his life of Apollo, informs us, that
the statue looked to the east, and that it spoke as soon as the rays
of the rising sun fell upon its mouth. Pausanias, who saw the statue
in its dismantled state, says, that it is a statue of the sun, that
the Egyptians call it Phamenophis, and not Memnon, and _that it emits
sounds every morning at sunrise, which can be compared only to that of
the breaking of the string of the lyre_. Strabo speaks only of a single
sound which he heard; but Juvenal, who had probably heard it often
during his stay in Egypt, describes it as if it emitted several sounds:

    Dimidio magicæ resonant ubi Memnone chordæ.
    Where broken Memnon sounds his magic strings.

The simple sounds which issued from the statue were, in the progress
of time, magnified into intelligible words, and even into an oracle of
seven verses, and this prodigy has been recorded in a Greek inscription
on the left leg of the statue. But though this new faculty of the
colossus was evidently the contrivance of the Egyptian priests, yet we
are not entitled from this to call in question the simple and perfectly
credible fact that it emitted sounds. This property, indeed, it seems
to possess at the present day; for we learn,[29] that an English
traveller, Sir A. Smith, accompanied with a numerous escort, examined
the statue, and that at six o’clock in the morning he heard very
distinctly the sounds which had been so celebrated in antiquity. He
asserts that this sound does not proceed from the statue, but from the
pedestal; and he expresses his belief that it arises from the impulse
of the air upon the stones of the pedestal, which are arranged so as
to produce this surprising effect. This singular description is, to a
certain extent, confirmed by the description of Strabo, who says, that
he was quite certain that he heard a sound which proceeded either _from
the base_, or from the colossus, or from some one of the assistants. As
there were no Egyptian priests in the escort of Sir A. Smith, we may
now safely reject this last, and, for many centuries, the most probable
hypothesis.

 [29] _Revue Encyclopédique_, 1821, tome ix., p. 592.

The explanation suggested by Sir A. Smith had been previously given in
a more specific form by M. Dussaulx, the translator of Juvenal. “The
statue,” says he, “being hollow, the heat of the sun heated the air
which it contained, and this air, issuing at some crevice, produced the
sounds of which the priests gave their own interpretation.”

Rejecting this explanation, M. Langles, in his dissertation on the
vocal statue of Memnon, and M. Salverte, in his work on the occult
sciences, have ascribed the sounds entirely to Egyptian priestcraft;
and have even gone so far as to describe the mechanism by which
the statue not only emitted sounds, but articulated distinctly the
intonations appropriate to the seven Egyptian vowels, and consecrated
to the seven planets. M. Langles conceives that the sounds may be
produced by a series of hammers, which strike either the granite
itself, or sonorous stones like those which have been long used in
China for musical instruments. M. Salverte improves this imperfect
apparatus, by supposing that there might be adapted to these hammers a
clepsydra, or water-clock, or any other instrument fitted to measure
time, and so constructed as to put the hammers in motion at sunrise.
Not satisfied with this supposition, he conjectures that the spring of
all this mechanism was to be found in the art of concentrating the rays
of the sun, which was well known to the ancients. Between the lips of
the statue, or in some less remarkable part of it concealed from view
by its height, he conceives an aperture to be perforated, containing a
lens or a mirror capable of condensing the rays of the rising sun upon
one or more metallic levers, which by their expansion put in motion
the seven hammers in succession. Hence he explains why the sounds were
emitted only at sunrise, and when the solar rays fell upon the mouth of
the statue, and why they were never again heard till the sun returned
to the eastern horizon. As a piece of mechanism, this contrivance is
defective in not providing for the change in the sun’s amplitude,
which is very considerable even in Egypt, for as the statue and the
lens are both fixed, and as the sounds were heard at all seasons of
the year, the same lens which threw the Midsummer rays of the sun upon
the hammers could not possibly throw upon them his rays in winter. But
even if the machinery were perfect, it is obvious that it could not
have survived the mutilation of the statue, and could not, short of a
miracle, have performed its part in the time of Sir A. Smith.

If we abandon the idea of the whole being a trick of the priesthood,
which has been generally done, and which the recent observations of
Sir A. Smith authorise us to do, we must seek some natural cause for
the phenomena similar to that suggested by Dussaulx. It is curious
to observe how the study of nature gradually dispels the consecrated
delusions of ages, and reduces to the level of ordinary facts what time
had invested with all the characters of the supernatural: and in the
present case it is no less remarkable that the problem of the statue of
Memnon should have been first solved by means of an observation made
by a solitary traveller wandering on the banks of the Orinoco. “The
granitic rock,” says Baron Humboldt, “on which we lay, is one of those
where travellers on the Orinoco have heard from time to time, towards
sunrise, subterraneous sounds resembling those of the organ. The
missionaries call these stones _loxas de musica_. ‘It is witchcraft,’
said our young Indian pilot. We never ourselves heard these mysterious
sounds either at Carichana Vieja or in the upper Orinoco: but from
information given us by witnesses worthy of belief, the existence of a
phenomenon that seems to depend on a certain state of the atmosphere
cannot be denied. The shelves of rock are full of very narrow and
deep crevices. They are heated during the day to about 50°. I often
found their temperature at the surface during the night at 39°, the
surrounding atmosphere being at 28°. It may easily be conceived that
the difference of temperature between the subterraneous and the
external air attains its maximum about sunrise, or at that moment which
is at the same time farther from the period of the maximum of the heat
of the preceding day. May not these sounds of an organ, then, which are
heard when a person sleeps upon the rock, his ear in contact with the
stone, be the effect of a current of air that issues out through the
crevices? Does not the impulse of the air against the elastic spangles
of mica that intercept the crevices contribute to modify the sounds?
May we not admit that the ancient inhabitants of Egypt, in passing
incessantly up and down the Nile, had made the same observation on some
rock of the Thebaid, and that the music of the rocks there led to the
jugglery of the priests in the statue of Memnon?”

This curious case of the production of sounds in granite rocks at
sunrise might have been regarded as a transatlantic wonder which was
not applicable to Egypt; but by a singular coincidence of observation,
Messrs. Jomard, Jollois, and Devilliers, who were travelling in Egypt
nearly about the same time that M. Humboldt was traversing the wilds of
South America, heard, _at sunrise, in a monument of granite_, situated
near the centre of the spot on which the palace of Carnac stands, _a
noise resembling that of a breaking string_, the very expression by
which Pausanias characterizes the sound in the Memnonian granite. The
travellers regarded these sounds as arising from the transmission
of rarefied air through the crevices of a sonorous stone, and they
were of the same opinion with Humboldt, that these sounds might have
_suggested_ to the Egyptian priests _the juggleries of the Memnonium_.
Is it not strange that the Prussian and the French travellers should
not have gone a step farther, and solved the problem of two thousand
years, by maintaining that the sound of the statue of Memnon was itself
a natural phenomenon, or a granitic sound elicited at sunrise by the
very same causes which operated on the Orinoco and in the temple of
Carnac, in place of regarding it as a trick in imitation of natural
sounds? If, as Humboldt supposes, the ancient inhabitants of Egypt
had, in passing incessantly up and down the Nile, become familiar with
the music of the granite rocks of the Thebaid, how could the imitation
of such natural and familiar sounds be regarded by the priests as a
means of deceiving the people? There could be nothing marvellous in
a colossal statue of granite giving out the very same sounds that
were given out at the same time of the day by a granite rock; and in
place of reckoning it a supernatural fact, they could regard it in no
other light than as the duplicate of a well-known natural phenomenon.
It is a mere conjecture, however, that such sounds were common in the
Thebaid; and it is therefore probable that a granite rock, possessing
the property of emitting sounds at sunrise, had been discovered by the
priests, who were at the same time the philosophers of Egypt, and that
the block had been employed in the formation of the Memnonian statue
for the purpose of impressing upon it a supernatural character, and
enabling them to maintain their influence over a credulous people.

The inquiries of recent travellers have enabled us to corroborate
these views, and to add another remarkable example of the influence of
subterraneous sounds over superstitious minds. About three leagues to
the north of Tor in Arabia Petræa, is a mountain, within the bosom of
which the most singular sounds have been heard. The Arabs of the Desert
ascribe these sounds to a convent of monks preserved miraculously
underground; and the sound is supposed to be that of the _Nakous_, a
long narrow metallic ruler suspended horizontally, which the priest
strikes with a hammer for the purpose of assembling the monks to
prayer. A Greek was said to have seen the mountain open, and to have
descended into the subterranean convent, where he found fine gardens
and delicious water; and, in order to give proof of his descent, he
produced some fragments of consecrated bread, which he pretended to
have brought from the subterranean convent. The inhabitants of Tor
likewise declare that the camels are not only frightened, but rendered
furious, when they hear these subterraneous sounds.

M. Seetzen, the first European traveller who visited this extraordinary
mountain, set out from Wodyel Nackel on the 17th of June, at five
o’clock in the morning. He was accompanied by a Greek Christian and
some Bedouin Arabs, and after a quarter of an hour’s walk they reached
the foot of a majestic rock of hard sand-stone. The mountain itself was
quite bare and entirely composed of it. He found inscribed upon the
rock several Greek and Arab names, and also some Koptic characters,
which proved that it had been resorted to for centuries. About noon the
party reached the foot of the mountains called _Nakous_, where at the
foot of a ridge they beheld an insulated peaked rock. This mountain
presented upon two of its sides two sandy declivities about 150 feet
high, and so inclined that the white and slightly adhering sand which
rests upon its surface is scarcely able to support itself; and when the
scorching heat of the sun destroys its feeble cohesion, or when it is
agitated by the smallest motions, it slides down the two declivities.
These declivities unite behind the insulated rock, forming an acute
angle, and like the adjacent surfaces, they are covered with steep
rocks which consist chiefly of a white and friable free-stone.

The first sound which greeted the ears of the travellers took place
at an hour and a quarter after noon. They had climbed with great
difficulty as far as the sandy declivity, a height of seventy or
eighty feet, and had rested beneath the rocks where the pilgrims are
accustomed to listen to the sounds.

While in the act of climbing, M. Seetzen heard the sound from beneath
his knees, and hence he was led to think that the sliding of the sand
was the cause of the sound, and not the effect of the vibration which
it occasioned. At three o’clock the sound became louder and continued
six minutes, and after having ceased for ten minutes, it was again
heard. The sound appeared to have the greatest resemblance to that
of the humming-top, rising and falling like that of an Æolian harp.
Believing that he had discovered the true origin of the sound, M.
Seetzen was anxious to repeat the experiment, and with this view he
climbed with the utmost difficulty to the highest rocks, and sliding
down as fast as he could, he endeavoured, with the help of his hands
and feet, to set the sand in motion. The effect thus produced far
exceeded his expectations, and the sand in rolling beneath him made so
loud a noise, that the earth seemed to tremble to such a degree that he
states he should certainly have been afraid if he had been ignorant of
the cause.

M. Seetzen throws out some conjectures respecting the cause of
these sounds. Does the rolling layer of sand, says he, act like the
fiddle-bow, which, on being rubbed upon a plate of glass, raises
and distributes into regular figures the sand with which the plate
is covered? Does the adherent and fixed layer of sand perform here
the part of the plate of glass, and the neighbouring rocks that of
the sounding body? We cannot pretend to answer these questions,
but we trust that some philosopher competent to the task will have
an opportunity of examining these interesting phenomena with more
attention, and describing them with greater accuracy.

The only person, so far as I can learn, who has visited El-Nakous,
since the time of Seetzen, is Mr. Gray, of University College,
Oxford; but he has not added much to the information acquired by his
predecessor. During the first visit which he made to the place, he
heard at the end of a quarter of an hour a low continuous murmuring
sound beneath his feet, which gradually changed into pulsations as
it became louder, so as to resemble the striking of a clock, and at
the end of five minutes it became so strong as to detach the sand.
Returning to the spot next day, he heard the sound still louder than
before. He could not observe any crevices by which the external air
could penetrate; and as the sky was serene and the air calm, he was
satisfied that the sounds could not arise from this cause.[30]

 [30] See _Edinburgh Journal of Science_, No. xi., p. 153, and No.
 xiii., p. 51.




LETTER X.

 Mechanical inventions of the ancients few in number--Ancient
 and modern feats of strength--Feats of Eckeberg particularly
 described--General explanation of them--Real feats of strength
 performed by Thomas Topham--Remarkable power of lifting heavy
 persons when the lungs are inflated--Belzoni’s feat of sustaining
 pyramids of men--Deception of walking along the ceiling in an
 inverted position--Pneumatic apparatus in the foot of the house-fly
 for enabling it to walk in opposition to gravity--Description of
 the analogous apparatus employed by the gecko lizard for the same
 purpose--Apparatus used by the Echineis remora, or sucking-fish.


The mechanical knowledge of the ancients was principally theoretical,
and though they seem to have constructed some minor pieces of mechanism
which were sufficient to delude the ignorant, yet there is no reason
for believing that they had executed any machinery that was capable
of exciting much surprise, either by its ingenuity or its magnitude.
The properties of the mechanical powers, however, seem to have been
successfully employed in performing feats of strength which were beyond
the reach even of strong men, and which could not fail to excite the
greatest wonder when exhibited by persons of ordinary size.

Firmus, a native of Seleucia, who was executed by the Emperor Aurelian
for espousing the cause of Zenobia, was celebrated for his feats of
strength. In his account of the life of Firmus, who lived in the third
century, Vopiscus informs us, that he could suffer iron to be forged
upon an anvil placed upon his breast. In doing this he lay upon his
back, and resting his feet and shoulders against some support, his
whole body formed an arch, as we shall afterwards more particularly
explain. Until the end of the sixteenth century, the exhibition of
such feats does not seem to have been common. About the year 1703, a
native of Kent, of the name of Joyce, exhibited such feats of strength
in London and other parts of England, that he received the name of the
second Samson. His own personal strength was very great; but he had
also discovered, without the aid of theory, various positions of his
body in which men even of common strength could perform very surprising
feats. He drew against horses, and raised enormous weights; but as
he actually exhibited his power in ways which evinced the enormous
strength of his own muscles, all his feats were ascribed to the same
cause. In the course of eight or ten years, however, his methods
were discovered, and many individuals of ordinary strength exhibited
a number of his principal performances, though in a manner greatly
inferior to Joyce.

Some time afterwards, John Charles Van Eckeberg, a native of
Harzgerode, in Anhalt, travelled through Europe under the appellation
of Samson, exhibiting very remarkable examples of his strength.
This, we believe, is the same person whose feats are particularly
described by Dr. Desaguliers. He was a man of the middle size, and
of ordinary strength; and as Dr. Desaguliers was convinced that his
feats were exhibitions of skill and not of strength, he was desirous
of discovering his methods, and with this view he went to see him,
accompanied by the Marquis of Tullibardine, Dr. Alexander Stuart, and
Dr. Pringle, and his own mechanical operator. They placed themselves
round the German, so as to be able to observe accurately all that he
did, and their success was so great that they were able to perform most
of the feats the same evening by themselves, and almost all the rest
when they had provided the proper apparatus. Dr. Desaguliers exhibited
some of the experiments before the Royal Society, and has given such a
distinct explanation of the principles on which they depend, that we
shall endeavour to give a popular account of them.

[Illustration: _Fig. 52._]

1. The performer sat upon an inclined board A B, placed upon a frame
C D E, with his feet abutting against the upright board C. Round his
loins was placed a strong girdle F G, to the iron ring of which at G
was fastened a rope by means of a hook. The rope passed between his
legs through a hole in the board C, and several men or two horses,
pulling at the other end of the rope, were unable to draw the
performer out of his place. His hands at G seemed to pull against the
men, but they were of no advantage to him whatever.

[Illustration: _Fig. 53._]

2. Another of the German’s feats is shown in Fig. 53. Having fixed the
rope above-mentioned to a strong post at A, and made it pass through
a fixed iron eye at B, to the ring in his girdle, he planted his feet
against the post at B, and raised himself from the ground by the rope,
as shown in the figure. He then suddenly stretched out his legs, and
broke the rope, falling back on a feather-bed at C, spread out to
receive him.

3. In imitation of Firmus, he laid himself down on the ground, as shown
in Fig. 54, and when an anvil A was placed upon his breast, a man
hammered with all his force the piece of iron B, with a sledge hammer;
and sometimes two smiths cut in two with chisels a great cold bar of
iron laid upon the anvil. At other times a stone of huge dimensions,
half of which is shown at C, was laid upon his belly, and broken with a
blow of the great hammer.

[Illustration: _Fig. 54._]

4. The performer then placed his shoulders upon one chair and his
heels upon another, as in Fig. 55, forming, with his backbone, thighs,
and legs, an arch springing from its abutments at A and B. One or two
men then stood upon his belly, rising up and down while the performer
breathed. A stone, one and a half feet long, one foot broad, and
half a foot thick, was then laid upon his belly, and broken by a
sledge-hammer; an operation which may be performed with much less
danger than when his back touched the ground, as in Fig. 54.

[Illustration: _Fig. 55._]

5. His next feat was to lie down on the ground, as in Fig. 56; a man
being then placed on his knees, he draws his heels towards his body,
and, raising his knees, he lifts up the man gradually, till having
brought his knees perpendicularly under him, as in Fig. 57, he raises
his own body up, and placing his arms round the man’s legs, he rises
with him, and sets him down on some low table or eminence of the same
height as his knees. This feat he sometimes performed with two men in
place of one.

[Illustration: _Fig. 56._]

[Illustration: _Fig. 57._]

6. The last and apparently the most wonderful performance of the German
is shown in Fig. 58, where he appears to raise a cannon A placed upon
a scale, the four ropes of the scale being fixed to a rope or chain
attached to his girdle in the manner already described. Previous to the
fixing of the ropes, the cannon and scale rest upon two rollers B, C;
but when all is ready, the two rollers are knocked from beneath the
scale, and the cannon is sustained by the strength of his loins.

[Illustration: _Fig. 58._]

The German also exhibited his strength in twisting into a screw a flat
piece of iron like A, Fig. 59. He first bent the iron into a right
angle as at B, and then wrapping his handkerchief about its broad upper
end, he held that end in his left hand, and with his right applied to
the other end, twisted about the angular point, as shown at C. Lord
Tullibardine succeeded in doing the same thing, and even untwisted one
of the irons which the German had twisted.

[Illustration: _Fig. 59._]

It would lead into details by no means popular were I to give a minute
explanation of the mechanical principles upon which these feats depend.
A few general observations will perhaps be sufficient for ordinary
readers. The feats Nos. 1, 2, and 6, depend entirely on the natural
strength of the bones of the pelvis, which form a double arch, which
it would require an immense force to break, by any external pressure
directed to the centre of the arch; and as the legs and thighs are
capable of sustaining four or five thousand pounds when they stand
quite upright, the performer has no difficulty in resisting the force
of two horses, or of sustaining the weight of a cannon weighing two or
three thousand pounds.

The feat of the anvil is certainly a very surprising one. The
difficulty, however, really consists in sustaining the anvil, for when
this is done, the effect of the hammering is nothing. If the anvil
were a thin piece of iron, or even two or three times heavier than the
hammer, the performer would be killed by a few blows; but the blows
are scarcely felt when the anvil is very heavy, for the more matter
the anvil has, the greater is its inertia, and it is the less liable
to be struck out of its place; for when it has received by the blow
the whole momentum of the hammer, its velocity will be so much less
than that of the hammer, as its quantity of matter is greater. When the
blow, indeed, is struck, the man feels less of the weight of the anvil
than he did before, because in the reaction of the stone all the parts
of it round about the hammer rise towards the blow. This property is
illustrated by the well-known experiment of laying a stick with its
ends upon two drinking-glasses full of water, and striking the stick
downwards in the middle with an iron bar. The stick will in this case
be broken without breaking the glasses or spilling the water. But if
the stick is struck upwards, as if to throw it up in the air, the
glasses will break if the blow be strong, and if the blow is not very
quick, the water will be spilt without breaking the glasses.

When the performer supports a man upon his belly as in Fig. 55, he does
it by means of the strong arch formed by his backbone, and the bones of
his legs and thighs. If there were room for them, he could bear three
or four, or, in their stead, a great stone to be broken with one blow.

A number of feats of real and extraordinary strength were exhibited,
about a century ago, in London, by Thomas Topham, who was five feet
ten inches high, and about thirty-one years of age. He was entirely
ignorant of any of the methods for making his strength appear more
surprising, and he often performed by his own natural powers what he
learned had been done by others by artificial means. A distressing
example of this occurred in his attempt to imitate the feat of the
German Samson, by pulling against horses. Ignorant of the method which
we have already described, he seated himself on the ground with his
feet against two stirrups, and by the weight of his body he succeeded
in pulling against a single horse; but in attempting to pull against
two horses, he was lifted out of his place, and one of his knees was
shattered against the stirrups, so as to deprive him of most of the
strength of one of his legs. The following are the feats of real
strength which Dr. Desaguliers saw him perform:--

1. Having rubbed his fingers with coal-ashes to keep them from
slipping, he rolled up a very strong and large pewter plate.

2. Having laid seven or eight short and strong pieces of tobacco-pipe
on the first and third finger, he broke them by the force of his middle
finger.

3. He broke the bowl of a strong tobacco-pipe placed between his first
and third finger, by pressing his fingers together sideways.

4. Having thrust such another bowl under his garter, his legs being
bent, he broke it to pieces by the tendons of his hams without altering
the bending of his leg.

5. He lifted with his teeth, and held in a horizontal position for a
considerable time, a table six feet long, with half a hundred weight
hanging at the end of it. The feet of the table rested against his
knees.

6. Holding in his right hand an iron kitchen poker three feet long and
three inches round, he struck upon his bare left arm, between the elbow
and the wrist, till he bent the poker nearly to a right angle.

7. Taking a similar poker and holding the ends of it in his hands, and
the middle against the back of his neck, he brought both ends of it
together before him, and he then pulled it almost straight again. This
last feat was the most difficult, because the muscles which separate
the arms horizontally from each other are not so strong as those which
bring them together.

8. He broke a rope about two inches in circumference, which was partly
wound about a cylinder four inches in diameter, having fastened the
other end of it to straps that went over his shoulder.

9. Dr. Desaguliers saw him lift a rolling-stone of about 800lb. weight
with his hands only, standing in a frame above it, and taking hold
of a frame fastened to it. Hence Dr. Desaguliers gives the following
relative view of the strengths of individuals:--

  Strength of the weakest men   125lbs.
  Strength of very strong men   400
  Strength of Topham            800

The weight of Topham was about 200.

