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


[Illustration:

  DR. WILLIAM KONRAD ROENTGEN. pp. 69 to 85.
  Born in Holland, 1845.
  From a photograph by Hanfstaengl, Frankfort-on-the-Main.
]


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


                             ROENTGEN RAYS

                                  AND

                               PHENOMENA

                                 OF THE

                           ANODE AND CATHODE.



                _PRINCIPLES, APPLICATIONS AND THEORIES_

                                   BY

                     EDWARD P. THOMPSON, M.E., E.E.
                      Mem. Amer. Inst. Elec. Eng.
                       Mem. Amer. Soc. Mech. Eng.
             Author of “Inventing as a Science and an Art.”


                          _CONCLUDING CHAPTER_

                                   BY

                       PROF. WILLIAM A. ANTHONY,
                    Formerly of Cornell University.
                 Past President Amer. Inst. Elec. Eng.
  Author, with Prof. Brackett of Princeton, of “Text-Book of Physics.”



                      60 Diagrams. 45 Half-Tones.



                               NEW YORK:
                        D. VAN NOSTRAND COMPANY,
                    23 MURRAY AND 27 WARREN STREET.


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




                            Copyright, 1896,
                                   BY
                          EDWARD P. THOMPSON,
                    Temple Court Building, New York.




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




                                PREFACE.

                                -------

IN addition to the illustrated feature for exhibiting the nature and
practical application of X-rays, and for simplifying the descriptions,
the book involves the disclosure of the facts and principles relating to
the phenomena occurring between and around charged electrodes, separated
by different gaseous media at various pressures. The specific aim is the
treatment of the radiant energy developed within and from a discharge
tube, the only source of X-rays.

Having always admired the plan adopted by German investigators in
publishing accounts of their experiments by means of numbered paragraphs
containing cross-references and sketches, the author has likewise
treated the investigations of a large number of physicists. The
cross-references are indicated by the section sign (§). By reference,
the _analogy_, _contrast_, or _suggestiveness_ may be meditated upon.
All knowledge of modern physics is based upon experiments as the
original source. Inasmuch as many years may be expected to elapse before
the innumerable peculiarities of the electrical discharge will be
reduced to a pure science, and also in order that the contents of the
book may be of value in the future as well as at present, the
characteristic experiments of electricians and scientists are described,
in general, by reference to their object, the apparatus used, the
result, the inferences of the experimenter, and the observations of
cotemporaneous or later physicists, together with a presentation here
and there of theoretical matters and allusion to practical applications.

The classes of reader to which the book is adapted may best be known, of
course, after perusal, but some advance intimation of the kind that the
author had in view may be desired. Let it be known that, first, the
student and those generally interested in science ought to be able to
comprehend the subject-matter, because experiments are described, which
are always the simplest means (_e.g._, in a popular lecture) for
explaining the wonders of any given scientific principles or facts. Thus
did Crookes, Tyndall, Thomson (both Kelvin and J. J.), Hertz, etc.,
disseminate knowledge—by describing their researches and reasoning
thereon.

In view of the tremendous amount of experimenting which has been
carried on during the past few years in connection with the electric
discharge, it was difficult to determine just how far back to begin
(without starting at the very beginning), so that the student and
general reader, whose object is to become acquainted especially with
the properties of cathode and X-rays, might better understand them.
The author realized that it was necessary to go back further and
further in this department of science, and he could not easily stop
until he had reached certain investigations of Faraday, Davy, Page,
and others, which are briefly noticed in an introductory sense. Take,
for example, the inaction of the magnet upon X-rays in open air. § 79.
Of course, it would be of interest for the student to know about
Lenard’s investigations relating to the action of the magnet upon
cathode rays inside of the observing tube. § 72_a_. It would follow,
further, that he would desire to know about Crookes’ experiment
relating to the attraction of the magnet upon cathode rays within the
tube. § 59. In order that he might not infer that Crookes was the
first to investigate the action of the magnet upon the discharge, it
was evident that the book could be made of greater value by relating
the experiments of Prof. J. J. Thomson as to the discharge across and
along the lines of magnetic force, § 31, and Plücker’s experiment on
the action of the magnet upon the cathode column of light. § 30. The
interest became increased, instead of diminished, by noting De la
Rive’s experiment on the rotation of the luminous effect of the
discharge by means of the magnet. § 29. Being now quite impossible to
stop, Davy’s electric arc and magnetic action upon the same had to be
alluded to, at least briefly. § 28. On the other hand, the very
earliest experiments with the discharge in rarefied air are not
described—occurring as remotely as the eighteenth century—so ably
treated of in Park Benjamin’s work. Those facts that have some mutual
bearing are brought forward to serve as stepping-stones to the
investigation of cathode and X-rays.

Secondly, the author often imagined that he was writing in behalf of the
surgeon and physician and those who intend to experiment, especially
when he found in his investigations of recent publications descriptions
in detail of the electrical apparatus employed in experimenting with
X-rays. He improved the opportunity of repeating the statements of the
difficulties, and how they were overcome; also, the precautions
necessary to be taken, and, besides, the kind of discharge tubes and
apparatus best adapted for particular kinds of experiments. The chapter
on applications in diagnosis and anatomy, etc., is of especial interest
to physicians.

Thirdly, as the discovery of the Roentgen rays has established a new
department of photography, those who are interested in this art may be
benefited by the results and suggestions disclosed in connection with
photographic plates, time of exposure, adjuncts for best results,
precautions for obtaining sharp shadows, and steps of the process, from
beginning to end, for carrying on the operation.

Fourthly, expert physicists and electricians, professors, etc., need
something that the above classes do not, and this is the reason why the
author has not assumed the burden of carrying any line of thought or
theory from the beginning to the end of the treatise, nor has he made
the book in any way a personal matter by criticising experiments, nor
even by favoring the views of one over the other, unless it is in an
exceptional case here and there; but in each instance the investigator’s
name is given, and that of the publication in which the account may be
found, so that the scientist may refer thereto to test the correctness
of the author’s version of the matter, or to learn the nature of the
minute details and circumstances.

The author suggests that the study of the phenomena of the discharge
tube would not be amiss in scientific schools and colleges. He argues
that in view of all experimenters in this line having been made
enthusiastic and fascinated by reason of (1) the beautiful effects, (2)
the field being always open to new discoveries, (3) the direct practical
and theoretical bearing of the peculiar actions upon other departments
of electricity, light, heat, and magnetism, (4) the pleasure in
attempting to obtain results reported by others, and especially the
large amount of valuable theoretical and practical instruction resulting
therefrom, by repeating the experiments or studying them, and (5) the
possible applications of the discharge tube in connection with electric
lighting and in the new department of sciagraphy by X-rays, and for
other good and valuable considerations—it follows that students who have
been through or who are studying a text-book of physics and electricity
would be greatly benefited by a course in the discharge-tube phenomena.

In view of the large amount of dictation necessary in order to complete
the work in such a short period, and in order that the subject-matter
might involve the treatment of the latest work of the French and German
as well as of the English and American, and inasmuch as the journals of
the latter did not always contain complete translations and, for better
service in behalf of the readers, the authorship was shared with others,
and, therefore, much credit is due to Prof. Anthony for final chapter,
to Mr. Louis M. Pignolet for assistance in connection with French
periodicals and academy papers (§ § 63_a_, 84, 99, 101_a_, 103_a_,
112_a_, 124_a_, 128, _at end_, 139_a_, 154, 155, 156, 157, 158, and
159); to Mr. N. D. C. Hodges, formerly editor and proprietor of
_Science_, who obtained some pertinent accounts, (§ 97_a_, 97_b_, 99_A_,
_B_, _C_, _D_, to 99_T_, inclusive) by investigations of recent
literature at the Astor Library, New York; and also to Mr. Ludwig
Gutmann (Member American Institute of Electrical Engineers) for a few
translations from the German.

Credit is given in each instance to all societies and publications by
naming them in the respective paragraphs herein. In nearly every case
the author prepared his material from original articles and papers
contributed by the investigators to the societies or periodicals.

The author has prepared himself to withstand, with about half as much
patience as he expects will be required, all criticisms based upon
disappointments which may be experienced by the true, or the alleged
true, first discoverer of any particular property of the electric
discharge not duly credited. He has been particular in presenting
knowledge as to physical facts and principles, but not equally, perhaps,
as to the originator of the experiment, or as to the actual first
discoverer, for the simple reason that the book is in no sense a history
not a biography. Where the paragraph has been headed, for example,
“Swinton’s Experiment,” it means that that party (according to the
article purporting to be written by him) made that experiment. Some one
else may have made exactly the same experiment previously, yet the
instruction is equally as valuable as though the researches of the first
discoverer had been related. On the other hand, the author has never had
any intention of giving credit to the wrong party. The dates in the
captions indicate the general chronological order in behalf of those
thus interested. With this explanation, it is thought that the claimants
will be much more lenient in their criticisms concerning priority of
discovery. While the developments have generally followed each other
historically, as well as appropriately for the purpose of instruction,
yet now and then it was preferable to place the description of a
comparatively recent experiment in conjunction with some description of
an experiment made at a much earlier date. For this reason, also, the
book is not of a chronological nature. The subject-matter, as usual, is
divided into chapters, but the sections are to be considered as
subordinate chapters, having different shades of meaning, and the one
not necessarily bearing a direct relation to the contents of its
neighbor, but as, in a novel or a treatise on geometry, having its
important part to play in conjunction with some later or preceding
section.

                                                     EDWARD P. THOMPSON.

    TEMPLE COURT BUILDING, NEW YORK,
              August, 1896.


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




                               CONTENTS.


                                -------


                               CHAPTER I.


       § 1. Secondary Current by Induction. No             FARADAY
              Increased E. M. F.

         2. Electric Spark and Increased E. M. F.             PAGE
              by Induced Current.

         3. Spark in Secondary Increased by                 FIZEAU
              Condenser in Primary.

         4. Atmosphere around an Incandescent Live      VINCINTINI
              Wire.

         5. Magnetizing Radiations from an Electric          HENRY
              Spark.

         6. Arcing Metals at Low Voltage.                  FARADAY

         7. Non-arcing Metals at High Voltage.               WURTS
              Practical Application.

         8. Duration of Spark Measured.                 WHEATSTONE

      8_a_. Discharge—Intermittent, Constant, and        FEDDERSEN
              Oscillatory—by Variation of
              Resistance.

         9. Musical Note by Discharge with Small           FARADAY
              Ball Electrodes. Invisible Discharge.

      9_a_. Pitch of Sound Changed by Approach of      FARADAY and
              Conductor Connected to Earth.                  MAYER

        10. Brush Discharge. Color. Striæ. Nitrogen        FARADAY
              Best Transmitter of a Spark, and its
              Practical Bearing in Atmospheric
              Lightning. Cathode Brushes in
              Different Gases.

        11. Glow by Discharge. Glow Changed to             FARADAY
              Spark. Motion of Air. Apparent
              Continuous Discharge during Glow.

        12. Spark. Solids Perforated.                       LULLIN

        13. Spark. Glass Perforated. Holes Close              FAGE
              Together. Practical Application for
              Porous Glass.

     14 and Spark. Penetrating Power. Conducting    KNOCHENHAURER,
     14_a_.   Power of Gas. Relation of E. M. F. to     BOLTZMANN,
              Pressure of Gases. Discharge through         THOMSON
              Hydrogen Vacuum Continued with Less        (KELVIN),
              Current than that Required to Start         MAXWELL,
              it.                                          VARLEY,
                                                       HARRIS, and
                                                            MASSON

        15. Dust Particles or Rust on the                   GORDON
              Electrodes Hasten Discharge.

        16. Where the Distance is Greater, the             THOMSON
              Dielectric Strength is Smaller, Both        (KELVIN)
              Distances Being Minute.

        17. Discharge through Gases under Very High      CAILLETET
              Pressures. Increased Dielectric
              Strength.

        18. Discharges in Different Chemical Gases         FARADAY
              Variably Resisted.

        19. Gas as a Conductor. Molecule for        THOMSON, J. J.
              Molecule, its Conductivity Greater
              than that for Gases.

        20. Relation of Light to Electricity. The       BOLTZMANN,
              Square Root of the Dielectric                GIBSON,
              Capacity Equal to the Refractive            BARCLAY,
              Index.                                HOPKINSON, and
                                                         GLADSTONE

        21. Hermetically Sealed Discharge Tubes        PLÜCKER and
              with Platinum Leading-in Wires.             GEISSLER

        22. Luminosity of Discharge Tubes Produced        GEISSLER
              by Rubbing. Increased by Low
              Temperature.

        23. Different Vacua Needed for Luminosity       ALVERGNIAT
              by Friction and by Discharge.

        24. Phenomena of Discharge around the Edges      STEINMETZ
              of an Insulating Sheet.

        25. Highest Possible Vacuum Considered as a         MORGAN
              Non-conductor.

        26. Constant Potential at the Terminals of   DE LA RUE and
              a Discharge Tube.                             MÜLLER

     26_a_. Polarity of Discharge-tube Terminals in    KLINGENBERG
              Secondary of Ruhmkorff Coil.
              Mathematical Deductions.

        27. Pressure in Discharge Tube Produced by     KINNERSLEY,
              a Spark.                                 HARRIS, and
                                                             RIESS


                              CHAPTER II.

        28. Actions of Magnetism upon the Arc and            DAVY,
              Flame.                                BANCALARI, and
                                                              QUET

        29. Rotation of Luminous Discharge by a         DE LA RIVE
              Magnet. Application in Explaining
              Aurora Borealis.

        30. Action of Magnet on the Cathode Light.     PLÜCKER and
              Relations Different according to the         HITTORF
              Position Relatively to the Magnetic
              Lines of Force.

        31. Discharge Retarded Across, and          THOMSON, J. J.
              Accelerated Along, the Lines of
              Magnetic Force.

        32. Resistance of Luminosity of the         THOMSON, J. J.
              Discharge Afforded by a Thin
              Diaphragm.

        33. Forcing Effect of the Striæ at a              SOLOMONS
              Perforated Diaphragm.


                              CHAPTER III.

        34. Electric Images.                                 RIESS

        35. Electrographs on Photographic Plate by     SANFORD and
              Discharge.                                     MCKAY

        36. Positive and Negative Dust Pictures        LICHTENBERG
              upon Lines Drawn by Electrodes.

     36_a_. Photo-electric Dust Figures.                    HAMMER

     36_b_. Dust Portrait.                                  HAMMER

        37. Electrical Images by Discharge                 KARSTEN
              Developed by Condensed Moisture.

     37_a_. MAGNETOGRAPHS.                                   MCKAY

        38. Bas-relief Facsimiles by Electric          PILTCHIKOFF
              Discharge.

        39. Distillation of Liquids by Discharge.           GERNEZ

        40. Striæ. Black Prints on Walls of Tube.    DE LA RUE and
                                                            MÜLLER


                              CHAPTER IV.

        41. Discharge Tube in Primary Current.             GASSIOT
              Striæ. Least E. M. F. Required.

        42. Current Interrupted Inside of Discharge    POGGENDORFF
              Tube instead of Outside.

        43. Source of Striæ at the Anode. Color      DE LA RUE and
              Changed by Change of Current.                 MÜLLER

        44. Dark Bands by Small Discharges                SOLOMONS
              Disappear on Increase of Current, and
              Appear Again by Further Increase.

        45. Motion of Striæ. Method of Obtaining      SPOTTISWOODE
              Motion when Desired and of Stopping
              the Same.

        46. Motion of Striæ Checked at the Cathode. THOMSON, J. J.
              Tube, 50 ft. Long. The Anode the
              Starting-point.

        47. Electrolysis in Discharge Tube.         THOMSON, J. J.

        48. Heat Striæ without Luminous Striæ.       DE LA RUE and
                                                            MÜLLER

        49. Sensitive State. Method of Obtaining.     SPOTTISWOODE
              Telephone Used to Prove                  and MOULTON
              Intermissions.

     49_a_. Cause of Sensitive State Detected by      SPOTTISWOODE
              Telephone.                               and MOULTON

        50. Sensitive State Illustrated by a        REITLINGER and
              Flexible Conductor within the             URBANITZKY
              Discharge Tube.

        51. System of Operating Discharge Tubes.             TESLA
              Excessively High Potential and
              Enormous Frequency.

        52. Discharge-tube Phenomena by                      MOORE
              Self-induced Currents.


                               CHAPTER V.

        53. Dark Space around the Cathode.                 CROOKES

        54. Relation of Vacuum to Phosphorescence.         CROOKES

        55. Phosphorescence of Objects within              CROOKES
              Discharge Tube.

        56. Darkness and Luminosity in the Arms of         CROOKES
              a V Tube.

        57. Cathode Rays Rectilinear within the            CROOKES
              Discharge Tube.

        58. Shadow Cast within the Discharge Tube.         CROOKES

     58_a_. Mechanical Force of Cathode Rays. Wheel        CROOKES
              Caused to Rotate.

        59. Action of Magnet upon Cathode Rays in          CROOKES
              Discharge Tube.

        60. Mutual Repulsion of Cathode Rays in            CROOKES
              Discharge Tube.

        61. Heat of Phosphorescent Spot.                   CROOKES

     61_a_. Theoretical Considerations of Thomson
              (Kelvin).

     61_b_, Velocity of Cathode Rays.               THOMSON, J. J.
       page
        46.

     61_b_, Cathode Rays Charged with Negative              PERRIN
       page   Electricity.
        47.

     61_c_, Zeugen’s Photograph of Mt. Blanc Not
              Due to Cathode Rays.

        62. Phosphorescence of Particular Chemicals      GOLDSTEIN
              by Cathode Rays.

        63. Spectrum of _Post_-phosphorescence of             KIRN
              Discharge Tube Compared with that of
              Red-hot Metals.

     63_a_. Chemical Action on Photographic Plate          DE METZ
              by Cathode Rays Inside of Discharge
              Tube.

     63_b_. The Passage of Cathode Rays through              HERTZ
              Thin Metal Plates within the
              Discharge Tube (no. § 64).


                               CHAPTER VI

      § 65, Cathode Rays Outside of the Discharge           LENARD
     top of   Tube whose Exit is an Aluminum
       page   Window. A Glow Outside of the Window.
        53.

       65., Properties of Cathode Rays in Open Air.         LENARD
     end of
       page
        53.

        66. Phosphorescence by Cathode Rays Outside         LENARD
              of the Discharge Tube.

     66_a_. Transmission Tested by Phosphorescence.

        67. The Aluminum Window a Diffuser of               LENARD
              Cathode Rays.

        68. Transmission of External Cathode Rays           LENARD
              through Aluminum and Thinly Blown
              Glass.

        69. Propagation of External Cathode Rays.           LENARD
              Turbidity of Air.

        70. Photographic Action by External Cathode         LENARD
              Rays and at Points beyond the Glow.
              No Other Chemical Power Probable.
              Shadows of Objects by Light and by
              External Cathode Rays Compared. No
              Heat Produced by External Cathode
              Rays.

        71. External Cathode Rays and the Electric          LENARD
              Spark Distinguished. Aluminum Window
              Not a Secondary Cathode.

        72. Cathode Rays Propagated, but Not                LENARD
              Generated, in the Highest Possible
              Vacuum. Air Less Turbid when
              Rarefied.

     72_a_. Cathode Rays, while Traversing the              LENARD
              Exhausted Observing Tube, Deflected
              by a Magnet. No Turbidity in a Very
              High Vacuum.

     72_b_. An Observing Tube for Receiving the             LENARD
              Rays and Adapted to be Exhausted.

        73. Phenomena of Cathode Rays in an                 LENARD
              Observing Tube Containing
              Successively Different Gases at
              Different Pressures. Phosphorescent
              Screen Employed for Making the Test.

        74. Cause of the Glow Outside of the                LENARD
              Aluminum Window. Glow Not Caused by
              External Cathode Rays. Sparks Drawn
              from the Aluminum Window.
              Transmission of External Cathode Rays
              Dependent Alone upon the Density of
              the Medium.

        75. External Cathode Rays of Different              LENARD
              Kinds Variably Diffused. Theoretical
              Observations.

        76. Law of Propagation of External Cathode          LENARD
              Rays.

        77. Charged Bodies Discharged by External           LENARD
              Cathode Rays. Discharge at Greater
              Distances than Phosphorescence. Not
              Certain as to the Discharge Being
              Directly Due to Intermediate Air.

        78. Source, Propagation, and Direction of     DE KOWALSKIE
              Cathode Rays. General Conclusions.


                              CHAPTER VII.

        79. X-rays Uninfluenced by a Magnet. Source       ROENTGEN
              of X-rays Determined by Magnetic
              Transposition of Phosphorescent Spot.

        80. Source of X-rays may be at Points             ROENTGEN
              within the Vacuum Space. Different
              Materials Radiate Different
              Quantities of X-rays.

        81. Reflection of X-rays.                         ROENTGEN

        82. Examples of Penetrating Power of              ROENTGEN
              X-rays.

        83. Permeability of Solids to X-rays              ROENTGEN
              Increases Much More Rapidly than the
              Thickness Decreases.

        84. X-rays Characterized. Fluorescence and        ROENTGEN
              Chemical Action.

        85. Non-refraction of X-rays Determined by        ROENTGEN
              Opaque and Other Prisms. Refraction,
              if Any, Exceedingly Slight.

        86. Velocity of X-rays Inferred to be the         ROENTGEN
              Same in All Bodies.

        87. Non-double Refraction Proved by Iceland   ROENTGEN and
              Spar and Other Materials.                      MAYER

        88. Rectilinear Propagation of X-rays             ROENTGEN
              Indicated by Pin-hole Camera and
              Sharpness of Sciagraphs.

        89. Interference Uncertain Because X-rays         ROENTGEN
              Tested were Weak.

        90. Electrified Bodies, whether Conductors        ROENTGEN
              or Insulators, or Positive or
              Negative, Discharged by X-rays.
              Hydrogen, etc., as the Intermediate
              Agency.

     90_a_. Application of Principle of Discharge         ROENTGEN
              by X-rays.

     90_A_, Supplementary Experiments on Charge and       MINCHIN,
       _b_,   Discharge by X-rays.                          RIGHI,
       _c_,                                               BENOIST,
       _d_.                                            HURMUZESCU,
                                                      and BORGMANN

        91. Focus Tube.                                  ROENTGEN,
                                                    SHALLENBERGER,
                                                          _et al._

     91_a_. Tribute to the Tesla Apparatus.               ROENTGEN

        92. X-rays and Longitudinal Vibrations.           ROENTGEN

        93. Longitudinal Waves in Luminiferous             THOMSON
              Ether by Electrical Means Early             (KELVIN)
              Predicted by

        94. Theory as to X-rays Being of a                SCHUSTER
              Different Order of Magnitude from
              those so far Known.

        95. Longitudinal Waves Exist in a Medium    THOMSON, J. J.
              Containing Charged Ions. Theoretical.

        96. Practical Application of X-rays              BOLTZMANN
              Foreshadowed.

        97. The Sciascope.                                  MAGIE,
                                                     SALVIONI, _et
                                                              al._


                             CHAPTER VIII.

     97_a_. Electrified Bodies Discharged by Light           HERTZ
              of a Spark, and the Establishment of
              a Radical Discovery.

     97_b_. Above Results Confirmed and More         WIEDEMANN and
              Specific Tests.                                EBERT

        98. Negatively Charged Bodies Discharged by    ELSTER  and
              Light. Discharge from Earth’s Surface         GEITEL
              Explained by Inference and
              Experiment.

        99. Relation between Light and Electricity.     ELSTER and
              Cathode of Discharge Tube Acted upon          GEITEL
              by Polarized Light and Apparently
              Made a Conductor Because of the
              Discharging Effect.

      99_A_ Briefs Regarding Action between              SCHUSTER,
         to   Electric Charge and Light.                    RIGHI,
     99_T_.                                              STOLSTOW,
                                                           BRANLY,
                                                         BORGMANN,
                                                       MEBIUS, _et
                                                              al._


                              CHAPTER IX.

       100. Stereoscopic Sciagraphs.                   THOMSON, E.

       101. Obtaining Manifold Sciagraphs              THOMSON, E.
              Simultaneously upon Superposed
              Photographic Films and through Opaque
              Materials, and thus Indicating
              Relative Sensitiveness of Different
              Films to X-rays. Intensifying Process
              Applicable in Sciagraphy. Thick Films
              Appropriate.

     101_a_. Sciagraph Produced through 150 Sheets         LUMIÈRE.
              of Photographic Paper.

       102. Discharge Tube Adapted for Both           THOMSON, E.,
              Unidirectional and Alternating           and SWINTON
              Currents.

       103. X-rays. Opalescence and Diffusion.        THOMSON, E.,
                                                       PUPIN,  and
                                                             LAFAY

     103_a_. Diffusion and Reflection in Relation to    IMBERT, _et
              Polish.                                         al._

       104. Fluorometer. Fluorescing Power of          THOMSON, E.
              Different Discharge Tubes Compared.

       105. Modified Sciascope for Locating the        THOMSON, E.
              Source and Direction of X-rays.
              Phosphorescence Not an Essential
              Accompaniment in Production of
              X-rays.

       106. X-rays from Discharge Tube Excited by     RICE, PUPIN,
              Wimshurst Machine. Full Details Given     and MORTON
              of the Electrical Features.

       107. Source of X-rays Determined by                    RICE
              Projection through a Small Hole upon
              Fluorescent Screen Adjustable to
              Different Positions.

     107_a_. Use of Stops in Sciagraphy.                  LEEDS and
                                                            STOKES

     107_b_. X-rays from Two Phosphorescent Spots.      MACFARLANE,
                                                      KLINK, WEBB,
                                                     CLARK, JONES,
                                                        and MORTON

       108. Source of X-rays Determined by Shadows           STINE
              of Short Tubes.

       109. Instructions Concerning Electrical               STINE
              Apparatus for Generating X-rays.

       110. Apparent Diffraction Really Due to               STINE
              Penumbral Shadows.

     110_a_. Non-diffraction.                                PERRIN

     159_a_. Non-Refraction

       111. Source of X-rays Tested by                SCRIBNER and
              Interceptance of Assumed Rectilinear         M’BERTY
              Rays from the Cathode.

       112. Source of X-rays on the Inner Surface     SCRIBNER and
              of the Glass Tube Determined by             M’BERTY,
              Pin-hole Images.                              PERRIN

     112_a_. Anode Thought to be the Source. Cause          DE HEEN
              of Error Suggested.

       113. Pin-hole Pictures by X-rays Compared             LODGE
              with Pin-hole Images by Light to
              Determine the Source. X-rays Most
              Powerful when the Anode is the Part
              Struck by the Cathode Rays.

       114. Valuable Points Concerning Electrical            LODGE
              Apparatus Employed.

       115. X-rays Equally Strong during Fatigue of          LODGE
              Glass by Phosphorescence.

       116. Area Struck by Cathode Rays Only an           ROWLAND,
              Efficient Source when Positively         CARMICHAEL,
              Electrified.                              and BRIGGS

       117. Transposition of Phosphorescent Spot         SALVIONI,
              and of Cathode Rays without a Magnet.        ELSTER,
                                                       GEITEL, and
                                                             TESLA

     117_a_. Molecular Sciagraphs in a Vacuum Tube.      HAMMER and
                                                           FLEMING


                               CHAPTER X.

       118. X-rays Begin before Striæ End.              EDISON and
                                                       THOMSON, E.

       119. Reason why Thin Walls are Better than           EDISON
              Thick.

       120. To Prevent Puncture of Discharge Tube           EDISON
              by Spark.

       121. Variation of Vacuum by Discharge and by         EDISON
              Rest.

       122. External Electrodes Cause Discharge             EDISON
              through a Higher Vacuum than
              Internal.

       123. Profuse Invisible Deposit from Aluminum     EDISON and
              Cathode.                                      MILLER

       124. Possible Application of X-rays.             EDISON and
              Fluorescent Lamp.                           FERRANTI

     124_a_. Greater (?) Emission of X-rays by          PILTCHIKOFF
              Easily Phosphorescent Materials.

       125. Electrodes of Carborundum.                      EDISON

       126. Chemical Decomposition of the Glass of          EDISON
              the Discharge Tube Detected by the
              Spectroscope.

       127. Sciagraphs. Duration of Exposure                EDISON
              Dependent upon Distances.

       128. Differences between X-rays and Light    EDISON, FROST,
              Illustrated by Different Photographic       CHAPPIN,
              Plates. Times of Exposure.                   IMBERT,
                                                      BERTIN-SANS,
                                                        and MESLIN

     128_a_. GEORGES MESLINS INSURED A REDUCTION OF
              TIME FOR TAKING SCIAGRAPHS BY THE
              DEFLECTION OF THE CATHODE RAYS BY
              MEANS OF A MAGNETIC FIELD

       129. Size of Discharge Tube to Employ for            EDISON
              Given Apparatus.

       130. Preventing Puncture at the                      EDISON
              Phosphorescent Spot.

       131. Instruction Regarding the Electrical        EDISON and
              Apparatus.                                     PUPIN

       132. Salts Fluorescent by X-rays. 1800               EDISON
              Chemicals Tested.

       133. X-rays Apparently Passed around a        EDISON, ELIHU
              Corner. Theoretical Consideration by        THOMSON,
              Himself and Others.                     ANTHONY, _et
                                                              al._

       134. Permeability of Different Substances to     EDISON and
              X-rays. A List of a Variety of                 TERRY
              Materials.

     134_a_. Illustration of Penetrating Power of            HODGES
              Light.

       135. Penetrating Power of X-rays Increased           EDISON
              by Reduction of Temperature. Tube
              Immersed in Oil, and the Oil Vessel
              in Ice. X-rays Transmitted through
              Steel 1/8 in. Thick.

       136. X-rays Not Obtainable from Other        EDISON, ROWLAND,
              Sources than Discharge Tube.                _et al._


                              CHAPTER XI.

       137. Kind of Electrical Apparatus for             TESLA and
              Operating Discharge Tube for Powerful  SHALLENBERGER
              X-rays.

       138. How to Maintain the Phosphorescent Spot          TESLA
              Cool.

       139. Expulsion of Material Particles through          TESLA
              the Walls of a Discharge Tube.

     139_a_. Giving to X-rays the Property of Being       LAFAY and
              Deflected by a Magnet.                         LODGE

     139_b_. Penetration of Molecules into the Glass           GOUY
              of the Discharge Tube.

       140. Vacuum Tubes Surrounded by a Violet          TESLA and
              Halo.                                         HAMMER

       141. Anæsthetic Properties of X-rays.             TESLA and
                                                            EDISON

       142. Sciagraphs of Hair, Fur, etc., by       TESLA, MORTON,
        and   X-rays. Pulsation of Heat detected.       and NORTON
     142_a_.

       143. Propagation of X-rays through Air to             TESLA
              Distances of 60 ft.

       144. X-rays with Moderate Vacuum and High             TESLA
              Potential.

       145. Detailed Construction and Use of Single          TESLA
              Electrode Discharge Tubes for
              Generating X-rays.

       146. Percentage of Reflection.               TESLA and ROOD

     146_a_. Reflected and Transmitted Rays                   TESLA
              Compared. Practical Application of
              Reflection in Sciagraphy. Analogy
              between Reflecting Power of Metals
              and their Position in the
              Electro-positive Series.

       147. Discharge Tube Immersed in Oil. Rays             TESLA
              Transmitted through Iron, Copper, and
              Brass, 1/4 in. Thick.

       148. Bodies Not Made Conductors when Struck           TESLA
              by X-rays.

       149. Non-conductors Made Conductors by a          APPLEYARD
              Current.

     149_a_. Appleyard’s Experiment. Non-conductors
              Made Conductors by Current.

       150. Electrical Resistance of Bodies Lowered        MINCHIN
              by the Action of Electro-magnetic
              Waves.


                              CHAPTER XII.

       151. Sciagraphic Plates Combined with                PUPIN,
              Fluorescent Salts.                      SWINTON, and
                                                            HENRY.

       152. Penetrating Power of X-rays Varies with   THOMPSON, S.
              the Vacuum.                                       P.

       153. Reduction of Contact Potential of               MURRAY
              Metals by X-rays.

       154. Transparencies of Objects to X-rays Not         NODON,
              Influenced by the Color. Detected by        LUMIÈRE,
              Simultaneous Photographic              BLEUNARD, and
              Impressions.                                 LABESSE

       155. Chlorine, Iodine, Sulphur, and                MESLANS,
              Phosphorus Combined with Organic       BLEUNARD, and
              Materials Increase Opacity.                  LABESSE

       156. Application of X-rays to Distinguish           BUQUET,
              Diamonds and Jet from Imitations.       GASCARD, and
                                                      THOMPSON, S.
                                                                P.

       157. Inactive Discharge Tubes Made Luminous          DUFOUR
              by X-rays.

       158. Non-refraction in a Vacuum.                   BEAULARD

       159. Bas-relief Sciagraphs by X-rays.        CARPENTIER and
                                                            MILLER

       160. Transparency of Eye Determined by          WUILLOMENET
              Sciagraph of Bullet Therein.

       161. Mineral Substances Detected in                  RANWEZ
              Vegetable and Animal Products.

       162. Hertz Waves and Roentgen Rays Not               ERRERA
              Identical.

       163. Non-mechanical Action by X-rays                GOSSART
              Determined by the Radiometer.

       164. X-rays within Discharge Tube.                 BATTELLI

       165. Combined Camera and Sciascope.                  BLEYER

       166. Non-polarization of X-rays.               THOMPSON, S.
                                                     P., MACINTYRE

       167. Diffuse Reflection. Dust Figures          THOMPSON, S.
              Indirectly by X-rays.                             P.

       168. Continuation of Experiments in § 113.            LODGE

       169. Thermopile Inert to X-rays.                     PORTER

       170. Non-diffraction of X-rays.                       MAGIE

       171. Resistance of Selenium Reduced by           GILTAY and
              X-rays.                                         HAGA

             _Total number of sections to this place, 199._


                             CHAPTER XIII.