One of the most remarkable and inexplicable experiments relative to the
strength of the human frame, which you have yourself seen and admired,
is that in which a heavy man is raised with the greatest facility, when
he is lifted up the instant that his own lungs and those of the persons
who raise him are inflated with air. This experiment was, I believe,
first shown in England a few years ago by Major H. who saw it performed
in a large party at Venice, under the direction of an officer of the
American Navy. As Major H. performed it more than once in my presence,
I shall describe as nearly as possible the method which he prescribed.
The heaviest person in the party lies down upon two chairs, his legs
being supported by the one and his back by the other. Four persons,
one at each leg and one at each shoulder, then try to raise him, and
they find his dead weight to be very great, from the difficulty they
experience in supporting him. When he is replaced in the chair, each
of the four persons takes hold of the body as before, and the person
to be lifted gives two signals by clapping his hands. At the first
signal he himself and the four lifters begin to draw a long and full
breath, and when the inhalation is completed, or the lungs filled,
the second signal is given for raising the person from the chair. To
his own surprise and that of his bearers, he rises with the greatest
facility, as if he were no heavier than a feather. On several occasions
I have observed that when one of the bearers performs his part ill,
by making the inhalation out of time, the part of the body which he
tries to raise is left as it were behind. As you have repeatedly seen
this experiment, and have performed the part both of the load and of
the bearer, you can testify how remarkable the effects appear to all
parties, and how complete is the conviction, either that the load has
been lightened, or the bearer strengthened by the prescribed process.

At Venice, the experiment was performed in a much more imposing
manner. The heaviest man in the party was raised and sustained upon
the points of the fore-fingers of six persons. Major H. declared that
the experiment would not succeed if the person lifted were placed upon
a board, and the strength of the individuals applied to the board. He
conceived it necessary that the bearers should communicate directly
with the body to be raised. I have not had an opportunity of making any
experiments relative to these curious facts; but whether the general
effect is an illusion, or the result of known or of new principles, the
subject merits a careful investigation.

Among the remarkable exhibitions of mechanical strength and dexterity,
we may enumerate that of supporting pyramids of men. This exhibition
is a very ancient one. It is described, though not very clearly, by
the Roman poet Claudian, and it has derived some importance in modern
times, in consequence of its having been performed in various parts of
Great Britain by the celebrated traveller Belzoni, before he entered
upon the more estimable career of an explorer of Egyptian antiquities.
The simplest form of this feat consists in placing a number of men on
each other’s shoulders, so that each row consists of a man fewer till
they form a pyramid terminating in a single person, upon whose head a
boy is sometimes placed with his feet upwards.

Among the displays of mechanical dexterity, though not grounded on any
scientific principle, may be mentioned the art of walking along the
ceiling of an apartment with the head downwards. This exhibition,
which we have witnessed in one of the London Theatres, never failed
to excite the wonder of the audience, although the movements of the
inverted performer were not such as to inspire us with any high
ideas of the mechanism by which they were effected. The following
was probably the method by which the performer was carried along the
ceiling. Two parallel grooves or openings were made in the ceiling at
the same distance as the foot-tracks of a person walking on sand. These
grooves were narrower than the human foot, so as to permit a rope,
or chain, or strong wire, attached to the feet of the performer, to
pass through the ceiling, where they were held by two or more persons
above it. In this way the inverted performer might be carried along
by a sliding or shuffling motion, similar to that which is adopted in
walking in the dark, and in which the feet are lifted from the ground.
A more regular motion, however, might be produced by a contrivance for
attaching the rope or chain to the sole of the foot, at each step, and
subsequently detaching it. In this way, when the performer is pulled
against the ceiling by his left foot, he would lift his right foot,
and having made a step with it, and planted it against the grooves,
the rope would be attached to it, and when the rope was detached from
the left foot, it would make a similar step, while the right foot was
pulled against the ceiling. These effects might be facilitated and
rendered more natural, by attaching to the body or to the feet of
the performer strong wires invisible to the audience, and by using
friction-wheels, if a sliding motion only is required.

[Illustration: _Fig. 60._]

A more scientific method of walking upon the ceiling is suggested by
those beautiful pneumatic contrivances by which insects, fishes, and
even some lizards are enabled to support the weight of their bodies
against the force of gravity. The house-fly is well known to have the
power of walking in an inverted position upon the ceilings of rooms,
as well as upon the smoothest surfaces. In this case the fly does not
rest upon its legs, and must therefore adhere to the ceiling, either by
some glutinous matter upon its feet, or by the aid of some apparatus
given it for that purpose. In examining the foot of the fly with a
powerful microscope, it is found to consist of two concavities, as
shown in Figs. 60 and 61, the first of which is copied from a drawing
by G. Adams, published in 1746, and the second by J. C. Keller, a
painter at Nuremberg, who drew it for a work published in 1766. The
author of this work maintains that these concavities are only used when
the fly moves horizontally, and that, when it moves perpendicularly or
on the ceiling, they are turned up out of the way, and the progressive
motion is effected by fixing the claws shown in the figure into the
irregularities of the surface upon which the fly moves, whether it is
glass, porcelain, or any other substance. Sir Everard Home, however,
supposes, with great reason, that these concave surfaces are (like
the leathern suckers used by children for lifting stones) employed to
form a vacuum, so that the foot adheres, as it were, by suction to
the ceiling, and enables the insect to support itself in an inverted
position.

[Illustration: _Fig. 61._]

This conclusion Sir Everard has been led to draw from an examination
of the foot of the Lacerta Gecko. Sir Joseph Banks had mentioned to him
in the year 1815, that this lizard, which is a native of the island of
Java, comes out in the evening from the roofs of the houses, and walks
down the smooth hard-polished chunam walls in search of the flies which
settle upon them, and which are its natural food. When Sir Joseph was
at Batavia, he amused himself in catching this lizard. He stood close
to the wall at some distance from the animal, and by suddenly scraping
the wall with a long flattened pole, he was able to bring the animal to
the ground.

Having procured from Sir Joseph a very large specimen of the Gecko,
which weighed 5¾ ounces avoirdupois, Sir Everard Home was enabled
to ascertain the peculiar mechanism by which the feet of this animal
have the power of keeping hold of a smooth hard perpendicular wall, and
carry up so heavy a weight as that of its body.

[Illustration: _Fig. 62._]

[Illustration: _Fig. 63._]

The foot of the Gecko has five toes (as shown in Fig. 62), and at
the end of each of them, except the thumb, is a very sharp and
highly-curved claw. On the under surface of each toe are sixteen
transverse slits, leading to as many cavities or pockets, the depth of
which is nearly equal to the length of the slit that forms the surface.

[Illustration: _Fig. 64._]

This structure is shown in Figs. 63 and 64, the former representing the
under surface of one of the toes of the natural size, and the latter
a toe dissected and highly magnified, to show the appearance of the
cavities in its under surface, their fringed edge, the depth of the
cavities, and the small muscles by which they are drawn open. The edge
of the pockets or cavities is composed of rows of a beautiful fringe
which are applied to the surface on which the animal walks against
gravity, while the pockets themselves are pulled up by the muscles
attached to them, so as to form the cavities into suckers.

This structure Sir Everard Home found to bear a considerable
resemblance to that portion of the head of the _Echineis Remora_, or
sucking-fish, by which it attaches itself to the shark, or the bottoms
of ships. This apparatus is shown in Fig. 65: it is an oval form, and
is surrounded by a broad loose moveable edge, capable of applying
itself closely to the surface on which it is set. It consists of two
rows of cartilaginous plates connected by one edge to the surface on
which they are placed, the other, on the external edge, being serrated
like that in the cavities of the feet of the Gecko. The two rows are
separated by a thin ligamentous partition, and the plates, being raised
or depressed by the voluntary muscles, form so many vacua, by means of
which the adhesion of the fish is effected.

[Illustration: _Fig. 65._]

These beautiful contrivances of Divine Wisdom cannot fail to arrest the
attention and excite the admiration of the reader; but though there
can be little doubt that they are pneumatic suckers wrought by the
voluntary muscles of the animals to which they belong, yet we would
recommend the further examination of them to the attention of those who
have good microscopes at their command.




LETTER XI.

 Mechanical automata of the ancients--Moving tripods--Automata
 of Dædalus--Wooden pigeon of Archytas--Automatic clock of
 Charlemagne--Automata made by Turrianus for Charles V.--Camus’s
 automatic carriage made for Louis XIV.--Degenne’s mechanical
 peacock--Vaucanson’s duck which ate and digested its food--Du
 Moulin’s automata--Baron Kempelen’s automaton chess-player--Drawing
 and writing automata--Maillardet’s conjurer--Benefits derived from
 the passion for automata--Examples of wonderful machinery for useful
 purposes--Duncan’s tambouring machinery--Watt’s statue-turning
 machinery--Babbage’s calculating machinery.


We have already seen that the ancients had attained some degree of
perfection in the construction of automata, or pieces of mechanism
which imitated the movements of man and the lower animals. The tripods,
which Homer[31] mentions as having been constructed by Vulcan for the
banqueting-hall of the gods, advanced of their own accord to the table,
and again returned to their place. Self-moving tripods are mentioned by
Aristotle; and Philostratus informs us, in his life of Apollonius, that
this philosopher saw and admired similar pieces of mechanism among the
sages of India.

 [31] Iliad, lib. xviii., 373-378.

Dædalus enjoys also the reputation of having constructed machines that
imitated the motions of the human body. Some of his statues are said
to have moved about spontaneously; and Plato, Aristotle, and others
have related that it was necessary to tie them, in order to prevent
them from running away. Aristotle speaks of a wooden Venus, which moved
about in consequence of quicksilver being poured into its interior; but
Callistratus, the tutor of Demosthenes, states, with some probability,
that the statues of Dædalus received their motion from the mechanical
powers. Beckmann is of opinion that the statues of Dædalus differed
only from those of the early Greeks and Egyptians in having their eyes
open and their feet and hands free, and that the reclining posture of
some, and the attitude of others, “as if ready to walk,” gave rise to
the exaggeration that they possessed the power of locomotion. This
opinion, however, cannot be maintained with any show of reason; for if
we apply such a principle in one case, we must apply it in all, and
the mind would be left in a state of utter scepticism respecting the
inventions of ancient times.

We are informed by Aulus Gellius, on the authority of Favorinus,
that Archytas of Tarentum, who flourished about four hundred years
before Christ, constructed a wooden pigeon that was capable of flying.
Favorinus relates that, when it had once alighted, it could not again
resume its flight; and Aulus Gellius adds, that it was suspended by
balancing, and animated by a concealed aura, or spirit.

Among the earliest pieces of modern mechanism was the curious
water-clock presented to Charlemagne by the Kaliph Haroun al Raschid.
In the dial-plate there were twelve small windows corresponding with
the divisions of the hours. The hours were indicated by the opening of
the windows, which let out little metallic balls, which struck the hour
by falling upon a brazen bell. The doors continued open till twelve
o’clock, when twelve little knights, mounted on horseback, came out
at the same instant, and after parading round the dial, shut all the
windows and returned to their apartments.[32]

 [32] Annales Loisiliani, anno 807.

The next automata of which any distinct account has been preserved
are those of the celebrated John Muller, Regiomontanus, which have
been mentioned by Kircher, Baptista Porta, Gassendi, Lana, and Bishop
Wilkins. This philosopher is said to have constructed an artificial
eagle, which flew to meet the Emperor Maximilian when he arrived at
Nuremberg on the 7th June, 1740. After soaring aloft in the air, the
eagle is stated to have met the Emperor at some distance from the city,
and to have returned and perched upon the town gate, where it waited
his approach. When the Emperor reached the gate, the eagle stretched
out its wings, and saluted him by an inclination of its body. Muller
is likewise reported to have constructed an iron fly which was put
in motion by wheel-work, and which flew about and leapt upon the
table. At an entertainment given by this philosopher to some of his
familiar friends, the fly flew from his hand, and after performing a
considerable round, it returned again to the hand of its master.

The Emperor Charles V., after his abdication of the throne, amused
himself in his later years with automata of various kinds. The artist
whom he employed was Janellus Turrianus of Cremona. It was his custom
after dinner to introduce upon the table figures of armed men and
horses. Some of these beat drums, others played upon flutes, while a
third set attacked each other with spears. Sometimes he let fly wooden
sparrows, which flew back again to their nest. He also exhibited
corn-mills so extremely small that they could be concealed in a glove,
yet so powerful that they could grind in a day as much corn as would
supply eight men with food for a day.

The next piece of mechanism of sufficient interest to merit our
attention is that which was made by M. Camus, for the amusement of
Louis XIV. when a child. It consisted of a small coach, which was drawn
by two horses, and which contained the figure of a lady within, with a
footman and page behind. When this machine was placed at the extremity
of a table of the proper size, the coachman smacked his whip, and the
horses instantly set off, moving their legs in a natural manner, and
drawing the coach after them: when the coach reached the opposite edge
of the table, it turned sharply at a right angle, and proceeded along
the adjacent edge. As soon as it arrived opposite the place where the
king sat, it stopped; the page descended and opened the coach-door; the
lady alighted, and with a curtsey presented a petition, which she held
in her hand to the king. After waiting some time she again curtsied and
re-entered the carriage. The page closed the door, and having resumed
his place behind, the coachman whipped his horses and drove on. The
footman, who had previously alighted, ran after the carriage and jumped
up behind into his former place.

Not content with imitating the movements of animals, the mechanical
genius of the 17th and 18th centuries ventured to perform by wheels
and pinions the functions of vitality. We are informed by M. Lobat,
that Gen. Degennes, a French officer who defended the colony of St.
Christopher’s against the English forces, constructed a peacock which
could walk about as if alive, pick up grains of corn from the ground,
digest them as if they had been submitted to the action of the stomach,
and afterwards discharged them in an altered form. Degennes is said to
have invented various machines of great use in navigation and gunnery,
and to have constructed clocks without weights or springs.

The automaton of Degennes probably suggested to M. Vaucanson the idea
of constructing his celebrated duck, which excited so much interest
throughout Europe, and which was perhaps the most wonderful piece of
mechanism that was ever made. Vaucanson’s duck exactly resembled the
living animal in size and appearance. It executed accurately all its
movements and gestures, it ate and drank with avidity, performed all
the quick motions of the head and throat which are peculiar to the
living animal, and, like it, it muddled the water which it drank with
its bill. It produced also the sound of quacking in the most natural
manner. In the anatomical structure of the duck, the artist exhibited
the highest skill. Every bone in the real duck had its representative
in the automaton, and its wings were anatomically exact. Every cavity,
apophysis, and curvature was imitated, and each bone executed its
proper movements. When corn was thrown down before it, the duck
stretched out its neck to pick it up, it swallowed it, digested it, and
discharged it in a digested condition. The process of digestion was
effected by chemical solution, and not by trituration, and the food
digested in the stomach was conveyed away by tubes to the place of its
discharge.

The automata of Vaucanson were imitated by one Du Moulin, a
silversmith, who travelled with them through Germany in 1752, and who
died at Moscow in 1765. Beckmann informs us that he saw several of them
after the machinery had been deranged; but that the artificial duck,
which he regarded as the most ingenious, was still able to eat, drink,
and move. Its ribs, which were made of wire, were covered with duck’s
feathers, and the motion was communicated through the feet of the duck
by means of a cylinder and fine chains like that of a watch.

[Illustration: _Fig. 66._]

[Illustration: _Fig. 67._]

Ingenious as all these machines are, they sink into insignificance
when compared with the automaton chess-player, which for a long time
astonished and delighted the whole of Europe. In the year 1769, M.
Kempelen, a gentleman of Presburg in Hungary, constructed an automaton
chess-player, the general appearance of which is shown in the annexed
figures. The chess-player is a figure as large as life, clothed in a
Turkish dress, sitting behind a large square chest or box, three feet
and a half long, two feet deep, and two and a half high. The machine
runs on castors, and is either seen on the floor when the doors of the
apartment are thrown open, or is wheeled into the room previously to
the commencement of the exhibition. The Turkish chess-player sits on a
chair fixed to the square chest: his right arm rests on the table, and
in the left he holds a pipe, which is removed during the game, as it is
with this hand that he makes the moves. A chess-board, eighteen inches
square, and bearing the usual number of pieces, is placed before the
figure. The exhibitor then announces to the spectators his intention
of showing them the mechanism of the automaton. For this purpose he
unlocks the door A, Fig. 66, and exposes to view a small cupboard lined
with black or dark-coloured cloth, and containing cylinders, levers,
wheels, pinions, and different pieces of machinery, which _have the
appearance_ of occupying the whole space. He next opens the door B,
Fig. 67, at the back of the same cupboard, and holding a lighted candle
at the opening, he still further displays the inclosed machinery to
the spectators, placed in front of A, Fig. 66. When the candle is
withdrawn, the door B is then locked; and the exhibitor proceeds to
open the drawer G G, Fig. 66, in front of the chest. Out of this drawer
he takes a small box of counters, a set of chess-men, and a cushion for
the support of the automaton’s arm, as if this was the sole object of
the drawer. The two front doors C C, of the large cupboard, Fig. 66,
are then opened, and at the back-door D of the same cupboard, Fig. 67,
the exhibitor applies a lighted candle, as before, for the purpose of
showing its interior, which is lined with dark cloth like the other,
and contains only a few pieces of machinery. The chest is now wheeled
round, as in Fig. 67: the garments of the figure are lifted up, and the
door E in the trunk, and another door F in the thigh, are opened, the
doors B and D having been previously closed. When this exhibition of
the interior of the machine is over, the chest is wheeled back into its
original position on the floor. The doors A, C, C, in front, and the
drawer G, G, are closed and locked, and the exhibitor, after occupying
himself for some time at the back of the chest, as if he were adjusting
the mechanism, removes the pipe from the hand of the figure, and winds
up the machinery.

The automaton is now ready to play, and when an opponent has been found
among the company, the figure takes the first move. At every move
made by the automaton, the wheels of the machine are heard in action;
the figure moves its head, and seems to look over every part of the
chess-board. When it gives check to its opponent, it shakes its head
_thrice_, and only _twice_ when it checks the queen. It likewise shakes
its head when a false move is made, replaces the adversary’s piece on
the square from which it was taken, and takes the next move itself. In
general, though not always, the automaton wins the game.

During the progress of the game, the exhibitor often stands near the
machine, and winds it up like a clock, after it has made ten or twelve
moves. At other times he went to a corner of the room, as if it were to
consult a small square box, which stood open for this purpose.

The chess-playing machine, as thus described, was exhibited after its
completion in Presburg, Vienna, and Paris, to thousands, and in 1783
and 1784 it was exhibited in London and different parts of England,
without the secret of its movements having been discovered. Its
ingenious inventor, who was a gentleman and a man of education, never
pretended that the automaton itself really played the game. On the
contrary, he distinctly stated, “that the machine was a _bagatelle_,
which was not without merit in point of mechanism, but that the effects
of it appeared so marvellous only from the boldness of the conception,
and the fortunate choice of the methods adopted for promoting the
illusion.”

Upon considering the operations of this automaton, it must have been
obvious that the game of chess was performed either by a person
enclosed in the chest, or by the exhibitor himself. The first of these
hypotheses was ingeniously excluded by the display of the interior
of the machine, for as every part contained more or less machinery,
the spectator invariably concluded that the smallest dwarf could
not be accommodated within, and this idea was strengthened by the
circumstance, that no person of this description could be discovered
in the suite of the exhibitor. Hence the conclusion was drawn,
that the exhibitor actuated the machine either by mechanical means
conveyed through its feet, or by a magnet concealed in the body of
the exhibitor. That mechanical communication was not formed between
the exhibitor and the figure, was obvious from the fact, that no such
communication was visible, and that it was not necessary to place the
machine on any particular part of the floor. Hence the opinion became
very prevalent that the agent was a magnet; but even this supposition
was excluded, for the exhibitor allowed a strong and well-armed
loadstone to be placed upon the machine during the progress of the
game. Had the moving power been a magnet, the whole action of the
machine would have been deranged by the approximation of a loadstone
concealed in the pockets of any of the spectators.

As Baron Kempelen himself had admitted that there was an illusion
connected with the performance of the automaton, various persons
resumed the original conjecture, that it was actuated by a person
concealed in its interior, who either played the game of chess himself,
or performed the moves which the exhibitor indicated by signals. A Mr.
J. F. Freyhere, of Dresden, published a book on the subject in 1789,
in which he endeavoured to explain, by coloured plates, how the effect
was produced; and he concluded, “that a well-taught boy very thin and
tall of his age (sufficiently so that he could be concealed in a drawer
almost immediately under the chess-board), agitated the whole.”

In another pamphlet, which had been previously published at Paris in
1785, the author not only supposed that the machine was put in motion
by a dwarf, a famous chess-player; but he goes so far as to explain
the manner in which he could be accommodated within the machine. The
invisibility of the dwarf when the doors were opened was explained by
his legs and thighs being concealed in two hollow cylinders, while the
rest of his body was out of the box, and hid by the petticoats of the
automaton. When the doors were shut, the clacks produced by the swivel
of a ratchet-wheel permitted the dwarf to change his place, and return
to the box unheard; and while the machine is wheeled about the room,
the dwarf had an opportunity of shutting the trap through which he
passed into the machine. The interior of the figure was next shown, and
the spectators were satisfied that the box contained no living agent.

Although these views were very plausible, yet they were never generally
adopted; and when the automaton was exhibited in Great Britain in 1819
and 1820, by M. Maelzel, it excited as intense an interest as when it
was first produced in Germany. There can be little doubt, however,
that the secret has been discovered; and an anonymous writer has
shown in a pamphlet, entitled “_An attempt to analyse the Automaton
Chess-player of_ M. Kempelen,” that it is capable of accommodating an
ordinary sized man; and he has explained in the clearest manner how the
inclosed player takes all the different positions, and performs all the
motions which are necessary to produce the effects actually observed.
The following is the substance of his observations:--The drawer G G
when closed does not extend to the back of the chest, but leaves a
space O, behind it (see Figs. 74, 75, and 76), fourteen inches broad,
eight inches high, and three feet eleven inches long. This space is
never exposed to the view of spectators. The small cupboard seen at A
is divided into two parts, by a door or screen I, Fig. 73, which is
moveable upon a hinge, and is so constructed that it closes at the same
instant that B is closed. The whole of the front compartment as far as
I is occupied with the machinery H. The other compartment behind I is
empty, and communicates with the space O behind the drawer, the floor
of this division being removed. The back of the great cupboard C C is
double, and the part P Q, to which the quadrants are attached, moves
on a joint Q, at the upper part, and forms when raised an opening S,
between the two cupboards, by carrying with it part of the partition
R, which consists of cloth tightly stretched. The false back is shown
closed in Fig. 74, while Fig. 75 shows the same back raised, so as to
form the opening S between the chambers.

When the spectator is allowed to look into the trunk of the figure by
lifting up the dress, as in Fig. 75, it will be observed that a great
part of the space is occupied by an inner trunk N, Figs. 75, 76, which
passes off to the back in the form of an arch, and conceals from the
spectators a portion of the interior. This inner trunk N opens and
communicates with the chest by an aperture T, Fig. 77, about twelve
inches broad and fifteen high. When the false back is raised, the two
cupboards, the trunk N, and the space O behind the drawer, are all
connected together.

[Illustration: No. 68.]

[Illustration: No. 69.]

The construction of the interior being thus understood, the
chess-player may be introduced into the chest through the sliding panel
U, Fig. 74. He will then raise the false back of the large cupboard,
and assume the position represented by the shaded figure in Figs. 68
and 69. Things being in this state, the exhibitor is ready to begin his
process of deception. He first opens the door A of the small cupboard,
and from the crowded and very ingenious disposition of the machinery
within it, the eye is unable to penetrate far beyond the opening, and
the spectator concludes, without any hesitation, that the whole of the
cupboard is filled, as it appears to be, with similar machinery. This
false conclusion is greatly corroborated by observing the glimmering
light which plays among the wheel-work when the door B is opened, and a
candle held at the opening. This mode of exhibiting the interior of the
cupboard satisfies the spectator also, that no opaque body, capable of
holding or concealing any of the parts of a hidden agent, is interposed
between the light and the observer. The door B is now locked and the
screen I closed, and as this is done at the time that the light is
withdrawn, it will wholly escape observation.

The door B is so constructed as to close by its own weight, but as the
head of the chess-player will soon be placed very near it, the secret
would be disclosed if, in turning round, the chest door should by any
accident fly open. This accident is prevented by turning the key, and,
lest this little circumstance should excite notice, it would probably
be regarded as accidental, as the keys were immediately wanted for the
other locks.

As soon as the door B is locked, and the screen I closed, the secret
is no longer exposed to hazard, and the exhibitor proceeds to lead
the minds of the spectators still farther from the real state of
things. The door A is left open to confirm the opinion that no person
is concealed within, and that nothing can take place in the interior
without being observed.

[Illustration: _Fig. 70._]

The drawer GG is now opened, apparently for the purpose of looking
at the chess-men, cushion, and counters, which it contains; but
the real object of it is to give time to the player to change his
position, as shown in the annexed figure, and to replace the false
back and partition preparatory to the opening of the great cupboard.
The chess-player, as the figure shows, occupies with his body the
back compartment of the small cupboard, while his legs and thighs
are contained in the space O, behind the drawer GG, his body being
concealed by the screen I, and his limbs by the drawer GG.

The great cupboard CC is now opened, and there is so little machinery
in it, that the eye instantly discovers that no person is concealed in
it. To make this more certain, however, a door is opened at the back,
and a lighted candle held to it, to allow the spectators to explore
every corner and recess.

The front doors of the great and small cupboard being left open,
the chest is wheeled round to show the trunk of the figure, and the
bunch of keys is allowed to remain in the door D, as the apparent
carelessness of such a proceeding will help to remove any suspicion
which may have been excited by the locking of the door B.

When the drapery of the figure has been raised, and the doors E and F
in the trunk and thigh opened, the chest is wheeled round again into
its original position, and the doors E and F closed. In the mean time
the player withdraws his legs from behind the drawer, as he cannot so
easily do this when the drawer GG is pushed in.

In all these operations, the spectator flatters himself that he has
seen in succession every part of the chest, while in reality some parts
have been wholly concealed from his view, and others but imperfectly
shown, while at the present time nearly half of the chest is excluded
from view.

[Illustration: No. 71.]

[Illustration: No. 72.]

When the drawer G G is pushed in, and the doors A and C closed, the
exhibitor adjusts the machinery at the back, in order to give time
to the player to take the position shown in a front view in Fig. 71,
and in profile in Fig. 72. In this position he will experience no
difficulty in executing every movement made by the automaton. As his
head is above the chess-board, he will see through the waistcoat of the
figure, as easily as through a veil, the whole of the pieces on the
board, and he can easily take up and put down a chess-man without any
other mechanism than that of a string communicating with the finger of
the figure. His right hand, being within the chest, may be employed to
keep in motion the wheel-work for producing the noise which is heard
during the moves, and to perform the other movements of the figure,
such as that of moving the head, tapping on the chest, &c.

A very ingenious contrivance is adopted to facilitate the introduction
of the player’s left arm into the arm of the figure. To permit this,
the arm of the figure requires to be drawn backwards; and for the
purpose of concealing, and at the same time explaining this strained
attitude, a pipe is ingeniously placed in the automaton’s hand. For
this reason the pipe is not removed till all the other arrangements are
completed. When every thing has been thus prepared, the pipe is taken
from the figure, and the exhibitor winds up, as it were, the inclosed
machinery, for the double purpose of impressing upon the company the
belief that the effect is produced by machinery, and of giving a signal
to the player to put in motion the head of the automaton.

[Illustration: _Fig. 73._]

[Illustration: _Fig. 74._]

This ingenious explanation of the chess automaton is, our author
states, greatly confirmed by the _regular and undeviating_ mode of
disclosing the interior of the chest; and he also shows that the facts
which have been observed respecting the winding up of the machine,
“afford positive proof that the axis turned by the key is quite free
and unconnected either with a spring or weight, or any system of
machinery.”

In order to make the preceding description more intelligible, I shall
add the following more detailed explanation of the figures.

Fig. 66 is a perspective view of the automaton seen in front with all
the doors thrown open.

Fig. 67 is an elevation of the automaton, as seen from behind.

Fig. 68 is an elevation of the front of the chest, the shaded figure
representing the inclosed player in his first position, or when the
door A is opened.

Fig. 69 is a side elevation, the shaded figure representing the player
in the same position.

Fig. 70 is a front elevation, the shaded figure showing the player in
his second position, or that which he takes after the door B and screen
I are closed, and the great cupboard opened.

Fig. 71 is a front elevation, the shaded figure showing the player in
his third position, or that in which he plays the game.

Fig. 72 is a side elevation showing the figure in the same position.

Fig. 73 is a horizontal section of the chest through the line WW in
Fig. 71.

Fig. 74 is a vertical section of the chest through the line XX in Fig.
73.

[Illustration: _Fig. 75._]

[Illustration: _Fig. 76._]

Fig. 75 is a vertical section through the line YY Fig. 71, showing the
false back closed.

Fig. 76 is a similar vertical section showing the false back raised.

The following letters of reference are employed in all the figures:--

A. Front door of the small cupboard.

B. Back door of ditto.

C C. Front doors of large cupboard.

D. Back door of ditto.

E. Door of ditto.

F. Door of the thigh.

G G. The drawer.

H. Machinery in front of the small cupboard.

I. Screen behind the machinery.

K. Opening caused by the removal of part of the floor of the small
cupboard.

L. A box which serves to conceal an opening in the floor of the large
cupboard, made to facilitate the first position; and which also serves
as a seat for the third position.

M. A similar box to receive the toes of the player in the first
position.

N. The inner chest filling up part of the trunk.

O. The space behind the drawer.

P Q. The false back turning on a joint at Q.

R. Part of the partition formed of cloth stretched tight, which is
carried up by the false back to form the opening between the chambers.

S. The opening between the chambers.

T. The opening connecting the trunk and chest, which is partly
concealed by the false back.

U. Panel which is slipt aside to admit the player.

       *       *       *       *       *

Various pieces of mechanism of wonderful ingenuity have been
constructed for the purposes of drawing and writing. One of these,
invented by M. Le Droz, the son of the celebrated Droz of Chaux le
Fonds, has been described by Mr. Collinson. The figure was the size
of life. It held in its hand a metallic style, and when a spring was
touched, so as to release a detent, the figure immediately began to
draw upon a card of Dutch vellum previously laid under its hand.
After the drawing was executed on the first card, the figure rested.
Other five cards were then put in, in succession, and upon these it
delineated in the same manner different subjects. On the first card it
drew “elegant portraits and likenesses of the king and queen facing
each other;” and Mr. Collinson remarks, that it was curious to observe
with what precision the figure lifted up its pencil in its transition
from one point of the drawing to another, without making the slightest
mistake.

M. Maillardet has executed an automaton which both writes and draws.
The figure of a boy kneeling on one knee holds a pencil in his hand.
When the figure begins to work, an attendant dips the pencil in ink,
and adjusts the drawing-paper upon a brass tablet. Upon touching a
spring, the figure proceeds to write, and when the line is finished,
its hand returns to dot and stroke the letters when necessary. In this
manner it executes four beautiful pieces of writing in French and
English, and three landscapes, all of which occupy about one hour.

One of the most popular pieces of mechanism which we have seen is the
magician constructed by M. Maillardet for the purpose of answering
certain given questions. A figure dressed like a magician appears
seated at the bottom of a wall, holding a wand in one hand, and a book
in the other. A number of questions ready prepared are inscribed on
oval medallions, and the spectator takes any of these which he chooses,
and to which he wishes an answer, and having placed it in a drawer
ready to receive it, the drawer shuts with a spring till the answer
is returned. The magician then rises from his seat, bows his head,
describes circles with his wand, and, consulting the book as if in deep
thought, he lifts it towards his face. Having thus appeared to ponder
over the proposed question, he raises his wand, and striking with
it the wall above his head, two folding-doors fly open, and display
an appropriate answer to the question. The doors again close, the
magician resumes his original position, and the drawer opens to return
the medallion. There are twenty of these medallions, all containing
different questions, to which the magician returns the most suitable
and striking answers. The medallions are thin plates of brass of an
elliptical form, exactly resembling each other. Some of the medallions
have a question inscribed on each side, both of which the magician
answers in succession. If the drawer is shut without a medallion being
put into it, or if a _blank_ medallion, viz., one which contains no
question, is put into the drawer, the magician rises, consults his
book, shakes his head, and resumes his seat. The folding-doors remain
shut, and the drawer is returned empty. If two medallions are put into
the drawer together, an answer is returned only to the lower one. When
the machinery is wound up, the movements continue about an hour, during
which time about fifty questions may be answered. The method by which
the different medallions acted upon the machinery, so as to produce the
proper answers to the questions which they bore, was of course kept a
secret by the inventor, but it was discovered by Mr. Brockedon, who
has kindly communicated to me an account of it.

Upon examining the edge of the circular medallions, Mr. Brockedon
discovered in all of them, except the blanks, a small hole almost
concealed by the milling. This led Mr. Brockedon to examine the
receptacle for the medallion in the drawer, and he observed the edge
of a pin flush with the edge of the receptacle, whence the pin was
protruded by the machine into the holes in the medallion, the depth of
the hole regulating the answer. In order to prove this, Mr. B. cut a
slip from a cedar pencil small enough to enter easily the holes in the
medallion, if he found them to be of different depths. As the blank
medallions had no hole, and produced only a shake of the magician’s
head, Mr. B. took a medallion with a question, and having plugged the
hole with a bit of cedar, he cut it flush, and having placed it in the
receptacle, the conjuror shook his head, and thus bore testimony to the
truth of Mr. Brockedon’s discovery.

M. Maillardet has constructed various other automata, representing
insects and other animals. One of these was a spider entirely made of
steel, which exhibited all the movements of the animal. It ran on the
surface of a table during three minutes, and to prevent it from running
off, its course always tended towards the centre of the table. He
constructed likewise a caterpillar, a lizard, a mouse, and a serpent.
The serpent crawls about in every direction, opens its mouth, hisses,
and darts out its tongue.

Ingenious and beautiful as all these pieces of mechanism are, and
surprising as their effects appear even to scientific spectators, the
principal object of their inventors was to astonish and amuse the
public. We should form an erroneous judgment, however, if we suppose
that this was the only result of the ingenuity which they displayed.
The passion for automatic exhibitions, which characterized the 18th
century, gave rise to the most ingenious mechanical devices, and
introduced among the higher orders of artists habits of nice and
accurate execution in the formation of the most delicate pieces of
machinery. The same combination of the mechanical powers which made the
spider crawl, or which waved the tiny rod of the magician, contributed
in future years to purposes of higher import. Those wheels and pinions,
which almost eluded our senses by their minuteness, re-appeared in the
stupendous mechanism of our spinning-machines and our steam-engines.
The elements of the tumbling-puppet were revived in the chronometer,
which now conducts our navy through the ocean; and the shapeless wheel
which directed the hand of the drawing automaton has served, in the
present age, to guide the movements of the tambouring engine. Those
mechanical wonders, which in one century enriched only the conjuror
who used them, contributed in another to augment the wealth of the
nation; and those automatic toys, which once amused the vulgar, are now
employed in extending the power and promoting the civilization of our
species. In whatever way, indeed, the power of genius may invent or
combine, and to whatever low or even ludicrous purposes that invention
or combination may be originally applied, society receives a gift which
it can never lose; and though the value of the seed may not be at once
recognized, and though it may lie long unproductive in the ungenial
till of human knowledge, it will some time or other evolve its germ,
and yield to mankind its natural and abundant harvest.

Did the limits of so popular a volume as this ought to be permit it, I
should have proceeded to give a general description of some of these
extraordinary pieces of machinery, the construction and effects of
which never fail to strike the spectator with surprise. This, however,
would lead me into a field too extensive, and I shall therefore confine
myself to a notice of three very remarkable pieces of mechanism which
are at present very little known to the general reader, viz., the
tambouring machine of Mr. Duncan, the statue-turning machine of Mr.
Watt, and the calculating machinery of Mr. Babbage.

The tambouring of muslins, or the art of producing upon them ornamental
flowers and figures, has been long known and practised in Britain
as well as in other countries; but it was not long before the year
1790, that it became an object of general manufacture in the west of
Scotland, where it was chiefly carried on. At first it was under the
direction of foreigners; but their aid was not long necessary, and
it speedily extended to such a degree as to occupy, either wholly or
partially, more than 20,000 females. Many of these labourers lived
in the neighbourhood of Glasgow, which was the chief seat of the
manufacture; but others were scattered through every part of Scotland,
and supplied by agents with work and money. In Glasgow, a tambourer
of ordinary skill could not in general earn more than five or six
shillings a week by constant application; but to a labouring artisan,
who had several daughters, even these low wages formed a source of
great wealth. At the age of five years, a child capable of handling a
needle was devoted to tambouring, even though it could not earn more
than a shilling or two in a week; and the consequence of this was, that
female children were taken from school, and rendered totally unfit for
any social or domestic duty. The tambouring population, was, therefore,
of the worst kind, and it must have been regarded as a blessing rather
than as a calamity, when the work which they performed was entrusted to
regular machinery.

Mr. John Duncan of Glasgow, the inventor of the tambouring machinery,
was one of those unfortunate individuals who benefit their species
without benefiting themselves, and who died in the meridian of life,
the victim of poverty and of national ingratitude. He conceived the
idea of bringing into action a great number of needles at the same
time, in order to shorten the process by manual labour; but he at
first was perplexed about the diversification of the pattern. This
difficulty, however, he soon surmounted by employing two forces at
right angles to each other, which gave him a new force in the direction
of the diagonal of the parallelogram, whose sides were formed by the
original forces. His first machine was very imperfect; but after two
years’ study, he formed a company, at whose expense six improved
machines were put in action, and who secured the invention by a patent.
At this time the idea of rendering the machine automatic had scarcely
occurred to him; but he afterwards succeeded in accomplishing this
great object, and the tambouring machines were placed under the
surveillance of a steam-engine. Another patent was taken for these
improvements. The reader who desires to have a minute account of these
improvements, and of the various parts of the machinery, will be amply
gratified by perusing the inventor’s own account of the machinery
in the article CHAINWORK in the Edinburgh Encyclopædia. At present
it will be sufficient to state, that the muslin to be tamboured was
suspended vertically in a frame, which was capable of being moved both
in a vertical and a horizontal direction. Sixty or more needles lying
horizontally occupied a frame in front of the muslin web. Each of these
working needles, as they are called, was attended by a feeding-needle,
which, by a circular motion round the working-needle, lodged upon the
stem of the latter the loop of the thread. The sixty needles then
penetrated the web, and, in order that they might return again without
injuring the fabric, the barb or eye of the needle, which resembled the
barb of a fishing-hook, was shut by a slider. The muslin web then took
a new position by means of the machinery that gave it its horizontal
and vertical motion, so that the sixty needles penetrated it, at their
next movement, at another point of the figure or flower. This operation
went on till sixty flowers were completed. The web was then slightly
wound up, that the needles might be opposite that part of it on which
they were to work another row of flowers.

The flowers were generally at an inch distance, and the rows were
placed so that the flowers formed what are called diamonds. There were
seventy-two rows of flowers in a yard, so that in every square yard
there were nearly 4000 flowers, and in every piece of ten yards long
40,000. The number of loops or stitches in a flower varied with the
pattern, but on an average there were about thirty. Hence the number
of stitches in a yard were 120,000, and the number in a piece is
1,200,000. The average work done in a week by one machine was fifteen
yards, or 60,000 flowers, or 1,800,000 stitches; and by comparing this
with the work done by one person with the hand, it appeared that the
machine enabled one person to do the work of twenty-four persons.

One of the most curious and important applications of machinery
to the arts which has been suggested in modern times, was made by
the late Mr. Watt, in the construction of a machine for copying or
reducing statues and sculpture of all kinds. The art of multiplying
busts and statues, by casts in plaster of Paris, has been the means
of diffusing a knowledge of this branch of the fine arts; but from
the fragile nature of the material, the copies thus produced were
unfit for exposure to the weather, and therefore ill calculated for
ornamenting public buildings, or for perpetuating the memory of public
achievements. A machine, therefore, which is capable of multiplying
the labours of the sculptor in the durable materials of marble or of
brass was a desideratum of the highest value, and one which could
have been expected only from a genius of the first order. During many
years Mr. Watt carried on his labours in secret, and he concealed
even his intention of constructing such a machine. After he had made
considerable progress in its execution, and had thought of securing
his invention by a patent, he learned that an ingenious individual
in his own neighbourhood had been long occupied in the same pursuit;
and Mr. Watt informed me that he had every reason to believe that
this gentleman was entirely ignorant of his labours. A proposal was
then made that the two inventors should combine their talents, and
secure the privilege by a joint patent; but Mr. Watt had experienced
so frequently the fatal operation of our patent laws, that he saw many
difficulties in the way of such an arrangement, and he was unwilling,
at his advanced age, to embark in a project so extensive, and which
seemed to require for its successful prosecution all the ardour and
ambition of a youthful mind. The scheme was therefore abandoned;
and such is the unfortunate operation of our patent laws, that the
circumstance of two individuals having made the same invention has
prevented both from bringing it to perfection, and conferring a great
practical benefit upon their species. The machine which Mr. Watt had
constructed had actually executed some excellent pieces of work. I
have seen in his house at Heathfield copies of basso-relievos, and
complete statues of a small size; and some of his friends have in their
possession other specimens of its performance.

Of all the machines which have been constructed in modern times,
the calculating-machine is doubtless the most extraordinary. Pieces
of mechanism for performing particular arithmetical operations have
been long ago constructed, but these bear no comparison either in
ingenuity or in magnitude to the grand design conceived and nearly
executed by Mr. Babbage. Great as the power of mechanism is known to
be, yet we venture to say, that many of the most intelligent of our
readers will scarcely admit it to be possible that astronomical and
navigation tables can be accurately computed by machinery; that the
machine can itself correct the errors which it may commit; and that
the results of its calculations, when absolutely free from error,
can be printed off, without the aid of human hands, or the operation
of human intelligence. All this, however, Mr. Babbage’s machine can
do; and as I have had the advantage of seeing it actually calculate,
and of studying its construction with Mr. Babbage himself, I am able
to make the above statement on personal observation. The calculating
machine now constructing under the superintendence of the inventor
has been executed at the expense of the British Government, and is
of course their property. It consists essentially of two parts; a
calculating part, and a printing part, both of which are necessary to
the fulfilment of Mr. Babbage’s views; for the whole advantage would be
lost if the computations made by the machine were copied by human hands
and transferred to types by the common process. The greater part of the
calculating machinery is already constructed, and exhibits workmanship
of such extraordinary skill and beauty, that nothing approaching to it
has been witnessed. In order to execute it, particularly those parts of
the apparatus which are dissimilar to any used in ordinary mechanical
constructions, tools and machinery of great expense and complexity have
been invented and constructed; and in many instances contrivances of
singular ingenuity have been resorted to which cannot fail to prove
extensively useful in various branches of the mechanical arts.

The drawings of this machinery, which form a large part of the work,
and on which all the contrivance has been bestowed, and all the
alterations made, cover upwards of 400 _square feet of surface_, and
are executed with extraordinary care and precision.

In so complex a piece of mechanism, in which interrupted motions are
propagated simultaneously along a great variety of trains of mechanism,
it might have been supposed that obstructions would arise, or even
incompatibilities occur, from the impracticability of foreseeing
all the possible combinations of the parts; but this doubt has been
entirely removed, by the constant employment of a system of mechanical
notation invented by Mr. Babbage, which places distinctly in view, at
every instant, the progress of motion through all the parts of this or
any other machine, and by writing down in tables the times required for
all the movements, this method renders it easy to avoid all risk of two
opposite actions arriving at the same instant at any part of the engine.

In the printing part of the machine less progress has been made in the
actual execution than in the calculating part. The cause of this is
the greater difficulty of its contrivance, not for transferring the
computations from the calculating part to the copper or other plate
destined to receive it, but for giving to the plate itself that number
and variety of movements which the forms adopted in printed tables may
call for in practice.