       200. Needle Located by X-rays and then              HOGARTH
              Removed.

       201. Needle Located at Scalpel by X-rays and         SAVARY
              then Removed.

       202. Diagnosis with Fluorescent Screen.          RENTON and
                                                        SOMERVILLE

       203. Bullet Located by Five Sciagraphs.              MILLER

       204. Bones in Apposition Discovered by               MILLER
              X-rays and afterward Remedied by
              Operation. Other Cases.

     204_a_. Necrosis.                                       MILLER

       205. Application of X-rays in Dentistry.             MORTON

       206. Elements of the Thorax.                         MORTON

       207. A Colles’ Fracture Detected by X-rays.          MORTON

       208. Motions of Liver, Outlines of Spleen,       MORTON and
              and Tuberculosis Indicated.                 WILLIAMS

       209. Osteomyelitis distinguished from          LANNELONGUE,
              Periostitis.                             BARTHELEMY,
                                                        and OUDIN.

       210. Concluding Miscellaneous Experiments         ASHHURST,
              Relating to Similar Applications of         PACKARD,
              X-rays.                                MÜLLER, KEEN,
                                                    and MORTON, T.
                                                                G.


                              CHAPTER XIV.


 Theoretical Considerations, Arguments, and Kindred              ANTHONY
   Radiations.


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




                             INTRODUCTION.


                                -------

The new form of energy, for which there are two names—to wit, the
Roentgen ray and the X-ray—is radiated from a highly exhausted discharge
tube, which may be energized by an induction coil or other suitable
electrical apparatus, such as a Holtz or a Wimshurst electrical machine.
§ 106. The principle underlying the construction of the usual induction
(or Ruhmkorff) coil is disclosed in the subject-matter of § § 1, 2, and
3, and is represented in diagram in Figs. 1 and 2 on page 17. It would
be well for the amateur or general scientific reader to study these
sections carefully, for then he will have all the knowledge that is
necessary for understanding the apparatus by which the discharge tube is
energized. Of course, he will not comprehend the various mechanical
details, nor the many electrical and mathematical relations existing in
connection with an induction coil, but he will gain sufficient knowledge
to appreciate what is intended when such a device is referred to here
and there throughout the book. Since the time of Faraday, Page, and
Fizeau induction coils of very large dimensions have been constructed,
but none of them probably ever exceeded that built by Spottiswoode,
during or about 1875, which was so powerful as to produce between the
two electric terminals, in open air, a spark of 42 in. in the secondary
current with only 30 small galvanic cells of the Grove type in the
primary circuit. The cells are seldom used in this connection at the
present time, the same being replaced by the dynamo, and the current
being conveniently obtained from the regular incandescent-lamp circuit
which may be found in almost any city. Those, therefore, who intend to
become better acquainted with the details of the electrical apparatus
should study in conjunction with this book some elementary treatise
relating particularly to dynamos and electric currents.

The essential element in connection with the generation of X-rays is not
the coil nor the dynamo, but the electric discharge, especially when
occurring within a rarefied atmosphere, provided within a glass bulb,
called the discharge tube throughout the book, but which has usually
been called by different names, for example, the receiver of an air
pump, or a Geissler tube, when the air is not very highly exhausted, or
a Crookes tube (see picture at § 123) when the vacuum is definitely much
higher by way of contrast. It has also been called a Hittorff tube, the
Lenard tube, and by several other names, according to its peculiar
characteristics.


[Illustration:

  FIG. 1.—HEAD.
]


[Illustration:

  FIG. 2.—BROKEN ARM, OVERLAPPING.
  (Due to defective setting.)
]


[Illustration:

  FIG. 3.—RIBS.
]


[Illustration:

  FIG. 4.—KNEE, KNICKERBOCKER BUTTONS, BULLET IN FEMUR.
]

           FROM SCIAGRAPHS BY PROF. DAYTON C. MILLER. § 204.


For those who are not acquainted with the nature of the electric charge
and discharge, nor with the peculiar and exceedingly interesting
phenomena which various investigators have discovered from time to time,
nor with the variety of effects according to the nature and the pressure
of the atmosphere within the glass bulb, it is exceedingly difficult to
understand with any degree of satisfaction the properties, principles,
laws, theories, and manner of application of cathode and X-rays.
Consequently, the greater part of the book treats of the electric charge
and discharge in conjunction with certain kindred phenomena. Primarily,
the meaning of the electric discharge may be derived by referring to
Fig. 2, page 17, where there is shown an electric spark, indicated by
radial lines between the terminals of a fine wire forming the long and
fine coil or secondary circuit. Imagine that the wires are at great
distances apart. Let them be brought closer and closer together. By
suitable tests it will be found, for example, that no current passes
through the wire, but when the points are brought sufficiently close
together a spark will occur between the two terminals. § 2. Sometimes
instead of what is understood as a spark, a brush or glow takes place (§
§ 10 and 11), and in fact a numerous variety of effects occur, a general
name for all being conveniently termed an electric discharge. Even if no
sudden discharge takes place, yet, as when the terminals are far apart,
there may be a charge or a tendency, or, as it is technically called, a
difference of potential, between the two electrodes, one of which is the
cathode and the other the anode. This is comparable to a weight upon
one’s hand, tending continually to fall, and always exerting a pressure,
and it will fall when the hand is suddenly removed. This is in the
nature more of an analogy than of an exact correspondence. A discharge
through open air, while adapted to produce a great many curious as well
as useful effects, does not act as a generator of X-rays. § 136. Another
class of phenomena is obtainable by exhausting the air to a certain
extent from a discharge tube, thereby obtaining what is usually called a
low vacuum. Such bulbs have been called Geissler tubes. Neither can
X-rays be generated therefrom to any practicable extent, but only feebly
if at all. § 118. Hittorff, Varley (§ 61_a_), Crookes (§ § 53 to 61,
inclusive), were the first to discover and study the different phenomena
that are obtained by diminishing the pressure within the discharge tube
to a decrement of several thousand millionths of an atmosphere. This
will explain why so many allusions have been made to the Crookes tube,
for when the electric discharge is caused to take place in such a high
vacuum X-rays are propagated in full strength.

Upon the first announcement of the discovery, electricians, eminent and
otherwise, were of one mind in assuming the possibility of obtaining
Roentgen rays from other sources than that of the highly evacuated
discharge tube. Instead of speculating and theorizing, hosts of crucial
tests were instituted, resulting negatively, and it is now safe to
conclude that the electric discharge is the only primary source, and it
is reasonably safe to assert that the discharge must take place within a
highly evacuated enclosure.

The next stage of exhaustion, of no advantage to be considered, is that
at which no discharge takes place (§ 25), and neither are any Roentgen
rays propagated therefrom.


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




                               CHAPTER I


                                -------

1. FARADAY’S EXPERIMENT, 1831. SECONDARY CURRENT BY INDUCTION.
_Experimental Researches, Proc. Royal. So. 1841._—In brief, the
experiment involved the elements illustrated in the accompanying
diagram, Fig. 1, p. 17; a ring made of iron; upon the ring, two coils of
copper wire, suitably insulated from each other and from the iron; a
galvanometer included in circuit with one coil, and an electric battery
of ten cells placed in circuit with the other coil. He found that upon
breaking or completing connection with the battery, the needle was
powerfully deflected. Without entering into further detail, it is
important, however, to notice that he did not perform any experiments
tending to establish the principle of increase of E. M. F. by making the
very slight change now known to be necessary. § 2.


2. PAGE’S EXPERIMENT, 1838. ELECTRIC SPARK BY INDUCED CURRENT.
_Pynchon_, p. 427. Dr. Page performed an experiment in which the primary
coil was but a few feet in length, while the secondary coil was 320 ft.
He included, in the primary circuit, only a few cells of battery. The
manner in which he first caused rapid interruptions of the circuit of
the primary coil was by the use of what may be called a coarse file,
Fig. 2, p. 17. He discovered that the E. M. F. during the rapid
interruption was so much increased over that of the small battery, that
an electric spark would pass between the secondary terminals without
first bringing them into contact with each other. § 6. The result of
these experiments was not only the generation of a current of high E. M.
F. from a generator of low E. M. F., but also a current of great
quantity as compared with currents obtained from frictional and
influence machines, whose complete history is found in Mascart’s work on
Electricity.


3. FIZEAU’S EXPERIMENT. SPARK IN SECONDARY INCREASED BY CONDENSER IN
PRIMARY, 1853. _Pynchon_, p. 456.—He connected the plates of a condenser
respectively to the terminals of an automatic circuit breaker in the
primary circuit, and noticed that the sparks between the two terminals
of the interrupter produced by the self-induced current were greatly
diminished, while those of the secondary coil were about double in
length. Since that time it has been universally customary to equip
induction coils with condensers in like manner.


4. VINCENTINI’S EXPERIMENT. CONDITION OF A GAS AROUND A LIVE WIRE.
_Nuovo Cimento_, Vol. XXXVI., No. 3. _Nature_, Lon., March 28, ’95, p.
514. _The Elect._, Lon., Feb. 8, ’95, p. 433. G. Vincentini and M.
Cinelli found that the molecules of a gas at and near the surface of a
platinum wire, rendered incandescent by a current, are electrified, and
that with hydrogen their potential is about .025 volt above the mean
potential of the wire. With air and carbonic acid gas the increment is
about 1 volt. The apparatus, Fig. II., consists essentially of means for
passing a current along a platinum wire, a bulb for preventing draughts,
and an electrometer having a platinum disc electrode that could be
adjusted to different positions. It was noticeable that the
electrification did not reach a maximum instantaneously upon closing the
current through the wire, but the time was less at points below the wire
than above.


[Illustration:

  _II_
]


5. HENRY’S EXPERIMENT. MAGNETIZING RADIATIONS FROM AN ELECTRIC SPARK.
_Proc. Inter. Elect. Cong._, 1893, p. 119. Preece alluded to Prof.
Henry’s original experiment illustrating the action of an electric
discharge § 2 at a distance. He placed a needle in the cellar.
Disruptive discharges of a Leyden jar at 30 ft. distant, in an upper
room, produced a magnetic effect upon the needle.


6. FARADAY’S EXPERIMENT. ARC MAINTAINED BY CERTAIN METALLIC ELECTRODES
AT LOW VOLTAGE. _Experimental Researches. Phil. Trans._, _Se._ IX.,
Dec., 1894. § 107. to 1078. The generator employed in this experiment
consisted of a few cells of a chemical battery, and he obtained, what he
called, a voltaic spark. He observed that when the two terminals touched
each other, a burning took place and an appearance as if the spark were
passing on making the contact, the terminals being pointed and formed of
metal. When mercury was the terminal, the luminosity of the spark was
much greater than with platinum or gold, although the same quantity of
current passed in both cases. He attributed the difference to a greater
amount of combustion in the case of mercury, than in those of gold and
platinum. He obtained almost a continuous spark by bringing down a
pointed copper wire to the surface of mercury and withdrawing it
slightly. Wheatstone, in 1835, analysed the light of sparks, and found
them to be so characteristic that by means of the prism and the spectra
formed, the metal could be known.


[Illustration:

  _III_
]


7. WURTS’S EXPERIMENT. NON-ARCING METALS AT HIGH VOLTAGE. _Trans. Amer.
Inst. Elect. Eng._ March 15, 1892. _Ann. Chem. Phar. Sup._ VII, 354 and
VIII, 133. _Chem. News_, VII, 70; X, 59, and XXXII, 21, 129.—Mendelejeff
and Meyer discovered that chemical elements occur in natural groups by a
principle which they termed the periodic law. One of these groups
includes zinc, cadmium, mercury and magnesium; and another group,
antimony, bismuth, phosphorus and arsenic. Alex. J. Wurts, of the
Westinghouse Electric Co. found that the metals of these groups are
non-arcing, by which he means that with an alternating current dynamo of
a thousand or more volts, and with the said metals as electrodes in the
air only just escaping each other, it is impossible to maintain an arc
as in the case of an ordinary arc lamp having carbon electrodes or in a
lightning arrester usually having copper electrodes. He suggested and
theorized that certain chemical reactions served to explain the
phenomena. With low voltage—as 500, the arc was maintained between all
metals. § 6. A two pole lightning arrester is shown in Fig. III The arc
formed, ceased instantly. One of the best metals for practical use is an
alloy of 1/2 zinc and 1/2 antimony, or any metal electroplated with a
non-arcing metal. Freedman observed a critical point with electrodes of
brass. The current was gradually reduced until the arc became like the
discharge of a Holtz machine whose condensers have been disconnected.
See _Elect. Power_, N.Y., Feb. 1896, p. 119.


8. WHEATSTONE’S EXPERIMENT. DURATION OF SPARK. _Phil. Tran._ 1834.—The
short duration of an electric spark produced by a single disruptive
discharge is easily made apparent by a rapidly rotating disc, having
radial sectional areas of different colors. With reflected sunlight, the
colors seem to blend into one tint upon the principle of the persistence
of vision; (See Swain’s experiment. _Trans. R. So. Edin._ ’49 and ’61.);
but when viewed by the flash of a spark, the colors are seen as
distinctly separated as if the disc were at rest. By calculation, based
directly upon a series of experiments, he found the duration of the
spark to be about .000042 sec. It was discovered also, by the rotating
mirror, that the apparently single spark was composed of several
following each other in quick succession, and he concluded that the
current during the discharge was intermittent. He considered each of the
divisions of the spark as an electric discharge. Prof. Nichols, of
Cornell University, and McKittrick obtained curves indicating the
variation of E. M. F. during the existence of a spark. _Trans. Amer.
Inst. Elect. Eng._ May 20, ’96.


8_a_. Feddersen, who used a Leyden jar, modified the experiment by
having high resistances in the circuit through which the charge was
effected. The duration of the spark was found to be increased. In one
experiment, he employed a slender column of water as the resistance, 9
mm. in length. The spark endured .0014 second. With a tube of water 180
mm. the duration was .0183 second. He noticed also that the duration
increases directly with the striking distance and with the electrical
dimensions of the electrical generator. By varying the resistance of the
circuit, he found as it became less, the discharge was intermittent,
when further reduced, _continuous_, (difficult to obtain) § 11 and when
very small, oscillatory—_i.e._, alternately in opposite directions.


9. FARADAY’S EXPERIMENT. BRUSH DISCHARGE SOUND. _Phil. Trans._ Jan.
1837. _Se._ XII.—The brush discharge was caused to occur, in his
experiments, generally from a small ball about .7 of an inch in
diameter, at the end of a long brass rod, acting as the anode. With
smaller balls he noticed that the pitch of the sound produced was so
much higher as to produce a distinct musical note, and he suggested that
the note could be employed as a means of counting the number of
intermissions per second. See Mayer’s book on “Sound” § 77, on measuring
number of vibrations in a musical note.


9_a_. Upon bringing the hand toward the brush the pitch increased. § 49.
With still smaller balls and points, in which case the brush could
hardly be distinguishable, the sound was not heard. He alluded to the
rotating mirror of Wheatstone as becoming not only useful but necessary
at this stage. He considered the brush as the form of discharge between
the contact and the air or else some other non or semi-conductor, but
generally between the conductor and the walls of the room or other
objects which are nearest the electrodes, the air acting as the
dielectric. One experiment, he performed with hydrochloric acid led him
to believe that that particular gas permitted of a dark or invisible
discharge. Sometimes the air was electrically charged § 4 to a less
distance than the length of the brush or light.


10. BRUSH IN DIFFERENT GASES. STRIAE CATHODE BRUSHES. In the air, at the
ordinary pressure he found the color to be “purple;” when rarefied still
more purple, and then approaching to rose; in oxygen, at the ordinary
pressure, a dull white; when rarefied, “purple;” and with nitrogen, the
color was particularly easily obtained at the anode, and when nitrogen
was rarefied the effect was magnificent. The quantity of light was
greater than with any other gas that he tried. Hydrogen, as to its
effect, fell between nitrogen and oxygen. The color was greenish grey at
the ordinary pressure and also at great rarity. The striae were very
fine in form and distinctness, pale in color and velvety in appearance,
but not as beautiful as those in hydrogen. With coal gas, the brushes
were not easily produced. They were short and strong and generally
green, and more like an ordinary spark. The light was poor and rather
grey. Also in carbonic acid gas the brush was crudely formed at the
ordinary pressure as to the size, light and color. The tendency of the
discharge in this case was always towards the formation of the spark as
distinguished from the brush. When rarefied, the light was weak, but the
brush was better in form and greenish to purple, varying with the
pressure and other circumstances. As to hydrochloric acid, it was
difficult to obtain a brush at the ordinary pressure. He tried all kinds
of rods, balls and points, and while carrying on all these experiments
he kept two other electrodes out in the air for comparison, and while he
could not obtain any satisfactory brush in the hydrochloric acid gas,
there were simultaneously beautiful brushes in the air. In the rarefied
gas, he obtained striae of a blue color.

He compared the appearances also of the anode and cathode brushes in
different gases at different pressures. He noticed that in air, the
superiority of the anode brush was not very marked (§ 41 at end.) In
nitrogen, this superiority was greater yet. A line of theory ran through
Faraday’s mind in connection with all these experiments, whereby he held
that there is “A direct relation of the electric forces with the
molecules of the matter concerned in the action.” § 47. He made a
practical application of the principles in the explanation of lightning,
because nitrogen gas forms 4/5 of the atmosphere, and as the discharge
takes place therein so easily.


[Illustration:

  FROM MAGNETOGRAPHS BY PROF. MCKAY. p. 25.
  1. Platinum wire.
  2. Copper gauze.
  3. Iron gauze.
  4. Tinfoil.
  5. Gold-foil.
  6. Brass protractor.
  7. Silver coin.
  8. Platinum-foil.
  9. Brass.
  10. Lead-foil.
  11. Aluminum.
  12. Magnesium ribbon.
  13. Copper objects.
]


[Illustration:

  FROM SCIAGRAPH OF VARIOUS OBJECTS. p. 130.
  By Prof. Terry, U. S. Naval Academy.
]


11. GLOW BY DISCHARGE. GLOW CHANGED TO SPARK. MOTION OF AIR. CONTINUOUS
DISCHARGE DURING GLOW. The glow was most easily obtained in rarefied
air. The electrodes were of metal rods about .2 of an inch in diameter.
He also obtained a glow in the open air by means of one or both of the
small rods. He noticed some peculiarities of the glow. In the first
place, it occurred in all gases and slightly in oil of turpentine. It
was accompanied by a motion of the gas, either directly from the light
or towards it. He was unable to analyze the glow into visible elementary
intermittent discharges, nor could he obtain any evidence of such an
intermittent action, § 8_a_. No sound was produced even in open air. §
9. He was able to change the brush into a glow by aiding the formation
of a current of air at the extremity of the rod. He also changed the
glow into a brush by a current of air, or by influencing the inductive
action near the glow. The presentation of a sharp point assisted in
sustaining or sometimes even in producing the glow; so also did
rarefaction of the air. The condensation of the air, or the approach of
a large surface tended to change the glow into a brush, and sometimes
into a spark. Greasing the end of the wire caused the glow to change
into a brush.


12. LULLIN’S EXPERIMENT. SPARK. PENETRATING POWER. PASSAGE THROUGH
SOLIDS. _Encyclo. Brit._ Article Electricity. He placed a piece of
cardboard between two electrodes and discovered that a spark penetrated
the material and left a hole with burnt edges. When the electrodes were
not exactly opposite each other, the perforation occurred in the
neighborhood of the negative pole. Later experiments have shown that a
glass plate, 5 or 6 cm. in thickness, can be punctured by the spark of a
large induction coil. The plate should be large enough to prevent the
spark from going around the edges. The spark is inclined, also, to
spread over the surface of the glass instead of piercing it, § 24. Glass
has been cracked by the spark in some experiments.


13. FAGE’S EXPERIMENT. SPARK. PENETRATING GLASS. HOLES CLOSE TOGETHER.
PRACTICAL APPLICATION. _La Nature_, 1879. _Nature_, Dec. 26, 1879, p.
189. The length of the spark from the secondary coil in air was 12 cm.
One terminal of the secondary passed through an ebonite plate (18 cm. ×
12) and touched the glass. Olive oil was spread around said terminal (§
11 at end), and served to insulate the same. Oil dielectric in this
connection originally employed at least prior to 1870. Remembered by
Prof. Anthony as far back as 1872, who often performed the experiment
according to instructions contained in a publication. The other terminal
of the secondary coil was brought against the glass opposite the first
terminal. The spark was then passed and the glass perforated, § 12. By
pushing the glass along to successive positions and passing the spark at
each movement, holes could be made very close together. In _Nature_, of
1896, the author noticed that certain manufacturers were introducing
glass perforated with invisible holes to be used for windows as a means
of ventilation without strong draughts. Perhaps the fine holes were made
by means of the electric spark.


14. KNOCHENHAURER’S EXPERIMENTS. CONDUCTING POWER OF GAS. SPARK.
PENETRATING POWER. RELATION OF E. M. F. TO PRESSURE OF GAS. 1834. _Pogg.
Ann._, Vol. LVII., and _Gordon_, Vol. II. Boltzmann’s experiment (_Pogg.
Ann._, CLV., ’75), and calculation indicated that a gas at ordinary
pressure and temperature must have a specific resistance at least
10^{26} times that of copper. _Pogg. Ann._, CLV., ’75. Sir William
Thomson (Kelvin) confirmed this limit for steam, and Maxwell the same
for mercury and sodium vapor, steam and air. From _Maxwell’s MSS._
Herwig was not sure but that the Bunsen burner flame and mercury vapor
conducted. He allowed for the conductivity of the walls of the glass
container. Braun treated of the conductivity of flames. _Pogg. Ann._,
’75.


14_a_. Varley found that 323 Daniel cells only just initiated a current
through a hydrogen Geissler tube, and only 308 cells continued the
current after once started. Knochenhaurer found that Harris’ (_Phil.
Trans._, 1834) law did not hold exactly true, and that the _ratio_
between the E. M. F. and the air pressure becomes _greater and greater_
as the pressure becomes less and less. Harris thought the ratio was
constant. The limits of his pressures were from 3 to 27.04 inches of
mercury. Stated in other words, his results were the same as those of
Harris and Masson (_Ann. de Chimie_, XXX., 3rd Se.), except that a small
constant quantity should be added. § 16.


15. GORDON’S EXPERIMENT. DUST PARTICLES HASTEN DISCHARGE. _Gordon_, Vol.
II. Other experimenters had investigated the phenomena of the electric
spark with different densities of the dielectric by a spark produced by
a frictional or an influence machine, or, in a few cases, by powerful
batteries without coils, while Gordon claims to be the first to carry
out these experiments with an induction coil. He observed that when the
discharging limit was nearly reached, small circumstances, such as a
grain of dust or a rusting of the terminal by a former discharge, would
cause the discharge to take place at a lower E. M. F., which should be
allowed for.


16. KELVIN’S EXPERIMENT. _Proc. R. So._, 1860. _Encyclo. Brit._, Art.
Elect. He used as the terminals, two plates. One of them was perfectly
plane, while the other had a curvature of a very long radius. The object
of this arrangement was to obtain a definite length of spark for each
discharge. The plates were gradually moved away until the spark would no
longer pass, and the reading of the distance was noted. The law which he
found cannot well be expressed in the form of a rule or principle,
because it is of a rather intricate nature, but a discovery resulted,
namely in the case where the distance was greater, the dielectric
strength was smaller for respective distances of .00254 and .535 cm.
Many theoretical considerations in reference to this matter have been
presented, notably that of Maxwell in his treatise on Electricity and
Magnetism, Vol. I.


17. CAILLETET’S EXPERIMENT. SPARK. PENETRATING POWER. HIGH PRESSURES.
INCREASED DIELECTRIC STRENGTH. _Mascart_, Vol. I. He experimented with
dry gas up as high as pressures of 700 lbs. per sq. inch. He found that
the dielectric strength continues to increase with increase of pressure.
He used about 15 volts in the primary and a powerful induction coil. The
dielectric strength was so great that at the maximum pressure named
above, the spark would not pass between the electrodes when only .05 mm.
apart. § 25 and 11, near end.


18. FARADAY’S EXPERIMENT. DISCHARGES IN DIFFERENT CHEMICAL GASES
VARIABLY RESISTED. _Exper. Res. Phil. Trans._, Se. XII., Jan. ’36.
Faraday passed on from the consideration of the effect of pressure,
temperature, etc., and wondered whether there would be any difference in
the law according to what gas was used. He arranged apparatus so that he
could know, with air as a standard, whether another gas had a greater or
less dielectric power. (Cavendish before him had noticed a difference.)
He tabulated the results. They exhibited the following facts, namely
that gas, when employed as dielectrics, depend for their power upon
their chemical nature. § 10. Hydrochloric acid gas was found to have
three times the dielectric strength of hydrogen, and more than twice
that of oxygen, nitrogen or air; therefore the law did not follow that
of specific gravities nor atomic weights. See also De la Rue, _Proc.
Royal So._, XXVI., p. 227.


19. THOMSON’S EXPERIMENTS. GAS AS A CONDUCTOR. VISIBLE INDICATION BY
DISCHARGE. _Nature_, Lon., Aug. 23, ’94, p. 409; Jan. 31, ’95, p. 332,
and other references cited below. Lec. _Royal Inst. Proc. Brit. Asso._,
Aug. 16, ’94. In making comparisons, things of like nature should be
considered. Take, for example, gas at .01 m. The number of molecules in
such a rarefied atmosphere is comparatively small, while in an
electrolyte there are molecules sufficient in number to produce 15,000
lbs. of pressure, if imagined in the gaseous state within the same
space. By an experiment and rough calculation, Prof. J. J. Thomson,
F.R.S., calculated that the conductivity of a gas estimated _per
molecule_ is about 10 million times that of an electrolyte, for example,
sulphuric acid. § 14. This is greater than the molecular conductivity of
the best conducting metals. The experiment which is illustrated in Fig.
IV. was a second experiment which did not serve as a basis for
calculation, but exhibited very strikingly to the eye that gases having
different pressures have different conductivities. For this apparatus he
had two concentric bulbs, as indicated, one being contained within the
other. The inner one had air rarefied to the luminous point. The outer
one had a vacuum as high as it was practical to make it, and contained
in a projection a drop of mercury, which, when heated, would gradually
increase the pressure. Two Leyden jars were employed, and their outer
coatings were connected to the coil which is seen surrounding the outer
bulb, and the inner coatings were connected to the coils of a Wimshurst
machine. The operation was as follows: When the mercury was cold, that
is, with a high vacuum in the outer compartment, a bright discharge
passed through the _inner_ bulb, while the _outer_ bulb was dark. When
the mercury was heated, the outer bulb was bright, and the inner one was
almost dark. By well-known principles of conductors and non-conductors,
the operation was explained by Prof. Thomson, who assumed that the gas
in the outer bulb is a conductor; then, at each spark will the
alternating current in the coil induce currents of an opposite direction
in the gas, which will become luminous, as occurred when the mercury was
heated. The currents circulating in the gas act as a shield to the
induction of the currents in the inner bulb. However, with the vacuum
exceedingly high in the outer bulb, the air therein being a
non-conductor comparatively, or for the given E. M. F., does not prevent
the discharge through the inner bulb, which becomes, therefore,
luminous. He next compared the dielectric power of a gas, a liquid and a
solid. He found that the E. M. F. had to be raised, in order to produce
the discharge,—higher in the liquid than in the gas, and higher in the
solid than in the fluid. § 12.


[Illustration:

  IV.
]


20. BOLTZMANN, GIBSON, BARCLAY, HOPKINSON AND GLADSTONE’S EXPERIMENTS.
SQUARE ROOT OF THE DIELECTRIC CAPACITY EQUAL TO THE REFRACTIVE INDEX.
_Phil. Trans._, 1871, p. 573. _Maxwell_, Vol. II., § 788. Maxwell has
argued elaborately upon results of some of the above experimenters upon
the theory that the luminiferous ether is the medium for transmission of
electricity, light and magnetism; therefore he predicted that the
relation stated in the title above should exist. He acknowledged that
the relation is sufficiently near a constant to show in connection with
other results, especially those obtained, that his theory is probably
correct.


21. PLÜCKER’S EXPERIMENT. HERMETICALLY SEALED VACUUM TUBE. _Encycl.
Brit._, vol. 8, p. 64. _Pogg. Ann._, 1858, and vol. CXXXVI, 1869.—He
engaged Geissler (according to Hittorf) to make a glass tube in which
the platinum wire electrodes were sealed in the glass by fusion, as in
the modern incandescent lamp. After the air was exhausted by a
mechanical air pump through a capillary tube, the same was sealed with
the flame of a spirit lamp. He thus established means whereby a
practically permanent vacuum could be maintained within a glass bulb.
Platinum expands by heat at about the same rate as glass: hence there is
no tendency to crack and admit air.


22. GEISSLER’S EXPERIMENT. LUMINOSITY OF VACUUM TUBES BY FRICTION.
INCREASED BY LOW TEMPERATURE. _Science Record_, 1873.—By rubbing the
vacuum tubes with an insulator—cat skin, silk, etc.—he observed that
light was generated and that its color depended upon the particular gas
forming the residual atmosphere. At a low temperature, the colors were
more luminous. § 135. The best form of tube consisted of a spiral tube
contained within another tube. A modified construction involved the
introduction of mercury. By exhausting the air, and shaking the tube,
the friction or motion of the mercury against the glass produced
luminous effects according to the gas. Only chemically pure mercury
would cause the light, which endured for an instant after the rubbing
ceased. § 63.


23. ALVERGNIAT’S EXPERIMENT. LUMINOSITY OF VACUUM TUBES BY FRICTION AND
DISCHARGES. DIFFERENT VACUA REQUIRED. _Sci. Rec._, 1873, p. 111.
_Comptes Rendus_, 1873.—To obtain luminosity by charging the tubes with
the coil, it was necessary to increase the degree of the vacuum—but when
this was done the rubbing of the tube would not cause light. The tube
employed was 45 cm. in length, and contained a small quantity of silicic
bromide. The atmospheric pressure within the tube for obtaining the
glimmer by friction was 15 mm.


24. STEINMETZ’S EXPERIMENT. LUMINOUS EFFECTS BY ALTERNATING CURRENT AND
SOLID DIELECTRICS. _Trans. Amer. Inst. Elec. Eng._, Feb. 21, ’93.—In
carrying on experiments in the accurate measurement of dielectric
strength, he noticed that upon placing mica between the electrodes, as
is hereinafter set forth, a spark did not at first form, but that which
he called a corona. He attributed the appearances to a condenser
phenomenon, or at least he suggested this as an explanation. § 3. As
soon as the corona reached the edge of the plate, the disruptive
discharge took place, by means of the sparks passing over the edge of
the dielectric. § 38. He employed an alternating current dynamo of about
50 volts and 1 h.p., frequency of 150 complete periods per second. The
E. M. F. of the alternator was varied, by changing the exciting current,
up to 90 volts. Step-up transformers were employed. With a difference of
potential in the secondary of 830 volts, and a thickness of mica of 1.8
mm. and when the experiment was performed in a dark room a faint bluish
glow appeared between the mica and the electrodes. At 970 volts the glow
was brighter, while at 1560 volts the luminosity was visible in broad
day-light, and kept on increasing with the increase of E. M. F. He
modified the experiment by using mica of a thickness of 2.3 mcm. The
difference of potential was 4.5 kilo-volts. In addition to the bluish
glow, violet streams or creepers broke out and increased in number and
length as the E. M. F. became greater, forming a kind of aurora around
the electrodes and on both sides of the mica sheet. A loud hissing noise
occurred. § 9. As soon as the corona reached the edges of the mica, the
disruptive discharge occurred in the form of intensely white sparks and
it was noticeable that the length of these sparks was 10 fold greater
than could be obtained in the air at 17 kilo-volts. These sparks were so
hot as to oxidize the mica, as apparent from the white marks remaining.
The electrodes also became very hot, and the mica was contorted and
finally broke down.


25. MORGAN’S EXPERIMENT. NO DISCHARGE IN HIGH VACUA. _Wiedemann_, vol.
2. _Phil. Trans._, 1875, vol. 75.—He was led to believe by an
experiment, that when the vacuum is sufficiently perfect, no
electromotive force could drive the spark from one terminal to the
other, however close together they may be. § 18. Details of Morgan’s
Experiments were as follows, given roughly in his own words:—A mercurial
gauge about fifteen inches long, carefully and accurately boiled till
every particle of air was expelled from the inside, was coated with
tinfoil five inches down from its sealed end, and being inverted into
mercury through a perforation in the brass cap which covered the mouth
of the cistern, the whole was cemented together and the air was
exhausted from the inside of the cistern, through a valve in the brass
cap, which, producing a perfect vacuum in the gauge, formed an
instrument peculiarly well adapted for experiments of this kind. Things
being thus adjusted (a small wire having been previously fixed on the
inside of the cistern, to form a communication between the brass cap and
the mercury, into which the gauge was inverted), the coated end was
applied to the conductor of an electrical machine, and notwithstanding
every effort, neither the smallest ray of light nor the slightest charge
could ever be procured in this exhausted gauge.


26. DE LA RUE AND MÜLLER’S EXPERIMENT. CONSTANT POTENTIAL AT THE
TERMINALS OF A DISCHARGE TUBE. _Phil. Trans._, part 1, vol. 169, p. 55
and 155.—The apparatus consisted of an exhausted bulb, a chloride
battery of 2400 cells and a large resistance adapted to be varied
between very wide limits. The result was a constant potential at the
electrodes of the bulb, during all the variations of the resistance.
They concluded, therefore, that the discharge in highly rarefied gases
is disruptive, the same as in air at ordinary pressure.