The practical object of the calculating engine is to compute and print
a great variety and extent of astronomical and navigation tables,
which could not be done without enormous intellectual and manual
labour, and which, even if executed by such labour, could not be
calculated with the requisite accuracy. Mathematicians, astronomers,
and navigators, do not require to be informed of the real value of such
tables; but it may be proper to state, for the information of others,
that _seventeen_ large folio volumes of logarithmic tables alone were
calculated, at an enormous expense, by the French Government; and that
the British Government regarded these tables to be of such national
value, that they proposed to the French Board of Longitude to print
an _abridgement_ of them at the joint expense of the two nations, and
offered to advance 5000_l._ for that purpose. Besides logarithmic
tables, Mr. Babbage’s machine will calculate tables of the powers
and products of numbers, and all astronomical tables for determining
the positions of the sun, moon, and planets; and the same mechanical
principles have enabled him to integrate innumerable equations of
finite differences, that is, when the equation of differences is given,
he can, by setting an engine, produce at the end of a given time
any distant term which may be required, or any succession of terms
commencing at a distant point.

Besides the cheapness and celerity with which this machine will perform
its work, the _absolute accuracy_ of the printed results deserves
especial notice. By peculiar contrivances, any small error produced by
accidental dust, or by any slight inaccuracy in one of the wheels, is
corrected as soon as it is transmitted to the next, and this is done
in such a manner as effectually to prevent any accumulation of small
errors from producing an erroneous figure in the result.

In order to convey some idea of this stupendous undertaking, we may
mention the effects produced by a small trial engine constructed by
the inventor, and by which he computed the following table from the
formula _x^2_ + _x_ + 41. The figures, as they were calculated by the
machine, were not exhibited to the eye as in sliding-rules and similar
instruments, but were actually presented to the eye on two opposite
sites of the machine, the number 383, for example, appearing in figures
before the person employed in copying.

_Table calculated by a small Trial Engine._

   41   131   383    797   1373
   43   151   421    853   1447
   47   173   461    911   1523
   53   197   503    971   1601
   61   223   547   1033   1681
   71   251   593   1097   1763
   83   281   641   1163   1847
   97   313   691   1231   1933
  113   347   743   1301   2021

While the machine was occupied in calculating this table, a friend of
the inventor undertook to write down the numbers as they appeared.
In consequence of the copyist writing quickly, he rather more than
kept pace with the engine, but as soon as five figures appeared, the
machine was at least equal in speed to the writer. At another trial
_thirty-two_ numbers of the same table were calculated in the space of
_two minutes and thirty seconds_; and as these contained _eighty-two_
figures, the engine produced thirty-three figures every minute, or
more than one figure in every two seconds. On another occasion it
produced _forty-four_ figures per minute. This rate of computation
could be maintained for any length of time; and it is probable that few
writers are able to copy with equal speed for many hours together.

Some of that class of individuals who envy all great men, and deny all
great inventions, have ignorantly stated that Mr. Babbage’s invention
is not new. The same persons, had it suited their purpose, would
have maintained that the invention of spectacles was an anticipation
of the telescope; but even this is more true than the allegation
that the arithmetical machines of Pascal and others were the types
of Mr. Babbage’s engine. The object of these machines was entirely
different. Their highest functions were to perform the operations of
common arithmetic. Mr. Babbage’s engine, it is true, can perform these
operations also, and can extract the roots of numbers, and approximate
to the roots of equations, and even to their impossible roots. But
this is not its object. Its function, in contradistinction to that
of all other contrivances for calculating, is to embody in machinery
the method of differences, which has never before been done; and the
effects which it is capable of producing, and the works which in the
course of a few years we expect to see it execute, will place it at an
infinite distance from all other efforts of mechanical genius.[33]

 [33] A popular account of this engine will be found in Mr. Babbage’s
 interesting volume _On the Economy of Manufactures_, lately published.




LETTER XII.

 Wonders of chemistry--Origin, progress, and objects of alchemy--Art
 of breathing fire--Employed by Barchochebas, Eunus, &c.--Modern
 method--Art of walking upon burning coals and red-hot iron, and of
 plunging the hands in melted lead and boiling water--Singular property
 of boiling tar--Workmen plunge their hands in melted copper--Trial
 of ordeal by fire--Aldini’s incombustible dresses--Examples of their
 wonderful power in resisting flame--Power of breathing and enduring
 air of high temperatures--Experiments made by Sir Joseph Banks, Sir
 Charles Blagden, and Mr. Chantrey.


Chemistry has from its infancy been pre-eminently the science of
wonders. In her laboratory the alchemist and the magician have revelled
uncontrolled, and from her treasures was forged the sceptre which was
so long and so fatally wielded over human reason. The changes which
take place in the bodies immediately around us are too few in number
and too remote from observation to excite much of our notice; but when
the substances procured directly from nature, or formed casually by
art, become objects of investigation, they exhibit in their simple or
combined actions the most extraordinary effects. The phenomena which
they display, and the products which they form, so little resemble
those with which we are familiar, that the most phlegmatic and the
least speculative observer must have anticipated from them the creation
of new and valuable compounds. It can scarcely, therefore, be a
matter of surprise that minds of the highest order, and spirits of
the loftiest ambition, should have sought in the transmutations of
chemistry for those splendid products which were conceived to be most
conducive to human happiness.

The disciple of Mammon grew pale over his crucible in his ardour to
convert the baser metals into gold; the philosopher pined in secret
for the universal solvent which might develop the elements of the
precious stones and yield to him the means of their production; and the
philanthropist aspired after a universal medicine, which might arrest
disease in its course, and prolong indefinitely the life of man. To
us, who live under the meridian of knowledge, such expectations must
appear as presumptuous as they were delusive; but when we consider
that gold and silver were actually produced by chemical processes from
the rude ores of lead and copper--that some of the most refractory
bodies had yielded to the disintegrating and solvent powers of chemical
agents, and that the mercurial preparations of the Arabian physicians
had operated like charms in the cure of diseases that had resisted
the feeble medicines of the times, we may find some apology for the
extravagant expectations of the alchemists.

An object of lofty pursuit, even if it be one of impossible attainment,
is not unworthy philosophical ambition. Though we cannot scale the
summit of the volcanic cone, we may yet reach its heaving flanks; and
though we cannot decompose its loftiest fires, we may yet study the
lava which they have melted and the products which they have sublimed.
In like manner, though the philosopher’s stone has not been found,
chemistry has derived rich accessions from its search;--though the
general solvent has not been obtained, yet the diamond and the gems
have surrendered to science their adamantine strength;--and though
the elixir of life has never been distilled, yet other medicines have
soothed the “ills which flesh is heir to,” and prolonged in no slight
degree the average term of our existence.

Thus far the pursuits of the alchemist were honourable and useful;
but when his calling was followed, as it soon was, by men prodigal
of fortune and of character, science became an instrument of crime;
secrets unattained were bartered for the gold of the credulous and the
ignorant, and books innumerable were composed to teach these pretended
secrets to the world. An intellectual reaction, however, soon took
place; and those very princes who had sought to fill their exhausted
treasuries at the furnace of the chemist, were the first to enact
laws against the frauds which they had encouraged, and to dispel the
illusions which had so long deceived their subjects.

But even when the moral atmosphere of Europe was thus disinfected,
chemistry supplied the magician with his most lucrative wonders, and
those who could no longer delude the public with dreams of wealth and
longevity, now sought to amuse and astonish them by the exhibition
of their skill. The narrow limits of this volume will not permit me
to give even a general view of those extraordinary effects which
this popular science can display. I must therefore select from its
inexhaustible stores those topics which are most striking in their
results, and most popular in their details.

One of the most ancient feats of magic was the art of breathing
flame,--an art which even now excites the astonishment of the vulgar.
During the insurrection of the slaves in Sicily, in the second century
before Christ, a Syrian named Eunus acquired by his knowledge the rank
of their leader. In order to establish his influence over their minds,
he pretended to possess miraculous power. When he wished to inspire his
followers with courage, he breathed flames or sparks among them from
his mouth, at the same time that he was rousing them by his eloquence.
St. Jerome informs us that the Rabbi Barchochebas, who headed the Jews
in their last revolt against Hadrian, made them believe that he was the
Messiah, by vomiting flames from his mouth; and at a later period, the
Emperor Constantius was thrown into a state of alarm when Valentinian
informed him that he had seen one of the body-guards breathing out
fire and flames. We are not acquainted with the exact methods by which
these effects were produced; but Florus informs us that Eunus filled
a perforated nut-shell with sulphur and fire, and having concealed it
in his mouth, he breathed gently through it while he was speaking.
This art is performed more simply by the modern juggler. Having rolled
together some flax or hemp, so as to form a ball the size of a walnut,
he sets it on fire, and allows it to burn till it is nearly consumed:
he then rolls round it while burning some additional flax, and by these
means the fire may be retained in it for a considerable time. At the
commencement of his exhibition he introduces the ball into his mouth,
and while he breathes through it the fire is revived, and a number
of burning sparks are projected from his mouth. These sparks are too
feeble to do any harm, provided he inhales the air through his nostrils.

The kindred art of walking on burning coals or red-hot iron remounts to
the same antiquity. The priestesses of Diana at Castabala in Cappadocia
were accustomed, according to Strabo, to walk over burning coals; and
at the annual festival which was held in the temple of Apollo on Mount
Soracte in Etruria, the Hirpi marched over burning coals, and on this
account they were exempted from military service, and received other
privileges from the Roman Senate. This power of resisting fire was
ascribed even by Varro to the use of some liniment with which they
anointed the soles of their feet.

Of the same character was the art of holding red-hot iron in the hands
or between the teeth, and of plunging the hands into boiling water or
melted lead. About the close of the seventeenth century, an Englishman
of the name of Richardson rendered himself famous by chewing burning
coals, pouring melted lead upon his tongue, and swallowing melted
glass. That these effects are produced partly by deception, and partly
by a previous preparation of the parts subjected to the heat, can
scarcely admit of a doubt. The fusible metal, composed of mercury,
tin, and bismuth, which melts at a low temperature, might easily have
been substituted in place of lead; and fluids of easy ebullition may
have been used in place of boiling water. A solution of spermaceti
or sulphuric ether, tinged with alkanet root, which becomes solid at
50° of Fahrenheit, and melts and boils with the heat of the hand, is
supposed to be the substance which is used at Naples when the dried
blood of St. Januarius melts spontaneously, and boils over the vessel
which contains it.

But even when the fluid requires a high temperature to boil, it may
have other properties, which enable us to plunge our hands into it
with impunity. This is the case with boiling tar, which boils at a
temperature of 220°, even higher than that of water. Mr. Davenport
informs us, that he saw one of the workmen in the Royal Dock-yard at
Chatham immerse his naked hand in tar of that temperature. He drew up
his coat-sleeves, dipped in his hand and wrist, bringing out fluid tar,
and pouring it off from his hand as from a ladle. The tar remained in
complete contact with his skin, and he wiped it off with tow. Convinced
that there was no deception in this experiment, Mr. Davenport immersed
the entire length of his fore-finger in the boiling cauldron, and
moved it about a short time before the heat became inconvenient. Mr.
Davenport ascribes this singular effect to the slowness with which
the tar communicates its heat, which he conceives to arise from the
abundant volatile vapour which is evolved, “carrying off rapidly
the caloric in a latent state, and intervening between the tar and
the skin, so as to prevent the more rapid communication of heat.”
He conceives also, that when the hand is withdrawn, and the hot tar
adhering to it, the rapidity with which this vapour is evolved from
the surface exposed to the air cools it immediately. The workmen
informed Mr. Davenport that, if a person put his hand into the cauldron
with his glove on, he would be dreadfully burnt; but this extraordinary
result was not put to the test of observation.

But though the conjurors with fire may have availed themselves of
these singular properties of individual bodies, yet the general secret
of their art consisted in rendering the skin of the exposed parts
callous and insensible to heat,--an effect which may be produced by
continually compressing or singeing them till the skin acquires a horny
consistence. A proof of this opinion is mentioned by Beckmann, who
assures us, that in September, 1765, when he visited the copper-works
at Awestad, one of the workmen, bribed by a little money to drink,
took some of the melted copper in his hand, and, after showing it to
the company, threw it against a wall. He then squeezed the fingers of
his horny hand close to each other, held it a few minutes under his
arm-pit, to make it perspire, as he said, and taking it again out, drew
it over a ladle filled with melted copper, some of which he skimmed
off, and moved his hand backwards and forwards very quickly by way of
ostentation. During this performance, M. Beckmann noticed a smell like
that of singed horn or leather, though the hand of the workman was
not burned. This callosity of the skin may be effected by frequently
moistening it with dilute sulphuric acid. Some allege that the juices
of certain plants produce the same effect, while others recommend the
frequent rubbing of the skin with oil. The receipt given by Albertus
Magnus for this purpose was of a different nature. It consisted of a
non-conducting calcareous paste, which was made to adhere to the skin
by the sap of the marsh-mallow, the slimy seeds of the flea-bane, and
the white of an egg.

As the ancients were acquainted with the incombustibility of asbestos
or amianthus, and the art of weaving it into cloth, it is highly
probable that it was employed in the performance of some of their
miracles, and it is equally probable that it was subsequently used,
along with some of the processes already described, in enabling the
victims of superstition to undergo without hazard the trial of ordeal
by fire. In every country where this barbarous usage prevailed, whether
in the sanctuary of the Christian idolater, or in the pagan temple of
the Bramin, or under the wild orgies of the African savage, Providence
seems to have provided the means of meeting it with impunity. In
Catholic countries this exculpatory judgment was granted chiefly
to persons in weak health, who were incapable of using arms, and
particularly to monks and ecclesiastics, who could not avail themselves
of the trial by single combat. The fire ordeal was conducted in the
church under the inspection of the clergy: mass was at the same time
celebrated, and the iron and the victims were consecrated by the
sprinkling of holy water. The preparatory steps were also under the
direction of the priests. It was necessary that the accused should be
placed three days and three nights under their care, both before and
after the trial. Under the pretence of preventing the defendant from
preparing his hands by art, and in order to ascertain the result of
the ordeal, his hands were covered up and sealed during the three days
which preceded and followed the fiery application; and it has been
plausibly conjectured by Beckmann, that during the first three days the
preventive was applied to those whom they wished to acquit, and that
the last three days were requisite to bring back the hands to their
natural condition. In these and other cases, the accused could not
have availed himself directly of the use of asbestos gloves, unless we
could suppose them so made as to imitate the human skin at a distance;
but the fibres of that mineral may have been imbedded in a paste which
applied itself readily to all the elevations and depressions of the
skin.

In our own times the art of defending the hands and face, and indeed
the whole body, from the action of heated iron and intense fire, has
been applied to the nobler purpose of saving human life, and rescuing
property from the flames. The revival and the improvement of this art
we owe to the benevolence and the ingenuity of the Chevalier Aldini of
Milan, who has travelled through all Europe to present this valuable
gift to his species. Sir H. Davy had long ago shown that a safety
lamp for illuminating mines, containing inflammable air, might be
constructed of wire-gauze alone, which prevented the flame within,
however large or intense, from setting fire to the inflammable air
without. This valuable property, which has been long in practical use,
he ascribed to the conducting and radiating power of the wire-gauze,
which carried off the heat of the flame, and deprived it of its power.
The Chevalier Aldini conceived the idea of applying the same material,
in combination with other badly conducting substances, as a protection
against fire. The incombustible pieces of dress which he uses for the
body, arms, and legs, are formed out of strong cloth, which has been
steeped in a solution of alum, while those for the head, hands, and
feet, are made of cloth of asbestos or amianthus. The head-dress is
a large cap which envelops the whole head down to the neck, having
suitable perforations for the eyes, nose, and mouth. The stockings and
cap are single, but the gloves are made of double amianthus cloth, to
enable the fireman to take into his hand burning or red hot bodies. The
piece of ancient asbestos cloth preserved in the Vatican was formed,
we believe, by mixing the asbestos with other fibrous substances;
but M. Aldini has executed a piece of nearly the same size, nine
feet five inches long and five feet three inches wide, which is much
stronger than the ancient piece, and possesses superior qualities,
in consequence of having been woven without the introduction of any
foreign substance. In this manufacture the fibres are prevented from
breaking by the action of steam, the cloth is made loose in its fabric,
and the threads are about the fiftieth of an inch in diameter.

The metallic dress which is superadded to these means of defence
consists of five principal pieces, viz. a _casque_ or cap, with a mask
large enough to leave a proper space between it and the asbestos cap; a
cuirass with its brassets; a piece of armour for the trunk and thighs;
a pair of boots of double wire-gauze; and an oval shield 5 feet long
by 2½ wide, made by stretching the wire-gauze over a slender frame of
iron. All these pieces are made of iron wire-gauze, having the interval
between its threads the twenty-fifth part of an inch.

In order to prove the efficacy of this apparatus, and inspire the
firemen with confidence in its protection, he showed them that a finger
first enveloped in asbestos, and then in a double case of wire-gauze,
might be held a long time in the flame of a spirit-lamp or candle
before the heat became inconvenient. A fireman having his hand within
a double asbestos glove, and its palm protected by a piece of asbestos
cloth, seized with impunity a large piece of red-hot iron, carried it
deliberately to the distance of 150 feet, inflamed straw with it, and
brought it back again to the furnace. On other occasions the fireman
handled blazing wood and burning substances, and walked during five
minutes upon an iron grating placed over flaming fagots.

In order to show how the head, eyes, and lungs are protected, the
fireman put on the asbestos and wire-gauze cap, and the cuirass, and
held the shield before his breast. A fire of shavings was then lighted,
and kept burning in a large raised chafing-dish; the fireman plunged
his head into the middle of the flames with his face to the fuel, and
in that position went several times round the chafing-dish for a period
longer than a minute. In a subsequent trial, at Paris, a fireman placed
his head in the middle of a large brazier filled with flaming hay and
wood, as in Fig. 77, and resisted the action of the fire during five or
six minutes, and even ten minutes.

[Illustration: _Fig. 77._]

In the experiments which were made at Paris in the presence of a
committee of the Academy of Sciences, two parallel rows of straw and
brushwood, supported by iron wires, were formed at the distance of
three feet from each other, and extended thirty feet in length. When
this combustible mass was set on fire, it was necessary to stand at
the distance of eight or ten yards to avoid the heat. The flames from
both the rows seemed to fill up the whole space between them, and rose
to the height of nine or ten feet. At this moment six firemen, clothed
in the incombustible dresses, and marching at a slow pace behind each
other, repeatedly passed through the whole length between the two rows
of flame, which were constantly fed with additional combustibles.
One of the firemen carried on his back a child eight years old, in a
wicker-basket covered with metallic gauze, and the child had no other
dress than a cap made of amianthine cloth.

In February, 1829, a still more striking experiment was made in the
yard of the barracks of St. Gervais. Two towers were erected two
stories high, and were surrounded with heaps of inflamed materials,
consisting of fagots and straw. The firemen braved the danger with
impunity. In opposition to the advice of M. Aldini, one of them, with
the basket and child, rushed into a narrow place, where the flames were
raging eight yards high. The violence of the fire was so great that he
could not be seen, while a thick black smoke spread around, throwing
out a heat which was unsupportable by the spectators. The fireman
remained so long invisible that serious doubts were entertained of his
safety. He at length, however, issued from the fiery gulf uninjured,
and proud of having succeeded in braving so great a danger.

It is a remarkable result of these experiments, that the firemen
are able to breathe without difficulty in the middle of the flames.
This effect is owing not only to the heat being intercepted by the
wire-gauze as it passes to the lungs, in consequence of which its
temperature becomes supportable, but also to the singular power which
the body possesses of resisting great heats, and of breathing air of
high temperatures.

A series of curious experiments were made on this subject by M. Tillet
in France, and by Dr. Fordyce and Sir Charles Blagden in England. Sir
Joseph Banks, Dr. Solander, and Sir Charles Blagden entered a room
in which the air had a temperature of 198° Fahr., and remained ten
minutes; but as the thermometer sank very rapidly, they resolved to
enter the room singly. Dr. Solander went in alone, and found the heat
210°, and Sir Joseph entered when the heat was 211°. Though exposed
to such an elevated temperature, their bodies preserved their natural
degree of heat. Whenever they breathed upon a thermometer it sank
several degrees: every expiration, particularly if strongly made, gave
a pleasant impression of coolness to their nostrils, and their cold
breath cooled their fingers whenever it reached them. On touching his
side, Sir Charles Blagden found it cold like a corpse, and yet the
heat of his body under his tongue was 98°. Hence they concluded that
the human body possesses the power of destroying a certain degree
of heat when communicated with a certain degree of quickness. This
power, however, varies greatly in different media. The same person
who experienced no inconvenience from air heated to 211°, could just
bear rectified spirits of wine at 130°, cooling oil at 129°, cooling
water at 123°, and cooling quicksilver at 117°. A familiar instance of
this occurred in the heated room. All the pieces of metal there, even
their watch-chains, felt so hot that they could scarcely bear to touch
them for a moment, while the air from which the metal had derived all
its heat was only unpleasant. Messrs. Duhamel and Tillet observed,
at Rochefoucault in France, that the girls who were accustomed to
attend ovens in a bakehouse were capable of enduring for ten minutes a
temperature of 270°.

The same gentlemen who performed the experiments above described
ventured to expose themselves to still higher temperatures. Sir Charles
Blagden went into a room where the heat was 1° or 2° above 260°, and
remained eight minutes in this situation, frequently walking about
to all the different parts of the room, but standing still most of
the time in the coolest spot, where the heat was above 240°. The air,
though very hot, gave no pain, and Sir Charles and all the other
gentlemen were of opinion that they could support a much greater heat.
During seven minutes Sir C. Blagden’s breathing continued perfectly
good, but after that time he felt an oppression in his lungs, with
a sense of anxiety, which induced him to leave the room. His pulse
was then 144, double its ordinary quickness. In order to prove that
there was no mistake respecting the degree of heat indicated by the
thermometer, and that the air which they breathed was capable of
producing all the well-known effects of such a heat on inanimate
matter, they placed some eggs and a beef-steak upon a tin frame near
the thermometer, but more distant from the furnace than from the wall
of the room. In the space of twenty minutes the eggs were roasted quite
hard, and in forty-seven minutes the steak was not only dressed, but
almost dry. Another beef-steak, similarly placed, was rather overdone
in thirty-three minutes. In the evening, when the heat was still more
elevated, a third beef-steak was laid in the same place, and as they
had noticed that the effect of the hot air was greatly increased by
putting it in motion, they blew upon the steak with a pair of bellows,
and thus hastened the dressing of it to such a degree that the
greatest portion of it was found to be pretty well done in thirteen
minutes.

Our distinguished countryman, Sir F. Chantrey, has very recently
exposed himself to a temperature still higher than any which we have
mentioned. The furnace which he employs for drying his moulds is about
14 feet long, 12 feet high, and 12 feet broad. When it is raised to
its highest temperature, with the doors closed, the thermometer stands
at 350°, and the iron floor is red hot. The workmen often enter it
at a temperature of 340°, walking over the iron floor with wooden
clogs, which are of course charred on the surface. On one occasion
Sir F. Chantrey, accompanied by five or six of his friends, entered
the furnace, and, after remaining two minutes, they brought out a
thermometer which stood at 320°. Some of the party experienced sharp
pains in the tips of their ears, and in the septum of the nose, while
others felt a pain in their eyes.




LETTER XIII.

 Spontaneous combustion--In the absorption of air by powdered
 charcoal--and of hydrogen by spongy platinum--Dobereiner’s
 lamp--Spontaneous combustion in the bowels of the earth--Burning
 cliffs--Burning soil--Combustion without flame--Spontaneous combustion
 of human beings--Countess Zangari--Grace Pett--Natural fire-temples
 of the Guebres--Spontaneous fires in the Caspian Sea--Springs of
 inflammable gas near Glasgow--Natural light-house of Maracaybo--New
 elastic fluids in their cavities--of gems--Chemical operation going
 on in their cavities--Explosions produced in them by heat--Remarkable
 changes of colour from chemical causes--Effects of the nitrous oxide
 of Paradise gas when breathed--Remarkable cases described--Conclusion.


Among the wonderful phenomena which chemistry presents to us, there
are few more remarkable than those of spontaneous combustion, in which
bodies both animate and inanimate emit flames, and are sometimes
entirely consumed by internal fire. One of the commonest experiments
in chemistry is that of producing inflammation by mixing two fluids
perfectly cold. Becker, we believe, was the first person who discovered
that this singular effect was produced by mixing oil of vitriol with
oil of turpentine. Borrichios showed that aqua-fortis produced the
same effect as oil of vitriol. Tournefort proved that spirit of nitre
and oil of sassafras took fire when mixed; and Homberg discovered that
the same property was possessed by many volatile oils when mixed with
spirit of nitre.

Every person is familiar with the phenomena of heat and combustion
produced by fermentation. Ricks of hay and stacks of corn have been
frequently consumed by the heat generated during the fermentation
produced from moisture; and gunpowder-magazines, barns, and paper-mills
have been often burned by the fermentation of the materials which they
contained. Galen informs us that the dung of a pigeon is sufficient
to set fire to a house; and he assures us that he has often seen it
take fire when it had become rotten. Casati likewise relates, on good
authority, that the fire which consumed the great church of Pisa was
occasioned by the dung of pigeons that had for centuries built their
nests under its roof.

Among the substances subject to spontaneous combustion, pulverized
or finely-powdered charcoal is one of the most remarkable. During
the last thirty years no fewer than four cases of the spontaneous
inflammation of powdered charcoal have taken place in France. When
charcoal is triturated in tuns with bronze bruisers, it is reduced
into the state of the finest powder. In this condition it has the
appearance of an unctuous fluid, and it occupies a space three times
less than it does in rods of about six inches long. In this state of
extreme division it absorbs air much more readily than it does when
in rods. This absorption, which is so slow as to require several days
for its completion, is accompanied with a disengagement of heat which
rises from 340° to 360° nearly of Fahrenheit, and which is the true
cause of the spontaneous inflammation. The inflammation commences near
the centre of the mass, at the depth of five or six inches beneath
its surface, and at this spot the temperature is always higher than
at any other. Black charcoal, strongly distilled, heats and inflames
more easily than the orange, or that which is little distilled, or
than the charcoal made in boilers. The most inflammable charcoal
must have a mass of at least 66lbs. avoirdupois, in order that it
may be susceptible of spontaneous inflammation. With the other less
inflammable varieties, the inflammation takes place only in larger
masses.

The inflammation of powdered charcoal is more active in proportion
to the shortness of the interval between its carbonization and
trituration. The free admission of air to the surface of the charcoal
is also indispensable to its spontaneous combustion.

Colonel Aubert, to whom we owe these interesting results, likewise
found that when sulphur and saltpetre are added to the charcoal, it
loses its power of inflaming spontaneously. But as there is still an
absorption of air and a generation of heat, he is of opinion that it
would not be prudent to leave these mixtures in too large masses after
trituration.[34]

 [34] See _Edinburgh Journal of Science_, New Series, No. viii. p. 274.

A species of spontaneous combustion, perfectly analogous to that now
described, but produced almost instantaneously, was discovered by
Professor Dobereiner of Jena in 1824. He found that when a jet of
hydrogen gas was thrown upon recently prepared spongy platinum, the
metal became almost instantly red hot, and set fire to gas. In this
case the minutely divided platinum acted upon the hydrogen gas in the
same manner as the minutely divided charcoal acted upon common air.
Heat and combustion were produced by the absorption of both gases,
though in the one case the effect was instantaneous, and in the other
was the result of a prolonged absorption.

[Illustration: _Fig. 78._]

This beautiful property of spongy platinum was happily applied to the
construction of lamps for producing an instantaneous light. The form
given to the lamp by Mr. Garden of London is shown in the annexed
figure, where AB is a globe of glass, fitting tightly into another
glass globe CD by a ground shoulder _m n_. The globe AB terminates
in a hollow tapering neck _m n o p_, on the lower end of which is
placed a small cylinder of zinc _o p_. A brass tube _a b c_, is
fitted at _a_ into the neck of the globe CD, and through this tube,
which is furnished with a stop-cock _d_, the gas can escape at the
small aperture _c_. A brass pin _c f_, carrying a brass box P, is made
to slide through a hole _h_, so that the brass box P, in which the
spongy platinum is placed, can be set at any required distance from
the aperture _c_. If sulphuric acid, diluted with an equal quantity of
water, is now poured into the vessel AB by its mouth at S, now closed
with a stopper, the fluid will descend through the tube _m n o p_, and
if the cock _d_ is shut, it will compress the air contained in CD. The
dilute acid thus introduced into CD will act upon the ring of zinc _o
p_, and generate hydrogen gas, which, after the atmospheric air in CD
is let off, will gradually fill the vessel CD, the diluted acid being
forced up the tube _o p m n_, into the glass globe AB. The ring of zinc
_o p_ floats on a piece of cork, so that when CD is full of hydrogen,
the diluted acid does not touch the zinc, and consequently is prevented
from producing any more gas. The instant, however, that any gas is let
off at _c_, the pressure of the fluid in the globe AB, and tube _m n o
p_, overcomes the elasticity of the remaining gas in CD, and forces the
diluted acid up to the zinc _o p_, so as to enable it to produce more
gas to supply what has been used.

The lamp being supplied with hydrogen in the manner now described,
it is used in the following manner. The spongy platinum in P being
brought near _c_, the cock _d_ is turned, and the gas is thrown upon
the platinum. An intense heat is immediately produced, the platinum
becomes red-hot, and the hydrogen inflames. A taper is then lighted at
the flame, and the cock _d_ is shut. Professor Cumming, of Cambridge,
found it necessary to cover up the platinum with a cap after every
experiment. This ingenious chemist likewise found, that, with platinum
foil the 9,000th part of an inch thick kept in a close tube, the
hydrogen was inflamed; but when the foil was only the 6,000th of an
inch thick, it was necessary to raise it previously to a red heat.

Spontaneous combustion is a phenomenon which occurs very frequently
and often to a great extent within the bowels of the earth. The heat
by which it is occasioned is produced by the decomposition of mineral
bodies and other causes. This heat increases in intensity till it is
capable of melting the solid materials which are exposed to it. Gases
and aqueous vapours of powerful elasticity are generated, new fluids
of expansive energy imprisoned in cavities under great pressure are
set free, and these tremendous agents, acting under the repressing
forces of the superincumbent strata, exhibit their power in desolating
earthquakes; or, forcing their way through the superficial crust of the
globe, they waste their fury in volcanic eruptions.

When the phenomena of spontaneous combustion take place near the
surface of the earth, its effects are of a less dangerous character,
though they frequently give birth to permanent conflagrations, which no
power can extinguish. An example of this milder species of spontaneous
combustion has been recently exhibited in the burning cliff at
Weymouth; and a still more interesting one exists at this moment near
the village of Bradley, in Staffordshire. The earth is here on fire,
and this fire has continued for nearly sixty years, and has resisted
every attempt that has been made to extinguish it. This fire, which
has reduced many acres of land to a mere calx, arises from a burning
stratum of coal about four feet thick and eight or ten yards deep, to
which the air has free access, in consequence of the main coal having
been dug from beneath it. The surface of the ground is sometimes
covered for many yards with such quantities of sulphur that it can be
easily gathered. The calx has been found to be an excellent material
for the roads, and the workmen who collect it often find large beds of
alum of an excellent quality.

A singular species of invisible combustion, or of combustion without
flame, has been frequently noticed. I have observed this phenomenon in
the small green wax tapers in common use. When the flame is blown out,
the wick will continue red-hot for many hours; and if the taper were
regularly and carefully uncoiled, and the room kept free from currents
of air, the wick would burn on in this way till the whole of the taper
is consumed. The same effects are not produced when the colour of the
wax is red. In this experiment the wick, after the flame is blown out,
has sufficient heat to convert the wax into vapour, and this vapour
being consumed without flame, keeps the wick at its red heat. A very
disagreeable vapour is produced during this imperfect combustion of the
wax.

Prof. Dobereiner, of Jena, observed that, when the alcohol in a spirit
of wine lamp was nearly exhausted, the wick became carbonized, and
though the flame disappeared, the carbonized part of the wick became
red-hot, and continued so while a drop of alcohol remained, provided
the air in the room was undisturbed. On one occasion the wick continued
red-hot for twenty-four hours, and a very disagreeable acid vapour was
formed.

[Illustration: _Fig. 79._]

On these principles depend the _lamp without flame_ which was
originally constructed by Mr. Ellis. It is shown in the annexed
figure, where AB is the lamp, and _h_ a cylindrical coil of platinum
wire, the hundredth part of an inch in diameter. This spiral is so
placed that four or five of the twelve coils of which the cylinder
consists are upon the wick, and the other seven or eight above it. If
the lamp is lighted, and continues burning till the cylindrical coil
is red-hot, then if the flame is blown out, the vapour which arises
from the alcohol will by its combustion keep the coils above the wick
red-hot, and this red heat will in its turn keep up the vaporization
of the alcohol till the whole of the alcohol is consumed. The heat of
the wire is always sufficient to kindle a piece of German fungus or
saltpetre paper, so that a sulphur match may at any time be lighted.
Mr. Gill found that a wick composed of twelve threads of the cotton
yarn commonly used for lamps will require half an ounce of alcohol to
keep the wire red-hot for eight hours. This lamp has been kept burning
for sixty hours; but it can scarcely be recommended for a bed-room, as
an acid vapour is disengaged during the burning of the alcohol. When
perfumes are dissolved in the alcohol, they are diffused through the
apartment during the slow combustion of the vapour.

A species of combustion without flame, and analogous to that which
has been described, is exhibited in the extraordinary phenomenon of
the spontaneous combustion of living bodies. That animal bodies are
liable to internal combustion, is a fact which was well known to the
ancients. Many cases which have been adduced as examples of spontaneous
combustion are merely cases of individuals who were highly susceptible
of strong electrical excitation. In one of these cases, however, Peter
Bovisteau asserts, that the sparks of fire thus produced, reduced to
ashes the hair of a young man; and John de Viana informs us, that the
wife of Dr. Freilas, physician to the Cardinal de Royas, Archbishop of
Toledo, emitted by perspiration an inflammable matter of such a nature,
that when the ribbon which she wore over her shift was taken from her,
and exposed to the cold air, it instantly took fire, and shot forth
like grains of gunpowder. Peter Borelli has recorded a fact of the very
same kind respecting a peasant whose linen took fire, whether it was
laid up in a box when wet, or hung up in the open air. The same author
speaks of a woman who, when at the point of death, vomited flames; and
Thomas Bartholin mentions this phenomenon as having often happened to
persons who were great drinkers of wine or brandy. Ezekiel de Castro
mentions the singular case of Alexandrinus Megetius, a physician, from
one of whose vertebræ there issued a fire which scorched the eyes of
the beholders; and Krantzius relates, that during the wars of Godfrey
of Bouillon, certain people of the territory of Nevers were burning
with invisible fire, and that some of them cut off a foot or a hand
where the burning began, in order to arrest the calamity. Nor have
these effects been confined to man. In the time of the Roman consuls
Gracchus and Juventius, a flame is said to have issued from the mouth
of a bull without doing any injury to the animal.

The reader will judge of the degree of credit which may belong to these
narrations when he examines the effects of a similar kind which have
taken place in less fabulous ages, and nearer our own times. John Henry
Cohausen informs us that a Polish gentleman in the time of the Queen
Bona Sforza, having drunk two dishes of a liquor called brandy-wine,
vomited flames, and was burned by them, and Thomas Bartholin[35] thus
describes a similar accident: “A poor woman at Paris used to drink
spirit of wine plentifully for the space of three years, so as to take
nothing else. Her body contracted such a combustible disposition, that
one night, when she lay down on a straw couch, she was all burned
to ashes except her skull and the extremities of her fingers.” John
Christ. Sturmius informs us, in the German Ephemerides, that in the
northern countries of Europe flames often evaporate from the stomachs
of those who are addicted to the drinking of strong liquors; and he
adds, “that seventeen years before, three noblemen of Courland drank by
emulation strong liquors, and two of them died scorched and suffocated
by a flame which issued from their stomachs.”

 [35] Acta Medica et Philosophica Hafniensia, 1673.

One of the most remarkable cases of spontaneous combustion is that
of the Countess Cornelia Zangari and Bandi of Cesena, which has been
minutely described by the Reverend Joseph Bianchini, a prebend in the
city of Verona. This lady, who is in the sixty-second year of her age,
retired to bed in her usual health. Here she spent above three hours
in familiar conversation with her maid, and in saying her prayers; and
having at last fallen asleep, the door of her chamber was shut. As her
maid was not summoned at the usual hour, she went into the bed-room
to wake her mistress; but receiving no answer, she opened the window,
and saw her corpse on the floor in the most dreadful condition. At
the distance of four feet from the bed there was a heap of ashes. Her
legs, with the stockings on, remained untouched, and the head, half
burned, lay between them. Nearly all the rest of the body was reduced
to ashes. The air in the room was charged with floating soot. A small
oil lamp on the floor was covered with ashes, but had no oil in it; and
in two candlesticks, which stood upright upon a table, the cotton wick
of both the candles was left, and the tallow of both had disappeared.
The bed was not injured, and the blankets and sheets were raised on
one side, as if a person had risen up from it. From an examination
of all the circumstances of this case, it has been generally supposed
that an internal combustion had taken place; that the lady had risen
from her bed to cool herself, and that, in her way to open the window,
the combustion had overpowered her, and consumed her body by a process
in which no flame was produced which could set fire to the furniture
or the floor. The Marquis Scipio Maffei was informed by an Italian
nobleman who passed through Cesena a few days after this event, that
he heard it stated in that town, that the Countess Zangari was in
the habit, when she felt indisposed, of washing all her body with
camphorated spirit of wine.

So recently as 1744, a similar example of spontaneous combustion
occurred in our own country, at Ipswich. A fisherman’s wife, of the
name of Grace Pett, of the parish of St. Clement’s, had been in the
habit for several years of going down stairs every night, after she was
half undressed, to smoke a pipe. She did this on the evening of the 9th
of April, 1744. Her daughter, who lay in the same bed with her, had
fallen asleep, and did not miss her mother till she awaked early in
the morning. Upon dressing herself, and going down stairs, she found
her mother’s body lying on the right side, with her head against the
grate, and extended over the hearth, with her legs on the deal floor,
and appearing like a block of wood burning with a glowing fire without
flame. Upon quenching the fire with two bowls of water, the neighbours,
whom the cries of the daughter had brought in, were almost stifled with
the smell. The trunk of the unfortunate woman was almost burned to
ashes, and appeared like a heap of charcoal covered with white ashes.
The head, arms, legs, and thighs, were also much burned. There was no
fire whatever in the grate, and the candle was burned out in the socket
of the candlestick, which stood by her. The clothes of a child on one
side of her, and a paper screen on the other, were untouched: and the
deal floor was neither singed nor discoloured. It was said that the
woman had drunk plentifully of gin overnight in welcoming a daughter
who had recently returned from Gibraltar.

Among the phenomena of the natural world which are related to those
of spontaneous combustion, are what have been called the natural
fire-temples of the Guebres, and the igneous phenomena which are
seen in their vicinity. The ancient sect of the Guebres or Parsees,
distinguished from all other sects as the worshippers of fire,
had their origin in Persia; but, being scattered by persecution,
they sought an asylum on the shores of India. Those who refused
to expatriate themselves continued to inhabit the shores of the
Caspian Sea, and the cities of Ispahan, Yezd, and Kerman. Their great
fire-temple, called Attush Kudda, stands in the vicinity of Badku,
one of the largest and most commodious ports on the Caspian. In the
neighbourhood of this town the earth is impregnated with naphtha, an
inflammable mineral oil; and the inhabitants have no other fuel, and no
other light, but what is derived from this substance.

The remains of the ancient fire-temples of the Guebres are still
visible about ten miles to the north-east of the town. The temple in
which the deity is worshipped under the form of fire, is a space about
thirty yards square, surrounded with a low wall, and containing many
apartments. In each of these a small volcano of sulphureous fire issues
from the ground through a furnace or funnel in the shape of a Hindoo
altar. On closing the funnel, the fire is instantly extinguished;
and by placing the ear at the aperture, a hollow sound is heard,
accompanied with a strong current of cold air, which may be lighted
at pleasure by holding to it any burning substance. The flame is of a
pale, clear colour, without any perceptible smoke, and emits a highly
sulphureous vapour, which impedes respiration, unless when the mouth
is kept beneath the level of the furnace. This action on the lungs
gives the Guebres a wan and emaciated appearance, and oppresses them
with a hectic cough, which strangers also feel while breathing this
insalubrious atmosphere.

For about two miles in circumference, round the principal fire, the
whole ground, when scraped to the depth of two or three inches, has
the singular property of being inflamed by a burning coal. In this
case, however, it does not communicate fire to the adjacent ground: but
if the earth is dug up with a spade, and a torch brought near it, an
extensive but instantaneous conflagration takes place, in which houses
have often been destroyed, and the lives of the people exposed to
imminent danger.

When the sky is clear and the weather serene, the springs in their
ebullition do not rise higher than two or three feet; but in gloomy
weather, and during the prevalence of stormy clouds, the springs are
in a state of the greatest ebullition, and the naphtha, which often
takes fire spontaneously at the earth’s surface, flows burning in great
quantities to the sea, which is frequently covered with it, in a state
of flame, to the distance of several leagues from the shore.

Besides the fires in the temple, there is a large one which springs
from a natural cliff in an open situation, and which continually burns.
The general space in which this volcanic fire is most abundant is
somewhat less than a mile in circuit. It forms a low flat hill, sloping
to the sea, the soil of which is a sandy earth, mixed with stones. Mr.
Forster did not observe any violent eruption of flame in the country
around the Attush Kudda; but Kinneir informs us, that the whole country
round Badku has at times the appearance of being enveloped in flames.
“It often seems,” he adds, “as if the fire rolled down from the
mountains in large masses, and with incredible velocity; and during the
clear moonshine nights of November and December, a bright blue light is
observed at times to cover the whole western range. The fire does not
consume; and if a person finds himself in the middle of it, no warmth
is felt.”

The inhabitants apply these natural fires to domestic purposes, by
sinking a hollow cane or merely a tube of paper, about two inches in
the ground, and by blowing upon a burning coal held near the orifice
of the tube, there issues a slight flame, which neither burns the cane
nor the paper. By means of these canes or paper tubes, from which the
fire issues, the inhabitants boil the water in their coffee-urns, and
even cook different articles of food. The flame is put out by merely
plugging up the orifice. The same tubes are employed for illuminating
houses that are not paved. The smell of naphtha is of course diffused
through the house: but after any person is accustomed to it, it ceases
to be disagreeable. The inhabitants also employ this natural fire
in calcining lime. The quantity of naphtha procured in the plain to
the south-east of Badku is enormous. It is drawn from wells, some of
which yield from 1,000 to 1,500lbs. per day. As soon as these wells
are emptied, they fill again till the naphtha rises to its original
level.[36]

 [36] See Forster’s Travels, and Kinneir’s Geog. Memoir.

Inflammable gases issuing from the earth have been used both in
the old and the new world for domestic purposes. In the salt mine
of Gottesgabe, at Rheims, in the county of Fecklenburg, there is a
pit called the _Pit of the Wind_, from which a constant current of
inflammable gas has issued for sixty years. M. Roeder, the inspector of
the mines, has used this gas for two years, not only as a light, but
for all the purposes of domestic economy. In the pits which are not
worked, he collects the gas, and conveys it in tubes to his house. It
burns with a white and brilliant flame, has a density of about O.66,
and contains traces of carbonic acid gas and sulphuretted hydrogen.[37]

 [37] _Edinburgh Journal of Science_, No. xv., p. 183.

Near the village of Fredonia, in North America, on the shores of
Lake Erie, are a number of burning springs, as they are called. The
inflammable gas which issues from these springs is conveyed in pipes
to the village, which is actually lighted by them.[38]

 [38] _Edinburgh Journal of Science_, No. xv., p. 183.

In the year 1828 a copious spring of inflammable gas was discovered in
Scotland, in the bed of a rivulet which crosses the north road between
Glasgow and Edinburgh, a little to the east of the seventh mile-stone
from Glasgow, and only a few hundred yards from the house of Bedlay.
The gas is said to issue for more than half a mile along the banks of
the rivulet. Dr. Thompson, who has analysed the gas, saw it issuing
only within a space about fifty yards in length, and about half as much
in breadth. “The emission of gas was visible in a good many places
along the declivity to the rivulet in the immediate neighbourhood of a
small farm-house. The farmer had set the gas on fire in one place about
a yard square, out of which a great many small jets were issuing. It
had burnt without interruption during five weeks, and the soil (which
was clay) had assumed the appearance of pounded brick all around.