[Illustration]


26_a_. KLINGENBERG’S CALCULATIONS. DIRECTION OF DISCHARGE TUBE CURRENT
IN SECONDARY OF RUHMKORFF COIL. _Translated from the German, by Ludwig
Gutmann. Extract of paper read by G. Klingenberg before the
Electro-technischer Verein._ It would naturally be inferred that an
induction coil, the primary current of which is intermitted, and of one
direction, would produce an alternating current in the secondary coil.
The fact of the matter is, however, that a good induction coil will
produce the sparking only in but one direction. § 41. The reason is the
following: If the coil had no self-induction nor capacity, then the
current impulses would be represented by a rectangle _a_, Fig. 1. On
closing, the current would suddenly reach its maximum, which is
determined by the terminal pressure and circuit resistance, and this
current strength would be maintained as long as the circuit remained
closed. On the opening of the circuit, the current would decrease just
as suddenly; if not, the arc on opening of the circuit would oppose such
sudden fall, therefore the corner will be slightly rounded at _a_, Fig.
2. The influence of self-induction, which we find in any coil, is the
force that will tend to oppose any change in the current strength.
Therefore, the self-induction will be the cause of a retardation of the
minimum current. On the other hand, it increases the size of the spark
on opening. Next a condenser is enclosed in the main circuit, so that
the spool is closed through it at the moment the current is intercepted.
If we assume, for simplicity sake, that the magnetization of the iron is
proportional to the current strength, then the primary current curve
represents at the same time, the curve of the rate of change of line of
force in the magnetic field. The secondary E. M. F. is determined by e =
_n_(_dw_/_dt_)_t_ _t_; the rise then will have a smaller E. M. F. than
at the fall, like Fig. 3, _except_ that the curve representing the fall
should be shown as more nearly perpendicular to the abscissa.


[Illustration:

  V
]


27. KINNERSLEY, HARRIS AND RIESS’S EXPERIMENTS. SPARK. PRESSURE PRODUCED
BY. _Ganot_, § 790, et al. _Encyclo. Brit. Art. Elect._—These
experimenters passed a spark through air contained over mercury, so that
if the pressure of the air were increased, the mercury would move along
through a capillary tube, having a scale so that the amount could be
represented to the eye, as in the cut. (Fig. V.) The experiments proved
that when a spark passes through the air, the pressure is increased, and
it was concluded in view of several experiments, that the spark being
the source of an intense, but small amount of heat, expanded the air,
thereby causing the pressure in a secondary manner, through the agency
of heat. A spark as short as 2 mm. will produce a considerable pressure
of the mercury. Riess performed an experiment also in causing the spark
to pass through cardboard, and also through mica located within the air
chamber. § 12. Other things being equal, the increase of temperature was
less by using the solid material like mica or cards, than without. This
illustrated that a part of the energy of the spark was converted into
heat and a part into mechanical force, and explained why sound, § 24, is
produced by a spark and by lightning.


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




                               CHAPTER II


                                -------

[Illustration:

  VI
]

28. DAVY, BANCALARI AND QUET’S EXPERIMENTS. ELECTRIC ARC, MAGNETISM AND
FLAME. SOUND PRODUCED. PRACTICAL APPLICATION OF ELECTRIC ARC. _Phil.
Mag._, 1801.—When the electric arc, for example between two carbon
electrodes, occurs, in a powerful magnetic field, it is violently drawn
to one side as first shown by Sir Humphry Davy, as if the wind were
blowing it and sometimes it is broken into two parts. Fig. VI. Again a
loud noise is produced. § 9. Without the magnet, the appearance is as at
the left. With the energized magnet, the arc and light, as a whole, are
as shown at the right.


29. DE LA RIVE’S EXPERIMENT. ROTATION OF LUMINOUS EFFECT BY MAGNET.
APPLICATION TO EXPLAIN AURORA BOREALIS. _Phil Trans._, vol. 137, 1847.
_Pynchon_, p. 471. _Ganot_, Sect. 928.—An oval discharge tube was
employed, having a highly exhausted atmosphere (for those days) of
spirits of turpentine. A cylindrically shaped pole of a magnet extended
into the bulb half way, Fig. 4, p. 17. The inner end of the magnetic
pole formed one electrode of the tube, and the other electrode was a
ring within the vacuum at the foot of the magnetic pole. A fountain of
light extended from one end of the magnet pole to the other, and
remained stationary, while the magnet was not energized; but the light
was condensed into an arc and travelled around the magnet pole when a
current was passed through the coils of the magnet. For similar action
of magnet on a flexible and movable wire carrying a current, see
experiments of Spottiswoode and Stokes, _Proc. R. So._, 1875. The aurora
borealis rotates around the pole of the earth, and therefore, De La Rive
thought that the phenomenon in his laboratory and in nature were but one
and the same thing and different only in degree. He also extinguished an
arc in open air by means of a powerful magnet.


[Illustration:

  VII
]

30. PLÜCKER AND HITTORF’S EXPERIMENTS. ACTION OF MAGNET ON CATHODE
COLUMN OF LIGHT. _Pogg. Ann._, 1858 and 1869. Plücker found that the
magnet acts on the cathode light in a rarefied atmosphere in a different
manner from that on the anode light. In the former the light follows the
magnetic curves and strike the side of the bulb, according to position
of the poles, see Fig. VII. “Where the discharge is perpendicular to the
line of the poles, it is separated into two distinct parts, which can be
referred to the different action exerted by the electro-magnet on the
two extra currents produced in the discharge.” _Ganot._ § 925.


31. THOMSON’S EXPERIMENT. A DISCHARGE RETARDED ACROSS AND ACCELERATED
ALONG THE LINES OF MAGNETIC FORCE. _Nature_, Lon., Jan. 31, 1895, p.
333. _Lect. Royal Inst._—Prof. J. J. Thomson, F. R. S., performed an
experiment which illustrates that the electrical discharge is retarded
in flowing across the lines of magnetic force and accelerated in flowing
with or parallel to such lines. As illustrated in Fig. 20, p. 17, he
employed a large electro-magnet adapted to be cut in and out of circuit.
He had two air chambers, one a bulb, indicated by a circle, and the
other a tube bent into a rectangle, indicated by the dotted square.
Between these, was an adjustable coil having its terminals connected to
the outside coatings of Leyden jars. When the discharge took place
between the poles of the magnet, that is, in the direction of the lines
of force, the discharge was helped along by the magnetic field, but when
it took place across the bulb, that is, across the lines of force, the
discharge was retarded. “The coil can be adjusted so that when the
magnet is ‘off’ the discharge passes through the bulb, but not round the
square tube; when, however, the magnet is ‘on,’ the discharge passes in
the square tube but not in the bulb.”


[Illustration:

  SOME EXPERIMENTS PRIOR TO LENARD’S.
]


32. THOMSON’S EXPERIMENT. RESISTANCE OFFERED TO STRIAE BY A THIN
DIAPHRAGM. _Lect. Royal Inst. Nature_, Lon. Jan. 31, ’95, p. 333.—It has
often been remarked that lightning always takes the easiest path. The
same has been noticed with references to the artificial electric spark.
Prof. J. J. Thomson, F.R.S. performed an experiment, which not only
confirms this principle but does so in an emphatic manner, and proves it
true in reference to the electric discharge in rarefied gases. He
arranged a very thin platinum diaphragm so as to divide a Geissler tube
into two compartments, Fig. 19, p. 17. He then formed a passage way
around the diaphragm, which could be opened and closed by mercury, by
respectively lowering and raising the lower vessel of mercury along the
barometer tube. When the passage way is opened around the diaphragm, the
luminosity extends through the passage way in preference to going
through the diaphragm. When the passage way is closed by mercury, the
discharge goes through the thin metal plate. The same was found to occur
when the platinum leaf was replaced by a mica scale.


33. SIR DAVID SOLOMON’S EXPERIMENT IN 1894. _Proc. Royal So._, June 21,
’94. _Nature_, Lon. Sept. 13, ’94, p. 490.—With a tube having a
perforated diaphragm, he noticed a “forcing effect” at and near the
hole. The striae had the appearance of being pushed through from the
longer part of the tube—the diaphragm not being in the centre. There was
no passage way around the diaphragm—only through the small puncture. §
19.


[Illustration]


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




                              CHAPTER III


                                -------

34. RIESS’S EXPERIMENT. ELECTRIC IMAGES. _Riess’s Reibungs._ vol. 2, §
739.—He laid a coin upon a plate of glass and charged the same
electrically about one-half of an hour or more. Upon removing the coin
and sprinkling the plate with dust, an engraving of the coin was visible
upon the glass. § 13. A suitable dust is licopodium powder.


35. SANFORD AND MCKAY’S EXPERIMENT. ELECTROGRAPHS. ORIGINAL CONTRIBUTION
BY PROF. MCKAY OF PACKER INST., Brooklyn, May, ’96.—The picture of the
coins in Fig. IX, was produced by the apparatus shown in Fig. VIII, _t_,
_t_, tinfoil, _p_, photographic plate with coins on sensitive side, all
wrapped in black paper. Fig. VIII represents the general arrangement for
taking electrographs. This particular one was made by removing the upper
tinfoil and touching each coin successively with wire from one of the
poles, while the other wire was connected with tinfoil on the opposite
side. The condenser thus formed is charged and discharged many times by
a Holtz machine or induction coil. This is not a new discovery, it was
first described by Prof. Sanford, I think, of Leland Stanford
University, two or three years ago. Other claimants of earlier date
probably exist.


36. LICHTENBERG’S EXPERIMENT. DUST FIGURES. PICTURES DRAWN WITH ANODE
AND CATHODE. _Göttingen_, 1778-79. MOTUM FLUIDI ELECTRICITI.—He drew two
independent superposed pictures upon a flat surface of an insulating
material, for example, rosin. One picture was drawn with one terminal of
a charged Leyden jar. Another picture was drawn with the other terminal
of a charged Leyden jar. He sprinkled upon the surface over the two
pictures, a dust made of a mixture of red lead and sulphur powder. The
former became attracted to the picture drawn with the cathode, and the
latter to that made with the anode, so that the two figures were clearly
visible. Before sprinkling the powders upon the surface it is necessary
to stir them together whereby they become oppositely electrified.


[Illustration:

  VIII
  ARRANGEMENTS FOR TAKING ELECTROGRAPHS. § 35, p. 19.
]


[Illustration:

  FROM ELECTROGRAPHS OF COINS. § 35, p. 19.
  Taken by Prof. McKay.
]


[Illustration:

  X
]

The sulphur arranges itself in tufts with diverging branches and the red
lead in small circular patches. The particular materials, namely, the
sulphur and red lead were first used by Villarsy. In case only one
powder is employed, for example, licopodium, it adheres to both the
positively and negatively electrified portion of the insulating plate,
but in larger quantities upon the latter portions. Fig. X, shows rosin
disc covered with licopodium powder after touching the disc with the
knob of a Leyden jar.


36_a_. HAMMER’S PHOTO-ELECTRIC DUST FIGURES. _From personal
interview._—According to experiments of Elster and Geitel, hereinafter
noted, § 98, Hammer’s dust figures shown in the accompanying half-tone
cut may possibly be accounted for on the principle of the discharge of
negatively electrified bodies by light. Mr. William J. Hammer, _Mem.
Amer. Inst. Elect. Eng._, has a historical collection of incandescent
lamps (_Elect. Eng._, N.Y., April 29, ’96, p. 446.) which were arranged
on shelves in a glass case standing obliquely in the sunlight about an
hour a day. After the lapse of many months, the very fine dust within
the case lodged upon the inner surface of the glass in such a manner as
to produce oval dust figures corresponding somewhat to the shapes of the
lamps and some of them, appear after reproduction by the half-tone
process in the accompanying cut. When the figures are inspected closely
and the circumstances are known, no one can doubt that the sun and lamps
acted as agents in their formation. As to the correct explanation, the
matter has not been sufficiently discussed by scientists (presented here
for the first time) to enable the author to render the opinions of
others, but it is of interest in connection with Roentgen rays and the
discharge of electrified bodies by light. As a matter of course, the
surfaces of the lamps would reflect the light in such a way as to make
bright spots (movable, however, with the sun) upon the glass of the
containing case, and if the latter were in any sense charged by negative
atmospheric electricity, this light would cause a variable amount of
dust to be attracted according to the intensity of the rays striking the
glass. These remarks are in the nature merely of a suggestion of a
hypothesis. The heavy curved black line in the cut is a part of the
frame of the glass case. The incandescent lamps do not show, simply
because the case was empty when the photograph was taken. That the
figures were not due to chemical action was shown by rubbing off some of
the dust with the fingers. Finger marks were pictured on the figures.
Off hand, Mr. Hammer and Prof. Anthony intimate air convection by
differentiation of temperature, as a possible cause.


[Illustration:

  FIG. 1.—HAMMER’S DUST-FIGURE ON GLASS. § 36., p. 21.
]


[Illustration:

  FIG. 2.—HAMMER’S HISTORICAL COLLECTION OF INCANDESCENT LAMPS,
    CONTAINED IN CASE HAVING THE DUST FIGURES. § 36, p. 21.
]


36_b_. Independently of the above peculiar phenomenon, Mr. Hammer
recently had on exhibition at the Electrical Exposition of the National
Electric Light Association in New York, 1896, a portrait formed of fine
dust upon a pane of glass. The circumstances were as follows, as
remembered by the author. Mr. Hammer happened to be in some place where
an artisan was removing a photograph from an old frame. The glass which
protected the portrait exhibited a fac-simile in dust on the inner
surface. The glass had not been in contact with the photograph, because
of a thick passe-partout surrounding the picture. Neither was the glass
an old negative photographic plate. Further test and inspection tended
to prove that the dust picture was executed by some action of the heat
or light of the sun. Prof. Benjamin F. Thomas, of the University of the
State of Ohio, in an interview, scarcely thought that the result was due
to convection, because the dust print was so sharply defined. The
principle of the discharge of bodies by light may be applicable perhaps,
but further experiment would be necessary as a more secure foundation.
It is common to find the print of a picture in a book upon the opposite
page, being due merely to the pressure of the inked surface, as in the
art of printing. This explanation cannot be applied to the dust
portrait, because there was no contact between the photograph and the
glass.


37. KARSTEN’S EXPERIMENT. ELECTRICAL IMAGES DEVELOPED BY CONDENSED
MOISTURE. _Riess’s Reibungselect._, vol. II., § 739.—He arranged the
following articles in the following order: First, a metal plate suitably
insulated; secondly, a piece of a glass plate on top of the metal plate,
and, thirdly, a coin or small metal object on top of the glass. Sparks
were then allowed to pass for several minutes from a Holtz or similar
machine to the coin. The image of the latter appeared by removing the
glass plate and breathing upon it. The bas-relief of the image on the
coin also was visible in all its details, appearing as in Sanford’s
Electrograph, § 35. Theoretical considerations led others to believe
that the figures of Riess and Karsten are due to a different cause from
that involved in the figures of Lichtenberg, for the former are thought
to be due to a molecular action of a permanent nature upon an insulating
material. A slight change in the color often occurs, thereby outlining
the object.


[Illustration:

  DUST-PORTRAIT ON GLASS, § 36., p. 23, DISCOVERED BY WILLIAM J. HAMMER.

  Lighter portions, dust; darker portions, due to less or no dust.
    Finger-marks across the shoulder and at right. Exposure 8 years.
    Portrait as sharp and clear as a daguerreotype. During exposure in
    frame, distance of glass from photograph, 1/16 inch. Above half tone
    was made _from a photograph of the dust-portrait_ only after several
    unsuccessful attempts by different photographers. The original
    dust-portrait is scarcely visible. Let every one examine closely
    glass plates when taken from old frames.
]


37_a_. MCKAY’S EXPERIMENT. MAGNETOGRAPHS. FROM PERSONAL NOTES BY
REQUEST. April, 1896.—Although this experiment does not belong to that
class connected with discharge tubes, yet the phenomenon has a
theoretical interest in connection with X-rays. He obtained a photograph
of different objects in the dark by means of radiations from the poles
of an electro-magnet after two hours’ exposure, but it need not have
been so long, as he obtained clear images in five minutes in one
experiment with frequent variations of current by means of a rheostat,
and by approach and recession of the armature. The elements involved in
the experiment were arranged in the following order: First, a large
inverted magnet for supporting 100 lbs., the poles hanging downward.
Next in order was a wooden board pressing flatwise against the ends of
the poles of the magnet. Next, the objects and the sensitive plates
backed thereby and all enclosed in a completely opaque wrapping
extending over the sides, face, back, etc., of these two elements. Next
in order was an armature about as heavy as the magnet would support. The
cut herein represents the photograph that was produced of the different
objects named. By reading Prof. McKay’s very detailed description in the
_Scientific American_, April 18, 1896, p. 249, the reader may feel
certain that the photograph was not due to light for he tried the
experiments in different ways and with various precautions. In a course
of experiments carried on by student Austin, about Feb. 15, ’96, in the
Dartmouth laboratory, a sciagraph of what appeared to be the lines of
force was obtained by means of X-rays, but upon repeating the experiment
the result was negative. See _Elect. Engineer_, Mar. 11, ’96, p. 257.
Article by E. B. Frost.


[Illustration:

  XI
]

38. PILTCHIKOFF’S EXPERIMENT. LIQUID BAS-RELIEF FACSIMILES BY ELECTRIC
DISCHARGE. _Pro. Acad. Sci._, Paris, March, ’94. _The Electr._, Lon.,
April 13, ’94, p. 656.—These shadow pictures were obtainable either with
the anode or cathode, the particular machine employed being a large
Voss. To either pole was electrically connected a pointed wire which was
held just above the surface of castor oil, in a copper pan. A remarkable
effect was obtained of the shadow of a piece of mica, Fig. XI, of
whatever shape, located between the point and the surface. § 24. Let it
be observed that this shadow was not one in the sense of light and
darkness but it consisted of a plateau within a depression, the former
being of the same shape as though it were a shadow of the mica triangle.
To illustrate the experiment better, let the mica be supposed to be
removed, then will there be a depression formed in the oil upon bringing
the metallic point near to the surface. Now insert the insulating sheet
between the point and the surface, then will there be an elevation
within the depression of the same shape that the shadow would be.


39. GERNEZ’S EXPERIMENT. DISTILLATION OF LIQUIDS BY DISCHARGE. _Phys.
So._, Paris, 1879. _Nature_, Nov. 20, 1879, p. 72.—In order that the
apparatus with which he experimented may be understood, imagine a tube
standing vertically in another tube. The two concentric tubes
communicate with each other at the top only. The Holtz machine is the
generator. The liquids in the two tubes at the beginning stand at the
same level. Sparks are passed through the adjacent air, which is in
contact with both liquids. The liquid at the cathode rises and at the
anode falls. § 38. Such was the experiment performed by Gernez. He was
inclined to conclude that the effect was due to “An electrical transport
of liquids along the moistened surfaces of the tubes.” When the liquid
was alcohol, it actually went over as by distillation, three times as
fast as water. A soluble salt in water increased the rate of
distillation; and so also did the addition of a small quantity of
sulphuric acid or ammonia. No distillation of bi-sulphide of carbon,
tetra chloride of carbon, nor turpentine occurred. Query: Can alcohol be
concentrated or practically distilled upon this principle?


40. DE LA RUE AND MÜLLER’S EXPERIMENT. STRIAE. BLACK PRINTS ON WALLS OF
TUBE. _Phil. Trans._, 59, ’78.—Particles of the metal of the electrodes
were deposited upon the inside of the glass forming permanent black
striae or bands § 44, at points corresponding to the spaces between the
luminous striae. § 6. near the end.


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




                               CHAPTER IV


                                -------

41. GASSIOT’S EXPERIMENT. STRIAE. TUBE IN PRIMARY CURRENT. CURRENT
VIBRATORY. _Phil. Trans._, ’59, p. 137. _Bakerian Lectures. Phil.
Trans._, ’58, p. 1. _Proc. R. So._, x., pp. 36, 393, 404; xii., p. 329;
xxiii., p. 356.—The form of tube in which to obtain luminous striae to
the best advantage was that of a dumbbell with the electrodes located
respectively in the balls—afterwards confirmed by Sir David Solomons,
Bart. _Proc. Royal So._, June 21, ’94. _Nature_, Lon., Sept. 13, ’94, p.
490. He obtained in the vacuum luminosity with 500 Daniell’s cells,
which he found to be the least E. M. F. that could be employed. He
omitted, and apparently overlooked, the introduction of an automatic
interrupter in the circuit and the use of a very low E. M. F. § 52. In
conjunction with Spottiswoode, 1,080 cells of chloride of silver (about
2,000 volts) were employed, first without, and then with condensers. One
of the condensers consisted of the usual tinfoil type, and the other of
a self-induction kind, namely of about 1,000 feet of wire. The results
were striae with the condensers, and no striae without the condensers. §
8_a_. The results suggested to them that there was some relation in
principle between the striae and vibration of the current. They
therefore built an ingenious apparatus to test whether this was true or
not, and they found such was the case by the following related means. If
a current passing directly from the primary battery through the
condenser and the discharge tube is undulatory or intermittent in any
sense, then it would be able to induce a current in the secondary of the
induction coil. § 8 at centre. They found that there was a current thus
induced, and they detected it by means of a small discharge tube which
became luminous. Fig. 3 p. 17. This was an independent tube near the top
of the figure, having nothing to do with the one containing striae,
which were produced by the primary current and shown at the right. Dr.
Oliver Lodge, F.R.S., in treating of the cathode and X-rays in _The
Elect._, Lon., Jan. 31, ’96, p. 438, stated the following with reference
to Gassiot’s experiments: “In the days of Gassiot and other early
workers (§ 43) on the discharge in rarefied air, it was the stream from
the anode that chiefly excited attention. It is this which developed the
well-known gorgeous effects which used to be shown at nearly every
scientific conversazione.”


42. POGGENDORFF’S EXPERIMENT. EFFECTS OF INTERRUPTING A CURRENT WITHIN
DISCHARGE TUBE. _Phil. Mag._, 4th Se., vol. x., 1855, p.
203-207.—Imagine an electric bell vibrator and magnet within the glass
receiver upon an air pump. Upon connecting the magnet and vibrator in
series with a small electric battery, it is evident that in the open
air, as usual in electric bells, there will be a minute violet spark at
the terminals of the circuit breaker. § 6. Now, let the air be exhausted
as far as possible by means of a mechanical pump as constructed in 1855.
Poggendorff performed such an experiment, and he noticed that in the
poor vacuum the ordinary violet spark became yellow, while blue light
like a small enveloping tube surrounded the hammer of the vibrator and
wire leading to the opposite contact and a little projection extending
away from the hammer. His experiment was unique, because showing for the
first time that a current from a battery, if interrupted in the vacuum,
will not only produce the usual minute spark, but that a blue tube of
light will be produced around the conductors within the vacuum.


43. DE LA RUE AND MÜLLER’S EXPERIMENT. SOURCE OF THE STRIAE AT THE
ANODE. NUMBER OF STRIAE VARIED BY CHANGE OF CURRENT. _Phil. Trans._,
1878.—By an arrangement of means for causing different pressures, they
made a discovery, namely, that as far as the eye is concerned the striae
begin to have their existence at the anode. § 46. Imagine the internal
gas pressure to become less and less. First, a violet luminosity occurs
around the anode as in § 42. As the pressure becomes less and less,
luminous striae move toward the cathode accompanied by more and more
striae, which increase either to form a column reaching a certain
distance or else extending through the whole distance between the
electrodes. § 46. They observed that when the E. M. F. was constant and
the current changed, the variation in the appearance of the striae was
very regular. § 41. With some tubes the number of striae increased with
the increase of current, while with a decrease of current the number of
striae became less and less. § 8_a_. With some tubes the number of
striae increased while the current decreased. § 8_a_. With the use of a
condenser, then as the E. M. F. decreased together with a diminution of
current, the number of striae varied. The striae nearest the anode
vanished first, as they diminished in number with the fall of the E. M.
F. The striae on the other hand originated at the anode, when the charge
of the condenser was gradually increased from a minimum, and then the
striae continued to increase from the anode as the source. As to the
color of the striae, the same was changed by an alteration of the
current.


44. SOLOMONS’ EXPERIMENT. DARK BANDS BY SMALL DISCHARGES. _Nature_,
Lon., Sept. 13, ’94. _Proc. R. So._, June 21, ’94.—Solomons found that
in a very dark room, striae (alternate light and darkness) appeared with
very _minute_ discharges, and as the current was increased, they
vanished, appearing again when the discharge was strong. He could not
obtain them until the luminous column extended to the glass forming the
large glass tube. § 40.


45. SPOTTISWOODE’S EXPERIMENT. GOVERNING THE MOTION OF STRIAE. EFFECT
UPON MOTION BY DIAMETER OF DISCHARGE TUBE. MOTION STOPPED BY MAGNET.
_Proc. R. So._, vol. 33, p. 455.—Spottiswoode found that he could obtain
motion when he desired. He introduced some constant resistances and also
a rheostat of fine adjustment. The least change of resistance caused
some effect upon the striae. The general principle that he established
was that letting it be assumed that the striae are stationary then; “An
increase of resistance produces a forward flow, and a decrease of the
resistance a backward flow,” differences of as little as 1 ohm in the
primary current caused the effect. Sometimes the velocity of the flow is
fast and sometimes slow, being so rapid in certain instances that the
unaided eye cannot distinguish them, but they are known to exist by the
use of the revolving mirror. § 46. With tubes of small diameter,
compared with their length, he noticed the fact that the striae in one
portion of the tube moved faster than those in another portion. § 46.
Sometimes one group moved while the other one was stationary. Sometimes
they moved in opposite directions. This last named phenomenon occurred
also in very wide tubes. The points at which the charge took place he
called nodes. He discovered external means for stopping this action. He
did it by means of a magnet located opposite one end of the tube. § 31.
When the magnet was energized, all motion ceased. § 31.


[Illustration:

  FROM SCIAGRAPH OF FOOT DEFORMED BY POINTED SHOES. § 204.
  By Prof. Miller.
]


[Illustration:

  FROM HAMMER’S MOLECULAR SCIAGRAPH. § 117., p. 114.
]


46. THOMSON’S EXPERIMENT. VELOCITY OF STRIAE CHECKED AT THE CATHODE.
_Nature_, Lon. Jan. 31, ’96, p. 330.—A tube 50 ft. long was exhausted, §
8_a_., as to striking distance. In this particular experiment, he caused
a single interruption in the primary of the induction coil, and observed
the motion of the striae from the anode to the cathode by means of a
rotating mirror. § 43. The luminosity began at the anode and travelled
toward the negative with a high velocity, but upon its arrival at the
negative pole its velocity was checked. He said that the striae did not
disappear at the cathode like a rabbit would in entering a hole, but
they lingered around the electrode for some time. As a consequence of
this delay, he found as expected, an accumulation of positive
electricity, § 4, in the neighborhood of the cathode. It is a general
principle, therefore, that when a discharge passes between a gas and
metal, there is an accumulation, illustrating that the discharge
experiences a difficulty or resistance. § 32 and 33. The experimenter,
Prof. J. J. Thomson, acknowledged that Profs. Liveing and Davy had
noticed similar effects.


47. THOMSON’S EXPERIMENT. DISRUPTIVE DISCHARGE AND ELECTROLYSIS.
_Nature_, Lon. Jan. 31, ’95. _Lect. S. Inst. The Electr._, Lon. vol. 31,
p. 291, 316, and vol. 35, p. 578. _Trans. R. So._, ’95.—The discharge of
electricity through conducting liquids is, with scarcely an exception,
(example, mercury) accompanied by a chemical action. Faraday and Davy
both performed early experiments in this direction. Prof. J. J. Thomson
has set forth some instructive facts and which act as evidence that
there is a close relation between the disruptive discharge and chemical
action between the dielectric and electrodes. § 6 and 7. He made this
experiment in connection with his investigations relating to the
difficulty the positive electricity experiences in passing from a gas to
the negative electrode. § 46. He carried this experiment further, by
testing gases of different chemical natures. The apparatus he employed
consisted first of an alternating current generator, a high tension
converter, a bulb for containing first one gas and then another, whose
metal electrodes were connected with the secondary of the transformer,
and an electrometer connected to a third electrode which could be moved
about within the bulb. The operation was as follows: when the bulb
contained oxygen which is an electro-negative gas, the third movable
electrode received a positive charge in whatever part of the bulb it was
moved to, but with hydrogen instead of oxygen at atmospheric pressure,
the third electrode received a positive charge far away from the arc
between the other electrodes, but very near the arc it received a
negative charge. He then rarefied the atmosphere of hydrogen and he
noticed that the space where the third electrode became negative,
contracted, and at about 1/3 of an atmosphere became practically
nothing, so that the said third electrode connected to the electrometer
became slightly positive at all points within the hydrogen. § 4. The
next step consisted in using a bulb, having oxydized copper electrodes
and a hydrogen atmosphere at the pressure where there was only positive
electricity, that is about 1/3 of an atmosphere. This remarkable
phenomenon occurred; there was no positive electricity, but only
negative. When the copper oxide was reduced, the positive electricity
only, existed in all parts of the bulb. In brief, bright copper
electrodes left a positive charge in the gas, while oxydized electrodes
left a negative charge. He argued upon the results of this experiment to
account for the delay in the passage of the electricity from the gas to
the metal, § 46. In later experiments, he used the spectroscope to
detect decomposition. § 6, at end.


48. DE LA RUE AND MÜLLER’S EXPERIMENT. HEAT STRIAE. _Phil. Trans._, vol.
159, 1878—They arranged for the best conditions, that is, when a small
number of striae occurred in conjunction with a wide, dark interval. §
44. They found that the heat was greatest at the position of maximum
luminosity, but they also found that heat was generated at the dark
spaces. A novel feature was the discovery of the development of heat in
the middle of the tube even when there was no luminosity, § 9_a_, near
end, so that they thought it probable there may be what might be termed
heat striae, independently of luminous striae.


49. SPOTTISWOODE AND MOULTON’S EXPERIMENT. SENSITIVE STATE. AIR-GAP IN
CIRCUIT FORMS BEST METHOD OF OBTAINING. BRANCH CURRENT TO EARTH VERIFIED
BY A TELEPHONE. SENSITIVE STATE BY A SINGLE QUICK DISCHARGE. _Phil.
Trans._, 1879, p. 165, and April 8, 1880.—By sensitive state of luminous
effects in a Geissler tube is meant the susceptibility of the light (§
28) to an outside conductor connected to earth. Fig. 5, p. 17. When
one’s hand is brought near a Geissler tube the change near the hand
sometimes occurs and sometimes it does not. § 8. In the first place, the
effect is more easily noticeable if the vacuum tube is comparatively
wide or thick in diameter. With the electric egg, for example, the
luminous effect, instead of extending more or less across the space
between the electrodes, reaches from one of the poles to a conductor on
the outside of the egg, provided said conductor has an earth connection
or large capacity. Some of the light continues to exist nevertheless
between the two poles. The general principle is that the division exists
because of the re-distribution or branching of the disruptive discharge.
It was not known why the luminosity should be affected by such an
outside conductor sometimes, and remain the same at other times but the
above named experimenters discovered causes which could be depended upon
to produce the sensitive state. The apparatus will be described. They
had the usual Geissler tube with the platinum wire electrodes, and a
Holtz machine as the generator. They were led to believe that
intermissions of the current had a great deal to do with the production
of the sensitive state, and accordingly they arranged for an air-gap in
circuit with the machine and with the vacuum tube. § 51. They not only
observed that such a gap caused the sensitive state, but that an
increase in the length of the gap made the luminous column more
sensitive. They increased the gap so much that the ramifications of the
light could be seen. If an induction coil is employed as the secondary
generator, a condenser should be coupled up in connection with it. The
two in combination thereby produce the sensitive state, but upon cutting
out the coil and charging the tubes from the condenser the sensitiveness
can not be detected. Instead of the permanent air-gap, may be employed a
rapid circuit interrupter, coupled up between a Holtz machine and a
vacuum tube. The manner of coupling up is to place the interrupter in a
shunt to the vacuum tube. Difficulty had been found in early experiments
to obtain the sensitive state with those vacua which give striae. With a
rapid circuit interrupter and an induction coil, the breaks occurring
240 per second, the luminous column was not only broken up into striae,
but were acted upon by the approach of an outside conductor connected to
earth. The sensitive state is not always made apparent by the appearance
of attraction of the luminous light to the outside conductor. Sometimes
the light seems to be repelled. These two phenomena may be caused in the
same tube. This feature of the sensitive state constitutes the beginning
of radiations of energy through the walls of a vacuum bulb, like X-rays.
Some action or other in these cases takes place through the glass. They
tried an experiment in which one of the electrodes of the vacuum tube
was entirely on the outside. The electrical discharge was found to be
sensitive, for the discharge was changed in its appearances by the
presence of an outside conductor connected to earth. Another cause of
the sensitive state was observed, namely, the brevity of the charge.
This may be illustrated with a Leyden jar, which is known to give an
almost practically instantaneous discharge. A single discharge from such
a jar produced a flash of light which was in the sensitive state. The
nomenclature by which the experimenters defined the cause of the
phenomena is made up of the words: Re-distribution of electricity, and a
relief of the external strain.


49_a._ No re-distribution took place unless the outside conductor was
connected to earth or to a conductor of large capacity, nor would an
outside conductor, which was already charged, serve to exhibit the
sensitive state. The re-distribution effect was proved by means of a
telephone connected in circuit between the outside conductor and the
earth Fig. 5, p. 17. When the state was sensitive, that is, during the
use of the air-gap, the telephone produced a sound in unison with the
intermissions occurring at the air-gap. § 9 and 9_a_.


50. REITLINGER AND URBANITZKY’S EXPERIMENT. SENSITIVE STATE ILLUSTRATED
BY A FLEXIBLE CONDUCTOR WITHIN THE DISCHARGE TUBE. _Proc. Vienna Acad._,
1879. _Nature_, Nov. 20, 1879.—The discharge tube was 20 cm. long. It
had the usual platinum electrodes, and it stood upright. From the upper
electrode, was suspended a strip of tinfoil in the middle of the tube,
which was connected to a pump so that the density of the gas could be
varied. At atmospheric pressure, the secondary current of a Ruhmkorff
coil connected to the electrodes caused the strip to be attracted to the
glass tube. The attraction was less and less as the process of
exhaustion was carried on, and when a pressure indicated by 7 mm. was
reached, the strip was neither attracted nor repelled, but hung downward
the same as without any electricity whatever, but it was _attracted_ by
a neighboring shell-lac rod which had been rubbed with cloth, and it was
_repelled_ by a glass rod which had been rubbed with amalgam, it being
assumed that the strip was connected to the anode. § 36. The opposite
action took place when it was connected to the cathode. As the
exhaustion continued and became greater and greater, these actions died
away also up to a rarefaction of about 4 mm. Independently of the degree
of rarefaction, the flexible strip of tinfoil was always deflected by an
outside conductor connected to earth. § 49.


51. TESLA’S EXPERIMENT. INCANDESCENT ELECTRODE BY HIGH POTENTIAL AND
ENORMOUS FREQUENCY. SYSTEM REFERRED TO BY ROENTGEN FOR GENERATING
POWERFUL X-RAYS. _U. S. Letters Pat._, No. 454, 622, June 23, ’91.
_Martin’s Researches of Tesla_; _Trans. Amer. Inst. Elec. Engineers_,
May 20, ’91; _Elec. Review_, N.Y., June 24, ’93, p. 226; _Lect. Franklin
Inst._, Feb. 24, ’93, and _Nat. Elec. Light Asso._, Mar. 1, ’93; also
_Lect. in Europe_. Later he again experimented in this direction, see
_Elec. Review_, N.Y., May 20, ’96, p. 263.—By the U. S. Patent Office he
was granted, among other claims, the following: “The improvement in the
art of electric lighting herein described, which consists in generating
and producing for the operation of lighting devices, currents of
enormous frequency and excessively high potential, substantially as
herein described.” A simple combination of circuits together with great
skill in the construction of apparatus involving high powers of
insulation, resulted in the production, within a vacuum, of an electrode
radiating intensely white light. The circuit may be easily traced in the
diagram Fig. 17 p. 17. Briefly described, there may be noticed an
alternating current generator of comparatively low E. M. F. The current
from this generates a secondary current by means of an induction coil.
This secondary current generates a tertiary current by a second
induction coil. An air-gap for automatic and intermittent disruptive
discharges, § 49 near end, is in the circuit of the secondary coil of
the first named induction coil, which is directly charged by the
alternating current generator. The gap may be noticed between the two
balls. In shunt to the air-gap is a condenser (see Fizeau, chapter I.)
represented by several parallel lines. The lamp consists merely of an
evacuated bulb having an electrode of carbon or other refractory
material, which is connected to one pole of the last secondary coil
while the other pole may be outside, and may consist, for example, of
the walls of a room, which in such a case should be of some electric
conducting material. The higher the vacuum the more intense the light;
he found no limit to this rule. Fig. 16_a_ p. 17 illustrates his ideal
method of lighting a room. He found that with two plates at a distance
apart as indicated and connected to the poles of the coil, and with
electrodeless vacuum bulbs, the latter became bright in space—no
mechanical or electrical connection other than air and the assumed
ether.


52. MOORE’S EXPERIMENT. LUMINOSITY IN DISCHARGE TUBE BY SELF-INDUCED
CURRENTS. _Trans. Amer. Inst. Elect. Eng._, Sept. 20, ’93 and April 22,
’96. _Several U. S. Letters Patent._ Invented 1892.—During or about
1831, Prof. Henry discovered that when the circuit of a primary battery
was interrupted, a self-induced current, which he called an extra
current, was produced. When the circuit was closed, there was also a
self-induced current, but very much feebler than that obtained on
interruption. The self-induced current occurred only at or about the
instant of interruption or completion. He found also that the
self-induced current produced by interruption was enormously increased
in E. M. F. if the circuit included a helix of very long and fine wire.
It was further increased by the presence of an iron core. With one or
two cells, the spark upon interruption was scarcely visible, but with a
fine wire 30 or 40 feet long, an appreciable spark was obtained during
interruption. With but a comparatively few cells, and with a magnet for
example like a telegraph relay, the E. M. F. arose to several thousand
volts at the instant of interruption. D. McFarland Moore introduced into
such a circuit a Geissler tube and provided a rapid automatic
interrupter. Page, Ruhmkorff and others had, at an early date, noticed
the desirability, in operating Geissler tubes by secondary currents, to
obtain quick interruption in the primary circuit in order to produce the
best effects in the Geissler tube. Moore caused the interruptions to
take place in a vacuum, so high that a disruptive electrical discharge
could not pass. The break was therefore, absolutely instantaneous and
complete. By this system, illustrated in diagram in Fig. 18, p. 17, he
obtained all the luminous effects, actions by magnets, the sensitive
state, striae and all the other phenomena heretofore noticed in Geissler
tubes and some of those obtained by Tesla with his apparatus as just
described. In greater detail, it will be noticed that he had a dynamo of
rather low E. M. F., generally 100 volts, and a high vacuum containing a
circuit interrupter operated automatically by a magnet outside like a
vibrator in an electric bell. The magnet served also as the self
inductive device. The magnet and interrupter were in series with each
other, therefore, while the Geissler tube was in series with the magnet,
and the electrodes extended either inside of the Geissler tube or
remained on the outside. He performed numerous experiments on similar
lines and developed the system on a large scale, whereby rooms (e.g. the
hall of the _Amer. So. Mech. Eng._, N.Y.) have been illuminated as if by
other artificial illuminants, by employing long and numerous vacuum
tubes. Among several discoveries was that of the production of a bright
pencil of light along the axis of a long open helix, which formed one of
the internal electrodes. The Patent Office made strenuous efforts to
determine the degree of novelty, assuming that some one else must have
conceived the idea of employing a self-induced current to operate
Geissler tubes; but nothing nearer than Poggendorff’s experiment § 42
could be found, and therefore the following claim (in patent 548576,
Oct. 22, ’95,) was granted among a hundred or so relating to
developments and details and particularly covering the vacuum
interrupter. “The method of producing luminous effects, consisting in
converting a current of low potential into one of high potential, by
rapidly and repeatedly interrupting the low potential current in its
passage through a self-inductive resistance, and passing the former
current through a Geissler tube, thereby producing light within the
tube.”


[Illustration:

  EDISON’S BENEFICENT X-RAY EXHIBIT, § 82, p. 71, and § 132, p. 126.
  Calcic tungstate screen at center, sciascope near right.
]


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




                               CHAPTER V


                                -------

53. CROOKES’ EXPERIMENT. DARK SPACE AROUND THE CATHODE. _Lect. Brit.
Asso., Shef., Eng._, Aug. 22, ’79.—According to Lenard (_The Electr.,
Lond._, Mar. 23, ’94) Hittorf discovered the cathode rays, and Varley, §
61_a_., and Crookes studied them. The pressure of the residual gas was 1
M. of an atmosphere. Prof. Crookes, F.R.S., maintained the evacuated
space in communication with the air pump and with an absorbent material.
Before his time most experimenters worked with a vacuum not much less
than 30,000 M. The first experiment is illustrated in diagram, at Fig. 6
p. 17, but the vacuum was not the highest in this type. The tube was
cylindrical and was provided with electrodes at the ends. Another
electrode was located at the centre and was made the cathode, while the
two terminal electrodes were made the same pole; namely, the anode. Upon
connecting the tube in circuit with the secondary of a large induction
coil, the luminosity did not extend either continuously or in striae
throughout the length of the tube. Former investigators had likewise
noticed the dark space. The space and glass on each side of the central
cathode were dark. The dark space extended for about one inch on each
side of the negative pole. It is not intended here, any more than in
former cases, to present theories in explanation further than to briefly
allude to any conclusion at which the experimenter himself arrived.
Crookes’ explanation of the phenomena has not been universally accepted,
nor has it been proved otherwise. The knowledge of the existence of
rays, now known as Roentgen rays, will assist in formulating theories
upon the Crookes’ phenomena and may either confirm some of his views or
overthrow them. Crookes considered that the residual atmosphere was in
such a state as to be as different in its properties from gas, as gas is
from liquid and liquid from solid, and therefore he named the attenuated
atmosphere radiant matter, or fourth state of matter. He concluded that
the remaining particles of the gas forming the radiant matter moved in
straight lines over a great distance as compared with that moved through
by molecules at the ordinary pressure. He called this distance the “mean
free path.” If his theory is correct, this dark space is due to the fact
that the molecules in motion at and near the cathode do not bombard each
other and therefore do not produce the effect of light. When the motion
is arrested by particles of gas themselves, within the bulb, then is
light generated. The force propelling the particles from the positive
pole was supposed to be less. In order to let the experiments speak for
themselves, as much as possible, without being too much influenced by
the opinion of the experimenter; the theory is only briefly alluded to
as above, and will not be further applied in the presentation of his
other experiments. In view of the radical discoveries of Lenard and
Roentgen, after the installation of the Crookes phenomena, it has been
the policy of the author to present all the experiments as facts for
evidence in behalf of the general theories, which may be hereafter
formulated independently of old theories. Therefore, the reader should
bear in mind the teachings of the various experiments with the view of
arriving at general principles and hypotheses.


54. RELATION OF VACUUM TO PHOSPHORESCENCE.—He started with such a high
vacuum that he could not obtain any electrical discharge. § 25. There
was, therefore, no phosphorescence in the glass tube, whatever. The
caustic potash, which had been employed to absorb the last trace of
moisture and carbonic acid gas, was slightly heated, and very gradually.
Then it was noticed that a current began to pass and that the glass
became green, and apparently on the inner surface. As the heat
continued, the green passed gradually away and was replaced by striae,
which first appeared to extend across the whole diameter of the glass
tube (§ 40) which was a long cylindrical tube, and then became
concentrated toward the axial line of the tube. Finally, the light
consisted of a pencil of purple. § 10. When the source of heat was
removed so that the moisture and carbonic acid gas could be absorbed
again by the potash, the striae appeared, and then the other effects
just named, only in the reversed order, until the tube acted like an
infinite resistance. Phosphorescence is the correct word, because the
light existed for a few seconds after cutting off the current.


55. PHOSPHORESCENCE OF OBJECTS WITHIN THE VACUUM TUBE.—The construction
in Fig. 7, p. 17, shows how a diamond was caused to phosphoresce within
a Crookes’ tube, being supported in a convenient manner in the centre of
one of the tubes, while electrodes were located near the ends and were
formed of disks facing the diamond. Upon connecting the disks to the
respective poles of the secondary conductor, and by performing the
experiment in a rather dark room, the diamond became brilliantly
phosphorescent, radiating light in all directions. He experimented with
many substances in this way, but found that the diamond was the
best—almost equal to one candle power. In order to exhibit the
phosphorescence of glass in a striking manner, he charged three small
tubes simultaneously. One was made of uranium glass which radiated a
green light. Another was an English glass which appeared blue, and the
remaining one was German glass which phosphoresced a bright green.
Notice difference with respect to light which does not perceptibly cause
phosphorescence of glass. The uranium glass was the most luminous.
Luminous paint, as prepared by Becquerel, and later by Balmain, which
has the property of storing up light and afterwards radiating it in a
dark room for several hours, became more phosphorescent in the Crookes
tube than when subject to day-light. Phosphorescence of the mineral
phenakite, the chemical name of which is glucinic aluminate, was blue,
the emerald, crimson, and spodumene, which is a double silicate, were
yellow. The ruby phosphoresced red, whatever its tint by day-light. In
one tube he had rubies of all the usual tints by day-light, but they
were all of one shade of red by the action of the disruptive discharge
in the tube.


56. DARKNESS AND LUMINOSITY IN ARMS OF V TUBE. See Fig. 8, p. 17. It
will be noticed that in Fig. 6, p. 17, the tube was straight. Crookes
desired to see what effect would take place in a bent tube. He therefore
employed a V shaped tube, having electrodes in the ends—one in each arm.
Upon causing the electrical discharge to take place through the tube,
one arm was luminous and the other was dark. Whatever the E. M. F. was,
the appearances remained the same. No luminosity would bend from one arm
of the V shaped tube to the other. The cathode arm was always luminous
and the anode dark. With a less degree of vacuum, both arms were
luminous, according to early experimenters who thus brilliantly lighted
tubes of the most fantastic shapes.


57. CATHODE RAYS RECTILINEAR. RADIATE NORMALLY FROM THE SURFACE OF THE
CATHODE. In his lecture he had, side by side, two bulbs, one, in which
the vacuum was of such a degree, that a blue stream of light existed
between the negative pole and positive pole, § 54, at centre. It is
evident that the vacuum in this bulb was not very high. Fig. 9, p. 17,
shows a stream extending from the negative to the positive pole, Fig.
10, p. 17, is the same kind of a tube only the vacuum is about 1 to 2 m.
In other words, the vacuum in the latter was just so high that a
discharge took place, and instead of the luminous effect being like that
with a low vacuum, there was a patch of green light directly opposite
the concave negative pole. The radiations from this pole were
rectilinear, crossing each other at a focus within the bulb and
producing upon the glass a phosphorescent spot. It should be remembered
that the word radiations is used as a mere matter of convenience.
Directly opposite the concave cathode, there was a green patch of light
on the inner surface of the glass. It was shown that it made no
difference where the anode was. This fact becomes useful in carrying on
experiments in connection with Roentgen rays, and it may have a great
deal to do with the solution of the theoretical problems in connection
with electrical discharges in vacuum tubes. In regard to the three
streams shown in Fig. 9, p. 17, it may be stated that only one occurred
at a time in the experiment, for, first one anode was connected in
circuit, and then the next by itself, and then the third one by itself,
while the concave pole was always negative. Each time the anode was
changed, the stream changed, and connected that pole which was in
circuit, § 43, but similar changes made upon the tube with a high
vacuum, did not alter the position of the phosphorescent spot. This and
other experiments show that the radiations took place perpendicularly
from the surface of the cathode.


58. SHADOW CAST WITHIN THE DISCHARGE TUBE. This is illustrated in Fig.
11, p. 17, where there is a negative polar disk at the small end of the
egg shaped tube, and a cross near the large end, the same forming the
positive pole. The cross is made of aluminum. There was a novel action,
however, discovered in addition to the mere casting of a shadow. The
glass which had become phosphorescent except within the shadow, became
after a while, less phosphorescent. Its property to phosphoresce became
less as proved by removing the cross, which was arranged to fall down
upon tipping the bulb. Immediately, the part which was within the shadow
became brighter than the rest of the glass, thereby reversing the
appearances, by making a luminous picture of the cross upon only
partially phosphorescent glass. A remarkable feature is that the glass
never recovered its first exhibited power of phosphorescence, neither
did this power entirely become nothing, however many times the tube was
employed. Was the deposit of metal from the cathode the cause?


58_a_. MECHANICAL MOTION PRODUCED BY RADIATIONS FROM THE NEGATIVE POLE.
It occured to Crookes that the radiations from the cathode might perhaps
cause a wheel to turn around. He therefore had a minute wheel made by
Mr. Gimingham, like an undershot water wheel, and its axle rested on two
rails of glass, so that it might roll along from one end of the tube to
the other. The vanes were exactly opposite to the plane surface of the
cathode. The molecular stream or radiations, or whatever they may be,
possibly vibrations, from the cathode, were so powerful mechanically
that the wheel was caused to run up hill, the tube being inclined very
slightly. On the principle that action and reaction are equal, he built
another device in which the negative electrode was movable, and he
observed that when the current was on, the negative electrode moved
slightly. Upon these principles he built the well-known Crookes
radiometer in which the vanes rotated by reaction of the radiations. The
vanes in this form of radiometer were made of aluminum, and a cup of
hard steel served as the bearing, Fig. 12, p. 17. One side of each disk
was coated with a thin scale of mica. The aluminum disks formed the
cathode, while the anode was located at the top. The operation consisted
in connecting the terminals as stated, so that the vanes were the
negative poles and it was observed that the little wheel rotated. The
vacuum was not as high as that for obtaining phosphorescence. With a low
vacuum, an envelope of violet light existed near the surface of the
aluminum vanes. Effects were carefully studied by maintaining connection
with the pump. At the pressure of .5 mm. there was a dark cylinder
opposite the aluminum extending to the glass, and this was the pressure
at which the vanes began to rotate. The dark spaces opposite each vane
became larger and larger in width, until they appeared to be opposed or
resisted by the inner surface of the glass, and then the rotation became
very rapid. He modified this experiment by having vanes entirely of
mica, and by having the cathode disconnected electrically from the
vanes, Fig. 13, p. 17. A coil of metal near the vanes served as the
cathode. The anode was at a distance in the top of the tube as in Fig.
12, p. 17. During the electrical discharge, the wheels rotated by
radiations from the coil which formed the cathode. He made the discovery
that when this coil was heated red hot conveniently by a current from a
primary battery, the vanes also rotated, showing that there is probably
some relation between the radiations from the cathode and heat rays. The
fact remains however, that both kinds of rays produced rotation,
directly or indirectly.


59. ACTION OF MAGNET UPON CATHODE RAYS.—He had two tubes, one of which
is shown in Fig. 14 and the other in Fig. 15, on page 17. In the former,
the vacuum was so low that a violet stream of light existed between the
electrodes. In the other, the rays were invisible, but were converted
into luminosity by projection at an exceedingly slight angle, upon a
phosphorescent screen arranged along the length of the tube and inside
thereof. Inasmuch as the whole surface of the cathode in the latter case
radiated parallel and invisible rays, he cut off some of them by a mica
screen having a hole in the centre and located near the negative pole,
so that only a pencil of invisible rays could go through the mica screen
and act upon the phosphorescent screen. In both cases, there was visible
a straight pencil of light. Now notice the effect which took place upon
locating a magnet as indicated in the figures. With the low vacuum, the
pencil was bent out of its course but returned again to the line of its
original path. § 28. With the high vacuum, the rays were bent but did
not return to their original direction nor parallel thereto. In the
former case, the magnet acted as upon a very delicate flexible
conductor, while in the latter, it acted, as Crookes said, like the
earth upon projectiles. He modified the latter experiment in order to
determine if the similarity between this phenomenon and gravitation
existed in other respects. He anticipated that if the molecular
resistance to the rays were increased they would be bent more out of
their course like a horizontally projected bullet. He therefore heated
the caustic potash sticks slightly, and in view of the liberation of
molecules of water within the vacuum tube, the rays, he thought, would
be resisted; and such was the case to all appearances, for then the
pencil of light was bent out of its course to a greater extent, although
the magnetic power remained the same as well as the E. M. F. producing
the electric discharge. He therefore established, apparently, the
principle that the magnetic actions upon cathode rays vary somewhat in
their nature according to the degree of vacuum. In either case, it may
be stated incidentally, that when the magnet was moved to and fro, the
pencils of light waved back and forth.

In the modified form of construction over that shown in Fig. 15, p. 17,
he caused a wheel to rotate that was located in the high vacuum. The
vanes of the wheel were so located that the faces of the same were
perpendicular to the direction of the pencil of the rays radiating from
the cathode. When the magnet deflected the rays, the wheel ceased
rotation.


60. MUTUAL REPULSION OF CATHODE RAYS.—If the little mica screen, as
shown in Fig. 16, p. 17 has two holes, and if there are two cathodes
instead of one, there will also be two pencils of light. He performed an
experiment involving the latter modification, and the result was
something that could not have been predicted. The two pencils, as
displayed by the long fluorescent screen, repelled each other like
molecules similarly electrified. The white pencils, it will be noticed,
were repelled from each other and showed their condition when both of
the negative poles were in circuit. The black pencils show the location
of both of the pencils when only one pole is in circuit at a time, the
direction being perpendicular to the plane of the cathode disc (§ 57) at
end.


61. HEATING AND LIGHTING POWER OF CATHODE RAYS. HEAT OF PHOSPHORESCENT
SPOT.—By making the cathode concave as in Fig. 10, p. 17, and so
locating it that the focus of the cathode rays falls upon some
substance, the latter becomes very hot. In this way Crookes melted wax
on the outside of the bulb at the phosphorescent spot. Further than
this, the heat was so great that it cracked the glass without at first
injuring the vacuum; next the glass at this point softened, and the air,
by its pressure, rushed into the bulb, forcing a hole through the soft
part. He performed an experiment also which illustrated the intensity of
the heat when the rays were brought to a focus. He used an unusually
large electrode like a concave mirror, and in the focus, which was near
the centre of the bulb, he supported a small piece of iridio-platinum.
At first, with a moderately low E. M. F., the metal was made white hot.
When a magnet was caused to approach, the rays were drawn to one side, §
59, and the little piece of metal cooled. He then put in all the coils
of an inductorium, and allowed the metal not only to become white hot,
but to become so heated that it melted. How little did Prof. Crookes
know about the most important phenomena associated with his experiment.
Although he was so exceedingly enthusiastic and ingenious in planning
his experiments, and in reasoning, yet it seems almost mysterious that
he should have been subjected to what have become known as X-rays, which
passed into his body, and would have photographed portions of his
skeleton, and which would have performed outside of the tube many of the
acts that were noticed within. Seventeen years elapsed between the time
of Crookes on the one hand, and Lenard and Roentgen’s discoveries on the
other. Dr. Lodge, F.R.S., (_The Elect._, Lon., Jan. 31, ’96, p. 438,)
and Lenard, in his first paper, attributed to Hittorf the discovery of
the mere existence of cathode rays, but credited to Crookes the full
establishment of their properties, deduction of their principles and
formulation of an ingenious theory.


61_a_ As an appropriate conclusion to Crookes’ work, I cannot do better
than to let Lord Kelvin repeat what he said in his Pres. Addr., _Ro.
So._, Nov. ’93, see also _The Elect._, Lon. Feb. 14, ’96, p. 522,
showing that a small portion of the credit is due not only to Hittorf, §
53, but to Varley. “His short paper of 1871, which, strange to say has
lain almost or quite unperceived in the _Proceedings_ during the 22
years since its publication, contains an important first instalment of
discovery in a new field, the molecular torrent § 53, at centre, from
the ‘negative pole,’ the control of its course by a magnet, § 59, its
pressure against either end of a pivoted vane of mica, § 59, at end, and
the shadow produced by its interception by a mica screen, § 58. Quite
independently of Varley, and not knowing what he had done, Crookes
(_Roy. Inst. Proc._, April 4, ’79, vol. LX, p. 138. _Ro. So. Trans._,
’74, “On attractions and repulsions resulting from radiation” Part II,
’76, parts III and IV, ’76, part V, ’78, part VI, ’79) was led to the
same primary discovery, not by accident and not merely by experimental
skill and acuteness of observation.” * * * * “He brought all his work
more and more into touch with the kinetic theory of gases; so much so,
that when he discovered the molecular torrent he immediately gave it its
true explanation—molecules of residual air, or gas or vapor projected at
great velocities (probably, I believe not greater in any case than 2 or
3 kilometers per second, § 61_b_), by electric repulsion from the
negative electrode. This explanation has been repeatedly and strenuously
attacked by many other able investigators, but Crookes has defended
(Presidential address to the _Inst. Elect. Eng._, 1891.) it, and
thoroughly established it by what I believe is irrefragable evidence of
experiment. Skillful investigations perseveringly continued brought out
more and more wonderful and valuable results; the non-importance of the
position of the positive electrode, § 57, near end, the projection of
the torrent perpendicularly from the surface of the negative electrode,
§ 57, at end; its convergence into a focus and divergence thenceforward
when the surface is slightly concave, § 47, near beginning; the slight
but perceptible repulsion, § 60, between two parallel torrents due,
according to Crookes, to negative electrifications of their constituent
molecules; the change of the direction of the molecular torrent by a
neighboring magnet, § 59. the tremendous heating effect of the torrent
from a concave electrode when glass, metal or any ponderable substance
is placed in the focus, § 61. the phosphorescence procured on a plate
coated with sensitive paint by a molecular torrent skirting along it,
Fig. 15, p. 17; the brilliant colors—turquoise blue, emerald, orange,
ruby-red—with which grey, colorless objects, and clear, colorless
crystals glow on their struck faces when lying separately or piled up in
a heap in the course of a molecular torrent, § 55. “electrical
evaporation” of negatively electrified liquids and solids, § 59. (_Ro.
So. Proc._, June 11, ’91.) the seemingly red-hot glow, but with no heat
conducted inwards from the surface, of cool solid silver kept negatively
electrified in a vacuum 1/1,000,000 of an atmosphere, and thereby caused
to rapidly evaporate, § 40 and 139_a_. This last named result is almost
more surprising than the phosphorescent glow excited by molecular
impacts on bodies not rendered perceptibly phosphorescent by light, §
55, at centre. Both phenomena will usually be found very telling in
respect to the molecular constitution of matter and origination of
thermal radiation, whether visible as light or not. In the whole train
of Crookes investigations on the radiometer, the viscosity of gases at
high exhaustion, and the electro-phenomena of high vacuums, ether seems
to have nothing to do except the humble function of showing to our eye
something of what the molecules and atoms are doing. The same confession
of ignorance must be made with reference to the subject dealt with in
the important researches of Schuster and J. J. Thomson on the passage of
electricity through gases. Even in Thomson’s beautiful experiments,
showing currents produced by circuital electro-magnetic induction in
complete poleless circuits, the presence of molecules of residual gas or
vapor seems to be _the essential_. It seems certainly true that without
the molecules, electricity has no meaning. But in obedience to logic, I
must withdraw one expression I have used. We must not imagine the
“presence of molecules is _the_ essential.” It is certainly _an_
essential. Ether is certainly also _an_ essential, and certainly has
more to do than merely to telegraph to our eyes to tell us what the
molecules and atoms are about. If the first step towards understanding
the relations between ether and ponderable matter is to be made it seems
to me that the most hopeful foundation for it is knowledge derived from
experiment on electricity in high vacuum; and if, as I believe is true
there is good reason for hoping to see this step made, we owe a debt of
gratitude to the able and persevering workers of the last 40 years who
have given us the knowledge we have; and we may hope for more and more
from some of themselves and from others encouraged by the fruitfulness
of their labors to persevere in the work.”


61_b_. THOMSON’S EXPERIMENT. VELOCITY OF CATHODE RAYS. _The Elect._,
Lon., Oct. 5, ’94, p. 762; _Phil. Mag._, ’94.—The object of the
experiment of J. J. Thomson was to determine whether the velocity
approached that of light or that of molecules. The apparatus he employed
involved the rotating mirror, which was fully described in _Proc. Royal
So._, ’90, slightly modified. The rays were caused to produce
phosphorescence, while the mirror was so adjusted that when at rest, the
two images on the phosphorescent strips appeared in the same rectilinear
line. Many other elements comprised the apparatus. All the steps were
performed carefully and according to the best methods, but the results
are those which in this experiment are of particular interest, for by
knowing the velocity of the rays, their nature is better appreciated and
that of the X-rays can be better deduced. The velocity bore a close
relation to that of the mean square of the molecules of gases at
temperatures zero ° C. or in the case of hydrogen, 1.8 × 10^5 cm. per
second. As compared with such a velocity, that of the cathode rays was
found to be in the neighborhood of 100 times as great, and this agrees
very nearly with the velocity of a negatively electrified atom of
hydrogen acquired under the influence of the potential fall, which
occurred at the cathode. In further evidence of the verity of this
statement, he made a rough calculation upon the curve or displacement
produced by a magnet upon the rays. § 59. He stated: “The action of a
magnetic force in deflecting the rays shows, assuming that the
deflection is due to the action of a magnet on a moving electrified
body, that the velocity of the atom must be at least of the order we
have found.”


[Illustration:

  FIG. 1.
]


61_b_. PERRIN’S EXPERIMENT. CATHODE RAYS CHARGED WITH NEGATIVE
ELECTRICITY. CORRESPONDING POSITIVE CHARGES PROPAGATED IN THE REVERSE
DIRECTION AND PRECIPITATED UPON THE CATHODE. _Comptes Rendus_, CXXI.,
No. 20, p. 1130; _The Elect._, Lon., Feb. 14, ’96, p. 523.—Jean Perrin’s
object was to discover whether or not internal “Cathode rays were
charged with negative electricity.” That they were had often been
assumed by others, namely, Prof. J. J. Thomson, who considered cathode
rays as due to negatively charged matter moving at high speed. § 61_b_.
Again, Prof. Crookes, principally, and others, showed that they were
possessed of mechanical properties and that they were deflected by a
magnet. § 59. Perrin called attention to the above investigations and
also alluded to the theoretical considerations of Goldstein, Hertz and
Lenard, who favored the analogy of cathode rays to light—whose phenomena
are well answered by the accepted theory concerning assumed etherial
vibrations, which, in both cases, have rectilinear propagation, § 57,
excite phosphorescence, § 54 and 55, and produce chemical action upon
photographic plates. Great ingenuity was displayed, as might be
expected, in the manner in which Jean Perrin proved the proposition
named in the title of this section, at the Laboratory of the École
Normale and also in M. Pallet’s Laboratory. First, therefore, let the
elements of the discharge tube be thoroughly understood. As usual, the
disk N is the cathode, referring to accompanying Fig. 1. A, B, C, D, is
a metal cylinder having a small opening at the right hand end toward the
cathode. Concentrically, is a similar cylinder, acting as an electrical
screen and having a like opening similarly located as indicated. It
corresponds to and plays the part of the Faraday cylinder, being
connected to earth. The principle involved in this apparatus was based
upon the laws of influence, which permitted him to ascertain the
introduction of electric charges within a conducting envelope, and to
measure such charges. During the discharge, the cathode rays were
propagated from the cathode to and within the cylinder A, B, C, D, which
immediately and invariably became charged with negative electricity. To
prove that the charge was due to the cathode rays, he deflected them
away from the opening in the protecting cylinder E, F, G, H. The
cylinder was not under these circumstances charged, the rays being
outside. He went further and made some quantitative analysis in a rough
way to begin with. He related: “I may give an idea of the amount of the
charges obtained when I state that with one of my tubes, at a pressure
of .001 m. of mercury, and for a single interruption of the primary
coil, the cylinder A, B, C, D, received sufficient electricity to bring
a capacity of 600 C. G. S. units to a potential of 300 volts.” Upon the
principle of the conservation of energy, he was induced, he said, to
search for corresponding positive charges. “I believe I have found them
in the very region where the cathode rays are generated, and that they
travel in the reverse direction and precipitate themselves on to the
cathode.” He verified this corollary by means of a modified feature of
the apparatus shown in Fig. 2. The construction was the same except that
there was a diaphragm having a perforation β´ within the protecting
cylinder and opposite the smaller cylinder exactly as indicated, so that
the positive electricity which had entered through β could only act on
the cylinder A, B, C, D, by traversing also the hole β´. “When N was the
cathode, the rays emitted traversed the two apertures at β and β´
without any difficulty, and caused the gold leaves of the electroscope
to diverge widely. But when the protecting cylinder was the cathode, the
positive flux, which, as was shown by a previous experiment, enters by
the aperture β, did not succeed in separating the gold leaves, except at
very low pressures. If we substitute an electrometer for the
electroscope we shall see that the action of the positive flux is real,
but that it is very small and increases as the pressure decreases.”


[Illustration:

  FIG. 2.
]


He inferred that: “These results, taken as a whole, do not appear to be
easily reconcilable with the theory that the cathode rays are
ultra-violet light. On the contrary, they support the theory that
attributes these rays to radiant matter, § 54, near centre, a theory,
which may at present, it seems to me, be enunciated as follows: In the
vicinity of the cathode the electric field is sufficiently strong to
tear asunder into _ions_ some of the molecules of the residual gas. The
negative ions start off toward the region where the potential increases,
acquire a considerable velocity, and form cathode rays; their electric
charge, and consequently their mass (at the rate of one gramme
equivalent per 100,000 coulombs) is easily measured. The positive ions
move in the reverse direction; they form a diffused tuft, susceptible to
magnetism, but are not a regular radiation.”


61_c_. ZEUGEN. _Comptes Rendus_, Jan. 27, 1896.—In a note regarding the
experiments of Roentgen, called attention to his own communications to
the Academie des Sciences in February and August 1886, describing his
photographs of Mt. Blanc taken in the night by the invisible
ultra-violet rays. This note is entered as many newspapers reported the
photograph to be due to cathode rays, imagine the intense
phosphorescence upon a screen at the top of the mountain, if such were
the case.


62. GOLDSTEIN’S EXPERIMENT. PHOSPHORESCENCE OF PARTICULAR CHEMICALS BY
CATHODE RAYS. _Nature_, Lon. Feb. 21, ’95, p. 406. _Weid. Ann._, No. II,
’95.—Lithium chloride when acted upon by cathode rays, phosphoresced to
a dark violet color or heliotrope, which it retained for some time in a
sealed tube. Chlorides generally and other haloid salts of potassium and
sodium showed similar effects. The colors were superficial and could be
driven away rapidly either by heating or the action of moisture.


63. KIRN’S EXPERIMENT. SPECTRUM OF POST PHOSPHORESCENCE OF DISCHARGE
TUBES. _Wied. Ann._, May, ’94. _Nature_, Lon. June 7, ’94, p. 131.—Carl
Kirn compared the spectra of the phosphorescence of a vacuum bulb,
during and immediately after the discharge. The details are as follows:
The spectrum of the after-glow, § 54, at end and 22, was found to be
continuous. In this connection, see a plate showing different kinds of
spectra, for example, _Ganot’s Physics_, frontispiece. The spectrum
shortened from both directions to a band between the wave lengths of 555
and 495µµ. The spectrum then continued to grow shorter and shorter until
it disappeared at the line E, which is the position of the greatest
luminosity of the solar spectrum. For experiments on spectrum, see
Fraunhofer in _Gilbert’s Ann._, LVI. During the discharge, the
spectroscope showed a line spectrum corresponding very closely to those
of carbonic acid gas and nitrogen. Some authorities had suggested that
perhaps the after phosphorescence and the beginning of the incandescence
of a solid body, were the same kind of light, but this experiment shows
that such is not the case, unless some relation exists on the ground
that the two phenomena are exactly opposite to each other, and it
confirms similar results obtained by Morrin and Riess. The result
indicates that the nature of the phenomenon is not identical in all
respects with light produced at a high temperature.