“The flame was yellow and strong, and resembled perfectly the
appearance which _carburetted hydrogen gas_ or _fire-damp_ presents
when burnt in daylight. But the greatest issue of gas was in the
rivulet itself, distant about twenty yards from the place where the gas
was burning. The rivulet, when I visited the place, was swollen and
muddy, so as to prevent its bottom from being seen. But the gas issued
up through it in one place with great violence, as if it had been in a
state of compression under the surface of the earth; and the thickness
of the jet could not be less than two or three inches in diameter. We
set the gas on fire as it issued through the water. It burnt for some
time with a good deal of splendour; but as the rivulet was swollen,
and rushing along with great impetuosity, the regularity of the issue
was necessarily disturbed, and the gas was extinguished.” Dr. Thompson
found this gas to consist of _two_ volumes of hydrogen gas, and _one_
volume of vapour of carbon; and as its specific gravity was 0.555,
and as it issues in great abundance, he remarks that it might be used
for filling air-balloons. “Were we assured,” he adds, “that it would
continue to issue in as great abundance as at present, it might be
employed in lighting the streets of Glasgow.”[39]

 [39] _Edinburgh Journal of Science_, No. 1, New Series, p. 71-75.

A very curious natural phenomenon, called the _Lantern_ or _Natural
Lighthouse_ of Maracaybo, has been witnessed in South America. A bright
light is seen every night on a mountainous and uninhabited spot on the
banks of the river Catatumbo, near its junction with the Sulia. It is
easily distinguished at a greater distance than _forty_ leagues, and as
it is nearly in the meridian of the opening of the Lake of Maracaybo,
navigators are guided by it as by a light-house. This phenomenon is
not only seen from the sea-coast, but also from the interior of the
country--at Merida, for example, where M. Palacios observed it for
two years. Some persons have ascribed this remarkable phenomenon to
a thunder-storm, or to electrical explosions which might take place
daily in a pass in the mountains; and it has even been asserted,
that the rolling of thunder is heard by those who approach the spot.
Others suppose it to be an air-volcano, like those on the Caspian Sea,
and that it is caused by asphaltic soils like those of Mena. It is
more probable, however, that it is a sort of carburetted hydrogen, as
hydrogen gas is disengaged from the ground in the same district.[40]

 [40] Humboldt’s Personal Narrative, vol. iv. p. 254, note.

Grand as the chemical operations are which are going on in the great
laboratory of Nature, and alarming as their effects appear when they
are displayed in the terrors of the earthquake and the volcano, yet
they are not more wonderful to the philosopher than the minute though
analogous operations which are often at work near our own persons,
unseen and unheeded. It is not merely in the bowels of the earth
that highly expansive elements are imprisoned and restrained, and
occasionally called into tremendous action by the excitation of heat
and other causes. Fluids and vapours of a similar character exist in
the very gems and precious stones which science has contributed to
luxury and to the arts.

In examining with the microscope the structure of mineral bodies, I
discovered in the interior of many of the gems thousands of cavities
of various forms and sizes. Some had the shape of hollow and regularly
formed crystals; others possessed the most irregular outline, and
consisted of many cavities and branches united without order, but
all communicating with each other. These cavities sometimes occurred
singly, but most frequently in groups forming strata of cavities, at
one time perfectly flat and at another time curved. Several such
strata were often found in the same specimen, sometimes parallel to
each other, at other times inclined, and forming all varieties of
angles with the faces of the original crystal.

These cavities, which occurred in _sapphire_, _chrysoberyl_, _topaz_,
_beryl_, _quartz_, _amethyst_, _peridot_, and other substances, were
sometimes sufficiently large to be distinctly seen by the naked eye,
but most frequently they were so small as to require a high magnifying
power to be well seen, and often they were so exceedingly minute, that
the highest magnifying powers were unable to exhibit their outline.

[Illustration: _Fig. 80._]

The greater number of these cavities, whether large or small, contained
two new fluids different from any hitherto known, and possessing
remarkable physical properties. These two fluids are in general
perfectly transparent and colourless, and they exist in the same cavity
in actual contact, without mixing together in the slightest degree. One
of them expands _thirty_ times more than water, and at a temperature of
about 80° of Fahrenheit it expands so as to fill up the vacuity in the
cavity. This will be understood from the annexed figure, where A B C D
is the cavity, _m n p o_ the highly expansible fluid in which at low
temperatures there is always a vacuity V, like an air-bubble in common
fluids, and A _m n_, C _o p_, the second fluid occupying the angles A
and C. When heat such as that of the hand is applied to the specimen,
the vacuity V gradually contracts in size, and wholly vanishes at a
temperature of about 80°, as shown in Fig. 81. The fluids are shaded,
as in these two figures, when they are seen by light reflected from
their surfaces.

[Illustration: _Fig. 81._]

[Illustration: _Fig. 82._]

When the cavities are large, as in Fig. 82, compared with the quantity
of expansible fluid _m n p o_, the heat converts the fluid into vapour,
an effect which is shown by the circular cavity V becoming larger and
larger till it fills the whole space _m n o p_.

When any of these cavities, whether they are filled with fluid
or with vapour, is allowed to cool, the vacuity V reappears at a
certain temperature. In the fluid cavities the fluid contracts, and
the small vacuity appears, which grows larger and larger till it
resumes its original size. When the cavities are large, several small
vacuities make their appearance and gradually unite into one, though
they sometimes remain separate. In deep cavities a very remarkable
phenomenon accompanies the reappearance of the vacuity. At the instant
that the fluid has acquired the temperature at which it quits the
sides of the cavity, an effervescence or rapid ebullition takes place,
and the transparent cavity is for a moment opaque, with an infinite
number of minute vacuities, which instantly unite into one that goes
on enlarging as the temperature diminishes. In the vapour cavities the
vapour is reconverted by the cold into fluid, and the vacuity V, Fig.
82, gradually contracts till all the vapour has been precipitated. It
is curious to observe, when a great number of cavities are seen at once
in the field of the microscope, that the vacuities all disappear and
reappear at the same instant.

While all these changes are going on in the expansive fluid, the
other denser fluid at A and C, Fig. 80, 81, remains unchanged either
in its form or magnitude. On this account I experienced considerable
difficulty in proving that it was a fluid. The improbability of two
fluids existing in a transparent state in absolute contact, without
mixing in the slightest degree, or acting upon each other, induced
many persons to whom I showed the phenomenon to consider the lines _m
n_, _o p_, Fig. 80, 81, as a partition in the cavity, or the spaces A
_m n_, _o p_ C, either as filled with solid matter, or as corners into
which the expanding fluid would not penetrate. The regular curvature,
however, of the boundary line _m n_, _o p_, and other facts, rendered
these suppositions untenable.

[Illustration: _Fig. 83._]

This difficulty was at last entirely removed by the discovery of a
cavity of the form shown in the annexed figure, where A, B, and C are
three portions of the expansible fluid separated by the interposition
of the second fluid D E F. The first portion A of the expansible fluid
had four vacuities V, X, Y, Z, while the other two portions B, C, had
no vacuity. In order to determine if the vacuities of the portions B,
C, had passed over to A, I took an accurate drawing of the appearances
at a temperature of 50°, as shown in the figure, and I watched the
changes which took place in raising the temperature to 83°. The portion
A gradually expanded itself till it filled up all the four vacuities
V, X, Y, and Z, but as the portions B, C, had no vacuities, they could
expand themselves only by pushing back the supposed second fluid D E
F. This effect actually took place. The dense fluid quitted the side
of the cavity at F. The two portions B, C, of the expansible fluid
instantly united, and the dense fluid having retreated to the limit _m_
_n_ _o_, its other limit advanced to _p_ _q_ _r_, thus proving it to
be a real fluid. This experiment, which I have often shown to others,
involves one of those rare combinations of circumstances which nature
sometimes presents to us in order to illustrate her most mysterious
operations. Had the portions B, C, been accompanied, as is usual, with
their vacuities, the interposed fluid would have remained immoveable
between the two equal and opposite expansions; but owing to the
accidental circumstance of these vacuities having passed over into the
other branch A of the cavity, the fluid yielded to the difference of
the expansive forces between which it lay, and thus exhibited its fluid
character to the eye.

[Illustration: _Fig. 84._]

When we examine these cavities narrowly, we find that they are actually
little laboratories, in which chemical operations are constantly going
on, and beautiful optical phenomena continually displaying themselves.
Let A B D C, for example, be the summit of a crystallized cavity in
topaz, S S representing the dense, N N the expansible fluid, bounded
by a circular line _a b c d_, and V V the vacuity in the new fluid,
bounded by the circle _e f g h_. If the face A B D C is placed under a
compound microscope, so that light may be reflected at an angle less
than that of total reflexion, and if the observer now looks through
the microscope, the temperature of the room being 50°, he will see the
second fluid S S shining with a very feeble reflected light, the dense
fluid N N with a light perceptibly brighter, and the vacuity V V with
a light of considerable brilliancy. The boundaries _a b c d_, _e f g
h_, are marked by a well-defined outline, and also by the concentric
coloured rings of thin plates produced by the extreme thinness of each
of the fluids at their edges.

If the temperature of the room is raised slowly to 58°, a brown
spot will appear at _x_ in the centre of the vacuity V V. This spot
indicates the commencement of evaporation from the expansible fluid
below, and arises from the partial precipitation of the vapour in the
roof of the cavity. As the heat increases, the brown spot enlarges and
becomes very dark. It is then succeeded by a white spot and one or
more coloured rings rise in the centre of the vacuity. The vapour then
seems to form a drop, and all the rings disappear by retiring to the
centre, but only to reappear with new lustre. During the application
of heat, the circle _e f g h_ contracts and dilates like the pupil of
the eye. When the vaporization is so feeble as to produce only a single
ring of one or two tints of the second order, they vanish instantly
by breathing upon the crystal; but when the slight heat of the breath
reaches the fluid, it throws off fresh vapour, and the rings again
appear.

If a drop of ether is put upon the crystal when the rings are in a
state of rapid play, the cold produced by its evaporation causes them
to disappear, till the temperature again rises. When the temperature
is perfectly uniform, the rings are stationary, as shown between V and
V in fig. 84; and it is interesting to observe the first ring produced
by the vapour swelling out to meet the first ring at the margin of
the fluid, and sometimes coming so near it that the darkest parts of
both form a broad black band. As the heat increases, the vacuity V V
diminishes and disappears at 79°, exhibiting many curious phenomena,
which we have not room to describe.

Having fallen upon a method of opening the cavities, and looking at the
fluids, I was able to examine their properties with more attention.
When the expansible fluid first rises from the cavity upon the surface
of the topaz, it neither remains still like the fixed oils, nor
disappears like evaporable fluids. Under the influence, no doubt, of
heat and moisture, it is in a state of constant motion, now spreading
itself on a thin plate over a large surface, and now contracting itself
into a deeper and much less extended drop. These contractions and
extensions are marked by very beautiful optical phenomena. When the
fluid has stretched itself out into a thin plate, it ceases to reflect
light like the thinnest part of the soap-bubble; and when it is again
accumulated into a thicker drop, it is covered with thin coloured rings
of thin plates.

After performing these motions, which sometimes last for ten minutes,
the fluid suddenly disappears, and leaves behind it a sort of granular
residue. When examining this with a single microscope, it again started
into a fluid state, and extended and contracted itself as before. This
was owing to the humidity of the hand which held the microscope, and
I have been able to restore by moisture the fluidity of these grains
twenty days after they were formed from the fluid. This portion was
shown to the Rev. Dr. Fleming, who remarked, that, had he observed
it accidentally, he would have ascribed its apparent vitality to the
movements of some of the animals of the genus Planaria.

After the cavity has remained open for a day or two, the dense fluid
comes out and quickly hardens into a transparent and yellowish
resinous-looking substance, which absorbs moisture, though with less
avidity than the other. It is not volatilized by heat, and is insoluble
in water and alcohol. It readily dissolves, however, with effervescence
in the sulphuric, nitric, and muriatic acids. The residue of the
expansible fluid is volatilized by heat, and is dissolved, but without
effervescence, in the above-mentioned acids. The refractive power of
the dense fluid is about 1.295, and of the expansible one 1.131.

The particles of the dense fluid have a very powerful attraction for
each other and for the mineral which contains them, while those of
the expansible fluid have a very slight attraction for one another,
and also for the substance of the mineral. Hence the two fluids never
mix, the dense fluid being attracted to the angles of angular cavities,
or filling the narrow necks by which two cavities communicate. The
expansible fluid, on the other hand, fills the wide parts of the
cavities, and in deep and round cavities it lies above the dense fluid.

When the dense fluid occupies the necks which join two cavities,
it performs the singular function of a fluid valve, opening and
shutting itself according to the expansions or contractions of the
other fluid. The _fluid valves_ thus exhibited in action may suggest
some useful hints to the mechanic and the philosopher, while they
afford ground of curious speculation in reference to the functions of
animal and vegetable bodies. In the larger organizations of ordinary
animals, where gravity must in general overpower, or at least modify,
the influence of capillary attraction, such a mechanism is neither
necessary nor appropriate; but, in the lesser functions of the same
animals, and in almost all the microscopic structures of the lower
world, where the force of gravity is entirely subjected to the more
powerful energy of capillary forces, it is extremely probable that the
mechanism of immiscible fluids and fluid valves is generally adopted.

In several cavities in minerals I have found crystallized and other
bodies, sometimes transparent crystals, sometimes black spicular
crystals, and sometimes black spheres, all of which are moveable within
the cavity. In some cavities the two new fluids occur in an indurated
state, and others I have found to be lined with a powdery matter. This
last class of cavities occurred in topaz, and they were distinguished
from all others by the extraordinary beauty and symmetry of their
form. One of these cavities represented a finely ornamented sceptre,
and, what is still more singular, the different parts of which it is
composed lay in different planes.

When the gem which contains the highly expansive fluid is strong, and
the cavity not near the surface, heat may be applied to it without
danger; but in the course of my experiments on this subject, the
mineral has often burst with a tremendous explosion, and in one case
wounded me on the brow. An accident of the same kind occurred to a
gentleman who put a crystal into his mouth for the purpose of expanding
the fluid. The specimen burst with great force and cut his mouth, and
the fluid which was discharged from the cavity had a very disagreeable
taste.

In the gems which are peculiarly appropriated for female ornaments,
cavities containing the expansive fluid frequently occur, and if these
cavities should happen to be very near the surface or the edge of the
stone, the fever heat of the body might be sufficient to burst them
with an alarming and even dangerous explosion. I have never heard of
any such accident having occurred; but if it has, or if it ever shall
occur, and if its naturally marvellous character shall be heightened by
any calamitous results, the phenomena described in the preceding pages
will strip it of its wonder.

There are no facts in chemistry more interesting than those which
relate to the changes of colour, which are produced by the mixture of
fluids, and to the creation of brilliant colours by the combination
of bodies in which no colouring matter is visible. Facts of this kind
are too common and too generally known to require to be noticed in a
work like this. The art of producing such changes was known to some of
the early impostors, who endeavoured to obtain a miraculous sanction
to their particular dogmas. Marcos, the head of one of the sects that
wished to engraft paganism upon Christianity, is said to have filled
three transparent glasses with white wine, and while he prayed, the
wine in one of the glasses became red like blood, that in another
became purple, and that in the third sky-blue. Such transformations
present no difficulty to the chemist. There are several fluids, such
as some of the coloured juices of plants, which change their colour
rapidly and without any additional ingredient: and in other cases,
there would be no difficulty in making additions to fluids which should
produce a change of colour at any required instant.

A very remarkable experiment of an analogous nature has been publicly
exhibited in modern times. Professor Beyruss, who lived at the court
of the Duke of Brunswick, one day pronounced to his highness that the
dress which he wore should during dinner became red; and the change
actually took place, to the astonishment of the prince and the rest
of his guests. M. Vogel, who has recorded this curious fact, has not
divulged the secret of the German chemist; but he observes, that if
we pour lime-water into the juice of beet-root, we shall obtain a
colourless liquid; and that a piece of white cloth dipped in this
liquid and dried rapidly, will in a few hours become red by the mere
contact of air. M. Vogel is also of opinion that this singular effect
would be accelerated in an apartment where champagne or other fluids
charged with carbonic acid are poured out in abundance.

Among the wonders of chemistry we must number the remarkable effects
produced upon the human frame by the inhalation of _paradise_ or
_intoxicating gas_, as it has been called. This gas is known to
chemists by the name of the _nitrous oxide_, or the _gaseous oxide of
azote_, or the _protoxide of nitrogen_. It differs from atmospheric
air only in the proportion of its ingredients, atmospheric air
being composed of twenty-seven parts of oxygen, and seventy-three
of nitrogen, while the nitrous oxide consists of thirty-seven parts
of oxygen, and sixty-seven of nitrogen. The most convenient way of
procuring the gas is to expose nitrate of ammonia in a tubulated
glass retort to the heat of an Argand’s lamp between 400° and 500° of
Fahrenheit. The salt first melts; bubbles of gas begin to rise from
the mass, and in a short time a brisk effervescence takes place, which
continues till all the salt has disappeared. The products of this
operation are the nitrous oxide and water, the watery vapour being
condensed in the neck of the retort, while the gas is received over
water. The gas thus obtained is generally white, and hence, when it
is to be used for the purposes of respiration, it should remain at
least an hour over water, which will absorb the small quantity of acid
and of nitrate of ammonia which adhere to it. A pound of the nitrate
of ammonia will in this way yield five cubic feet of gas fit for the
purpose of inhalation.

It was discovered by Sir Humphrey Davy, that this gas could be safely
taken into the lungs, and that it was capable of supporting respiration
for a few minutes. In making this experiment he was surprised to find
that it produced a singular species of intoxication, which he thus
describes: “I breathed,” says he, “three quarts of oxide from and into
a silk bag for more than half a minute without previously closing my
nose or exhausting my lungs. The first inspiration caused a slight
degree of giddiness. This was succeeded by an uncommon sense of fulness
in the head, accompanied with loss of distinct sensation and voluntary
power, a feeling analogous to that produced in the first stage of
intoxication, but unattended by pleasurable sensations.” In describing
the effects of another experiment, he says, “Having previously closed
my nostrils and exhausted my lungs, I breathed four quarts of nitrous
oxide from and into a silk bag. The first feelings were similar to
those produced in the last experiment, but in less than half a minute,
the respiration being continued, they diminished gradually, and were
succeeded by a highly pleasurable thrilling, particularly in the
chest and the extremities. The objects around me became dazzling, and
my hearing more acute. Towards the last respiration the thrilling
increased, the sense of muscular power became greater, and at last an
irresistible propensity to action was indulged in. I recollect but
indistinctly what followed; I knew that my motions were varied and
violent. These effects very rarely ceased after respiration. In ten
minutes I had recovered my natural state of mind. The thrilling in the
extremities continued longer than the other sensations. This experiment
was made in the morning; no languor or exhaustion was consequent, my
feelings through the day were as usual, and I passed the night in
undisturbed repose.”

In giving an account of another experiment with this gas, Sir Humphrey
thus describes his feelings: “Immediately after my return from a
long journey, being fatigued, I respired nine quarts of nitrous
oxide, having been precisely thirty-three days without breathing any.
The feelings were different from those I had experienced on former
experiments. After the first six or seven respirations, I gradually
began to lose the perception of external things, and a vivid and
intense recollection of some former experiments passed through my mind,
so that I called out, ‘What an annoying concatenation of ideas!’”

Another experiment made by the same distinguished chemist was attended
by still more remarkable results. He was shut up in an airtight
breathing-box, having a capacity of about nine and a half cubic feet,
and he allowed himself to be habituated to the excitement of the gas,
which was gradually introduced. After having undergone this operation
for an hour and a quarter, during which eighty quarts of gas were
thrown in, he came out of the box and began to respire twenty quarts
of unmingled nitrous oxide. “A thrilling,” says he, “extending from
the chest to the extremities, was almost immediately produced. I felt
a sense of tangible extension highly pleasurable in every kind; my
visible impressions were dazzling and apparently magnified; I heard
distinctly every sound in the room, and I was perfectly aware of my
situation. By degrees, as the pleasurable sensation increased, I lost
all connexion with external things; trains of vivid visible images
rapidly passed through my mind, and were connected with words in such
a manner as to produce perceptions perfectly novel. I existed in a
world of newly connected and newly modified ideas. When I was awakened
from this same delirious trance by Dr. Kinglake, who took the bag from
my mouth, indignation and pride were the first feelings produced by
the sight of the persons about me. My emotions were enthusiastic and
sublime, and for a moment I walked round the room, perfectly regardless
of what was said to me. As I recovered my former state of mind, I felt
an inclination to communicate the discoveries I had made during the
experiment. I endeavoured to recall the ideas; they were feeble and
indistinct. One recollection of terms, however, presented itself, and
with the most intense belief and prophetic manner I exclaimed to Dr.
Kinglake, ‘Nothing exists but thoughts; the universe is composed of
impressions, ideas, pleasures, and pains!’”

These remarkable properties induced several persons to repeat the
experiment of breathing this exhilarating medicine. Its effects were,
as might have been expected, various in different individuals; but its
general effect was to produce in the gravest and most phlegmatic the
highest degree of exhilaration and happiness unaccompanied with languor
or depression. In some it created an irresistible disposition to laugh,
and in others a propensity to muscular exertion. In some it impaired
the intellectual functions, and in several it had no sensible effect,
even when it was breathed in the purest state, and in considerable
quantities. It would be an inquiry of no slight interest to ascertain
the influence of this gas over persons of various bodily temperaments,
and upon minds varying in their intellectual and moral character.