63_a_. DE METZ’S EXPERIMENT. CHEMICAL ACTION IN THE INTERIOR OF THE
DISCHARGE TUBE. INTERNAL CATHODE RAYS. _L’Ind. Eler._, May 10, ’96, and
_Comptes Rendus_, about April, ’96. Translated by Louis M. Pignolet. He
used a cylindrical discharge tube divided into two halves which fitted
together by an air-tight ground joint. In one-half were the anode and
the cathode; in the other half was the holder containing the sensitive
paper or films. The holder was exposed to the direct action of the
cathode rays and was closed by a cover of cardboard or sheet aluminum.
The objects to be photographed were placed between the cover and the
sensitive film or paper. The tube was connected to a Sprengel pump which
maintained its vacuum during the experiments. In this way, twelve
photographs were taken from which it appeared that cathode rays, like
X-rays, penetrate cardboard and aluminum, but are stopped by copper
(1.26 mm.) and platinum (0.32 mm.). Poincaré, in a note in the same
publications as the foregoing, criticised the results of the experiments
of De Metz, claiming they did not prove irrefutably that cathode rays
possessed the essential properties of X-rays, for the cathode rays in
impinging on the cover of the holder would generate X-rays, § 91, which
would give the results obtained. Poincaré did not deny the fact.


63_b_. HERTZ’S EXPERIMENT. THE PASSAGE OF CATHODE RAYS THROUGH THIN
METAL PLATES WITHIN THE DISCHARGE TUBE. DIFFUSION. _Wied. Ann._, N. F.
45; 28, 1892. Contributed by request, by Mr. N. D. C. Hodges of the
_Hodges Scientific News Agency_, N.Y. Found in records at Astor
Library.—A piece of uranium glass was covered partly on one side (which
he calls the front side) with gold-leaf, and on the gold leaf were
attached several pieces of mica. This front side was then exposed to
cathode rays. So long as the exhaustion had not proceeded far, and the
cathode rays filled the whole tube with a blue cone of light, only the
portion of the uranium glass outside the gold-leaf screen showed any
phosphorescence. But as soon as the exhaustion had progressed far
enough, and the light began to disappear, the genuine cathode rays
struck the covered glass, and the phosphorescence manifested itself
behind the gold-leaf. When the cathode rays were fully developed, the
gold-leaf hardly had any effect, while the mica cast deep black shadows.
The same experiment was tried with silver-leaf, aluminum and alloys of
tin, zinc and copper. Aluminum showed the best results; sheets which
allowed no light to pass, allowing the cathode rays free passage. The
rays after their passage through the metal screens did not continue
their straight course, but seemed to be diffused much as light is
diffused by passing through a cloudy medium. In this connection
reference is made to the work of Goldstein, who had noticed also the
reflection of “electric” rays. _Wied. Ann._, N. F. 15; 246, 1882. In
1893, Goldstein published further accounts concerning actions in
discharge tube. _Wied. Ann._, vol. 48, p. 785.


[Illustration:

  DIAGRAM OF LENARD’S APPARATUS. pp. 53 to 69.
]


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




                               CHAPTER VI


                                -------

65. LENARD’S EXPERIMENTS. CATHODE RAYS OUTSIDE OF THE DISCHARGE TUBE.
_Wied. Ann._, Jan., ’94, Vol. LVI., p. 225; _The Elect._, Lon., Mar. 23
and 30, ’94, Apr. 6, ’94; and _Elect. Rev._, Lon., Jan. 24, ’96, p.
99.—Of more importance in connection with X-rays is the consideration of
Lenard’s experiments than any others. The reader must bear in mind that
his exhaustive investigations resulted from his discovery (founded upon
a hint from Hertz) that the cathode rays might be transmitted to the
outside of the generating discharge tube. His interest, therefore, in
the discovery was so great that his researches extended to the minutest
details. Passing from these introductory remarks, the characteristics of
the tube that he employed will be explained first. Reference may now be
made to the accompanying Fig. A. He employed several different kinds of
tubes, but finally settled upon one of which the essential elements are
shown in the said figures. It was permanently connected to the pump, §
53, so that the pressure within could be varied. Opposite the cathode,
which consisted of a thin disk of aluminum, the end of the tube was
provided with a thick metal cap, having a perforation, which in turn was
closed by a thin aluminum sheet secured by marine glue in an air-tight
manner, and called a window. The anode was a heavy brass cylinder, shown
in section, within the discharge tube and surrounding the leading-in
wire of the cathode. The anode and the aluminum window were connected to
each other, electrically, and to earth, as well as two a secondary
terminal of an induction coil, whose electrodes were in shunt to those
of the discharge tube, in order that the operator might adjust the
sparking distance which rapidly increased with the exhaustion. The
induction coil had a mercury interrupter.


65. PROPERTIES OF CATHODE RAYS IN OPEN AIR.—In all directions around the
window upon the outside and in the open air, a faint bluish glow (§ 11
and 140) extended and vanished at a distance of 5 cm., as indicated by
dotted lines in Fig. B at beginning of this chapter. The degree of
luminosity may be judged by saying that it was not sufficient to admit
of investigation by the ordinary pocket spectroscope. A new window was
void of luminosity; but with use, bluish gray and green and yellow spots
occurred thereon.


66. PHOSPHORESCENCE BY CATHODE RAYS.—Substances which generally
phosphoresced by light and cathode rays in the generating bulb, § 55,
also phosphoresced under the influence of the rays in open air,
excepting eosin, gelatin, both phosphorescent in light, were not so in
cathode rays; so also with solutions of fluorescein, magdala red,
sulphate of quinine and chlorophyll. Phosphorescence was less if the
rays first passed through a tube of glass or tinfoil lengthwise. The
phosphorescent light of the phosphides of the alkaline group, uranium
glass, calcspar and some other substances, was so great that the
luminosity of the air was invisible by contrast. The maximum distance at
which phosphorescense was discernable in open air was about 8 cm. The
best phosphorescent screen consisted of paper saturated with
pentadecylparatatolylketone. In order to prepare it, he laid a sheet of
paper upon glass and applied the fused chemical with a brush. As to the
color of the phosphorescence and fluorescence of different substances,
and as to the degree of luminosity outside of the vacuum tube, they were
about the same as reported by Crookes when located within the discharge
tube. §55. Baric and potassic and other double cyanides of platinum,
common flint, glass, chalk and asaron all exhibited the same property as
when exposed to ultra-violet light, that is, fluoresced or
phosphoresced. Sulphide of quinine in the _solid_ state fluoresced, but
not in _solution_. Petroleum spread on a piece of wood fluoresced, and
also fluorescent-hydrocarbons generally.


66_a_. The cathode rays were not easily transmitted by tinfoil or glass,
because the degree of phosphorescence on the screen was greatly reduced
by interposing such sheets. The phosphorescense ceased also by
deflecting internal cathode rays from the window by a magnet. For full
treatment of the phenomena of phosphorescence, see Stokes’ experiments,
described in _Phil. Trans._, 1852, Art. “Change of Refrangibility of
Light.” In brief, Stokes’ theory assumes that such substances have the
power of reducing the refrangibility. Example: Ultra-violet light,
highly refractive, is changed to yellowish green, less refrangible, by
reflection from uranium glass.


67. THE ALUMINUM WINDOW, A DIFFUSER OF CATHODE RAYS. § 63_b_. The
conclusion arrived at by mounting the phosphorescent screen in different
positions and at different angles as well as by observance of the
gaseous luminosity, was that the aluminum window scattered the
rectilinear parallel cathode rays in all directions, § 57.


68. TRANSMISSION OF EXTERNAL CATHODE RAYS THROUGH METALS.—The
phosphorescence was not diminished apparently by an intervening
gold-leaf or silver or aluminum foil, while it was extinguished by
quartz .5 mm. thick which also cut off the atmospheric glow beyond
itself. The leaves and foil did not so act. The difference of thickness
should be borne in mind, as metal, as thick as the quartz did not
transmit. As to other substances, tissue paper cast a slight shadow,
which was darker with an additional sheet; but the shadow was
independent of color and blackness, § 154. Ordinary writing paper was
roughly, proportionally opaque, while the shadow was black with
cardboard .3 mm. thick. Glass films as made by blowing glass, cast faint
shadows when .01 mm. thick. He proved that there was little difference
as to the transmitting power of conductors and dielectrics when thin.
Mica and collodion sheets .01 mm. thick cast scarcely any shadow. The
reader may bear in mind the striking differences between these
properties of cathode rays, and X-rays, § 135, it being assumed always
that the generating devices are the same; for example, water permitted
the cathode rays (were these simply feeble X-rays?) to be transmitted
only when in very thin layers. Even soap water films which were only
.0012 mm. thick cast shadows, although very faintly. The shadows of
drops of water were black, while water several feet thick has been
traversed by X-rays from a small set of apparatus. By careful
measurements he found that the law of transmission must be different
from that of light, for in the latter, many substances are opaque
although exceedingly thin, while with cathode rays, the same will
traverse all films. Goldstein and Crookes reported that thin mica, glass
and collodion films made very dark shadows, § 58, within the discharge
tube, whereas Lenard found that outside of the vacuum tube, in open air,
the transparency was greater than according to the earlier
experimenters, but he acknowledged that Crookes and Goldstein were
inconvenienced and limited in the number of observations because it is
so difficult to carry on such experiments within an hermetically sealed
tube. Again, he acknowledged that perhaps the cathode rays of those
experimenters were of a different kind. The construction shown in the
above figures was modified by using a very thin glass window instead of
aluminum, and the results were the same allowing for the different
opacity, to ordinary light, of aluminum and glass.

The cathode rays acted upon the sense of smell and taste as the nose and
mouth could detect ozone, § 84, at end.


69. PROPAGATION. TURBIDITY OF AIR. Upon studying the shadows on the
phosphorescent screen, it was noticed that the rays were bent around the
edges of the object. Again, when the object had a slit, diffusion could
be noticed by the shape (as in Crookes Ex., Fig. 15, p. 17,) of the
luminous portion of the phosphorescent screen. In Fig. B, at beginning
of this chapter, the spatter work represents the shape of the luminous
portion, the darker part representing the most luminous surface of the
screen, the latter being held at right angles to the thick plate, having
the slit and opposite the aluminum window. By varying these experiments,
especially by changing the angle of the screen he found that not the all
rays were diffused, but as in the passage of light through milk, some
were transmitted in rectilinear lines.


70. PHOTOGRAPHIC ACTION.—He performed with sensitive silver compound
papers, an experiment somewhat similar to those with phosphorescent
bodies and also others. Behind a rather thick opaque plate the chemical
film was not acted upon, but the rate of blackening near the aluminum
window without obstruction of intermediate bodies was about the same as
that with befogged sunlight. The former, moreover, was acted upon at a
much greater distance than that at which phosphorescence was exhibited
and beyond the atmospheric luminosity. By means of shadow pictures or
sciagraphs, he compared the shadows produced by the external cathode
rays with those which would have been obtained by light. Referring to
Fig. C, beginning of this chapter, the sensitive plate was half covered
with a plate of quartz, Q, and half with a plate of aluminum, A´
overlapping the quartz. With light, the shadows would have appeared as
in said figure, that is, one-half black as produced by aluminum, a
quarter rather light as produced by quartz, and the other quarter
bright, or a similar arrangement, according to whether the negative or
the positive photograph is considered; but with the cathode rays, the
appearance of the developed plate was as in Fig. D., beginning of this
chapter. The quartz cast the black shadow, while the aluminum, the
lighter one. Furthermore, the luminosity of the air produced a variable
light on the other quarters. A similar appearance was produced by
casting shadows of such plates upon the phosphorescent screen; but, of
course, the picture was not a permanent one. The photographic plate
served to accumulate the power, for the cardboard which cast a faint
shadow upon the phosphorescent screen, showed a black shadow upon the
photographic paper by sufficiently long exposure. At the same time,
strips of thin metal were placed side by side between the chemical paper
and the cardboard, and they showed different degrees of shading. The
cardboard was quite thick, being .3 mm. Prof. Slaby (see _Elect. Rev._,
Lon., Feb. 7, ’96), _after_ Röntgen’s discovery, produced sciagraphs of
the bones of the hand at the window of the Lenard tube. Lenard doubted
whether the cathode rays produced direct chemical action. Iodine paper
became bluish, but he could not obtain other chemical effects usually
produced by light, and other agencies, for example, oxygen and hydrogen
mixed together in the proportion to form water, and which were in their
nascent state, and which were located in a soap-bubble, did not explode
or ignite. No effect was produced upon carbon bi-sulphide nor
hydrogen-sulphide, although the exposure was very long. Ammonia was not
formed when the rays acted upon a mixture of three parts hydrogen and
one part nitrogen, as to volume. He thought that he noticed a small
expansion of air, hydrogen and carbonic acid separately located in a
vessel having a capillary tube and water to indicate the expansion. He
attributed the slight expansion to an indirect action, although very
slight, caused by heat produced by the cathode rays, § 27, and yet
neither the thermopile nor the thermometer showed any calorific effects
although the thermopile responded to the flame of a candle 50 cm.
distant.


71. CATHODE RAYS AND ELECTRIC FORCES DISTINGUISHED. The earth connection
heretofore mentioned with the aluminum window was for the purpose of
dispensing with sparking, but even then the approach of another
conductor connected to earth would cause some sparking. Sparks could be
drawn when the cathode rays were deflected from the aluminum window by a
magnet. Fig. E, at beginning of chapter. He argued that the rays and the
electric forces of the spark are non-identical. He was not satisfied
with this as an absolute proof, and he instituted others. He enclosed
the whole generator in a large metal box. In the observation space, that
is, around and near the window, he located another box, having an
aluminum front facing the window. See Fig. E, at beginning of chapter.
It was within this second box that he took the sciagraph shown in Fig.
D, at beginning of chapter. It is important to notice that sparks could
not be drawn at points within the said second box, shown at the left,
even by a metallic point shown projecting thereinto. No spark occurred
whatever, not even from the aluminum front. Sparking occurred when the
pointed wire was extended to a considerable distance outside of the back
of the small box, but it was remarked that the electric force did not
enter through the front wall but was introduced “from behind into the
box, by the insulation of the wire.” No one can, therefore, enter the
objection that the cathode rays experimented with, were generated from
the aluminum window as a cathode. They came from the cathode referred to
entirely within the vacuum tube. Prof. J. J. Thomson, F. R. S., had at
an early date conjectured that cathode rays did not pass through thin
films of metal, but that these films acted as intermediate cathodes
themselves. See his book on “_Recent Researches_,” p. 26, also _The
Elect._, Lon. March 23, ’94, p. 573, in an article by Prof. Fitzgerald,
who names that citation.


72. CATHODE RAYS PROPAGATED, BUT NOT GENERATED IN A HIGH VACUUM.—The
proposition was proved by having two tubes, one called the generating
tube and one the observation tube, the former being like that shown in
Fig. A, at beginning of chapter, which is partly repeated in Fig. F, at
beginning of chapter, combined with the observation tube, which contains
the two electrodes for casual use; but the one on the right is a disk
extending nearly throughout the cross sectional area, and having a small
central opening. Although both tubes were connected to the air pump,
yet, by means of stop-cocks, the vacuum in one tube could be maintained
at a maximum degree for hours, while the other was at a minimum. The
first experiment was performed with a vacuum, about as high as that
employed in Crookes’ phosphorescent experiments, § 53. There was a patch
of green light, § 57, at the extreme left end of the observation tube
and the glass was green at the right, § 54, and a little to the left of
the perforated disk electrode _a_. The other electrode of this tube was
located at the upper left and lettered _k_.


72_a_. The magnet deflected the rays _in the observing tube_ as
indicated by the partial extinction of the phosphorescent patch. He
noticed that with the rarefied atmosphere the amount of turbidity was
enormously reduced, or in other words, that the rays were propagated
more nearly in rectilinear lines. All the experiments on the cathode
rays, in this observing tube, were of about the same nature as those
which could be produced in the discharge tube.


[Illustration:

  FROM SCIAGRAPH OF CAT’S LEG, BY PROF. WILLIAM F. MAGIE.
  Copyright, 1896, by William Beverly Harison, pub. of X-ray pictures,
    59 Fifth Ave., New York City.
]


72_b_. The principal experiment consisted in exhausting the observing
tube to such a degree that cathode rays could not be generated therein.
The vacuum was so perfect that when used as a discharge tube all
phosphorescence gradually died away until it disappeared, and no current
passed (§ 25) except on the outside surface of the glass. The coil was
so large, electrically, that the length of the spark between spheres was
15 cm. Upon charging the right hand tube and generating cathode rays, it
was determined by means of magnetic deflection, phosphorescence and
other effects, that the cathode rays traversed the highest possible
vacuum (§ 19, near end, where energy must have passed through the high
vacuum to produce luminosity in the inner bulb). The external and
internal rays were certainly different forms of energy. Inasmuch as he
noticed that rarefied air was less turbid and less absorptive than air
at ordinary pressures, it occurred to him to make a very long tube,
namely, 1 m, or a little over 3 feet. He employed very severe steps for
obtaining an exceedingly high vacuum, the operation occupying several
days. The pump used was a Toepler-Hagen, while a Geissler pump was
employed separately for the discharge tube. The pencil of cathode rays
traversed the whole length of the long tube. See a portion of the
apparatus in Fig. G, at beginning of this chapter. One disk was of metal
and perforated with a pin hole and the other was a phosphorescent
screen, so that when the cathode pencil passed through the hole in the
plate a patch was seen upon the phosphorescent screen. The
phosphorescent spot was always, no matter what the relative distances of
the disks were from each other, and from the end of the tube,
substantially the same as it would have been by calculation assuming
that there was no turbidity effect. The patches, in each instance, were
a little smaller in diameter than the calculated ones. For example with
one measurement, at certain distances, the actual diameter of the patch
was 2.5 mm., while the calculated diameter was 2.9 mm. In his
experiments with light under the same conditions, the luminous spots
were also a little smaller than the calculated or geometrical. The disks
had iron shoes and were moved to different positions by a magnet. He
concluded, therefore, that in what may be called a perfect vacuum, light
and cathode rays have a common medium of propagation, namely, the
assumed ether. Prof. Fitzgerald, in _The Elect._, Lon. Mar. 23, ’94,
does not agree broadly with him in this; neither does he contradict him.
He argues rather on the point that the cathode rays and light rays are
not identical, but Lenard does not affirm this, because the magnet will
attract the former and not the other. Prof. Fitzgerald admits this and
calls to mind that even in a vacuum, as obtained by Lenard, there were
still ten thousand million molecules per cu. mm. and therefore he thinks
it is better to look to matter rather than ether as the medium of
propagation of cathode rays. § 61_b_. On the other hand, Lenard agrees
with certain other predecessors, Wiedemann, Hertz and Goldstein, in
favor of cathode rays being etheric phenomena. See _Wied. Ann._, IX., p.
159, ’80; X., p. 251, ’80, XII., p. 264, ’81; XIX., p. 816, ’83; XX., p.
781, ’83. The vacuum with which Lenard operated, was .00002 mm.
pressure, obtained by cooling down the mercury to minus 21° C. This
vacuum was so high that all attempts to prove the presence of matter
failed. Neither did the exceedingly high vacuum deaden the cathode rays.
On the other hand, as noted, they were assisted rather than hindered. §
135.


73. CATHODE RAYS. PHENOMENA IN DIFFERENT GASES.—The apparatus consisted
of an observing tube having a tubular gas inlet and outlet both in one
end and arranged in line with the cathode of the discharge tube. See
construction in Fig. H, at beginning of this chapter, the tube being
about 40 cm. long and 3 cm. in diameter. He was very careful in every
case to chemically purify and dry the particular gas. He omitted the
perforated disk and provided an opaque strip of the phosphorescent
screen on the side toward the window and made his observations from the
other side, the object of the experiment being particularly to test the
transmission of cathode rays in different gases. With any particular
gas, he moved the phosphorescent screen along by means of a magnet until
the shadow on the screen became invisible. It is evident that the
distances of the screen from the window for different gases would
indicate the relative transmitting powers. He also modified the
experiment by varying the density of the gases, hydrogen being taken as
1 as usual, nitrogen 14, and so on. The transmitting power of hydrogen
was nearly five times as great as that of nitrogen, air, oxygen and
carbonic acid gas, which did not much differ. § 10 and 18. Sulphurous
acid was a very weak transmitter. All the gases became luminous near the
window as in air. § 65. The colors were all about the same as far as
distinguishable, § 11, which was difficult in view of the brightness of
the phosphorescence on the glass. It was a universal rule, that when the
density decreased, the transmitting power increased. In high vacua, in
all gases, the rays went through the space in rectilinear lines in all
directions from the window, and generally it made no difference what gas
was employed provided the vacuum was as high as hundredths of a
millimetre. At this pressure all gases acted the same. To be sure, the
phosphorescence did not occur at this high vacuum at a great distance as
might be expected, but it should be remembered that the intensity of the
rays varied as the square of the distance, and, therefore, at very great
distances, the action was very weak.


74. CAUSE OF LUMINOSITY OF GAS OUTSIDE THE DISCHARGE TUBE.—At ordinary
pressures, in the cases of hydrogen and air, as has been noted, the gas
became luminous in the observing tube, the effect being, of course, the
same as entering open air, represented in Fig. A, beginning of this
chapter. In order to determine the luminosity at less pressures, the
gas, of whichever kind, was enclosed in a rather long observing tube and
only at rather high vacua did the bluish and sometimes reddish gaseous
luminosity disappear. Upon grasping the tube with the hand or
approaching any conductor connected to earth, of large capacity, the
column stopped at that point so that the remainder of the tube, beyond
the hand, measured from the discharge, was dark. The phosphorescence on
the glass wall of the tube produced by the cathode rays was not
influenced in any way by outside conductors, such as the hand. Cathode
rays themselves were not stopped apparently by the hand, because the
phosphorescent screen and glass, located beyond the hand, became
luminous. He concluded, therefore, that the glowing of the gas had no
close connection with the cathode rays. He proved this also by
deflecting the cathode rays in the discharge tube from a certain space,
and yet the gaseous luminosity remained. As an exception, the cathode
rays sometimes appeared to be closely associated with the light column.
He attributed the luminosity of the gas in general, at low pressures,
not to the cathode rays, but directly to the electric current or some
kind of electric force, § 11 and 14, which, as already remarked,
permitted sparks to be drawn from the aluminum window and surrounding
points.


The negative glow light in Geissler tubes, § 30, is also to be regarded
as gas illuminated by cathode rays. (Compare Hertz, _Wied. Ann._, XIX.,
p. 807, ’83.) Between that phenomenon and the glow observed here and
attributed to irradiation, there exists a correspondence, inasmuch as in
both cases the light disappears at high exhaustions, § 53, appears
fainter and larger when the pressure increases, § 54, and then becomes
brighter and smaller, § 54. But, whereas, the glow in the Geissler tube
has become very bright and small at 0.5 mm. pressure, the gas in our
experiment remains much darker up to 760 mm. pressure, and yet the
illuminated spot is much larger. This difference cannot, therefore, be
attributed to an inferior intensity of the rays here used. But it will
be explained, § 76, as soon as we can show that at higher pressures
cathode rays of a different kind are produced, which are much more
strongly absorbed by gases than the rays investigated hitherto and
produced at very low pressures.


[Illustration:

  USE OF STOPS IN SCIAGRAPHY. (PERCH.) § 107., p. 101.
  By Leeds and Stokes.
]

Fig. I, p. 52, illustrates the apparatus by which he studied the
rectilinear propagation and whereby he found that it was rectilinear
only in a very high vacuum. In the figure, the gas is at ordinary
pressure, and it will be noticed that the turbidity of the same is
indicated by the curved lines while the dotted lines show the volume
that would be occupied by light or other rectilinear rays, unaccompanied
by any kind of diffusion. In the observing tube, there was a disc having
a central hole at _a_. Beyond this disc, measured from the aluminum
window, was a fluorescent screen which, as well as the perforated disc,
could be moved to different distances by means of a magnet acting on a
little iron base. It is evident that upon moving the fluorescent screen
to different distances, the diameter of the luminous patch would be a
measure of the amount of turbidity. The curved lines intersecting the
peripheries of the luminous spots indicate, therefore, the field of the
cathode rays, so that said field would appear like a kind of curved cone
if the same were visible. Although hydrogen is the least turbid gas, yet
the phosphorescent patches were all larger except with a high vacuum
than they could have been with rectilinear propagation. An additional
characteristic of the phosphorescent spot, was its being made up of a
central bright spot and a halo less luminous, appearing like some of the
pictures of a nebula, see Fig. I´, p. 52, the darker or centre
indicating the brighter portion. In a perfect vacuum the halo did not
exist. He performed a similar experiment with ordinary light. No halo
occurred on a paper screen which was used instead of the phosphorescent
screen, but upon introducing a glass trough of dilute milk between the
window and the perforated disc, or between the disc and the paper
screen, nuclei and halos were obtained, illustrating a case of the
effect of a turbid fluid upon light, and assisting in proving that gases
act as a turbid medium to cathode rays as milk and similar substances do
to light; also in other gases than hydrogen, and by the use of cathode
rays, nuclei and halos were not obtained at high exhaustion, all the
gases becoming limpid. Taking into account pressure and density, all
gases behaved the same as to the power of transmission when they were of
the same density, without any regard whatever to their chemical nature.
Density alone determined the matter, according to Lenard.


75. CATHODE RAYS OF DIFFERENT KINDS ARE VARIABLY DIFFUSED.—He discovered
the remarkable property, contrary to his expectation, that if the rays
are generated at high pressures, they are capable of more diffusion than
when generated at lower pressures. This can be easily proved by any one,
for it will be noticed that upon increasing the pressure in the
discharge tubes the spots on the phosphorescent screen will not only
grow darker but larger and more indefinite as to the nucleus and halo.
He called attention to the agreement with Hertz, who also found that
there were two different kinds of rays, see _Wied. Ann._, XIX, p. 816,
’83, also see Hertz’s experiment. Lenard also pointed out the analogue
in respect to light, which, when of short wave length, is more diffused
in certain turbid media than that of greater wave length. Although
Lenard held that his experiment proved that cathode rays were phenomena
in some way connected with the ether, yet he pointed out an important
difference in connection with the property of deflection of the rays by
the molecules even of elementary gases like hydrogen, producing
diffusion of the rays, which accordingly may be considered as behaving
like light in passing through, not gases, but vapors, liquids and dust.
In the case of the cathode rays the molecules of a gas acted as a turbid
medium, but in the case of light, turbidity is only exhibited by vapors
or certain liquids, as so eloquently explained by Tyndall, in “Fragments
of Science,” 1871, where it is shown that _aggregation_ of molecules,
like vapors or dust in the presence of light, make themselves known by
color and diffusion, whereas the substances in a molecular or atomic
state do not serve to show the presence of rays of light.


76. LAW OF PROPAGATION.—Lenard recognized continually that there were
two kinds of cathode rays. One of them may have been X-rays without his
knowing it. In the latter part of ’95, he made some experiments
especially of a quantitative nature as to the principle of absorption of
the rays by gases. By mathematical analysis, based upon experiments, he
arrived at the principle that the absorptivity of a gas is proportional
to its pressure, or what is the same thing, to its density, or as to
another way of stating the law, “the same mass of gas absorbs at all
pressures the same quantity of cathode rays.” See _Elect. Rev._, Lon.,
as cited, p. 100.


77. CHARGED BODIES DISCHARGED BY CATHODE RAYS.—An insulated metallic
plate was charged first with positive electricity and in another
experiment with negative electricity. In each instance, the plate was
discharged rapidly by the cathode rays as indicated by the electroscope,
and the same held true when a wire cage in contact with the aluminum
window, surrounded the electroscope and the metallic plate. The effect
was stopped by cutting off the cathode rays by quartz .5 mm. thick. The
discharge took place, however, through aluminum foil. A magnet was made
to deflect the internal cathode rays, whereupon the discharge did not
take place, all showing that the discharge of the insulated plate was
directly due to those rays. A remarkable occurrence was the
accomplishment of _the discharge at a much greater distance than that at
which phosphorescence was exhibited_. See also Roentgen’s experiment—who
suggested that Lenard had to do with X-rays in this experiment, but
thought they were cathode rays. The maximum distance for the discharge
was about 30 cm. measured normally to the aluminum window. He caused a
discharge of a plate also in rarefied air. He admitted that the
experiments were not carried far enough to know whether the effect was
due to the action of the cathode rays upon the surface of the window, or
upon the surrounding air, or upon the plate. The author could not find
in Lenard’s paper any positive or negative proof that he had actually
deflected the external cathode rays by a magnet while passing through
air or gas at ordinary pressure. He had deflected them while passing
through a very high vacuum in the observing tube. Dr. Lodge, who briefly
reviewed Lenard’s experiments, expressed the same opinion. See _The
Elect._, Lon., Jan. 31, ’96, p. 439. For theoretical considerations of
the electric nature of light, the discharge law in the photo-electric
phenomena, the simple validity of the discharge law, the occurrence of
interference surfaces in the blue cathode light, the cathode rays in the
axis of symmetry, the necessary degrees of longitudinal electric waves,
the frequency of the cathode rays, and proof of longitudinal character
of cathode rays, see Jaumann in _The Elect._, Lon., Mar. 6, ’96;
translated from _Wied. Ann._, 571, pp. 147 to 184, ’96, and succeeding
numbers of _The Elect._, Lon., which were freely discussed in foreign
literature contemporaneously.


78. DE KOWALSKIE’S EXPERIMENT. SOURCE, PROPAGATION AND DIRECTION OF
CATHODE RAYS. _Acad. Sci._, Paris, Jan. 14, ’95; _So. Fran. Phys._ Jan.
’95; _Nature_, Lon. Jan. 24, ’95; Feb. 21, ’95.—The conclusions he
arrived at are, 1. The production of the cathode rays does not depend on
the discharge from metallic electrodes across a rarefied gas, nor is
their production connected with the disintegration of metallic
electrodes. 2. They are produced chiefly where the primary illumination
attains suitable intensity, that is, where the density of the current
lines is very considerable. 3. Their direction of propagation is that of
the current lines at the place where the rays are produced, from the
negative to the positive poles. They are propagated in the opposite
direction to that in which the positive luminosity is supposed to flow.
§ 43. He employed a Goldstein tube reduced at the centre. § 41. It was
found that the cathode rays are formed not only at the negative
electrode, but also at the constriction, directly opposite the cathode.
De Kowalskie carried on further experiments in this line in order to be
satisfied with the principles named above, which he formulated. In one
tube, he was able to produce cathode rays at either end of the capillary
tube forming the constricted part of a long vacuum tube. No electrodes
were employed. The tube was merely placed near a discharger through
which “Tesla currents” were passed? He seems to have been working with
X-rays without knowing it; for his results agree with those of Roentgen
and later experimenters that the source of X-rays is the surface of a
substance where it is struck by cathode rays. The statements were about
as definite as could be expected at that date.


[Illustration:

  HAND, BY OLIVER B. SHALLENBERGER, TAKEN WITH FOCUS TUBE.
  § 137, p. 136.
]


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




                              CHAPTER VII


                                -------

79. ROENTGEN’S EXPERIMENTS. X-RAYS, AND A NEW ART. _Wurz. Physik. Med.
Gesell._ Jan. ’95; _Nature_, Lon., Jan. ’96; _The Elect._, Lon. April
24, 96; _Sitz. Wurz. Physik. Inst._ D. _Uni._ Mar. 9, 96.—UNINFLUENCED
BY A MAGNET IN OPEN AIR.—Although Lenard recognized several kinds of
cathode rays, which differed as to penetrating and phosphorescing power,
yet he always held, or inferred at least that they were deflected by a
magnet, outside, as well as inside, (proved § 72_a_.) of the discharge
tube. § 59. Prof. Wilhelm Konrad Roentgen subjected his newly discovered
rays to the action of very strong magnetic fields in the open air, but
no deviation was detected. This is the characteristic which more than
anything else has served to distinguish X-rays from cathode rays. This
property has been confirmed by others. He employed the principle of
magnetic attraction of internal cathode § 59, rays to shift the
phosphorescent spot, for then he noticed that the source of X-rays
fluctuated also.


80. SOURCE OF X-RAYS MAY BE AT POINTS WITHIN THE VACUUM SPACE.—In one
case, he employed a Lenard tube, and found that the X-rays were
generated from the window which was in the path of the cathode rays. §
67. Different bodies within the discharge tube were found to have
different quantitative powers of radiating X-rays when struck by the
cathode rays. He stated “If for example, we let the cathode rays fall on
a plate, one half consisting of a 0.3 mm. sheet of platinum and the
other half a 1 mm. sheet of aluminum, the pin-hole photograph of this
double plate will show that the sheet of platinum emits a far greater
number of X-rays than does the aluminum, this remark applying in every
case to the side upon which the cathode rays impinge.” On the reverse
side, however, of the platinum, no rays were emitted, but a large amount
was radiated from the reverse side of the aluminum. § 67. He admitted
that the explanation was simple; but, at the same time, he pointed out
that this, together with other experiments, showed that platinum is the
best for generating the most powerful X-rays. One form with which he
experimented is illustrated in Fig. J, in principle, being described as
a bulb in which a concave cathode was opposite a sheet of platinum,
placed at an angle of 45° to the axis of the curved cathode, and at the
focus thereof.


[Illustration:

  J
]


81. REFLECTION OF X-RAYS.—He emphasized the knowledge that there is a
certain kind and a certain amount of reflection, such as that produced
upon light and, as pointed out by Lenard, upon cathode rays, by certain
turbid media. The following quotation sets forth the exact experiment to
show slight reflection at metal surfaces. “I exposed a plate, protected
by a black paper sheet 1 to the X-rays (_e.g._ from bulb J) so that the
glass side 2 lay next to the discharge tube. The sensitive film was
partly covered with star-shaped pieces (4 slightly displaced in the
Fig.) of platinum, lead, zinc and aluminum. On the developed negative
the star-shaped impressions showed dark (comparatively) under platinum,
lead and more markedly, under zinc; the aluminum gave no image. It
seems, therefore, that the former three metals can reflect the X-rays;
as, however, another explanation is possible, I repeated the experiment
with only this difference, that a film of thin aluminum foil was
interposed between the sensitive film and the metal stars. Such an
aluminum plate is opaque to the ultra-violet rays, but transparent to
X-rays. In the result the images appeared as before, this pointing still
to the existence of reflection at metal surfaces.”