Although Sir Humphrey Davy experienced no unpleasant effects from the
inhalation of the nitrous oxide, yet such effects are undoubtedly
produced; and there is reason to believe that even permanent changes
in the constitution may be induced by the operation of this remarkable
stimulant. Two very interesting cases of this kind presented themselves
to Professor Silliman, of Yale College, when the nitrous oxide was
administered to some of his pupils. The students had been in the habit,
for several years, of preparing this gas, and administering it to
one another, and these two cases were the only remarkable ones which
deserved to be recorded. We shall describe them in Professor Silliman’s
own words:--

“A gentleman, about nineteen years of age, of a sanguine temperament,
and cheerful temper, and in the most perfect health, inhaled the usual
quantity of the nitrous oxide, when prepared in the ordinary manner.
Immediately his feelings were uncommonly elevated, so that, as he
expressed it, he could not refrain from dancing and shouting. Indeed
to such a degree was he excited, that he was thrown into a frightful
fit of delirium, and his exertions became so violent, that after a
while he sank to the earth exhausted, and there remained, until having
by quiet in some degree recovered his strength, he again arose, only
to renew the most convulsive muscular efforts, and the most piercing
screams and cries; within a few moments, overpowered by the intensity
of the paroxysm, he again fell to the ground, apparently senseless, and
panting vehemently. The long continuance and violence of the affection
alarmed his companions, and they ran for professional assistance. They
were, however, encouraged by the person to whom they applied to hope
that he would come out of his trance without injury; but for the space
of two hours these symptoms continued; he was perfectly unconscious of
what he was doing, and was in every respect like a maniac. He states,
however, that his _feelings vibrated_ between perfect happiness and the
most consummate misery. In the course of the afternoon, and after the
first violent effects had subsided, he was compelled to lie down two or
three times from excessive fatigue, although he was immediately aroused
upon any one’s entering the room. The effects remained in a degree for
three or four days, accompanied by a hoarseness, which he attributed
to the exertion made while under the immediate influence of the gas.
This case should produce a degree of caution, especially in persons of
a sanguine temperament, whom, much more frequently than others, we have
seen painfully, and even alarmingly affected.”

The other case described by Professor Silliman was that of a man of
mature age, and of a grave and respectable character. “For nearly
two years previous to his taking the gas, his health had been very
delicate, and his mind frequently gloomy and depressed. This was
peculiarly the case for a few days immediately preceding that time;
and his general state of health was such, that he was obliged almost
entirely to discontinue his studies, and was about to have recourse
to medical assistance. In this state of bodily and mental debility,
he inspired about three quarts of nitrous oxide. The consequences
were, an astonishing invigoration of his whole system, and the most
exquisite perceptions of delight. These were manifested by an uncommon
disposition for pleasantry and mirth, and by extraordinary muscular
power. The effects of the gas were felt without diminution for at least
thirty hours, and in a greater or less degree for more than a week.

“But the most remarkable effect was that _upon the organs of taste_.
Antecedently to taking the gas, he exhibited no peculiar choice in
the articles of food, but immediately subsequent to that event, he
_manifested a taste for such things only as were sweet_, and for
several days _ate nothing but sweet cake_. Indeed this singular taste
was carried to such excess, that he used _sugar and molasses, not
only upon his bread and butter, and lighter food, but upon his meat
and vegetables_. This he continues to do even at the present time;
and although eight weeks have elapsed since he inspired the gas, he
is still found _pouring molasses over beef, fish, poultry, potatoes,
cabbage, or whatever animal or vegetable food is placed before him_.

“His health and spirits since that time have been uniformly good, and
he attributes the restoration of his strength and mental energy to the
influence of the nitrous oxide. He is entirely regular in his mind, and
now experiences no uncommon exhilaration, but is habitually cheerful,
while before he was as habitually grave, and even to a degree gloomy.”

       *       *       *       *       *

Such is a brief and general account of the principal phenomena of
Nature, and the most remarkable deductions of science, to which
the name of Natural Magic has been applied. If those who have not
hitherto sought for instruction and amusement in the study of the
material world, shall have found a portion of either in the preceding
pages, they will not fail to extend their inquiries to other popular
departments of science, even if they are less marked with the
attributes of the marvellous. In every region of space, from the
infinitely distant recesses of the heavens to the “dark unfathomed
caves of ocean,” the Almighty has erected monuments of miraculous
grandeur, which proclaim the power, the wisdom, and the beneficence
of their Author. The inscriptions which they bear--the hand-writing
which shines upon their walls--appeal to the understanding and to
the affections, and demand the admiration and the gratitude of every
rational being. To remain willingly ignorant of these revelations of
the Divine Power is a crime next to that of rejecting the revelation
of the Divine Will. Knowledge, indeed, is at once the handmaid and the
companion of true religion. They mutually adorn and support each other;
and beyond the immediate circle of our secular duties, they are the
only objects of rational ambition. While the calm deductions of reason
regulate the ardour of Christian zeal, the warmth of a holy enthusiasm
gives a fixed brightness to the glimmering lights of knowledge.

It is one of the darkest spots in the history of man, that these noble
gifts have been so seldom combined. In the young mind alone can the two
kindred seeds be effectually sown; and among the improvements which
some of our public institutions require, we yet hope to witness a
national system of instruction, in which the volumes of Nature and of
Revelation shall be simultaneously perused.

  D. BREWSTER.

  ALLERLY, _April 24th, 1832_.


                               THE END.

J. HADDON, PRINTER, CASTLE STREET, FINSBURY.




A GENERAL DESCRIPTIVE

Catalogue

OF THE

FAMILY LIBRARY;

A SERIES OF

ORIGINAL AND SELECT WORKS.

_The Works sold separate, at_ =3s.= =6d.= _per Volume_.


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“MR. MURRAY’S Family Library.... A title, which, from the valuable
and entertaining matter the collection contains, as well as from the
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LONDON:

WILLIAM TEGG AND Co.,

85, QUEEN STREET, CHEAPSIDE.


ADDRESS.


It is a source of no inconsiderable gratification to find the
anticipations with which the FAMILY LIBRARY was commenced exceeded by
its success, and the liberal patronage bestowed on it.

The best proof of this is the fact that of many of the volumes more
than 40,000 copies have been sold in this country alone. It has been
warmly commended in the journals of Great Britain, in those of France,
Germany, Italy, and other parts of Europe.

Its general estimation is also proved by its having been reprinted in
America, and translated into most of the Continental Languages.

Upon the copyright alone of the Works of the Series, upwards of
£12,000 has been expended, and the list of Contributors embraces the
distinguished names of

  SIR WALTER SCOTT, BART.
  MR. SOUTHEY.
  MR. LOCKHART.
  REV. H. H. MILMAN.
  WASHINGTON IRVING.
  ALLAN CUNNINGHAM.
  MR. TYTLER.
  REV. J. WILLIAMS.
  MR. BARROW (of the Admiralty).
  REV. J. J. BLUNT.
  REV. E. SMEDLEY.
  REV. G. R. GLEIG.
  SIR DAVID BREWSTER.
  MR. COLERIDGE.
  MAJOR SIR F. B. HEAD.
  MR. DAVENPORT.
  MR. CROFTON CROKER.
  MR. LANDER.
  CYRUS EDMONDS.
  MR. BUCKE.
  W. E. AYTOUN.
  REV. T. CHETWODE EUSTACE.
  MR. ROSCOE.
  SIR FRANCIS PALGRAVE.

With the assistance of persons of such eminent talent was commenced the
design of supplying the deficiencies of English Literature, by a series
of Standard Works, which, with excellence of execution, should combine
the advantages of lowness of price, convenience of size and form, and
elegance of illustration.

While the moderate cost has placed the Work within the reach of all
classes of Readers, the interesting nature of the subjects, and the
popular mode of treating them, render it well suited for the perusal
of Young Persons, and calculated to stimulate in them a taste for
Literature and Science. In the beauty of its Embellishments, the FAMILY
LIBRARY has surpassed all its Contemporaries; and no pains or cost have
been spared to render each Volume as attractive externally, as it will
prove entertaining and useful on perusal. With these recommendations,
this Publication will be found to deserve a conspicuous place in every
well-selected Library; and as it may be purchased in its complete
state, or separate, _each work being complete in itself_, it will
furnish valuable Literary Presents, adapted to the means and tastes of
all classes of Purchasers.

The Volumes of which the FAMILY LIBRARY consists, may be classed under
the following heads:--

Biography.

  LIFE OF NAPOLEON.
  THE COURT AND CAMP OF BUONAPARTE.
  LIVES OF BRITISH PAINTERS, SCULPTORS, AND ARCHITECTS.
  LIFE OF COLUMBUS.
  LIVES AND ADVENTURES OF THE COMPANIONS OF COLUMBUS.
  LIFE OF NELSON.
  LIVES OF BRITISH PHYSICIANS.
  LIFE OF BRUCE.
  LIVES OF SCOTTISH WORTHIES.
  LIFE OF SIR ISAAC NEWTON.
  LIFE OF PETER THE GREAT.
  LIFE AND TIMES OF WASHINGTON.
  LIFE OF ALI PASHA.
  LIFE OF DUKE OF MARLBOROUGH.
  LIFE OF CERVANTES.
  LIFE OF CICERO.
  LIFE OF RICHARD CŒUR DE LION.
  LIFE OF MAHOMET.
  LIVES OF ENTERPRISING MEN.

History.

  HISTORY OF THE JEWS.
  HISTORY OF INDIA.
  HISTORY OF VENICE.
  HISTORY OF THE ANGLO-SAXONS.
  REFORMATION IN ENGLAND.
  TYTLER’S GENERAL HISTORY.
  DE FOE’S HISTORY OF THE PLAGUE YEAR.
  NARRATIVE OF NAPOLEON’S EXPEDITION TO RUSSIA.
  THE RUINS OF ANCIENT CITIES.
  THE MUTINY AT THE NORE.

Voyages and Travels.

  LANDER’S DISCOVERIES IN AFRICA.
  FAMILY TOUR IN HOLLAND.
  NARRATIVE OF THE MUTINY OF THE BOUNTY.
  SIX MONTHS IN THE WEST INDIES.
  EUSTACE’S CLASSICAL TOUR IN ITALY.

State Trials.

  TRIALS OF CHARLES THE FIRST AND THE REGICIDES.

Natural History and Science.

  A POPULAR NATURAL HISTORY OF INSECTS.
  LETTERS ON NATURAL MAGIC.
  DEMONOLOGY AND WITCHCRAFT.
  WESLEY’S NATURAL PHILOSOPHY.

Miscellaneous.

  SALMAGUNDI. BY WASHINGTON IRVING.
  SKETCH BOOK. BY DITTO.
  CROKER’S FAIRY LEGENDS.
  KNICKERBOCKER’S NEW YORK.
  SKETCHES OF IMPOSTURE AND CREDULITY.
  CHRONICLES OF LONDON BRIDGE.
  NARRATIVES OF PERIL AND SUFFERING.


THE

FAMILY LIBRARY.


A NEW HISTORY OF THE ANGLO-SAXONS.

_By_ SIR FRANCIS PALGRAVE. _With Illustrative Woodcuts._

This work (as the preface mentions) was intended in imitation of the
_Tales of my Grandfather_. “Let me hope,” the author says, “that
occasionally, whilst the younger branches find amusement in the tales
and adventures here brought together, some of the older folks may
not be unwilling to take this little summary in hand, as a temporary
substitute for the unmanageable folios produced by the unwearied
industry of Saville, Twysden, and Warton, and Wilkins.”


THE REFORMATION IN ENGLAND.

By the REV. J. J. BLUNT.

This is a compact but lively and entertaining sketch of the
Reformation, and the personal history of the founders of our National
Church.

The Reformation is one of the most remarkable events in our history,
whether in relation to politics or religion; for its influence was
most powerful upon both. The reading, profession, and taste of the
author have led him to regard it chiefly in the latter light; and,
therefore, brief as the sketch is, it will not be found of the nature
of an abridgment, but a continuous though succinct account of the rise,
progress, and consummation of that great revolution of the _Church of
England_.

⁂ This book is included in the list of works of the Society for
Promoting Christian Knowledge.


THE TRIALS OF CHARLES THE FIRST,

AND OF SOME OF THE REGICIDES.

_With Biographies of_ BRADSHAW, IRETON, HARRISON, _&c., and
Illustrative Notes, Legal and Historical. Portrait, Views, &c._

A clear and detailed account of the most remarkable and important of
English _Causes Célèbres_, with a narrative of the distinguishing
events of that interesting period of our history.


HISTORY OF THE EXPEDITION TO RUSSIA UNDERTAKEN BY THE EMPEROR NAPOLEON.

By GENERAL COUNT PHILIP DE SEGUR. 2 Vols.

The established interest created by Count Segur’s history renders any
commendation vain--any anticipation of its contents of no value. When
those recollections of the most disastrous campaign ever undertaken
were first published, they were charged with exaggeration, if not
falsehood; but a severe scrutiny has shown that, with the exception
of a few unimportant errors, every statement in this extraordinary
production is entitled to public confidence. The translation made
for the Family Library exhibits evidence of the utmost care, and the
misstatements into which the author inadvertently fell are corrected by
the translator.


THE

LIFE OF JOHN, DUKE OF MARLBORO’.

By CHARLES BUCKE.

Editorial ingenuity, and economy in printing, have reduced the
varied annals of the great Marlborough within the grasp of moderate
literary industry. The editor has drawn a fair and truthful picture
of the martial Duke, lauding his political and public virtues without
concealing those blemishes that his warmest advocates confess to
be equivocal. When the balance betwixt good and evil is struck,
Marlborough stands out in bold relief in the picture of history; and
had his brilliant victories been followed by firm and honest treaties,
their effects, like those of Waterloo, would have been felt in the
happiness of the British dominions.


THE LIFE AND WRITINGS OF MIGUEL DE CERVANTES SAAVEDRA.

_With Literary and Historical Illustrations by_ THOS. ROSCOE, Esq.

It is not strange that the writings of Cervantes, with the exception
of Don Quixote, should have so long remained unknown, since it was
generally asserted that “the Spaniards had but one good book, that
one which had made all the others ridiculous.” The _chef-d’œuvre_ is
translated into every language of Europe, while the same author’s
plays and novels are sealed against all but Spanish scholars; and his
chivalrous life, previous to this publication, buried in oblivion to
which the anarchy of Spain had consigned it. Cervantes flourished in
the reign of Philip II., and was contemporary with Lope de Vega.


THE LIFE OF NELSON.

By ROBERT SOUTHEY, Esq., LL.D., Poet Laureate, &c.

_With numerous Woodcuts from Designs by_ GEORGE CRUIKSHANK, _engraved
by_ THOMPSON _and_ WILLIAMS.

In order to promote the wishes and intention of the author, and to give
the work the widest circulation, it has been printed in its present
form, at _one-third of the original price_, with embellishments by the
most talented artists.

 “Many Lives of Nelson have been written, but one was yet wanting,
 clear and concise enough to become a manual for the young sailor,
 which he may carry about with him till he has treasured up the example
 in his memory and in his heart.”--_Author’s Preface._

 “A work which, as long as the English language is understood, will be
 regarded as one of the finest monuments that genius ever raised to
 valour.”--_Monthly Review._


THE LIFE OF MAHOMET,

FOUNDER OF THE RELIGION OF ISLAM, AND OF THE EMPIRE OF THE SARACENS.

By REV. SAMUEL GREEN.

With the exception of the religion of the Gospel, that of Mahomet has
produced the greatest revolution recorded in history, and effected the
greatest changes in the state of the civilized world; its history
and character, therefore, become an object of curiosity with every
enlightened mind. Considered as part of the general annals of the
world, unconnected with religion, it furnishes most interesting records
of the human race; but viewed as part of the chain of predicted events,
having a direct reference to the Christian Church, it urges a stronger
claim to our attention. The events of Mahomet’s life are to be found
in works inaccessible from their costliness, discouraging from their
bulk, and sometimes written in Eastern characters. This volume is a
compilation from the most authentic.


JOURNAL

OF AN EXPEDITION TO EXPLORE THE COURSE AND TERMINATION OF THE NIGER.

By RICHARD and JOHN LANDER.

_With Portraits, Engravings, and a Map, showing the course of the
Niger._

With slight encouragement from the Colonial Office, these young men set
out on an enterprise which in all previous instances had led to death;
and all who knew the nature of the climate, and the hardships they
must encounter, predicted that the only news their countrymen would
ever receive concerning them, would be some obscure rumour of their
destruction. The narrative shows how often such predictions were on
the point of being verified. There is scarcely a misery to be endured
by human nature that these young men have not encountered; they have
been frequently on the brink of death--they have been imprisoned--they
have been sold as slaves--they have been plundered, and obliged to swim
for their lives, not sure, in the end, that they were not swimming
into greater danger--and, to crown the whole, they have been brutally
treated and nearly sacrificed to the cupidity and revenge of savages
by one of their own countrymen. In spite of all these obstacles, by
means of patience and perseverance, by enthusiasm and resignation, by
courage and long-suffering, they finally triumphed over every species
of resistance, and, what is more, completely gained their object.

The result of Captain Clapperton’s discoveries was a very shrewd guess
that the Niger flowed westward, and into the Bight of Benin. With the
view of ascertaining this, the Landers were set down at the same point
of the coast of Guinea where the former expedition had commenced.


THE LIFE OF MARCUS TULLIUS CICERO.

By J. F. HOLLINGS.

The name of Cicero himself--the universal admiration of his genius--the
era in which he flourished--and the part he enacted, bring his memoirs
within the circle of subjects suited to domestic education. His Life,
by Middleton, is more acceptable to the learned than the learner, and
this conclusion has led to this epitome, in which the text contains the
uninterrupted personal memoir of the philosopher in a popular form;
while such information as belongs more distinctively to the department
of ancient literature is conveyed by means of notes and references.


SIX MONTHS IN THE WEST INDIES.

By HENRY NELSON COLERIDGE, M.A.

This little work, which has already received public approbation, is
calculated to amuse in no ordinary degree, for the descriptions of
scenery are vivid, the pictures of society graphic, and the adventures
and anecdotes interesting and varied.


LIVES

OF THE MOST EMINENT BRITISH PAINTERS, SCULPTORS, AND ARCHITECTS.

By ALLAN CUNNINGHAM.

_6 vols., with Portraits of Thirty-two of the most distinguished
British Artists, &c._

The author has collected in six small volumes the History of Art in
England, and the Lives, Characters, and Works of its Professors,--the
materials for which were previously scattered through many volumes.
On this account, these biographies have been considered a valuable
acquisition to literature; and although the critical observations will
render them valuable to the student, yet, being free from the dry
technicalities of virtù, and abounding with personal anecdote, they are
not less alluring to the ordinary reader.

The annals of Art, and the lives of its followers, though deficient
in the spirit-stirring incidents of the warrior and the politician,
possess an interest not less attractive. The labours and struggles
of genius, the success of perseverance, and the inutility of natural
talent separated from prudence, as exemplified in these biographies,
will afford a useful moral lesson, at the same time that the perusal of
the stories of such lives is a source of pleasure and entertainment.


THE HISTORY OF THE JEWS.

By REV. H. H. MILMAN. Complete in 3 vols.

_With Original Maps and Woodcuts._

With the exception of Josephus, we have no historian of the Jews, and
he lived at a period too remote and too limited to enable him to do
justice to his subject. It is true, many events have been narrated
by Rollin, and the authors of the Universal History, and noticed
by commentators,--but a narrative at once Christian and liberal in
its tone, spirited and elegant in its language, and depicting with
something like kindred enthusiasm and eloquence, the manners, wars,
religion, and policy of the most extraordinary of nations, was still
wanting.

The object of the present work is strictly historical,--yet it affords
elucidation of many obscure passages in the Old Testament; avails
itself of the casual evidence of heathen writers; and throws new light
on the manners and customs of the “Unchanging East,” by references to
the ablest modern travellers.


THE NATURAL HISTORY OF INSECTS.

_With very numerous Woodcuts. 2 vols._

The study of Natural History is at all times pleasing and instructive;
the object on this occasion has been to render it doubly captivating
by a plain and simple style, and by the numerous wood engravings. The
extravagant price of books of Natural History has deterred many, and it
is no exaggeration to assert that the information and embellishments
contained in these volumes could hardly be purchased in any other form
at a cost of less than several pounds.


COMPENDIUM OF NATURAL PHILOSOPHY:

A SURVEY OF THE WISDOM OF GOD IN THE CREATION.

By JOHN WESLEY. A New Edition, by ROBERT MUDIE. 3 Vols.

John Wesley’s name is a guarantee for the moral rectitude of the
original volumes, as well as the full information which they contained
at first publication; but since that time the progress of natural
science has been greater than during the whole previous period
of human history. Following Wesley’s arrangement, the editor has
incorporated the most recent discoveries, adding many new facts to
those of Baron Cuvier: he has pursued the history of invertebrated
animals down to the very verge of animal existence, and annexed a
full account of the vegetable kingdom. The re-edited work, therefore,
is not only introductory on detached portions of nature to students,
but recapitulatory to such as have already consulted the details. It
may not be immaterial to remark that, while controverted points are
studiously avoided, the very latest discoveries are introduced, and
the language employed is free from that technicality which may gratify
pedantry with out promoting knowledge.


THE LIFE OF ALI PASHA OF TEPELENI

VIZIER OF EPIRUS.

By R. A. DAVENPORT.

It is a common error to imagine that a greater number of individuals
rise in England than in other countries; more, certainly, attain wealth
and respectability under free than despotic governments; but it is
under the latter only that the very humblest and most illiterate, if
possessed of courage and cunning, may approach to the steps of the
throne itself. Of the numerous examples which Turkish history affords,
none ran a more celebrated career than Ali Pasha. Rendering himself
independent by a series of rebellions, his throne was supported by the
blood of thousands; yet, notwithstanding the means by which he acquired
power, Napoleon treated with him,--Lord Byron was his guest,--and
England accepted his friendship. Turkish history, being a record of the
indulgence of the worst passions of human nature, is always a terrible
romance, but the life of Ali Pasha exceeds in guilt and horror the
most infamous periods of Ottoman history. The great tragedy in which he
performed so principal a part, was concluded by his own assassination
in the throne-room of his palace, in a manner almost too merciful for
such a ferocious monster.


THE HISTORY OF BRITISH INDIA.

By the REV. G. R. GLEIG, F.R.S. 4 Vols.

_With a Map and 10 Engravings._

A History of India in a portable form, and familiar style, having been
considered a desideratum, the present work was undertaken. It commences
with the early annals and first civilization of the Hindoos, traces the
progress and decline of the Mahometan power, and brings the history of
the success of the British arms down to the permanent establishment of
the India Company, and the foundation of that stupendous Empire. It is
among the annals of the East that the real _Romance of History_ must
be sought. In the variety of marvellous incidents, the unexpected turn
of events, the sudden alternation of fortune, we might fancy we were
reading an Oriental fable--a tale from the Arabian Nights, rather than
sober history.