82. PENETRATING POWER. The transmitted energy was tested both by a
fluorescent screen and by a sensitive photographic plate. Either one was
acted upon by the rays after transmission through what have ordinarily
been called opaque objects. § 68. for example, 1000 pages of a book. As
in Lenard’s results, so in Roentgen’s, the color of the object had no
effect, even when the material was black. § 68, near beginning. A single
thickness of tinfoil scarcely cast a shadow on the screen. § 66_a_. The
same was true with reference to a pine board 2 or 3 cm. thick. They
passed also through aluminum 15 mm. thick. 63_b_. Glass was
comparatively opaque, § 66_a_, as compared with its power of
transmitting light, but nevertheless it must be remembered that the rays
passed through considerable thickness of glass. The tissues of the body,
water § 68, near centre, and certain other liquids and gases were found
exceedingly permeable § 67. Fluorescence could be detected through
platinum 2 mm. thick and lead 1.5 mm. thick. Through air the screen was
illuminated at a maximum distance of 1 m. A rod of wood painted with
white lead cast a great deal more shadow than without the paint, and in
general, bones, salts of the metals, whether solid or in solution,
metals themselves and minerals generally were among the most resisting
materials. § 155. The experiments were performed in a dark room by
excluding the luminosity of the tube by a thick cloth or card board
entirely surrounding the tube. He performed the wonderful experiment, so
often since repeated, of holding the hand between the screen of barium
platino cyanide and the discharge tube, and beholding the shadow picture
of the bones. This was the accidental step which initiated the new
department of photography, and which gave to the whole science of
electric discharge, a new interest among scientists and electricians and
which thoroughly awakened popular interest. The whole world concedes to
him the honor of being the originator of the new art. In view of
sciagraphs of the bones of the hand upon the screen, it occurred to him
in view also of Lenard’s experiments, on the photographic plate, to
produce a permanent picture of the skeleton of the hand with the flesh
faintly outlined. § 84. The accompanying half tone illustration, page
37, was made by the _Elect. Eng_. N.Y. (June 3, ’96) by permission, and
it represents the Edison X-ray exhibit at the New York Electrical
Exposition of the Electric Light Association, 1896. Thousands of people,
through the beneficence of Dr. Edison, were permitted to see the shadows
of their bones surrounded by living flesh. The screen was made of calcic
tungstate. The hand and arm were placed behind and viewed from the
front. § 132, near beginning.


83. PENETRATING POWER AND DENSITY OF SUBSTANCES.—Although he found that
there was some general relation between the thickness of materials and
the penetrating power, yet he was satisfied that the variation of the
power did not bear a direct relation to the density, (referring to
solids) especially as he noticed a peculiar result when shadows were
cast by Iceland spar, glass, aluminum and quartz of equal thickness. The
Iceland spar cast the least shadow upon suitable fluorescent or
photographic plate. The increased thickness of any one substance
increased the darkness of the shadow, as exhibited by tinfoil in layers
forming steps. Other metals, namely platinum, lead, zinc and aluminum
foil were similarly arranged and a table of the results recorded. §
63_b_.


                                       RELATIVE
                              THICKNESS. THICKNESS. DENSITY.

                   Platinum   .018 mm.     1     21.5

                   Lead       .050 mm.     3     11.3

                   Zinc       .100 mm.     6      7.1

                   Aluminum      3.500   200      2.6
                                   mm.


He concluded from these data that the permeability increased much more
rapidly than the thickness decreased.


84. FLUORESCENCE AND CHEMICAL ACTION. § 70 and 63_a_.—Among the
substances that fluoresced were barium platino cyanide, calcium
sulphide, uranium glass, Iceland spar and rock salt. In producing
sciagraphs on the photographic plates, he found it entirely unnecessary
to remove the usual ebonite cover, which, although black, and so opaque
to light, produced scarcely any resistance to the rays. The sensitive
plate, even when protected in a box, could not be kept near a discharge
tube, for he noticed that it became clouded. He was not sure whether the
effect upon the sensitive plate was directly due to the X-rays or to a
secondary action, namely, the fluorescent light which must have been
produced upon the glass plate having the film, it being well known that
light of fluorescence possesses chemical power. He called attention to
the fact that inasmuch as fluorescent light which can be reflected,
refracted, polarized, etc., was produced by the rays; therefore, all the
X-rays which fell upon a body did not leave it as such. § 67. No effect
was produced upon the retina of the eye although he temporarily
concluded that the rays must have struck the retina in view of the great
permeability of animal tissue and liquids. § 68, at end. Conclusions of
this kind not based on experiment, are never reliable, even when offered
by very high authorities. Again the rays were weak. Roentgen himself
admitted that the salts of metals in solution (§ 82, near centre)
rendered the latter rather opaque. The eye ball is continually moistened
with the solution of common salt. Further than this, Mr. Pignolet
noticed in _Comptes Rendus_, Feb. 24, ’96, an account of an experiment
of Darien and de Rochas. In anatomy it is common to experiment on fresh
pig’s eyes in order to make comparisons with human eyes. The above named
Frenchmen submitted the former to X-rays. The eyes were but slightly
permeable thereto.


[Illustration:

  THE PHYSICAL INSTITUTE, UNIVERSITY OF WÜRZBURG,
  WHERE PROF. ROENTGEN HAS HIS RESIDENCE, DELIVERS HIS LECTURES, AND
    PERFORMS HIS EXPERIMENTS.
  From photograph by G. Glock, Würzburg. (Not referred to in book.)
]


85. NON-REFRACTION AND BUT LITTLE REFLECTION OF X-RAYS.—He employed a
very powerful refracting prism made of mica and containing carbon
bi-sulphide and water. The same prism refracted light but did not
refract X-rays. No one would think of making prisms for examining light,
of ebonite or aluminum, but he made such a prism for testing X-rays. But
if there were any refraction he concluded that the refractive index
could not have been more than 1.05, which may be considered as a proof
that the rays cannot be refracted. He tried heavier metals, but the
difficulty of arriving at any satisfactory results was due to the
resistance of such metals to the transmission of the rays. Among other
tests was one consisting in passing the rays through layers of powdered
materials through which the rays were transmitted in the same quantity
as through the same substances not powdered. It is well known that light
passed into powdered transparent materials, is enormously cut off,
deviated, diffused, refracted etc., in view of the innumerable small
surfaces of the particles. Hence he concluded that there was little if
anything in the nature of refraction or reflection of X-rays. § 146. The
powdered materials employed were rock salt, and fine electrolytic and
zinc dust. The shadows, both on the screen and as recorded on the
photographic plate were of substantially the same shade as given by the
same materials of the same thickness in the coherent state. One of the
most usual ways of testing refraction of light is by means of a lens.
X-rays could not be brought to a focus with the lens of what ever
material it was made. Among the substances tried were ebonite and glass.
As expected, therefore, the sciagraph of a round rod was darker in the
middle than at the edges; and a hollow cylinder filled with a more
transparent liquid showed the centre portion brighter than its edges. If
one considers this observation in connection with others, namely the
transparency of powders, and the state of the surface not being
effective in altering the passage of the X-rays through a body, it leads
to the probable conclusion that regular reflection does not exist, but
that bodies behave to the X-rays as turbid media to light, § 69.


86. VELOCITY OF X-RAYS IN DIFFERENT BODIES. p. 46.—Although he performed
no direct experiment in this direction yet he inferred in view of the
absence of refraction at the surfaces of different media, that the rays
travel with equal velocities in all bodies.


87. DOUBLE REFRACTION AND POLARIZATION.—Neither could he detect any
action upon the rays by way of refraction by Iceland spar at whatever
angle the crystal was placed. As to this property of light see Huygen’s
Works of 1690 and Malus’ Works of 1810. quartz also gave negative
results. Prof. Mayer of Stevens Institute submitted to _Sci._, Mar. 27,
’96, the report of a crucial test for showing the non-polarization of
X-rays. On six discs of glass, 0.15 mm. thick and 25 mm. in diameter,
were placed very thin plates of Herapath’s iodo-sulphate of quinine. The
axes of these crystals crossed one another at various angles. When the
axes of two plates were crossed at right angles no light was
transmitted; the overlapping surfaces of the plates appearing black. If
the Roentgen rays be polarizable, the Herapath crystals, crossed at
right angles, should act as lead and not allow any of the Roentgen rays
to be transmitted. Prof. Mayer is well known as exceedingly expert in
connection with minute measurements and in the manipulation of
scientific experiments. Dr. Morton, Pres. Stevens Inst., attested the
results as an absolute demonstration that X-rays are incapable of
polarization. _Stevens Indicator_, Jan., ’96.


88. THE PROPAGATION OF X-RAYS RECTILINEAR.—There would be no difficulty
in producing photographs of the bones of the hand with the rays of
light, if it were not for the tremendous amount of reflection and
refraction causing so much diffusion that no sharply defined shadow of
the bones would be produced. By means of a powerful lens and a funnel
pointed into a dark room, the author noticed that the condensed light
thereby obtained when passed through the hand, and when the incident
rays were parallel, came out so diffused that one would think that the
light went through bones as easily as any part of the hand. An
experiment of this kind serves to emphasize that the success of
sciagraphy by X-rays is due not only to the great penetrating power, but
to practically no refraction nor reflection. In view of the sharp
shadows cast of objects even when located in vegetable or animal media,
Roentgen was justified in giving the name of ray to the energy. He
tested the sharpness of the shadow by making sciagraphs and fluorescent
pictures not only of the bones of the hand, but of a wire wound upon a
bobbin, of a set of weights in a box, of a compass, card and needle,
conveniently closed in a metal case, and of the elements of a
non-homogeneous metal. To prove the rectilinear propagation further, he
received the image of the discharge tube upon a photographic plate by
means of a pinhole camera. The picture was faint but unmistakable.


89. INTERFERENCE. The rays of light may be caused to interfere with each
other. See _Newton’s Principia_, Vol. III.; _Young’s Works_, Vol.
I.—Theory points out that waves of ether of two pencils of light, when
caused to be propagated at certain relative phases partially or wholly
neutralize or strengthen each other. Roentgen could obtain no
interference effects of the X-rays, but did not conclude that the
interference property was absent. He was not satisfied with the
intensity of the rays and therefore could not test the matter severely.


[Illustration:

  FIG. L.
]


90. ELECTRIFIED BODIES DISCHARGED BY X-RAYS. p. 47.—After Roentgen’s
first announcement, others, and probably J. J. Thomson as the first,
found that the X-rays would discharge both negatively and positively
electrified bodies. Roentgen, in his second announcement, stated that he
had already made such a discovery, but had not carried the investigation
far enough to report satisfactorily on the details. At last he put forth
an account of the whole phenomena and stated that the discharge varied
somewhat with the intensity of the rays, which was tested in each
instance by the relative luminosity of the fluorescent screen, and by
the relative darkness produced upon the photographic plate in several
instances. Electrified bodies, whether conductors or insulators, were
discharged when placed in the path of the rays. All bodies whatsoever
behaved in the same manner when charged. They were all discharged
equally by the X-rays. He noticed that “If an electrical conductor is
surrounded by a solid insulator such as paraffin instead of by air, the
radiation acts as if the insulating envelope were swept by a flame
connected to earth.” Upon surrounding said paraffin by a conductor
connected to earth, the radiation no longer acted on the inner
electrified conductor. The above observations led him to believe that
the action was indirect and had something to do with the air through
which the X-rays passed. In order to prove this, it was necessary for
him to show that air ought to be able to discharge the bodies if first
subjected to the rays, and then passed over the bodies. The apparatus
for performing an experiment to test this prediction is shown in Fig. L,
which serves to illustrate also the manner in which he prevented
electro-static influences of the discharge tube, leading in wires and
induction coil. § 71, near centre. For this purpose he built a large
room in which the walls were of zinc covered with lead. The door for his
entrance and exit was arranged to be closed in an air-tight manner. In
the side wall opposite the door there was a slit 4 cm. wide, covered
hermetically with a thin sheet of aluminum for the entrance of X-rays
from the vacuum tube outside of the room. All the electrical apparatus
connected with the generation of the X-rays was outside of the room. No
force whatever came into the room, therefore, except the X-rays through
the aluminum. § 71. In order to show that air which had been subjected
to the X-rays would discharge a body immediately afterwards upon coming
in contact therewith, he arranged matters so that the air was propelled
by an aspirator. He passed air along a tube made of thick metal so that
the rays could enter only through a small aluminum window near the open
end. At over a distance of 20 cm. from the window was an insulated ball
charged with electricity, and connected to any electroscope or
electrometer. The professor used a Hankel electroscope. No published
sketch was made by Roentgen; therefore, that shown in the figure was
produced by inference from the description. The operation was as
follows: The X-rays passed into the room through the aluminum window,
and then into the metal tube through its aluminum window. When the air
was at rest, the ball was not discharged. When the aspirator was at
work, however, so that the air moved past the aluminum window and past
the ball, the latter was discharged whether electrified positively or
negatively. He modified the operation by maintaining the ball at a
constant potential by means of accumulators, while the air which had
been treated by X-rays was passed by the ball. “An electric current was
started as if the ball had been connected with the wall of the tube by a
bad conductor.” He was not sure whether the air would retain its power
to discharge bodies as long as it remained out of contact with any
bodies. He determined, however, that any slight “disturbance” of the air
by a body having a large surface and not electrified, rendered the air
inoperative. He illustrated this by saying that “If one pushes, for
example, a sufficiently thick plug of cotton-wool so far into the tube
that the air which has been traversed by the rays must stream through
the cotton-wool before it reaches the ball, the charge of the ball
remains unchanged when suction is commenced.” With the cotton-wool
immediately in front of the window, it had no effect, showing,
therefore, that dust particles in the air are not the cause of the
communication of the force of the discharge from the X-rays to the
electrified body. Very fine wire gauze in several thicknesses also
prevented the air from discharging the body when placed between the
aluminum window and the ball within the thick metal tube, as in the case
of the cotton plug. Similar experiments were instituted with dry
hydrogen instead of air, and, as far as he could discern, the bodies
were equally well discharged, except possibly a little slower in
hydrogen. He experienced difficulty in obtaining equally powerful X-rays
at different times. All experimenters are acquainted with this
difficulty. Further, he called attention also to the thin layer of air
which clings to the surface of the bodies, and which, therefore, plays
an appreciable part in connection with the discharge. § 16, near end. In
order to test the matter further as to discharge of electrified bodies,
he placed the same in a highly exhausted bulb and found that the
discharge was in one case, for example, only 1/70 as rapid as in air and
hydrogen at ordinary pressure, thereby serving as another proof that gas
was the intermediate agency. Allowance should be made in all experiments
in connection with the discharging quality of X-rays. The surrounding
gas should be taken into account.


90_a_. APPLICATION OF PRINCIPLE OF DISCHARGE BY X-RAYS.—Professor Robb,
of Trinity College, (_Science_, Apr. 10, ’96), proposed and explained
and practically tested the principle of the discharge of X-rays to
determine the relative transparencies of substances to X-rays. He
plotted a curve in which the co-ordinate represented the charge of the
condenser in micro-coulombs, and the abscissæ the time between charging
and discharging the condenser. The same plan could be adopted, he
suggested, for making quantitative measurements of the intensity of
X-rays from different tubes or the same discharge tube at different
times. J. J. Borgmann, of St. Petersburg, probably was the first to show
that X-rays charged as well as discharged bodies. See _The Elect._,
Lon., Feb. 14, ’96, p. 501. Soon, a similar announcement was made by
Prof. Righi, of Bologna. § 90.


90_A_. BORGMANN AND GERCHUN’S EXPERIMENTS. ACTION OF THE X-RAYS ON
ELECTRO-STATIC CHARGES AND (LA DISTANCE EXPLOSIVE.) _Comptes Rendus_,
Feb. 17, ’96; from _Trans._, by Louis M. Pignolet.—A positively charged
zinc disk connected to an electroscope lost its charge almost instantly
and acquired a negative charge. When the charge on the zinc disk was
negative, the loss was much slower and was not complete, a certain
charge remaining. When the rays fell upon two small platinum balls
connected to the terminals of an induction coil but separated beyond its
sparking distance, sparking took place between them, showing that
X-rays, like ultra-violet rays, increase the sparking distance of static
charges.


90_b_. RIGHI’S EXPERIMENTS. BODIES IN THE NEUTRAL OR NEGATIVE STATE,
POSITIVELY ELECTRIFIED BY X-RAYS. _Comptes Rendus_, Feb. 17, 1896. From
Trans. by Louis M. Pignolet.—The measurements were made by this eminent
Italian physicist, with a Mascart electrometer connected with the bodies
upon which the X-rays impinged and enclosed in a grounded metallic case
(Faraday cylinder) provided with an aluminum window for the entrance of
the rays. A metallic disk connected with the electrometer lost its
charge rapidly whether positive or negative.


§ 99_S_. Initial positive charges were not completely dissipated;
negative charges were not only completely dissipated but the bodies
acquired positive charges. Disks in the neutral state were charged
positively by the X-rays the same as takes place with ultra-violet rays.
The final positive potential was greater for copper than for zinc and
still greater for retort carbon (“_le carbon de cornue_”) 90_c_. at end.
The various results are not conflicting if the particular materials are
taken into accounts. 90_c_ at end.


90_c_. The experiments of Prof. Minchin, an expert in such measurements,
are properly described here, in that they seem to clear up the
superficial ambiguity. He formulated the conclusion (_The Elect._, Lon.,
Mar. 27, ’96, p. 736) thus:—“The X-rays charge some bodies positively
and some negatively, and whatever charge a body may receive by other
means, the X-rays change it, both in magnitude and sign, to the charge
which they independently give to the body.” Thus, in the case of
magnesium, if the same is first positively charged by any suitable
means, then will the X-rays not only discharge it, but electrify it
negatively, while if this metal is first negatively charged, the X-rays
either diminish or increase the discharge. It must be remembered,
however, that this is not true with all metals, for he found that gold,
silver, copper, platinum, iron, aluminum, bismuth, steel and antimony,
are all positively electrified.


90_d_. BENOIST & HERMUZESCU’S EXPERIMENT. NEGATIVE CHARGES DISSIPATED
FASTER THAN POSITIVE BY X-RAYS. RATE DEPENDS UPON ABSORPTION. LAW
FORMULATED. _Comptes Rendus_, Feb. 3, Mar. 17 and April 27, ’96. They
observed that the rays dissipated entirely the charge of electrified
bodies in their path, and that negative charges were dissipated more
rapidly than positive. § 99_Q_. They also noticed the discharge augments
with the opaqueness of the body and that the effect is more considerable
with two thin superposed sheets than with one. In experimenting upon the
influence of the discharge of the gaseous dielectric in which the bodies
were located, they formulated the following law. The rapidity of the
dissipation of the electric charge of an electrified body under the same
condition varies as the square root of the density of the gas
surrounding the body. The dissipation of the electric charge depends
upon the nature of the electrified body, due to a sort of absorbing
power (§ 99_M_) connected with the opaqueness of the body and upon the
nature of the surrounding gas, due to the density of the gas or when
passing from one gas to another. (From trans. by Louis M. Pignolet.)


91. Before Roentgen published in his second paper of Mar. 9, ’96, an
account of his focus tube, the Kings College published a description of
an exactly similar one, represented in the cut. See _Elec. Rev._, Lon.,
Mar. 13. ’96, p. 340. The cathode is concave and the anode is formed of
platinum and is plane and at such an angle that the X-rays generated, §
63_b_., on diffusion of internal cathode rays, will be thrown out
through the thin walls of the bulb. § 55 and 57. As the rays emanate
from a point, the shadows are much clearer, especially in conjunction
with powerful rays permitting several feet between the object and the
tube. Mr. Shallenberger was among the first, and was the first as far as
the author knows (_Elect. World_, Mar. 7, ’96, see cut reproduced) to
originate the use of an X-ray focus tube.


[Illustration:

  TYPICAL FOCUS TUBE.
]


91_a_. APPARATUS EMPLOYED.—Prof. Roentgen paid tribute to Tesla, by
alluding to the advantages resulting from the use of the Tesla condenser
and transformer. In the first place, he noticed that the discharge
apparatus became less hot, and that there was less probability of its
being pierced. Again the vacuum lasted longer, at least in the case of
his particular apparatus. Above all, stronger X-rays were produced.
Again careful adjustment of the vacuum was not as necessary as with the
Ruhmkorff coil.


92. X-RAYS AND LONGITUDINAL VIBRATIONS.—Prof. Roentgen did not consider
X-rays and ultra-violet rays to be of the same nature, although they
produced many common effects. The X-rays, as he found, by the above
related experiments, behaved quite differently from the ultra-violet
rays, which are highly refrangible, practically all subject to
reflection, capable of being polarized, and absorbed according to the
density of the absorbents. For valid reasons, the X-rays cannot be
infra-red rays. While he does not affirm any theory, yet he suggests the
theory of longitudinal waves for explaining the properties of X-rays.
(This was not suggested again in his second announcement.) He stated
that the hypothesis needs a more solid foundation before acceptance. The
reason why Roentgen termed the energy X-rays is simply because X in
algebra represents an unknown quantity.


[Illustration:

  SHALLENBERGER APPARATUS AND FOCUS TUBE. § 91.
]


93. At the Johns Hopkins University, U. S., in 1884, Sir William
Thomson, (Kelvin) delivered a lecture in which he argued that the
production of longitudinal vibrations, by electrical means, is
reasonable and possible of occurrence. J. T. Bottomly, in _Nature_, Lon.
Feb., (see also _Elect. Eng._, N.Y., Feb. 19, ’96, p. 187) called
attention to this lecture as being of interest in view of Roentgen’s
suggestion about longitudinal vibrations. Lord Kelvin called attention
to what had been developed in connection with the electro-magnetic
theory of light and referred to his own work in 1854, in connection with
the propagation of electric impulses along an insulated wire surrounded
by gutta percha, but he said that at that time no one knew the relation
between electro-static and electro-magnetic units. The part of the
lecture referring particularly to the possibility of longitudinal waves
in luminiferous ether by electrical means reads as follows. “Suppose
that we have at any place in air, or in luminiferous ether (I cannot now
distinguish between the two ideas) a body that, through some action we
need not describe, but which is conceivable, is alternately, positively
and negatively electrified; may it not be that this will give rise to
condensational waves? Suppose, for example, that we have two spherical
conductors united by a fine wire, and that an alternating E. M. F. is
produced in that fine wire, for instance, by an alternate current
dynamo-electric machine, and suppose that sort of thing goes on away
from all other disturbance—at a great distance up in the air, for
example. The result of the action of the dynamo-electric machine will be
that one conductor will be alternately, positively and negatively
electrified, and the other conductor negatively and positively
electrified. It is perfectly certain, if we turn the machine slowly,
that in the air in the neighborhood of the conductors, we shall have
alternately, positively and negatively directed electric force with
reversals of, for example, two or three hundred per second of time, with
a gradual transition from negative, through zero to positive, and so on;
and the same thing all through space; and we can tell exactly what the
potential and what the electric force are at each instant at any point.
Now, does any one believe that, if that revolution were made fast
enough, the electro-static law of force, pure and simple, would apply to
the air at different distances from each globe? Every one believes that
if the process can be conducted fast enough, several million times, or
millions of millions times per second, we should have large deviations
from the electro-static law in the distribution of electric force
through the air in the neighborhood. It seems absolutely certain that
such an action as that going on would give rise to electrical waves.
Now, it does seem to me probable that these electrical waves are
condensational waves in luminiferous ether; and probably it would be
that the propagation of these waves would be enormously faster than the
propagation of ordinary light waves.” Notice that the above was written
twelve years prior to Roentgen’s discovery.


94. Prof. Schuster, in _Nature_, Lon., Jan. ’96, stated that the great
argument against the supposition of waves of very small length lies in
the absence of refraction, but questioned whether this objection is
conclusive. He further stated: “The properties of the ether may remain
unaltered within the greater part of the sphere of action of a molecule.
The number of molecules lying within a wave length of ordinary light is
not greater than the number of motes which lie within a sound wave, but,
as far as I know, the velocity of sound is not materially affected by
the presence of dust in the air. Hence there seems nothing impossible in
the supposition that light waves, smaller than those we know of, may
traverse solids with the same velocity as a vacuum. We know that
absorption bands greatly affect the refractive index in neighboring
regions; and as probably the whole question of refraction resolves
itself into one of resonance effects, the rate of propagation of waves
of very small lengths does not seem to me to be prejudged by our present
knowledge. If Roentgen rays contain waves of very small length, the
vibrations in the molecule which respond to them, would seem to be of a
different order of magnitude from those so far known. Possibly, we have
here the vibration of the electron with the molecule, instead of the
molecule carrying with it that of the electron.”


95. Prof. J. J. Thomson showed how it was possible that “longitudinal
waves can exist in a medium containing moving charged ions, and in any
medium, provided the wave length is so small as to be compared with
molecular dimensions, and provided the ether in the medium is in motion.
It follows from the equation of the electro-magnetic field that the
ether is set in motion in a varying electric field. These short waves
would not be refracted, but in this respect they do not differ from
transverse waves, which on the electro-magnetic theory would not be
refracted if the wave length were comparable with molecular distances.”
From _Elect. Eng._, N.Y., Mar. 18, ’96, p. 286, in reference to a paper
before the _Cam. Phil. So._


96. One of the very first questions asked in reference to a discovery is
as to its practical utility. Already, we have important applications in
one of the most humane directions, and that is in connection with
diagnosis. Sciagraphs can also be employed in schools for the purpose of
education, in some departments of anatomy, etc. The interest that it
excites and the amusement that it affords are not to be overlooked, for
anything in the nature of recreation possesses utility. However, we may
greatly thank all experimenters who have investigated the subject, and
who have not left its development alone to Roentgen; for predictions as
to the utility of a discovery, however, apparently exaggerated, are very
often proved, by subsequent developments, to have been underrated. Upon
this point Prof. Boltzmann, in _Zeit. Elect._, Jan. 15, ’96, see also,
_The Elec._, Lon., Jan. 31, ’96, p. 447, stated, “If we remember to what
discoveries the most insignificant new natural phenomenon, such as the
attraction of small objects by rubbed amber, of iron by the lode-stone,
the convulsive twitches of a frog’s leg due to electric discharges, the
influence of the electric current upon the magnetic needle,
electro-magnetic induction etc., has led us, one can imagine to what
applications an agent will be turned, which a few weeks after its
discovery has given rise to such surprising results.”


97. Soon after hearing, (about the first of Feb. ’96,) of the Roentgen
discovery, it occurred to the author to carry on experiments with
fluorescence, but finding that it was inconvenient to work in a
perfectly dark room, and, recognizing that black cardboard had
practically no effect upon absorbing the X-rays, he devised a sciascope
(_daily papers_, Feb. 13, and _Elect. Eng._, Feb. 19) which he
afterwards learned was independently invented and used at about the same
time by Prof. William F. Magie, of Princeton University, (see _Amer.
Jour. Med. Sci._, Feb. 7, ’96 and Feb. 15, ’96) and by Prof. E.
Salvioni, of Italy under the name of cryptoscope, (see _Med. Sur. Acad._
of Perugia, Italy, Feb. 8, ’96.) In about a month afterwards (_Elect.
Eng._, N.Y., Apr. 1, ’96, p. 340) the instrument (with phosphorescent
calcic tungstate § 13. in place of fluorescent barium platino cyanide)
was again published under the name of the Edison fluoroscope. There are
probably many other claimants—some professor in London—name forgotten.
They all consist of a tapering tube with a sight hole at one end and a
fluorescent screen in the other, which is closed by opaque card board.
(Frontispiece at Chap. X). For the sake of conformity, the words
sciagraph and sciagraphy and similar derivatives, and in view of the
meaning of the radical definitions, have been employed throughout the
book. The objection to the word fluoroscope is that the instrument is
practically universally employed in seeing the shadows of objects,
otherwise invisible to the naked eye, rather than to test fluorescence.
The name sciascope was early suggested by Prof. Magie. For those who
wish to make a screen, the author may state that he obtained a good one
by mixing pulverized barium platino cyanide with varnish and spreading
the mixture over a sheet of tracing cloth.


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




                              CHAPTER VIII


                                -------

[Illustration]

97_a_. HERTZ’ EXPERIMENTS. ELECTRIFIED BODIES DISCHARGED BY ULTRA-VIOLET
LIGHT OF A SPARK AND BY OTHER SOURCES OF LIGHT. _Berlin Akad._ II., p.
487, ’87. _Wied Ann._ XXXI, p. 983. English translation of the above.
Lon. and N.Y. Macmillan, p. 63, ’93. From notes by Mr. N. D. C.
Hodges.—This is the all-important initial work of H. Hertz. The source
of light was a spark, and the great discovery resulted from a
combination of circumstances and was unsought; but by studying and
testing the matter, he found the cause. Two induction coils, _a_ and
_b_, having interrupter _d_, were included in the same circuit, as shown
in the figure. The sparking of the active one (A) increased the length
of the spark of the passive (B) § 10. He sought the cause. The discharge
was more marked as the distance between the sparks was reduced. Sparks
between the knobs had the same effect as those between points; but the
effect was best displayed when the spark B was between knobs. The
relation between the two sparks was reciprocal. The discharging effect
of the active spark (A) spread out on all sides, according to the laws
of light, first suggesting that light was the cause. Most solid bodies
acted as screens, s. Liquid and gases served more or less as screens.
The intensity of the action increased by the rarefaction of the air
around the passive spark, __i.e.__, in a discharge tube. The radiations
from the spark, A, reflected from most surfaces, according to the laws
of light, and refracted according to the same laws, caused the
discharge. The ultra-violet light of the spark A was inferred to be the
active agent in producing the discharge. The same effect was produced by
other sources of light than the electric spark. The conclusions were
afterwards confirmed by many, and subordinate discoveries originated. §
98—99T.


97_b_. WIEDEMANN AND EBERT’S EXPERIMENT. LIGHT DISCHARGES CATHODE, BUT
HAS NO INFLUENCE UPON ANODE, NOR AIR-GAP. DIFFERENT GASES AND DIFFERENT
PRESSURES. _Wied. Ann._ XXXIII, p. 241. 1888. From notes by N. D. C.
Hodges.—The arc light was used in place of the active spark of Hertz.
Principal result was that the effect depended on the illumination of the
cathode (§ 99.) The illumination of the anode or of the spark-gap did
not influence the discharge. The very character of the charge was
altered by the action of light upon the cathode. The influence of the
illumination of the cathode did not consist solely at the starting of
the spark, but lasted as long as the sparks continued to pass. With
decreasing pressure of surrounding gas, the effect first increased (§
97_a_) to a maximum, and then decreased (§ 54). The illumination had an
effect on the path of the sparks, the path being perpendicular to the
rays of light. The best results were obtained with carbonic acid gas.
Hydrogen was next, and then air. They were contained in the tubes
surrounding the poles. The character of the gas also had an influence on
the rays which would produce the effect, with carbonic acid gas the
effect showing itself even with the visible rays.


98. ELSTER AND GEITEL’S EXPERIMENT. NEGATIVELY CHARGED BODIES DISCHARGED
BY LIGHT. _Wien. Berichte._ Vol. CI, p. 703, ’92. _Wied. Ann._ Vols.
XXXVIII, XXXIX, XLI, XLII, XLIII, XLIV, XLVI, XLVII, LII. _Nature_,
Lon., Sept. 6, ’94, p. 451.—The elements employed for carrying on the
experiment consisted of a delicate electroscope and certain metals,
including aluminum, amalgamated zinc, magnesium, rubidium, potassium and
sodium. Some of the experiments were made on the top of Mount Sonnblick,
the same being 3,100 m. high, where the discharging power of light was
found to be about twice as great as at Wolfenbuttel, which was at the
level of 80 m. The whole time for the discharge was only a matter of a
few seconds. The greater rapidity of discharge at the higher level was
attributed to the greater proportion of ultra-violet rays (Hertz), which
are the most easily absorbed by the atmosphere, according to Langley.
All metals are not discharged alike by the action of light. The law
follows the electro-positive series in such a way that the more
electro-positive the metal, the longer the wave length of light
necessary to produce the discharge. In experiments with potassium,
sodium and rubidium, they made them successively, the cathode in a bulb
of rarefied hydrogen. In this case it was found that the light of a
candle, even at so great a distance as 7 m., would cause the discharge.
Rubidium was sensitive in this respect to the red light from a heated
rod of glass. Elster and Geitel were able also to discharge, by light,
some non-metallic bodies, like calcic sulphide, when so prepared that it
had the property of phosphorescing, and also darkly colored fluorites.
Independently, the phenomenon is of importance, because Elster and
Geitel determined that there was some common cause as to the discharge
of bodies of light and the discharge from the earth’s surface. A series
of experiments lasting three years, consisted in investigating the
relation of the ultra-violet rays from the sun simultaneously to the
quantity of charge in the atmosphere. The results acted as evidence of
the explanation of the daily and annual variation of atmospheric
potentials. These experiments are of importance in connection with
X-rays, because Röntgen and Prof. J. J. Thomson subsequently, and
possibly others independently, discovered that X-rays produce, not only
a like, but a more extended action in that there is not so great a
difference between their power to discharge negatively and positively
electrified bodies. § 90_a_. In the further developments of their ideas,
they tried the action of diffused day-light upon a Geissler tube
traversed by vibrations which were produced by a Hertz vibrator (see
recent book on Hertzian waves), the tube having an electrode of metal of
the alkaline group. They were able to adjust the combination so that the
presence of a little day-light would initiate a luminous discharge,
while in the dark such a charge ceased. § 14_a_.


99. ELSTER AND GEITEL’S EXPERIMENT. EFFECT OF POLARIZED LIGHT UPON THE
CATHODE. _Berlin Akad._ ’95. _Nature_, Lon., March 28, ’95, p. 514.
_Proc. Brit. Asso._, Aug. 16, ’94; Aug. 23, ’94, p. 406.—The X-rays have
properties similar to those of light, and have their source in
electricity. Quincke discovered that light which has been polarized
perpendicularly to the plane of incidence is greatly increased as to its
power of penetrating metals. Elster and Geitel used the following
apparatus to determine the relation between polarized light and
electricity. The current varied according to the angle of incidence and
the plane of polarization. The apparatus comprised the following
elements: An exhausted bulb, provided with a platinum anode, and a
cathode consisting of potassium and sodium, combined in the form of a
liquid alloy having a bright surface of reflection. The source of light
was an oxyhydrogen flame, which played upon zircon instead of lime; a
lens changed the diverging rays to parallel rays, which were polarized
by a Nichol prism and allowed to fall upon the cathode. The electrodes
of the vacuum bulb were connected to the poles of a generator of a
current of about 400 volts. “The strength, of the current was greatest
when the plane of polarization was perpendicular to the plane of
incidence—__i.e.__, when the electric displacements constituting light,
took place in the plane of incidence, and when the angle of incidence
was about 60°, __i.e.__, the polarizing angle of the alloy itself.”
Prof. Sylvanus P. Thompson confirmed these results by experiment. The
rate of discharge was greatest, he said, when the plane of polarization
was such that the Fresnellian vibration “chopped into” the surface.
Polarized light, he reminded them, produced similar results upon
selenium.

Although the domain of this book is necessarily limited to the
consideration of phenomena connected with the internal and external
energy of a discharge tube, yet if any other one subject is of special
interest and utility in connection with the consideration of X-rays, it
is that concerning the relation between the electric discharge and
light, which has been thoroughly studied only during the past few years,
and the accounts of the researches recorded in various periodicals and
academy papers. Those readers, however, who desire to study this
exceedingly interesting and novel branch of science, which in connection
with the action of the internal cathode rays and X-rays upon electrified
bodies, tends to uphold Maxwell’s theory as developed by mathematics and
based upon early known facts and predicted discoveries, may find volumes
upon this subject by referring to the citations below, named by Mr. N.
D. C. Hodges and obtained by him by a search in the archives of the
Astor Library. Of especial interest are those of Branly, § 99_I_, 99_J_,
99_Q_, 99_S_, 99_T_. Some notion as to the contents of the citations are
given here and there.


99_A_. KOCH’S EXPERIMENT. THE LOSS OF ELECTRICITY FROM A GLOWING
ELECTRIFIED BODY. _Wied. Ann._, XXXIII., p. 454, ’88.


99_B_. SCHUSTER AND ANPENIUS’ EXPERIMENT. THE INFLUENCE OF LIGHT ON
ELECTROSTATICALLY CHARGED BODIES. _Proc. R. So._, Lon., LXII., p. 371,
’87; _Proc. Swedish Acad._, LXIV., p. 405, ’87.—Many recent periodicals
have set forth that ultra-violet light will discharge only negatively
charged bodies. While this is practically or sometimes the case, yet
these experimenters found that a positive charge was dissipated very
slowly. They confirmed the results that the ultra-violet rays played the
principle part in the removal of a negative charge. Polishing the
surface accelerated the action. § 99, near beginning.


99_C_. RIGHI’S EXPERIMENT. SOME NEW ELECTRIC PHENOMENA PRODUCED BY
LIGHT. Note 2-4, _Rend. R. Acad. die Lincei_, May 6, 20, and June 3,
’88.


99_D_. RIGHI’S EXPERIMENT. SOME NEW ELECTRIC PHENOMENA PRODUCED BY
ILLUMINATION. _Rend. R. Acad. die Lincei._ VI., p. 135, 187,
’88.—Confirmation of the results of other physicists, and a quantitative
measurement determining that the E. M. F. between copper and selenium
was increased 25 per cent. by illumination by an arc light. The selenium
was in the form of crystals mounted upon a metal plate.


99_E_. STOLSTOW’S EXPERIMENT. ACTINO-CURRENT THROUGH AIR. _C. R._, CVI.,
pp. 1593 to 95, ’88.—Liquids tested. Greatest absorbents of active rays
most quickly discharged.


99_F_. RIGHI AND STOLSTOW’S EXPERIMENTS. KIND OF ELECTRIC CURRENT
PRODUCED BY ULTRA-VIOLET RAYS. _C. R._, CVI, pp. 1149 to 52, ’88.—The
discharge was accelerated by using a chemically clean surface. The
burning of metals, for example, aluminum, zinc or lead in the arc light
increased the discharging power.


99_G_. BICHAT & BLONDOT’S EXPERIMENT. ACTION OF ULTRA-VIOLET RAYS ON THE
PASSAGE OF ELECTRICITY OF LOW TENSION THROUGH AIR. _Comptes Rendus._
CVI, pp. 1,349 to 51. ’88.—They employed arc lamps whose carbons had
aluminum cores.


99_H_. NACARRI’S EXPERIMENT. THE DISSIPATION OF ELECTRICITY THROUGH THE
ACTION OF PHOSPHOROUS AND THE ELECTRIC SPARK. _Atti di Torino._ XXV, pp.
252 to 257. ’90.—The loss of charge was eighteen times less rapid in the
dark through the air in a bottle, than when a piece of luminous
phosphorous was placed in the bottle. The introduction of turpentine,
which checked the glowing of the phosphorous, retarded the loss of
charge.


[Illustration:

  FROM SCIAGRAPH OF FROG, THROUGH SMALL HOLE IN DIAPHRAGM, AS IN FIG. 1,
    p. 100.
]


99_I_. BRANLY’S EXPERIMENT. PHOTO-ELECTRIC CURRENT BETWEEN THE TWO
PLATES OF A CONDENSER. _C. R._ CX, pp. 898 to 901. ’91.—A positive
charge was dissipated, and by a peculiar arrangement of the plates,
screens, etc., and with particular materials, he was able to show that
the rates of loss of a positive and negative charge were about equal.
Numerous tests were instituted. If he is not mistaken, how closely
related are X-rays and light. § 90. Those who wish to more thoroughly
investigate this matter and verify the same, should study these
experiments more in detail in connection with Schuster’s and Anpenius’
experiments (§ 99_B_), whose arrangement of the plates was the same as
those of Branly.


99_J_. BRANLY’S EXPERIMENT. LOSS OF BOTH ELECTRICITIES BY ILLUMINATION
WITH RAYS OF GREAT REFRANGIBILITY. _C. R._ CX, pp. 751 to 754. ’90.


99_K_. RIGHI’S EXPERIMENT. ELECTRIC PHENOMENA PRODUCED BY ILLUMINATION.
_Luer’s Rep._ XXV, pp. 380 to 382. ’89.


99_L_. BORGMANN. ACTINO-ELECTRIC PHENOMENA. _C. R._ CVIII, p. 733. ’89.
_Jour. d. Russ. Phys. Chan. Ges._ (2) XXI, pp. 23 to 26. ’89.—The
photo-electric effect not instantaneous. A telephone served in the place
of the galvanometer to detect the discharge.


99_M_. STOLSTOW’S EXPERIMENT. ACTINO-ELECTRIC INVESTIGATIONS. _Jour. d.
Russ. Phys. Chan. Ges._ (7-8) XXI, pp. 159 to 207.—It is necessary that
the rays of light should be absorbed by the charged surface before
having the discharging influence. § 99_E_. All metals are subject to the
action, and also the aniline dyes. Two plates between which there is a
contact difference of potential generate a current so long as the
negative plate is illuminated. The effect is increased with the increase
of temperature and is only found in gases, and is therefore of the
nature of convection. He determined these principles by continuous work
for two years. It should be remembered that in all these researches, the
arc light is preferable, because the ultra-violet spectrum is six times
as long as that given by the sun.


99_N_. MEBIUS’ EXPERIMENT. AN ELECTRIC SPARK AND A SMALL FLAME EMPLOYED.
_Bihang till K. Svenska Vet.-Akad. Hand._ 15, _Afd._ 1, No. 4, p. 30,
’89.


99_O_. WORTHINGTON’S EXPERIMENT. DISCHARGE OF ELECTRIFICATION BY FLAMES.
_Brit. Asso. Rep._, ’90, p. 225.


99_P_. FLEMING’S EXPERIMENT. DISCHARGE BETWEEN ELECTRODES AT DIFFERENT
TEMPERATURES IN AIR AND IN HIGH VACUA. § 99_M_, near end. _Proc. Ro.
So._, LXVII., p. 118.


99_Q_. BRANLY’S EXPERIMENT. HALLWACH AND STOLSTOW’S EXPERIMENT. LOSS OF
ELECTRIC CHARGE. _Lum. Elect._, LXI., pp. 143 to 144, ’91.—Branly
obtained quantitative results. Hallwach found with the use of the arc
light, a very small loss of positive electricity at high potentials;
Stolstow, no such loss at potentials under 200 volts. Branly, with a 50
element battery and an arc light as the source of illumination, caused a
discharge and thereby a constant deflection of 124 degrees of the
galvanometer needle. The action of the light upon a positive disk caused
a deflection of only three degrees by the same battery. With aluminum in
the electrodes, the deflections were about 1400 and 24 respectively. Is
it not sufficiently fully established that ultra-violet light will
discharge not only negative but positive electricity? He experimented
with substances heated to glowing or incandescence. Glass lamp chimneys
at a dull, red heat, when covered with aluminum, oxide of bismuth, or
lead oxides, withdraw positive charges. In the same way, for example,
behaves a nickel tube in place of the lamp chimney.


99_R_. WANKA’S EXPERIMENT. A NEW DISCHARGE EXPERIMENT. _Abk. d. Deuts.
Math. Ges. in Rrag._, ’92, pp. 57 to 63.—He confirms the principle that
the ultra-violet rays are the most powerful. A glass plate, which, as
well known, cuts off most of the ultra-violet rays, was properly
interposed and then removed and the difference noted.


99_S_. BRANLY’S EXPERIMENT. DISCHARGE OF BOTH POSITIVE AND NEGATIVE
ELECTRICITY BY ULTRA-VIOLET RAYS. _C. R._, CXIV., pp. 68 to 70, ’92.—He
further proves that ultra-violet rays of light will dissipate a positive
charge. The experiments in this connection seem to prove more and more
that the discharging power is only a matter of sufficiently high
refrangibility of the rays of light.


99_T_. BRANLY’S EXPERIMENT. LOSS OF ELECTRIC CHARGE IN DIFFUSE LIGHT AND
IN THE DARK. _C. R._, CXVI., pp. 741 to 744. ’93.—A polished aluminum
sheet was attached to the terminal of an electroscope properly
surrounded by a metal screen. After a few days, the plate acted like any
other metal plate polished or unpolished; it lost its charge very
slowly, positive or negative alike, independently of the illumination.
If it is then again polished, as for example, with emery paper and
turpentine, it loses its charge rapidly in diffused light, which has
passed through a pane of window glass, for example. Therefore, the
ultra-violet rays are not alone effective, although most effective. The
longer the time elapsing, after polishing, the slower the discharge
takes place. Zinc behaved likewise, only more slowly. Other metals were
tried. Bismuth acted differently from most metals. Whether charged
positively or negatively, they exhibited rapid loss in the dark, in dry
air under a metal bell, independently of the state of the polish.


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




                               CHAPTER IX


                                -------

100. THOMSON’S EXPERIMENTS. _Elect. Eng._, N.Y., Mar. 11, Apr. 8 and
Apr. 22, ’96. _Elect. Rev._, N.Y., Apr. 8, ’96, p. 183. STEREOSCOPIC
SCIAGRAPHS. _Elect. World_, N.Y., Mar. 14, ’96.—Prof. Elihu Thomson, of
the Thomson-Houston Electric Company, described experiments to determine
the practicability of making stereoscopic pictures by X-rays. A solid
object may be considered as composed of points which are at different
distances from the eye. By monocular vision, the solidity of an object
is not assured. However, by the use of both eyes, the objects appear
less flat. The experimenter used, as the different objects, a mouse,
also metal wires twisted together, and, again, a block of wood having
projecting nails. In order to produce a stereoscopic picture with
X-rays, he took a sciagraph in the ordinary way. He then caused the
relative displacement of the discharge-tube and the object, and took
another sciagraph. By mounting the two sciagraphs in a stereoscope, he
found that the effect was as expected, and in the case especially of the
skeleton of the mouse, it was very curious,—less like a shadow picture
and more like the real object. The picture was more realistic, as in the
well-known stereoscope for viewing photographs.


[Illustration:

  MULTIPLE SCIAGRAPHS. FIG. 1, § 101, p. 95.
]


[Illustration:

  MULTIPLE SCIAGRAPHS. FIG. 2, § 101, p. 95.
]


101. THOMSON’S EXPERIMENT. MANIFOLDING BY X-RAYS.—If one desires to take
a print of a negative, for example by means of sun-light, it is evident
that, on account of the opacity of the photographic paper, only one
sheet would be placed under the negative for receiving a print. However,
the X-rays are so penetrating in their power that it is possible for
them to produce sciagraphs through several sheets, and thereby to result
in the production of several pictures of the same object with one
exposure. Without an experiment to prove this, one might argue that the
chemical action of one sheet would absorb all the energy. The experiment
of Prof. Thomson shows that this is not so. The elements were arranged
as follows: First a discharge tube; then an object, namely, a key
escutcheon of iron; then yellow paper; then paste board; then black
paper; then two layers of albumen or sensitized paper; then two célérité
printing papers; then two platinum printing papers; then one célérité;
then six layers of sensitive bromide paper; then four layers of heavy
sensitive bromide paper (heavier); then three layers of black paper, and
finally, at the maximum distance from the discharge-tube, a sensitive
glass plate of dry gelatine, with its face up, thereby making
twenty-five layers in the aggregate. It is interesting to notice that an
induction coil was not employed, but a small Wimshurst machine, having
connected to each pole a small Leyden jar. § 106. 1,200 discharges
occurred during exposure. The results were as follows: No sciagraphs
developed upon the albumen, célérité nor platinum, which, it should be
noticed, were merely printing papers. § 128. The impressions on the ten
bromide papers were weak. See Multiple Sciagraphs, Fig. 2, p. 94. He
attributed the reason of this to the thinness of the film. Although the
glass plate was furthest away from the discharge tube, yet the
impression was greater than on any of the papers, the result being shown
in Multiple Sciagraphs, Fig. 1, p. 94. He suggested that the plates for
use with X-rays should have unusually thick films. Incidentally he found
that the intensifying process could be employed with profit to bring out
the small details distinctly. Dr. Lodge also recommended thick films.
See _The Elect._, Lon., Apr. 24, ’96., p. 865.


101_a_. LUMIÈRE’S EXPERIMENT. ENORMOUS TRANSPARENCY OF SENSITIVE
PHOTOGRAPHIC PAPER. _Comptes Rendus_, Feb. 17, ’96. Translated by Mr.
Louis M. Pignolet.—With a ten-minutes exposure, objects were sciagraphed
through 250 super-imposed sheets of gelatino-bromide of silver paper, to
observe the absorption of the X-rays by the sensitive films. The one
hundred and fiftieth sheet was found to have an impression.


102. PROPOSED DOUBLE CATHODE TUBE. See also _Elect. Rev._, N.Y., Apr.
15, p. 191.—The nature of this will be apparent immediately from the cut
which is herewith presented and entitled “Standard X-Ray Tube.” With
unidirectional currents the concave electrodes in the opposite ends may
each be a permanent cathode, while the upper terminal connected to the
angular sheet of platinum may be the anode. Cathode rays, therefore,
will be sent out from each concave disk, and striking upon the platinum
will be converted into X-rays, assuming that the platinum is the surface
upon which the transformation from one kind of ray to another takes
place. § 63, at end. This is called a standard tube, because it may be
employed with efficiency with any kind of generator. § 8_a_, 26_a_, 115,
116 and 145. It is interesting to notice a confirmation of the
efficiency of such a tube, for Mr. Swinton, in a communication to the
_Wurz Phys. Med. So._ (see _The Elect._, Lon., and _Elect. Eng._, N.Y.,
June 3,) showed and described a picture of an exactly similar tube. By
an experiment, the tube operated as expected. First proposed by Prof.
Elihu Thomson, who is an author also of the following experiment:


[Illustration:

  STANDARD X-RAY TUBE.
]


103. X-RAYS. OPALESCENCE AND DIFFUSION. _Elect. World_, Apr. 25, ’96.—He
alluded to opal glass and milk to illustrate that light is reflected not
only at the surface of a body, but from points, or molecules, or
particles, located underneath the surface. By some experiments with
X-rays, he found that they had a similar property only not to such a
large per cent., but on the other hand by the way of contrast, there are
many more substances opalescent to X-rays than there are to light, for
the reason that the former will penetrate more substances and to greater
distances. He made many observations with a modified sciascope, § 105,
by pointing it away from the discharge tube and towards different
substances struck by X-rays. To all appearances, such substances became
the sources of the X-rays. He alluded to Mr. Tesla’s experiments on
reflection, § 146, but noticed that there was a slight difference
between reflection and diffusion and he was satisfied that reflection
took place from the interior of the substances as well as from the
surface. Metal plates, he said, gave apparently little diffusive effect,
appearing to reflect feebly at angles equal to the incident angles. He
alluded to Edison’s experiment also, § 133, with a large thick plate
cutting off the X-rays and attributed the luminosity of his modified
sciascope to rays both reflected and diffused from surrounding objects,
which generally as a matter of course, are more of non-metallic objects
than metallic, such as floor, ceiling, walls, tables, chairs and so on.
Evidently, the interior of one’s hand causes diffusion; very little,
however, for a sciagraph by means of a focus tube gives wonderfully
clear outlines, and yet the rays do not come from a mathematical point.
§ 88. Prof. Thomson acknowledged that independently of himself, Dr. M.
I. Pupin, of Columbia College, had reported in _Science_, Apr. 10, ’96,
see also _Electricity_, Apr. 15, ’96, p. 208, upon investigations on the
same general subject, namely diffusion, and also referred to experiments
of Lenard, § 69, and Roentgen on diffusion. Agrees also with experiments
of A. Imbert and H. Bertin-Sans in _Comptes Rendus_, Mar. 2, ’96. He
suggested that this property of diffusion acted as an explanation why
sciagraphs can never have absolutely clearly cut shadows of the bones or
other objects imbedded in a considerable depth of flesh.


103_a_. A. IMBERT AND H. BERTIN-SANS’ DIFFUSION AND REFLECTION IN
RELATION TO POLISH. X-RAYS. _Comptes Rendus_, Mar. 2, ’96. Translated by
Louis M. Pignolet.—They concluded, under the conditions of their
experiments, that if X-rays were capable of reflection it was only in a
very small proportion; on the other hand, the rays can be diffused _en
assez grande quantité_, the intensity of the diffusion appearing to
depend much more upon the nature of the diffusing body than upon its
degree of polish. From this they attributed to the rays a very small
wave length, such that it would be impossible to get in the degree of
polish necessary to obtain their regular deflection. Perrin attempted
unsuccessfully to reflect the rays from a polished steel mirror and a
plate of “flint,” but with exposures of one hour and seven hours
respectively, nothing was obtained. From trans. by L. M. Pignolet,
_Comptes Rendus_, Jan., 96. By exposing a metal plate to the rays and
suitably inclining it in front of the opening, Lafay also proved
reflection, for it was possible to discharge the electrified screen;
hence, as he called it, diffused reflection. _Comptes Rendus_, Apr. 27,
’96; from trans. by L. M. Pignolet.


104. FLUOROMETER.—He constructed an instrument for comparing the merits
of different discharge tubes, and for indicating the comparative
luminosity of different screens subjected to the action of the same
discharge tube. The instrument served also to act as an indicator of the
diffusing power of different materials. “By placing two exactly similar
fluorescent screens at opposite ends of a dark tube, and employing a
Bunsen photometer screen, movable as usual between the screens, a
comparison of the diffusing power of different materials might be made
by subjecting the pieces placed near the ends of the photometer tube
outside, to equal radiation from the Crookes’ tube.” From Prof.
Thomson’s description.

The author performed some experiments (_Elect. Eng._, N.Y., Apr. 15,
’96, p. 379) in relation to candle-power of X-rays by looking into a
sciascope and moving it away until the luminosity just disappeared. He
then detached the black paper cover from the phosphorescent screen and
pointed the sciascope toward a candle flame and receded away until the
fluorescence also disappeared. The distances, with different candles,
would, of course, somewhat vary, but it would in the rough be a constant
quantity, while different discharge tubes would cause the vanishing
fluorescence at different distances. Now, assuming that the X-rays vary
inversely as the square of the distance, as believed by Röntgen, their
power to fluoresce could, therefore, always be named as so much of a
candle-power.


105. SIMPLE DEVICE FOR COMPARING AND LOCATING THE SOURCE AND DIRECTION
OF X-RAYS. PHOSPHORESCENCE NOT ESSENTIAL.—In the ordinary sciascope, the
fluorescent screen is located at one end, and the eyehole at the other.
He modified this construction by employing a long straight tube, made of
thick metal, so that X-rays could not enter through the wall. About at
the centre of the tube was a diaphragm of a fluorescent material. Now,
it is evident that if this is directed toward the phosphorescent spot
and placed very close to the same, and the other end be looked into, the
screen will become fluorescent, if X-rays are emitted from the area
expected. Such a result occurred. With this instrument, he was able to
show, in a similar way, that X-rays did not come from the anode, nor
from the cathode directly. In one case, he provided a piece of platinum
within the discharge tube, in such a position as to be struck by the
cathode rays. § § 91 and 116. The instrument showed that X-rays radiated
from the platinum, although the latter was not luminous nor
phosphorescent,—illustrating again that phosphorescence is not a
necessary accompaniment of X-rays, and assisting in upholding the
principle that as the phosphorescence diminishes by increase of vacuum
and increase of E. M. F., the X-rays increase. It should be noticed that
Prof. Thomson emphasizes that the tube should be made of thick metal.


106. RICE’S EXPERIMENT. APPARATUS FOR OBTAINING X-RAYS. § 109, 114, 131,
137. TUBE ENERGIZED BY A WIMSHURST MACHINE. _Elect. Eng._, N.Y., Apr.
22, p. 410.—Roentgen had always employed the induction coil. As to those
who first excited the discharge tube by the Holtz or Wimshurst machine
or generators of like nature, it is not certain; but, according to
public records, they were independently Prof. M. I. Pupin, of Columbia
College, and Dr. William J. Morton, of New York. See _Electricity_,
N.Y., Feb. 19, ’96. The accompanying cut marked “Rice’s Experiment, Fig.
1,” is a diagram representing the several elements of the apparatus,
while “Rice’s Experiment, Fig. 2,” shows what kind of a sciagraph can be
obtained by means of a Wimshurst machine. § 101, at centre. The details
of the apparatus as employed by Mr. E. Wilbur Rice, Jr., Technical
Director of the General Electric Co., were as follows: A Wimshurst
machine, having a glass plate 16 inches diameter, coupled up with the
usual small Leyden jars, spark under best conditions of atmosphere,
etc., 4 inches. “The usual method of taking pictures with such a machine
is to connect the interior coatings of the two jars, respectively, to
the positive and negative conductors of the machine, the terminals of
the discharge tube being connected between the external coatings of the
Leyden jars. In this condition, the disruptive discharge of the Leyden
jars passes through the tube and across the balls upon the terminals of
the conductors of the machine, the length of spark being regulated by
separating the balls in the usual way.” Later, he found that by omitting
the Leyden jars, the generation of the X-rays was practically
non-intermittent. He therefore connected the terminals of the discharge
tube directly to those of the Wimshurst machine as indicated in “Rice’s
Experiment, Fig. 1,” which also illustrates the details in the carrying
out of the experiment for obtaining the picture, Fig. 2, of the purse
containing the coins and a key. The principal feature was the
introduction of a lead diaphragm containing a small central opening 7-8
inch diameter opposite the fluorescent spot. Sciagraphs taken thus
required a little more time, about 60 minutes, while without the
diaphragm, the time could be shortened to about 30 minutes, but the
shadows were not so clear in the latter case. The figures are on p. 100.


[Illustration:

  RICE’S EXPERIMENT. FIG. 1, § 106, p. 99.
  Diagram.
]


[Illustration:

  RICE’S EXPERIMENT. FIG. 2, § 106, p. 99.
  Taken with the above apparatus.
]


107. SOURCE OF X-RAYS TESTED BY PROPAGATION THROUGH A SMALL HOLE.—This
would illustrate not only that the fluorescent spot is the source of
X-rays, but also that a very small portion comes from other parts that
are probably bombarded by stray cathode rays (due to irregular surface
of cathode § 57, or by reflected X-rays or cathode rays.

He tested the source of the X-rays by means of the following arrangement
of the apparatus: It will be noticed that the lead diaphragm is quite
close to the fluorescent spot. Upon holding the sciascope on the
opposite side, and pointing it toward the spot, the luminous area of the
fluorescent screen was about the same as that of the opening in the
diaphragm, but the size grew rapidly upon receding from the diaphragm.
If the rays had come from the cathode, however, the fluorescent spot on
the screen would not have increased in size so rapidly during recession,
and, therefore, the rays must have come from the spot on the glass
struck by the cathode rays. § 113, 116, 117.


107_a_. LEEDS’ AND STOKES’ EXPERIMENT. USE OF STOPS IN SCIAGRAPHY.
_Western Electrician_, Mar. 14, ’96.—In order to obtain clear
definitions of the shadows, Messrs. M. E. Leeds and J. B. Stokes
provided lead plates with holes, varying in size from 1/4 inch to an
inch between the discharge tube on one side and the object and
photographic plate on the other. In this manner they obtained excellent
sciagraphs of animals having very fine skeletons. See the picture of the
rattlesnake at § 135 and of a fish on page 63. See also the frog taken
abroad page 90.


107_b_. MACFARLANE, MORTON, KLINK, WEBB AND CLARK’S EXPERIMENT. X-RAYS
FROM TWO PHOSPHORESCENT SPOTS. _Elect. World_, Mar. 14, ’96.—By means of
nails projecting vertically from a board (similar to the process carried
out by Dr. William J. Morton, _Elect. Eng._, N.Y., Mar. 5, ’96), they
proved, undoubtedly, that the source of the X-rays was at the surface of
the glass directly opposite the cathode. By modification, which acted as
further proof, a tube was provided with a cathode at the centre. There
was a phosphorescent spot at each end. One board was placed laterally to
the tube, and two shadows of each of certain nails were cast, which were
caused as proved by measurement, by a double source of X-rays. This
experiment illustrates the importance of preventing double shadows. The
plate should be perpendicular to the line joining the two sources of the
X-rays when there are two such sources. Even with the focus tube Dr.
Philip M. Jones, of San Francisco, determined that there were two
phosphorescent spots. These should be taken into account in all cases
and attempts made to produce but one strong focus upon the platinum.
_Elect. World_, N.Y., May 23, ’96.


[Illustration:

  STINE’S EXPERIMENT. FIG. 1, § 108, p. 104.
]


[Illustration:

  STINE’S EXPERIMENT. FIG. 2, § 108, p. 104.
]


108. STINE’S EXPERIMENTS. SOURCE OF X-RAYS DETERMINED BY SCIAGRAPHS OF
SHORT TUBES. _Elect. World_, N.Y., Apr. 11, ’96, pp. 392, 393.—Prof.
Stine, of the _Armour. Inst. of Tech._, by means of the diagram shown in
Fig. 1, p. 102, clearly proved that the X-rays have their source at the
area struck by the cathode rays located directly opposite the disk
marked “cathode.” If the reader will investigate the diagram and the
sciagraphs, he will obtain a clearer knowledge of the evidence than by
any verbal description, further than to explain how the elements are
related to one another. In Fig. 1, therefore, will be noticed covered
photographic plates, located as indicated with reference to the extreme
left-hand end of the discharge tube, where the cathode rays strike. The
surface of Plate 5 is parallel to that of the cathode, and the
phosphorescent spot is in line between the two above named elements. The
result is shown in Fig. 2, p. 102, the objects sciagraphed being several
short sections of tubes with diameters varying from 1/2 to 3 inches.

A, in Figs. 3, 4, p. 104 and in Figs. 5, 6, p. 112, identifies the ends
lettered A in Fig. 1. The sciagraph in Fig. 3 was obtained on the plate
shown at the top in Fig. 1; that in Fig. 4, on Plate 2; that in Fig. 5,
on Plate 3; and that in Fig. 6, on Plate 4. Not only were direct shadows
visible, but also secondary shadows, indicating, therefore, that,
although the source of practically all the rays was at the
phosphorescent spot, yet a portion of the rays came slightly from other
directions, either by reflection or by actual production of rays, upon
other portions of the tube. Look now especially at Fig. 3, p. 104. If
the rays came from the anode, then would this appearance necessarily be
the same as that in Fig. 2. Similarly, the other sciagraphs may be
considered to show that the rays do not come from the anode. In the case
of the sciagraphs in Figs. 4, 5 and 6, only a single tube acted as the
body for casting a shadow. Prof. Stine stated that the experiments were
repeated over and over again, thereby establishing the phenomena as
uniform.


109. STINE’S ELECTRICAL APPARATUS EMPLOYED. § § 106, 112, 114, 131,
137.—Prof. Stine gave the following suggestive points:

“Among the first points investigated was the influence of the
interrupter. The coil was provided, first with the familiar mercury make
and break, and then an ordinary vibrator. The mercurial device gave very
good results.


[Illustration:

  STINE’S EXPERIMENT. FIG. 3, § 108, p. 104.
]


[Illustration:

  STINE’S EXPERIMENT. FIG. 4, § 108, p. 104.
]


The small interrupter was found the more reliable, and seemed to shorten
the needed time of exposure. A rotary contact-maker, giving two
interruptions of the current per revolution, was also tested. This was
driven by a motor with a condenser capacity of fourteen microfarads
connected across the brushes. Owing to the large capacity of the
condenser, a heavy current could be broken without marked sparking. The
circuit breaker was tested at speeds ranging from 500 to 4,000 per
minute, to note the influence on the time of exposure. The best results
were obtained at the lower speed.... As no especial advantage could be
noted when using the mercury breaker, it was abandoned for the vibrating
interrupter.” This point is noted in detail, since so many experimenters
seem to prefer such cumbersome devices, but they are, in reality,
unnecessary.


[Illustration:

  STINE’S EXPERIMENT, FIG. A. § 110.
]


110. APPARENT DIFFRACTION OF X-RAYS REALLY DUE TO PENUMBRAL SHADOWS.
_Elec. Eng._, Apr. 22, ’96, p. 408.—By referring to the diagram marked
“Stine’s Experiment, Fig. A,” the arrangement of the elements may be
seen, while the photographic print is shown in “Stine’s Experiment, Fig.
B.” p. 106. Prof. Stine described the investigation as follows:
Diffraction is naturally one of the first kinematical points to be
investigated in the Roentgen experiments. It was noticed that when the
opaque object was some distance from the plate, pronounced penumbral
shadows resulted. These were of such width as to indicate diffraction.
However, when such shadows are plotted back to the tube they are found
to be purely penumbral, and not caused by diffraction. To completely
demonstrate this point the experiment illustrated in Fig. A was
undertaken. Here A_{1} to A_{4} are brass plates one inch wide and 1/8
inch thick, and of the length of the dry plate employed. They were first
fastened together, so as to leave two parallel slots 1/8 of an inch
wide. These plates are placed within 3/8 of an inch of the bulb, were
one inch apart, and rested 1-1/8 inches above the dry plate. The
resulting sciagraph is shown in Fig. B. In the diagram S_{1} S_{2}, the
edges of the penumbral shadow are very sharp and distinct. The direction
of the rays is indicated, showing that there was absolutely no
diffraction. This experiment has been modified in a variety of tests,
with always the same result.”


110_a_. JEAN PERRIN’S NON-DIFFRACTION. _Comptes Rendus_, Jan. 27, ’96.
From trans. by Louis M. Pignolet.—The active part of a tube was placed
before a very narrow slit; 5 cm. further, there was a slit 1 mm. wide;
10 cm. further, there was the photographic plate. An exposure of nine
hours gave an image with sharply defined borders, upon which there was
no diffraction fringe.


[Illustration:

  STINE’S EXPERIMENT. FIG. B. § 110.
]


159a. NON-REFRACTION.—Refraction was attempted with prisms of paraffine
and of wax, but no refraction was noticed.


111. SCRIBNER AND M’BERTY’S EXPERIMENT. SOURCE OF X-RAYS DETERMINED BY
INTERCEPTION OF ASSUMED RECTILINEAR RAYS FROM THE CATHODE. _Elect.
Eng._, N.Y., Apr. 8, ’96, p. 358; _Amer. Inst. Elec. Eng._, Mar. 25,
’96. _West. Branch._—Refer now solely to Fig. 1, S. and M.’s experiment.
Notice the relative arrangement of the elements. First, the discharge
tube with the cathode at the upper part and the phosphorescent spot
opposite thereto; then below a thick lead plate with a single opening;
then a second lead plate with two small openings placed laterally at
such a distance that if there were rectilinear rays from the cathode
they could not strike (by passing through the small hole), the covered
photographic plate which was the next element in order. The description
did not state that the photographic plate was covered, but the
experimenters must have had the usual opaque cover upon it or else the
luminous rays could have produced images. The developed plate showed two
spots strongly acted upon and surrounded by portions which were less
acted upon, the same as would be produced by light radiating from a
surface as distinguished from a point. From the fact that they stated
that the exposures were very long, it may be concluded also that the
plates were covered by a material opaque to ordinary light. Measurement
showed that the rays which produced the images came from the
phosphorescent spot (§ 106, 109, 114, 131, 139) and not from the cathode
directly by rectilinear propagation.


[Illustration:

  S. & M.’S EXPERIMENT, FIG. 1. & 2.
]


112. SOURCE ON INNER SURFACE OF THE DISCHARGE TUBE DETERMINED BY
PIN-HOLE IMAGES. Reference may now be made to S. and M.’s Experiment,
Fig. 2.—The discharge tube has, as before, a cathode on one side, and
the phosphorescent spot during operation on the opposite side. Lead
plates were provided in positions indicated by the heavy black straight
lines, there being a pin hole in each one. Behind these lead plates,
measured from the discharge tube, were the covered photographic plates,
as indicated. By measurement, it was afterwards determined that
practically all the X-rays started from the phosphorescent spot. The
electrode was put in an oblique position, as indicated, so that the same
would not obstruct any X-rays trying to pass through the pin hole in the
uppermost plate. The experiment served specifically to show that the
X-rays started from the inner surface of the glass, because images
produced on the upper and lower plates were equally strong. Perrin also
found that the X-rays are developed at the interior sides of the tubes.
(_Comptes Rendus_, Mar. 23, ’96. From trans. by L. M. P.) The rays, in
producing each image, had to pass through an equal thickness of glass.
If the rays had come from the outer surface, for example, two
thicknesses would have been traversed by the rays striking the upper
plate, and no thickness by those impinging upon the lower plate. That no
rays came from any other portion or element of the discharge tube was
evident, because a picture of the phosphorescent spot was the only one
produced, and this picture was inverted, as usual, with pin hole
cameras. (A pin-hole camera is the same as any other, with the lens
replaced by a very small hole, which acts as a lens.)