SKETCHES FROM THE HISTORY OF VENICE.

_With eight Views after Prout, twenty-nine Cuts after_ TITIAN, _Maps,
etc._

Few can explore for themselves the treasures of the Italian Chronicles.
The author of this work has laid open their stores for the benefit of
English readers,--gleaning from them characteristic incidents, amusing
stories and anecdotes; while he has sustained all the dignity of
historical research.

The writer has avoided the mistakes into which mere compilers fall;--he
has not sunk into a mere annalist, transcribing a dry register of
facts, but he either passes over entirely, or touches very slightly,
events of minor importance, and reserves himself for those more
momentous and interesting transactions which require to be more fully
displayed. The beauty of style in which these volumes are written
has attracted general notice, and the applause of the most competent
judges,--in this respect, indeed, they yield to no work of the series.


LETTERS ON DEMONOLOGY AND WITCHCRAFT.

By SIR WALTER SCOTT, BART.

No subject could have been better adapted to the lamented author of
“Waverley” than “the history of that dark chapter of human nature” to
which this volume is devoted. Sir Walter has given sufficient evidence
in his novels and romances of his acquaintance with the superstitions
of our own and remoter times. In this volume he has laid open the
stores of his memory and reading, has condensed and elucidated the
subject; in many cases explaining by natural causes occurrences
supposed to be supernatural.


LETTERS ON NATURAL MAGIC.

ADDRESSED TO SIR WALTER SCOTT.

By SIR DAVID BREWSTER, K.G.H.

_A New Edition, Illustrated with upwards of 80 Woodcuts._

The author of this volume passes under review “the principal phenomena
of nature and the leading constructions of art which bear the impress
of a supernatural character,” and more especially “those singular
illusions of sense by which the most perfect organs either fail to
perform their functions or perform them faithlessly, and where the
efforts and the creations of the mind predominate over the direct
perceptions of external nature.”

These are themes full of interest and worthy of the labour bestowed
upon them by the philosophic author. It is lamentable to think how
many minds rest contented with the most unphilosophical apology for
ignorance, by designating the acts they do not examine, wonders or
mysteries,--while to the mass of men, such acts are inexplicable,
except on some theory of superhuman agency, as absurd as it is
erroneous. The Letters of Sir David Brewster will disabuse both
classes. To the first, he furnishes philosophical data for explaining
many hitherto puzzling appearances--to the last, he supplies the means
of escape from absurdities calculated to retain them in mental slavery.

The eye and the ear are of course the great organs of deception,
and accordingly optical illusions occupy a considerable portion of
the volume. The illusions depending on the ear succeed, and after
these, we are treated with amusing descriptions of feats of strength,
of mechanical automata, and of some of the more popular wonders of
chemistry. Under each of these divisions, anecdotes of the most
interesting kind illustrate the author’s explanations, and no subject,
in itself grave and important, was ever on the whole treated in a more
amusing manner.


LIFE AND TIMES OF WASHINGTON.

By CYRUS R. EDMONDS. 2 Vols.

As the foundation of the American Republic is attributable to British
error, its history is identified with our own. Those who have related
the events of that memorable period, and drawn the character of
the patriot-general, living too near the epoch, were dazzled, and
discovered only the beauty of republican principles. Written when
party-feeling had died away, and limited monarchy allowed to vindicate
its superiority, Mr. Edmonds’s Life of Washington is free from that
nationality which disfigures biography, and fearlessly defends British
institutions against the advocates of democracy. The more voluminous
memoirs of the virtuous republican chief abound with American
prejudices; these volumes are English both in style and sentiment.


THE LIFE OF NAPOLEON BUONAPARTE.

_With 15 Engravings on Steel and Wood, by_ FINDEN _and_ THOMPSON; _the
Woodcuts from Designs by_ GEO. CRUIKSHANK.

The fact that since the publication of this work, SEVEN-AND-TWENTY
THOUSAND copies have been disposed of in this country, beside various
editions in America,--will speak more in its favour than the most
artful and high-flown praise. It is an epitome of all that has been
_proved_ to be true concerning the career of the most extraordinary
man of the last thousand years. We possessed no previous epitome of
his history; and notwithstanding the smallness of space into which it
is compressed, the narrative is clear. The Life of Napoleon, doubly
interesting when relieved of the tediousness of useless detail, has
never been better told. Volumes so rich in information will be devoured
by youth, and are worthy to be consulted by the maturest reader.

The work is written with fairness and impartiality, free from
party-spirit, and the author has interwoven with his narrative all the
new illustrations and anecdotes furnished by Bourrienne and the other
fast-following memoirs of the French press.


THE RUINS OF ANCIENT CITIES.

By CHARLES BUCKE. 2 Vols. _Illustrated._

Cities, like men, flourish and decay, and each possess their annals.
The poetic conception of personifying these broken records of natural
grandeur originated with the editor himself; but, in carrying out his
design, he acknowledges Rollin as his guide. This elegant and accurate
writer confesses that he does not hesitate to rifle the cabinets of
others to enrich his own; that he often transcribed without quoting,
and introduced solid reflections borrowed from the sterling works of
others. This compilation is also a beautiful bead-roll, the precious
production of many minds: it is a fair fabric of costly materials
raised by a literary architect, whose industry, experience, and
candour, are already acknowledged by the public.


SALMAGUNDI;

OR, THE WHIM-WHAMS AND OPINIONS OF LAUNCELOT LANGSTAFF, ESQ.

_With numerous Cuts by_ GEORGE CRUIKSHANK.

The earliest paintings of the greatest masters sometimes differ
considerably from those of their maturer years, and not unfrequently
surpass them in brilliancy and freshness. If the Salmagundi Papers be
compared with the subsequent works of the same author, they will not be
found inferior in originality, vivacity, or virtuous tendency. While
satire is the adopted weapon of chastisement, it wounds the vicious
only. “We have,” say the authors, “no fear of the censures of the
wise, good, or fair, for they will ever be sacred from our attacks.
We reverence the wise, love the good, and adore the fair: we declare
ourselves champions in their cause--in the cause of morality--and we
throw our gauntlet to all the world besides.”


THE LIFE OF PETER THE GREAT.

_By_ JOHN BARROW, Esq., F.R.S., _Author of the “Eventful History of the
Mutiny of the Bounty.” With Portrait._

The author of this Biographical Memoir has arranged the scattered
fragments of Histories, Lives, Anecdotes, and Notices, manuscript or
print, of one of the most extraordinary characters that ever appeared
in the world, in any age or country;--being full of contradictions, yet
consistent; a promoter of literature, arts, and sciences, yet without
education; “he gave a polish,” says Voltaire, “to his nation, and was
himself a savage;” he taught his people the art of war, of which he was
himself ignorant; from the first glance of a cock-boat, five hundred
miles from the sea, he became an expert ship-builder, created a fleet,
partly constructed with his own hands, made himself an expert sailor, a
skilful pilot, a great captain: in short, he changed the manners, the
habits, the laws of the people, and the very face of the country.


SKETCHES OF IMPOSTURE, DECEPTION, AND CREDULITY.

Credulity is so comprehensive a term, that greater difficulties are
encountered in selecting than multiplying examples. These “Sketches”
take an extensive range over the Pagan superstitions--tell of pretended
Messiahs, false prophets, and mock miracles--describe Hindoo and other
Oriental deceptions in religious worship--relate of royal impostors,
military stratagems, literary cheats, and commercial bubbles--unfold
the mysteries of thefts and forgeries, and conclude with an interesting
account of the delusions of alchemy and medical frauds. The work may
be considered as a supplement to Scott’s “Letters on Demonology,” and
Brewster’s on “Natural Magic.”


THE CHRONICLES OF LONDON BRIDGE.

By AN ANTIQUARY. _Illustrated._

This is an original work, and the reader will at once perceive that
the “Nominis umbra” of “An Antiquary” conceals a mind of no ordinary
mould--the possessor of no common store of erudition. A velvet cushion
has been the nucleus of the History of the Reformed Church--a library
chair that of a history of literature. In this volume London Bridge is
selected as the bond that is to bind, the avenue that is to lead from,
ancient to modern London. Much valuable civic history and legend is
here adorned with language, precise, classical, and nervous; while the
illustrations, fifty-six in number, present more perfect reminiscences
of society and manners in the olden time than the most technical and
laboured descriptions.


THE LIFE OF ALEXANDER THE GREAT.

By the REV. JOHN WILLIAMS, M.A.,

_Head Master of the Edinburgh Academy. Map and Woodcuts._

This volume fills a blank in the Historical Library, and furnishes a
capital school-manual. It is not confined to the mere exploits of the
Macedonian hero, but contains a masterly view of the times in which
he lived, and of the manners, customs, etc. of the Greeks, Persians,
Egyptians, Arabs, and Indians, and other nations. The whole story is
told in a manner calculated to stimulate the curiosity and rouse the
reflection of the youthful reader.


THE

SKETCH BOOK OF GEOFFRY CRAYON, ESQ.

_2 Vols._

Had Mr. Irving left no other memorial of his genius than the Sketch
Book, it would be alone sufficient to a pedestal in the Palatine
Library of the XIXth. century. Justly may he contend with the
“Enchanter of the North” in the rare quality of story-telling, for
never was a tale more pleasantly told than “_The Legend of the Sleepy
Hollow_.” Neither is there a more exquisitely beautiful or sentimental
fragment in all the heart-moving scenes drawn by that able and amiable
writer than Irving’s sketch of “_The Broken Heart_.”


VOYAGES AND DISCOVERIES OF

THE COMPANIONS OF COLUMBUS.

By WASHINGTON IRVING. _With Illustrations._

The extraordinary actions and adventures of these men may be said to
unite romance and truth. Chivalry had left the land, and launched
upon the deep in the ships of these Spanish discoverers. Contempt
of danger, and fortitude of suffering, a passion for vain-glorious
exploit, and a bigoted zeal for the propagation of their faith, are
the characteristics of these marine heroes. The extravagant career of
the daring Ojeda, particularly his adventures along the coast of Terra
Firma, and the wild shores of Cuba--the sad story of Nicuessa--the
singular cruise of Juan Ponce de Leon, who fell upon the coast of
Florida, in his search after an imaginary fountain of youth--and above
all, the chequered fortunes of Vasco Nunez de Balboa, whose discovery
of the Pacific Ocean forms one of the most beautiful and striking
incidents in the history of the New World,--are so many examples of
knight-errantry upon the high seas. The charm of Mr. Irving’s style has
never been displayed more strikingly than in this little manual of true
romance.


THE UNIVERSAL HISTORY FROM THE CREATION OF THE WORLD.

By ALEXANDER FRASER TYTLER, LORD WOODHOUSELEE.

_6 Vols._

Perhaps few works in general literature were ever produced more
synthetically, or with more vigilant caution than “The Universal
History.” Mr. Gilpin requested his most learned and judicious friends
to criticize his MSS., and for many years they were submitted to this
wholesome ordeal. The Universal History at first appeared in the form
of Lectures, and was received with the most entire approbation of
the students. The sketch thus carefully made for oral delivery was
gradually filled up, and the picture completed in every part.

The Author’s style is terse, lucid, and nervous, and his plan not only
moral, but more instructive than any hitherto pursued in treating of
general history.


THE LIFE OF SIR ISAAC NEWTON.

By SIR DAVID BREWSTER, LL.D., F.R.S.

_Portrait and Woodcuts._

This is the only extended life of the greatest of English philosophers.
In attempting to fill up this gap in our philosophic and scientific
literature, Sir David Brewster has not only sought out, from resources
hitherto unknown, every fresh and novel particular regarding his
life, but has given the most lucid explanation of Newton’s great
discoveries--and has endeavoured to render these intelligible to all
classes of readers.


A JOURNAL OF THE PLAGUE YEAR.

By DANIEL DE FOE.

_A New Edition, with Historical Notes by_ E. W. BRAYLEY, F.S.A.

“From De Foe’s History of the Plague we may derive more information
than from all the other publications on the subject put together.
He has collected all the facts attending the rise, progress, and
termination of the malady; an accurate report of the number of deaths,
as published by authority; a faithful account of the regulations
adopted to arrest and mitigate its fury. But that which imparts life
to the whole, and forms its distinguishing feature, is its descriptive
imagery. The effects upon the affrighted minds of the inhabitants are
depicted with all the genuine pathos of nature, without any aim at
effect, but with the ease and simplicity of real life.”


A CLASSICAL TOUR THROUGH ITALY.

By the REV. T. CHETWODE EUSTACE.

_Seventh Edition. With great Additions and Translations of the various
Quotations from Ancient and Modern Authors. 3 Vols._

It was the fate of Eustace, like that of Bruce, to see his labours
rejected, and his veracity impeached; nor did these painful
insinuations originate in the chance of ignorance. His honesty was also
called in question. But truth in both instances eventually prevailed,
and the writings of both these amiable but injured travellers are
now appealed to as standard works. Eustace’s Journey is not only the
most accurate in topography, architecture, and politics, but is,
_par excellence, the classical_ tour through this land of poetry and
painting. Those tourists who would soar above Eustace, have vainly
sought to depreciate his learning. Those whose lot was cast below him,
have gathered from his rich plumage; but neither had the courage to
pass him by in silence. In this edition, which is sold at one-third the
cost of the earlier ones, the discoveries made by excavation since the
author’s, death have been introduced.


THE EVENTFUL HISTORY OF

THE MUTINY AND PIRATICAL SEIZURE OF THE BOUNTY.

By JOHN BARROW, Esq., _Secretary to the Admiralty. With Five Plates
from Original Sketches._

“The Author of this little volume has brought into one connected view
what has hitherto appeared only in detached fragments--and some of
these not generally accessible--the historical narrative of an event
which deeply interested the public at the time of its occurrence, and
from which the naval service in particular, in all its ranks, may still
draw instructive and useful lessons.

“The story in itself is replete with interest. We are taught by the
Book of Sacred History, that the disobedience of our first parents
entailed on our globe of earth a sinful and a suffering race; in
our time there has sprung up from the most abandoned of this sinful
family--from pirates, mutineers, and murderers--a little society,
which, under the precepts of that sacred volume, is characterized
by religion, morality, and innocence. The discovery of this happy
people, as unexpected as it was accidental, and all that regards their
condition and history, partake so much of the romantic, as to render
the story not ill-adapted for an epic poem.”--_Author’s Preface._


FAIRY LEGENDS

AND TRADITIONS OF THE SOUTH OF IRELAND.

By T. CROFTON CROKER. _With numerous Cuts._

Fairy Tales epitomize the customs, and manners, and superstitions of
a people in by-gone times, and are therefore valuable as auxiliary to
the interpretation of history. Mr. Croker’s Irish Legends are rich
in that racy humour that characterizes his countrymen, and appear to
have exhausted the traditionary treasures of the Emerald Isle. The
Illustrations are also redolent of Hibernian wit and genius,--they are
spirited designs, and in the happiest manner of Messrs. Brooke and
Maclise, with whose merits the public are familiar.


THE LIFE AND TIMES OF RICHARD I.

SURNAMED CŒUR-DE-LION, KING OF ENGLAND.

By WILLIAM E. AYTOUN, _Author of “Bothwell,” a Poem_.

None of our monarchs has achieved a wider fame than Cœur-de-Lion, yet
his personal history is of all others least studied or understood.
All men know that he rebelled against his father, but comparatively
few are aware of the cause. All know that he conducted a crusade, and
encountered Saladin; but few are acquainted with the extent of his
conquests, or the causes which drove him back a fugitive to Europe. No
period of the romantic ages is more interesting, or better entitled to
a close examination.


NARRATIVES OF PERIL AND SUFFERING.

By R. A. DAVENPORT. _2 Vols._

This wide field for the display of taste, talent, and general
acquaintance with the history of man in his social character, has
been occupied by Mr. Davenport, a veteran in elegant literature;
and the popularity which his selections from the children of sorrow
has acquired, is equal to that of his most successful labours. In
collecting so many tales of woe and of enterprise, the author disclaims
the mere vanity of having produced a work of amusement; he seeks
to inculcate the salutary lesson, “that there are few things that
may not be accomplished by perseverance and courage, accompanied by
self-command and presence of mind.”


THE LIFE OF BRUCE,

THE AFRICAN TRAVELLER.

By Major Sir FRANCIS B. HEAD, _Author of “Rough Notes,” &c._

Bruce’s Travels, as originally published, occupy five quarto volumes,
mixed up with Abyssinian history, and speculations on Egyptian
mythology. The author has contrived to compress into this little
volume the best parts of Bruce’s Life and voluminous and expensive
Travels, without omitting one incident of importance and interest. He
has vindicated the character of Bruce, by confronting the statements
of his accusers with the testimony of later travellers. The narrative
had been allowed universally to possess the interest of a romance,
from the graphic style in which he has described his adventures and
sufferings, and the strange people and countries which he visited: but
Major Head has secured for Bruce the credit of a trustworthy authority,
in addition to the reputation of an entertaining narrator.


THE COURT AND CAMP OF BUONAPARTE.

_With a full-length portrait of Prince Talleyrand, and other Portraits._

This volume is a suitable and indispensable companion to the Life of
Napoleon. It contains the cream “of many hundred volumes,” in the
shape of Memoirs, Lives, Narratives, Anecdotes, &c., connected with
Buonaparte, with which the press of France has for fifteen years been
teeming. It presents rapid, but vigorous sketches of the Emperor’s
Brothers, Wives, Sisters, Ministers, Marshals, and Generals; and those
who wish for competent knowledge of “_Napoleon and his Times_,” will
find no work in the English language which conveys such information in
a more concise shape or a more lively manner.


THE LIFE AND VOYAGES OF CHRISTOPHER COLUMBUS.

By WASHINGTON IRVING. _Abridged by him from his larger Work. With
Portraits, Maps, &c._

This little work has become a universal school-book in America. It
contains all that is most important in the original, in a form more
condensed, and more within the reach of the general reader; while the
story is told with the same spirit and grace as in the great work. As
a book of entertainment, it will bear comparison with any biographical
sketch of the age.


LIVES OF EMINENT BRITISH PHYSICIANS.

_With fine Portraits and Woodcuts._

The Lives of Physicians furnish a theme by no means deficient in
interest and value. From them have proceeded some of the greatest
benefactors of the human race; their history abounds in instances
of individuals, who, obscure and small, have, by the vigour of their
understanding and their perseverance, raised themselves among the
great of the land. The memoirs of Cullen, Hunter, and Baillie, afford
striking examples of talent and perseverance triumphing in the midst of
difficulties.

Of the topics discussed in the course of this volume, the most
prominent are--_The Discovery of the Circulation of the Blood_, by
Harvey. _The Sweating Sickness in the time of Edward III._ _A Sketch of
the Great Plague of London, in 1664-5._ _Jenner’s invaluable Discovery
of Vaccination._

To this edition the names of Clutterbuck, Paris, Merriman, Chambers,
and Halford, have been added.


HISTORY OF NEW YORK,

FROM THE BEGINNING OF THE WORLD TO THE END OF THE DUTCH DYNASTY.

By DIEDRICH KNICKERBOCKER. _Plates after_ CRUIKSHANK.

This is a satirical production, in which the follies of the day are
humorously depicted in the persons and costume of the ancient Dutch
colonists who founded New York. The scene is local, the application
directed to that city, to recent occurrences in the history of the
United States, and of measures of the government of the Model Republic.
The satire, however, is not personal, but aimed at human character and
conduct, and may, therefore, be generally felt.


LIVES OF INDIVIDUALS

WHO RAISED THEMSELVES FROM POVERTY TO EMINENCE OR FORTUNE.

By R. A. DAVENPORT.

The object of this work is not merely to inculcate a moral lesson to
youth, but to encourage virtue generally by creating submission to the
law of opinion. When mankind perceive meritorious exertions in every
rank rewarded, and in numerous instances crowned with success, they are
more strongly supported in their resistance to difficulties, and more
boldly encounter and conquer them. This single volume includes the most
varied memoirs; whence it will appear that industry and perseverance,
accompanied by rectitude of intention, obtain their merited reward in
every civilized nation of our globe.


HISTORY OF THE MUTINY AT SPITHEAD AND THE NORE.

By J. NEALE, Esq., Author of “Cavendish.”

_With an Inquiry into its Origin and Treatment. With a Portrait of_
RICHARD PARKER.

Resistance to authorities necessarily enlists so few abettors, that,
even when it originates in cruelty, injustice, and injury, its
correction is demanded by the voice of the nation. To this feeling must
be traced the flagrant partiality of our historians in describing the
Mutiny of the Nore, and their misrepresentation of the causes of that
calamity. Viewed at this distance of time, it is remembered as the
foundation of that splendid and perfect discipline which has ever since
pervaded and adorned the fleet, and as the cause for abolishing the
despotic practice of impressment. But from these memorable movements
legislators may receive a lesson, and learn how much more faithful
freemen are than slaves to a state in danger, and more binding the ties
of gratitude and affection than the terror of tyranny. This is the
moral reduced from the Mutiny of the Nore in the present history.


TOUR THROUGH SOUTH HOLLAND AND UP THE RHINE.

_With 10 Views, from Designs of_ LIEUT.-COL. BATTY.

It is strange that the history and condition of Holland should be so
little known, and that it till now should never have been made the
subject of a popular work. The object of this little book is not merely
to afford entertainment, but to furnish that valuable and practical
information, which will render it a desirable _guide-book_ to all who
are tempted to take a summer’s trip across Holland, up the Rhine, and
through Belgium; visiting Rotterdam, the Hague, Amsterdam, Cologne,
Coblentz, Frankfort, Brussels, and Antwerp.


THE LIVES OF SCOTTISH WORTHIES.

By PATRICK FRASER TYTLER, Esq. _3 Vols._

“Truth is strange, stranger than fiction.”--The romantic annals of
Scotland, and the characters of her ancient heroes--Wallace, Bruce, and
the like,--will go far to convert this expression into an axiom.

HADDON, BROTHERS, AND CO., PRINTERS, CASTLE STREET, FINSBURY.


       *       *       *       *       *


Transcriber’s Notes

Obvious typographical errors have been silently corrected and
hyphenation has been standardised. Other variations in spelling and
punctuation remain unchanged.

Italics are represented thus _italic_ and bold thus =bold=.