In the way of further evidence, if not enough already, Meslans early
determined that the phosphorescent spot on the glass is the source of
X-rays (_Comptes Rendus_, Feb. 24, ’96. From Trans. by Mr. Louis M.
Pignolet).

JEAN PERRIN’S EXPERIMENTS. THE ORIGIN OF X-RAYS. _Comptes Rendus_, Mar
23, ’96. From Trans. by Louis M. Pignolet.—He also confirmed that X-rays
radiate from the phosphorescent spot.


112_a_. DE HEEN’S EXPERIMENT. THE ANODE BELIEVED TO BE THE SOURCE OF
X-RAYS. _Comptes Rendus_, Feb. 17, ’96. From trans. by Louis M.
Pignolet.—A lead screen, pierced by several holes, was placed between
the discharge tube and the photographic plate. The shadows of the holes
on the plate indicated that the rays emanate from the positive pole of
the tube.

As both Thomson (E.) and Rowland, as well as De Heen, at first concluded
likewise, is it not probable that the anode was struck by the cathode
rays (see § § 113, 116)? For it was fully admitted that the anode,
otherwise, does not emit X-rays.


[Illustration]


113. LODGE’S EXPERIMENT. X-RAYS MOST POWERFUL WHEN THE ANODE IS THE PART
STRUCK BY THE CATHODE RAYS. PIN-HOLE PICTURES BY X-RAYS TO DETERMINE
SOURCE OF X-RAYS, AND PIN-HOLE IMAGES UPON GLASS COMPARED. _The Elect._,
Lon. Apr. 10, ’96, p. 784.—The object of the experiment was to confirm,
if possible, by a modified construction, the source of the X-rays, as
being the surface struck by cathode rays, whether the surface is that of
glass or any other substance. He had constructed, for this purpose, a
discharge tube, as illustrated in the diagram, which may be seen, at a
glance, to contain a concave electrode at one end, and a flat electrode
at the other. Between them, and connected to the concave electrode, is
an inclined sheet of aluminum, shading both electrodes. The wires
leading to the aluminum sheet are well protected by glass. He arranged
matters so that either the concave or the flat electrode could be made
positive or negative. The operation consisted first in taking through a
pin hole, 1/4 of an inch in diameter, X-ray pictures on photographic
plates, from different points, at measured distances. After these were
taken, glass plates received the luminous images at the positions of the
sensitive plate. Pencil drawings were then made, and compared with the
X-ray pictures. The experiment involved also the repetition of this
operation, except that the polarity of the terminals was changed.

“When the small flat disk was cathode, every part of the complicated
anode appeared strongly and quickly on the plate, especially the tilted
and first bombarded portion on a photographic plate placed above the
tube. The cathode disk itself did not show at all. On a plate placed
below the bulb, the anode cup appeared strong, but the tilted disk did
not appear. On the other hand, … its focus spot acted as a feeble point
source, by reason of a few rays reflected back on to it from the cup.

“When the current was _reversed_, the small disk anode showed faintly,
being excited by rays which had penetrated the interposed tilted disk,
but again the cathode hardly showed at all, not even the tilted portion
on a plate placed below the bulb. This is confirmed by J. Perrin. In no
case could an image of the cathode be obtained. (_Comptes Rendus_) Mar.
23, ’96. From trans. by L. M. P.) By giving a very long exposure (two
hours), some impression was obtained by Dr. Lodge about equal to that
from the shaded anode disk; but, of course, if the tilted plate had been
under these circumstances an anode, it is well known that a few minutes
would have sufficed to show it strong upon the plate beneath.

“Hence, undoubtedly, the X-rays do not start from the cathode _or from
anything attached to the cathode_ but do start from a surface upon which
the cathode rays strike, whether it be an actual anode or only an
‘anti-cathodic’ surface. Best, however, if it be an actual anode.
(Independently discovered by Rowland, § 116. and Roentgen, § 91.”)

“When the glass walls, instead of receiving cathode rays, are pierced
only by the true Roentgen rays from the disk in the middle, no evidence
is afforded by my photograph that the glass under these circumstances
acts as a source. It is well that it does not, for its only effect would
be a blurring one. § 91. With focus tubes, the glass phosphoresces under
the action of the X-rays as anything else would phosphoresce, but its
phosphorescence is not of the least use. It is a sign that a tube is
working well, and that the rays are powerful; but if by reason of
fatigue (§ 58) the glass ceases to phosphoresce strongly, the fact
constitutes not the slightest detriment.”


[Illustration]


X-RAY UNINFLUENCED BY A MAGNET. SEVERE TEST.—His first experiment on
magnetic deflection, the sciagraph of a magnet with a background of wire
gauze, only showed that if there were any shift by reason of passage of
rays between the poles it was very small; but he definitely asserted, as
in accompanying diagram, that a further experiment has been made which
effectually removes the idea of deflectibility from his mind, and
confirms the statement of Professor Roentgen. § 79. A strong though
small electro-magnet, with concentrated field, had a photograph of its
pole-pieces taken with a couple of wires, A and C, stretched across them
on the further side from the plate—nearer the source—and a third wire,
B, also stretched across them, but on the side close to the plate. These
three wires left shadows on the plate, of which B was sharp and
definite, while A and C were blurred. Two sciagraphs were taken by Mr.
Robinson, one with the magnet on, and one with the magnet reversed. On
subsequently superposing the two plates, with the sharp shadows of B
coincident, the very slightest displacement of shadows A and C could
have been observed, although those shadows were not sharp. But there was
absolutely no perceptible displacement, the fit was perfect.
Consequently the hypothesis of a stream of electrified particles is
definitely disproved as no doubt had already been effectively done in
reality by Professor Roentgen himself. But it must be noted, he stated,
that the hypothesis of a simple molecular stream—not an electrified
one—remains a possibility. The only question is whether such an
unelectrified bombardment would be able to produce the observed effects.
It must be remembered, Dr. Lodge stated, that Dr. Lenard found among his
rays two classes as regards deflectibility—some much deflected, others
less deflected; and it must be clearly understood that his deflections
were observed, not in the originating discharge tube, where the fact of
deflection is a commonplace, but outside, after the rays had been, as it
were, “filtered” through an aluminum window. He did not, indeed, observe
the deflection in air of ordinary density; it was in moderately rarefied
air that he observed it, § 72_a_, but he showed that the variation of
air density did not affect the amount, but only the clearness of the
minimum magnetic deflection. The circumstance that affected the amount
of the deflection was a variation in the contents of the originating or
high-vacuum tube.


114. LODGE’S EXPERIMENT. APPARATUS EMPLOYED. _The Elect._, Lon., April
10, ’96, p. 783.—With his apparatus, he was able to obtain rays
sufficiently powerful to illuminate the usual fluorescent screen after
passing through one’s skull. It is of interest to note about the details
of the electrical apparatus (§ § 106, 109, 131, 137) used by those who
experimented. The best results were obtained by a make and break of a
direct primary current at a point under alcohol, the primary battery
consisting of three storage cells, and the current of the primary acting
on a large secondary coil. Leyden jars he considered entirely
unnecessary, and he preferred direct currents to alternating currents
for the primary. He did not give the exact dimensions of the primary and
secondary coils, but, judging from reports of others and the author’s
own experience, it is highly preferable to have what is called a very
large inductorium, 15 in. spark in open air, or else the Tesla system (§
§ 51, 137). There is little satisfaction in trying to perform the
experiments with induction coils adapted to give only a 2 or 3 in. spark
in open air.


[Illustration:

  STINE’S EXPERIMENT. FIG. 5, § 108, p. 103.
]


[Illustration:

  STINE’S EXPERIMENT. FIG. 6, § 108, p. 103.
]


115. LODGE’S EXPERIMENT. X-RAYS EQUALLY STRONG DURING FATIGUE OF GLASS
BY PHOSPHORESCENCE. _The Elect._, Lon., Apr. 10, ’96.—In order to
explain in what way the rays were propagated, he says that it is not as
if the glass surface were a wave front from every point of which rays
proceed normally, but that the glass radiates X-rays just as a red-hot
surface radiates light, namely, a cone of rays starts from each point,
and all the rays of each cone start in a different direction. Every
point of the glass radiates the rays independently of all other points.
Crookes’ Experiment (§ 58) may now be called to mind in reference to the
fatiguing of the glass after phosphorescing for a while. Lodge tested
the fatiguing as to the power to emit X-rays, but found that there was
no such property whatever. The glass which became fatigued as to
luminous phosphorescence (§ 105) was not fatigued as to the power of
X-rays. He noticed that the phosphorescent spot became less and less
bright, and yet the X-rays remained of the same power.


116. ROWLAND, CARMICHAEL AND BRIGGS’ EXPERIMENT. AREA STRUCK BY CATHODE
RAYS ONLY AN EFFICIENT SOURCE WHEN POSITIVELY ELECTRIFIED.
_Electricity_, N.Y., Apr. 22, ’96, p. 219.—Experiments carried on at the
Johns Hopkins University led the above named investigators to think at
first that the source of the X-rays was at the anode. _Amer. Jour.
Sci._, March, ’96. Prof. Elihu Thomson was led to give the same opinion
during his first experiments. _Elect. Rev._, N.Y., Mar. 25, ’96. See
also § 112_a_. Many other experiments certify to the allegation that
X-rays are certainly generated at the phosphorescent spot on the glass.
§ 79, 105, 107, 108, 111, 112, 113. From the experiments of Prof.
Rowland, _et al._, the confusion is accounted for by the fact that they
overlooked the electrical condition of the spot struck by the cathode
rays. Prof. Rowland, _et al._, constructed a tube having a platinum
sheet located at the focus of the concave electrode, and _not_ connected
to the anode. Although the platinum became red hot, it emitted no
X-rays, but when the platinum was made the anode, there was profuse
radiation of X-rays in all directions from that side of the platinum
struck by the cathode rays, and no radiation from the other side. § 91.
(See also Roentgen and Tesla, concerning 1/2 platinum and 1/2 aluminum
and radiation therefrom.) They inferred as a final conclusion in
connection with this point, “That the necessary condition for the
production of X-rays is an anode bombardment by the cathode discharge.”
§ 113. They recognized apparently that it had been conclusively proved
that X-rays radiated from the phosphorescent spot on the glass. They
held that such a spot is “The induced anode formed on the glass.” § 49,
at end. They did not prove this by an experiment according to the
article referred to, but based it upon “The fact that the bombarding
cathode rays coming in periodical electrified showers alternately raise
and lower the potential of the glass, thus making it alternately an
anode and a cathode. In the case of the platinum, this could not occur
to the same extent.”


117. SALVIONI’S EXPERIMENT. TRANSPOSITION OF PHOSPHORESCENT SPOT.
_Elect. Rev._, Lon., Apr. 24, ’96, p. 550; _Med. Sur. Acad._, of
Perugia, Italy, Feb. 22, ’96. Personal interview with Prof. Salvioni in
_Elect. Rev._, N.Y., Apr. 8, ’96, p. 181.—In order to change the
location of the phosphorescent spot when desired, without a magnet, and
at the same time to concentrate or intensify the source of X-rays, he
placed near the same, on the outside of the tube, the hand or a metal
mass connected to earth. The spot immediately jumped to the other side
of the tube, § 49, near centre, and to all appearances was smaller and
brighter. Elster and Geitel had performed similar experiments at an
earlier date. (See _Wied. Ann._, LVI., 12, p. 733, also _Elect. Eng._,
about April, ’96.) They carried on the most minute investigations as to
the deflection of the cathode rays by an outside conductor. Tesla had
also noticed a similar deviation. See Martin’s _Tesla’s Researches_. He
used alternating currents as described in his system in § 51. Elster and
Geitel used the Tuma Alternating system. (See _Wied. Ann._, Ber. 102,
part 2A, p. 1352, ’94.) The source from which Salvioni’s description was
taken had no sketch, therefore the diagram made by Elster and Geitel is
reproduced. See Fig. 1. The cathode was aluminum and was connected to
one terminal of the transformer. The anode was connected to earth, and
also was the other terminal. Upon bringing the hand or other conductor
connected to earth to the phosphorescent spot, the cathode rays deviated
and the spot jumped over to the other side. § 50. The anode was a ring
surrounding the leading-in wires of the cathode, and the two leading-in
wires were surrounded by glass. It may be asked why the cathode rays
bent downward in the first place? Elster and Geitel found that they were
thrown thus in view of the nearness of some neighboring object connected
to earth. To overcome the action of surrounding objects, the tube was
surrounded by a ring as shown in Fig. 2. However, the rays were still
sensitive to objects well connected to earth, and when brought quite
close to the tube.


[Illustration:

  Figs. 1 and 2.
]


117_a_. HAMMER AND FLEMING’S MOLECULAR SCIAGRAPH, WITHIN A VACUUM TUBE.
(_Citations below._)—In view of the overwhelming evidence concerning the
generation of X-rays by the impact of cathode rays, within a high vacuum
upon the glass or material which preferably forms the anode, it becomes
appropriate, it is thought, to review the state of this department of
science, in order to arrive a little more closely at the relations which
exist between phenomena of low and high vacua. With the former, in that
condition in which striae are formed, permanent black bands or deposits
are produced upon the surface of the glass; the motion of the particles,
therefore, appearing to be in planes at right angles to the line joining
the anode and cathode. § 40. That the striae should touch the walls of
the tube seems to be necessary for the production of the deposit. § 44.
With a high vacuum, the direction of the cathode rays may be any that
one desires, it being only necessary to shape the cathode properly, on
the principle that the rays radiate normally from the surface. It is
known that the radiation is normal as much from the position of the
deposit as from that of the phosphorescent spot. It is certain that they
are rectilinear. § § 57 and 58. The phosphorescent spot becomes always,
sooner or later, when occurring upon the same part of the glass, the
location of a deposit from the cathode (§ 123), even when the cathode is
aluminum. § 123. The deposit is not the cause of the fatigue of the
glass. § 58. Puluj verified this. A wheel was made to rotate by the
radiations from the cathode, and therefore it is highly probable that
the motion of the molecules, which caused the deposit, is the force that
made the wheel rotate. § 58_a_. Why does it not follow that with
increase of E. M. F. the particles are thrown with such rapidity that
upon striking the proper surface (§ 80), X-rays are generated, but that
they are not generated when the velocity of the molecules is
insufficient. § 61_b_, p. 46. Attention is now invited to a phenomenon
which illustrates that a permanent sciagraph of objects may be impressed
upon the inner surface of a vacuum tube, by the deposit of molecules of
one of the electrodes. Refer, therefore, to the figure on page 30,
“Hammer and Fleming’s Molecular Sciagraph.” As will be seen from further
explanation and from the picture itself, the sciagraph _a b_ is made
because of the projection, in rectilinear lines, of molecules of carbon
or metal, from one of the electrodes, or at least from one more than the
other. One leg of the carbon, being in the way of the other, causes a
less deposit to be produced upon the glass at the intersection of the
plane of the horse-shoe filament and the wall of the vacuum tube.
Electrodes exist because the filament is of such a high resistance as to
produce a difference of potential between the two straight lower
portions of the filament. Mr. William J. Hammer possesses a remarkable
faculty for observing phenomena often overlooked by others. He first
observed a molecular shadow in 1880 and made records of his observations
in the Edison Laboratory note book. Since that time he has examined over
600 lamps, which were made at various periods during thirteen or
fourteen years, by twelve different manufacturers. (_Trans. Amer. Inst.
Electrical Eng._, Mar. 21, p. 161.) Every one, more or less, exhibited
the molecular shadow. It is a principle, therefore, that if the carbon
filament has both legs in the same plane, a sciagraph of one of them
will be produced. As the shadow is on one side of the bulb only, the
molecules fly off from only one electrode, viz., the cathode. By means
of photography, the effect is increased because of certain well-known
principles. The figure heretofore referred to is taken from a
photograph, but, of course, does not represent the sciagraph as well as
the original photograph, in view of the loss of effect by re-production
by the half-tone process. For further theoretical considerations, see
the Institute paper referred to, where the matter was discussed by
Profs. Elihu Thomson, Anthony and others. Independently of Mr. Hammer’s
discovery, Prof. J. A. Fleming, professor of electrical engineering in
the University College, London, England, discovered and studied the
matter, and presented it before the _Phys. Soc._ of London, appearing
about 1885 (_from memory_). The name “molecular sciagraph” is given by
the author because it is an accepted explanation that the deposit is due
to either molecules or atoms of the electrode, given off by evaporation
(page 46, lines 5 to 10), or electrical repulsion (§ 61_a_, lines 22 to
25), or, as some hold, by mere volatilization by the intense heat of
incandescence, or one or more combined; but electrical repulsion
certainly has something to do with the rectilinear propagation, for the
molecules are charged according to § 4.


[Illustration]


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




                               CHAPTER X


                                -------

118. EDISON’S EXPERIMENTS. CHARACTERISTICS OF DISCHARGE TUBE,
PHOTOGRAPHIC PLATES, ELECTRICAL APPARATUS, FLUORESCENCE, ETC. _Elec.
Eng._, N.Y., Feb. 19, ’96; Mar. 18 and 25; Apr. 1, 8, 15 and 29, ’96.
X-RAYS BEGIN BEFORE STRIAE END.—The reader may remember a former
section, § 10, pointing out that striae were usually obtainable without
very high vacua, and that phosphorescence of the glass occurs only with
high vacua. § 54. In carrying the vacuum up higher and higher, Edison
observed that feeble Roentgen rays were detected before the striae
ceased. Prof. Elihu Thomson independently performed a like experiment
and found that the Roentgen rays could be obtained even when the vacuum
was so low as to produce striae. (_Elec. Eng._, N.Y., Apr. 15, ’96.)
Victor Chabaud and D. Hurmuzescu also obtained X-rays from a vacuum .025
mm., being lower than Crookes employed, which was at a maximum .001 mm.
(_L’Industrie Elect._, Paris, May 25, ’96. From trans. by Louis M.
Pignolet.)


119. REASON WHY THIN WALLS ARE BETTER THAN THICK. X-RAYS AND
POST-PHOSPHORESCENCE.—This may be understood by explanation of the
discharge tube in Fig. 1. In one experiment, the portion struck by the
cathode rays, namely B, was made 1/8 inch thick. It became soon hot and
very luminous and melted, § 61, but the X-rays were weak. When blown
thin, (§ 83) however, the glass remained cool and the X-rays were much
stronger. What is known on the market as German glass (phosphoresces
green, § 55, at centre) was found more permeable than lead glass, the
thickness of the walls being the same in both cases. There were no
lingering X-rays from after-phosphorescence, (§ 54, at end) or, if any,
could not be detected by the sciascope. The photographic test would be
objectionable because of the brief duration. Prof. Battelli and Dr.
Garbasso, of Pisa, made a very _sensitive_ test in this connection,
proving by the discharge of an electrified body (§ § 90 and 90_a_) that
feeble X-rays were emitted after the current was cut off from the
discharge tube. (From trans. by Mr. Pignolet.)


[Illustration:

  DISCHARGE TUBE, FIG. 1. § 119.
  DISCHARGE TUBE, FIG. 3. § 120.
]


120. TO PREVENT PUNCTURE OF THE DISCHARGE TUBE BY SPARKS.—In the
illustration, Discharge Tube Fig. 2. shows a suitable type. It is drawn
to scale, showing the correct proportion of the length to the diameter.
The shaded ends represent tinfoil on the outside and connecting with the
leading-in wires, the same preventing puncture of the glass by the
spark. They may be caused to adhere by shellac or similar glue. In place
of the metallic coating detached supplementary electrodes may be
employed, as seen in the illustration marked “Discharge Tube Fig. 3.”
The power of the X-rays was increased, being due, it was thought, to the
fact that the construction embodied the combination of internal and
external electrodes. § 121.


121. VARIATION OF VACUUM BY DISCHARGE AND BY REST.—Prof. Pupin was among
the first to test the efficiency of external electrodes for generating
X-rays. Independently of the quality of the glass and of the kind of
pump and of the presence or absence of phosphoric anhydride, the
following peculiarities were noticed, which Edison attributed to a kind
of atomic electrolysis. § 47. 80 per cent. of the lamps exhibited the
phenomena as follows: First, such a high vacuum was obtained by the pump
that the line spectrum disappeared and pure fluorescence and generation
of X-rays at a maximum occurred. The lamp was then sealed off. After
three or four hours of rest, the vacuum deteriorated, so that striae and
other characteristics of low vacuum were obtained when connected up in
circuit, but upon continuing the current, the high vacuum gradually came
back, the line spectrum vanished, and suddenly X-rays were generated.
Again the bulb was left at rest for 24 hours, after which X-rays could
not be generated until the discharge had been continued for 4-1/2 hours.


[Illustration:

  DISCHARGE TUBE, FIG. 2. § 120.
]


122. EXTERNAL ELECTRODES DISCHARGE THROUGH HIGHER VACUUM THAN
INTERNAL.—A vacuum that was so high that no discharge took place with
internal electrodes was made luminous by the use of electrodes on the
outside of the glass bulb. Then he made the vacuum so high that even
with a 12-inch spark from Leyden jars, no discharge took place with
external electrodes, and the tube was dark, this part of the experiment
indicating another limit at which an extremely high vacuum is not a
conductor and appearing to overthrow, as Edison intimated, Edlund’s
theory that a vacuum is a perfect conductor. § 25.


123. DEPOSIT ON GLASS FROM ALUMINUM ELECTRODE.—It has always been common
to employ aluminum for electrodes in vacuum tubes, on the ground that no
deposit took place, and therefore no blackening, nor whitening of the
glass wall. § 40. Edison observed also that no blackening was visible,
but stated that his glass blower, Mr. Dally, upon breaking the bulb and
submitting the interior surface of the glass to an oxydizing process,
the oxide of aluminum was so thick as to be opaque to light. With
magnesium, also, a mirror was produced, of a lavender color, by
transmitted light. In the case of aluminum, he was able to obtain a
visible spot at the phosphorescent portion, but only after a great many
hours of use. See cut from a photograph of a discharge tube used for
several months by Prof. Dayton C. Miller, and having a heavy aluminum
deposit opposite the aluminum cathode. With the increase of the deposit,
the power of the X-rays diminished, but, he thought, not on account of
the absorption, but because, “through lack of elasticity at the
surface.”


[Illustration:

  DISCHARGE TUBE, § 123.
]


124. FLUORESCENT LAMP. In an English patent of ’82, granted to Rankin
Kennedy, there is described a vacuum bulb in which the electrodes are
covered with fluorescent or phosphorescent substances, intended for the
purpose of obtaining greater candle power by impact of cathode rays upon
anode of platinum, covered with alumina or magnesia. Edison coated the
inner wall of the discharge tube, for generating X-rays, with calcic
tungstate in the crystalline form. The luminosity, when measured,
amounted to about 2-1/2 C. P. As to the efficiency, he stated that this
was accomplished “with an extremely small amount of energy.” Such a
coating was found to weaken the X-rays radiated therefrom, which, of
course, was natural, because they had been converted into phosphorescent
light. The spectrum showed strongly at the red line, thereby suggesting
the reason why the light was of a pleasant character.


124_a_. PILTCHIKOFF’S EXPERIMENT. Greater emission of X-rays by a tube
containing an easily fluorescent substance. _Comptes Rendus_, Feb., 24,
’96. From trans. by Mr. Louis M. Pignolet. As the X-rays emanate from
the fluorescent spots on the glass of the discharge tube, he reasoned
that more powerful effects would be obtained by replacing the glass by a
more fluorescent material. He therefore tried a Puluj tube and found
that it shortened the time necessary for taking a photograph in a
“singular” degree. Experiments of others have certainly shown that as
phosphorescence decreases with increase of vacuum, the X-rays increase
to a certain maximum, § 105. Let it be noticed however, that this does
not prove that with the same vacuum, an increase of phosphorescence by a
superior phosphorescent material of equal thickness would not increase
the power of the X-rays. The best way to determine such points, is to go
to extremes. Edison applied so much easily phosphorescent material
(calcic tungstate) to the inside of the discharge tube, that much light
was radiated, but only feeble X-rays. On the other hand, without any of
the tungstate, the rays were strong, § 124. Experiments generally tend
to prove that it depends upon the chemical nature of the material rather
than its phosphorescing power, in other words upon the permeability. §
119, near end.


125. ELECTRODES OF SILICON CARBIDE. (Carborundum.) Edison called
attention to Tesla’s discovery that this substance is a good conductor
for high tension currents. Its advantages for electrodes in the
discharge tube are its high conductivity, no absorbed nor released gas
bubbles, and its infusibility and non-blackening power of glass even
when the voltage was increased to a point where the glass melted.


[Illustration:

  EDISON (AT RIGHT) AND T. COMMERFORD MARTIN USING THE SCIASCOPE. § 97,
    p. 84.
  Cut also shows Sprengel vacuum-pump. Discharge-tube is in the box.
]


126. CHEMICAL DECOMPOSITION OF THE GLASS BULB. During the generation of
the X-rays the sodium line of the spectrum appeared in the spectroscope,
thereby indicating decomposition of the glass. With combustion tubes the
glass gave the weakest soda line, while lime soda glass gave the
strongest, and was most permeable to the X-rays. “The continuous
decomposition of the glass makes it almost impossible to maintain a
vacuum except when connected to the pump and even then the effect of the
current is greater in producing gas than the capacity of the pump to
exhaust, but the ray is very powerful.” It is supposed that for this
reason, as well as for others easily apparent that Edison as well as
other experimenters have always carried on their investigations with the
discharge tube permanently connected to the pump. The next best thing is
to let the tube contain a stick of caustic potash for maintaining an
exceedingly high vacuum. By gradually heating this, the desired degree
of vacuum can be obtained. § 54.


127. SCIAGRAPHS. DURATION OF EXPOSURE DEPENDENT UPON DISTANCES. With the
given discharge tube, he obtained sciagraphs at a distance of 3/8 inch
from the phosphorescent spot in one second, a vulcanized cover being
between; at two ft. distant the time was 150 sec.; at three ft., 450
sec.; the opaque plate being interposed each time. Consequently
“Roughly, the duration of exposure may be reckoned as proportional to
the square of the distance.”


128. DIFFERENCE BETWEEN X-RAYS AND LIGHT ILLUSTRATED BY DIFFERENT
PHOTOGRAPHIC PLATES. TIME OF EXPOSURE. The rapid plate for light gave
not the deepest images by X-rays. Several different kinds of small
sensitive plates were laid side by side. A sciagraph of a metal bar was
taken upon them all simultaneously. In this way, he obtained the result,
whereby it would appear preferable to employ the mean rapid plate for
the purpose of obtaining sciagraphs. On account of the opacity of
platinum, it occured to E. B. Frost, (_Sci._, N.Y., Mar. 27, ’96,) to
try platinum photographic paper of the kind used for portraits, but such
paper (intended for long exposures in printing in sunlight) was far too
lacking in sensitiveness to produce any effect.


128_a_. GEORGES MESLINS INSURED A REDUCTION OF TIME FOR TAKING
SCIAGRAPHS BY THE DEFLECTION OF THE CATHODE RAYS BY MEANS OF A MAGNETIC
FIELD. _Comptes Rendus_, March 23 and 30, 1896. From trans. by Louis M.
Pignolet. The method consists in using a permanent or electro-magnet to
create a magnetic field perpendicular to the cathode rays in the tube.
By this means, the active fluorescent spot on the tube is condensed, and
the intensity of the X-rays generated there is increased. Another
advantage is that, when the active part of the tube becomes inactive
owing to the formation of a light brown deposit upon it, another part
can be used by very slightly altering the position of the magnets. Thus,
each time a new part of the tube can be used. The magnetic field must
not be uniform but must have a suitable variation to produce the desired
concentration of the cathode rays.

A. IMBERT AND H. BERTIN-SANS’ EXPERIMENT. (_Comptes Rendus_, March 23,
’96. (From trans. by L. M. P.) They shortened the time by use of a
magnet.

JAMES CHAPPIN’S EXPERIMENT. (_Comptes Rendus_, Mar. 30,’96. (From trans.
by L. M. P.)—Claimed priority in having shown publicly, on Feb. 19, a
sciagraph of a hand, marked “Photograph obtained by concentration of the
cathode rays, by means of a magnetic field.” The increase of the
intensity of the X-rays obtained by this means was in the proportion of
8 to 5, as measured by the time of fall of the leaves of a Hurmuzescu
electroscope.

Prof. Trowbridge, of Harvard University, in a lecture, gave an
interesting review (_Western Elect._, Feb. 29, ’96) of the length of
time required in the early days of photography. Improvements are being
made whereby the duration required in sciagraphy becomes less and less.
In 1827, by heliography, 6 hours’ exposure was necessary; in 1839, by
daguerreotype, 30 minutes; in 1841, by calotype, 3 minutes; in 1851, by
collodion, 10 seconds; in 1864, by collodion, 5 seconds; in 1878, by
gelatine, 1 second. The author remembers the photographs for use in the
Edison kinetoscope were taken at the rate of 20 per second. The focus
tube brings the time of exposure in behalf of X-rays down to a matter of
seconds instead of minutes. For an admirable review of authorities,
facts and theories relating to the causes of the darkening of
photographic plates by light, see Cottier, in _Elect. World_, N.Y., May
23, ’96.


129. SIZE OF DISCHARGE TUBE TO EMPLOY FOR GIVEN APPARATUS.—A small tube
required but a small E. M. F., and therefore should be employed with a
small induction coil. The greater the distance of the sensitive plate
and the object, considered together, from the discharge tube, the
sharper the shadow. In short exposures, the tube should be small and at
a short distance.


130. PREVENTING PUNCTURE AT THE PHOSPHORESCENT SPOT.—In experiments
where he employed a flat cathode, a very thin pencil of rays of
increased power came from the exact centre, and in two or three seconds
made the glass red hot at the centre of the phosphorescent spot.
Immediately, the atmospheric pressure perforated the bulb. This occurred
several times. He stated that “the best remedy is to permit the central
ray to strike the glass at a low angle; this greatly increases the area
and prevents the trouble.” EDISON.

Mr. Ludwig Gutmann furnished a translation of a note by Prof. Walter
König, found in _Eleck. Zeit._ of May 14, ’96, relating to this same
subject matter. Recognizing that the sharpness of the outlines is the
most important requirement in connection with sciagraphy, and that if
the rays start from a large surface the impressed shadows will be
uncertain in configuration, and noticing, as Edison and Tesla did, §
130, the frequent destruction of the tube at the place where the rays
were concentrated to a focus, he placed over the inner surface of the
glass, aluminum foil for distributing the heat over a larger area, at
the same time causing radiation of X-rays from a single point. The focus
tube outweighs this in importance. § 91.


131. ELECTRICAL DIMENSIONS OF APPARATUS. The best kind of instruction
for the student in reference to equipping a plant is to follow the
construction employed by those who have been successful. § § 106, 109,
114, 137. Edison used the usual incandescent-lamp current, voltage at
110 to 120 volts, current being continuous, but not connected directly
to the induction coil, there being a bank of eight to twenty 16 candle
power incandescent lamps arranged in parallel. The interrupter for the
primary consisted of a rotating wheel in appearance like a commutator of
a dynamo, and was rotated rapidly by a small electric motor, making
about 400 interruptions per second, and so constructed that the circuit
was closed twice as long as it was open. A sudden interruption was
caused by an air blast playing at the point of make and break, the use
of which made that of a condenser needless. § 3. The discharge tube
terminals were connected respectively and directly to those of the
secondary. Prof. Pupin, Columbia Univ. N.Y. (_Lect. N.Y., Acad. Sci._,
April 6, ’96, and _Science_, N.Y., April 10, ’96) gave valuable and
practical instruction concerning the apparatus, which the author
witnessed. “A powerful coil was found indispensable for strong effects
and satisfactory work. The vibrating interrupter is too slow and
otherwise unsatisfactory, and it was replaced by a rotary interrupter,
consisting of a brass pulley, 6 inches in diameter and 1-1/4 inches in
thickness. A slab of slate 3/4 inch thick was inserted and the
circumference was kept carefully polished. This pulley was mounted on
the shaft of a Crocker-Wheeler 1/8 H. P. motor giving 30 revolutions,
and, therefore, 60 breaks per second. Two adjustable Marshall condensers
of three microfarads each were connected in shunt with the break, and
the capacity adjusted carefully until the break-spark was a minimum and
gave a sharp cracking sound. Too much capacity will not necessarily
increase the sparking, but it will diminish the inductive effect which
is noticed immediately in the diminished intensity of the discharge. A
powerful coil with a smoothly working rotary interrupter will be found a
most satisfactory apparatus in experiments with Röntgen radiance.” §
106, 109, 114, 131, 137.


132. SALTS FLUORESCENCE BY X-RAYS. See also, _Elect. Rev._, N.Y., April
19, ’96, p. 165. Edison examined over 1800 chemicals to detect and
compare their fluorescent powers if any, under the action of X-rays
first transmitted through some opaque material such as thick cardboard.
Of all these, calcic tungstate by measurement, fluoresced with six times
the luminosity of barium platino cyanide, which was referred to in
connection with Roentgen’s experiment. Other authorities agree as to its
great sensitiveness. In making this comparison, it was assumed that the
power of the X-rays varied inversely as the square of the distance from
the discharge tube. Between the two above chemicals came strontic
tungstate. Baric and plumbic tungstate scarcely fluoresced. Salicylate
of ammonium crystals equalled the double cyanide of platinum and barium,
and differed therefrom in that the fluorescence increased with the
thickness of the layer of crystals up to 1/4 of an inch, showing great
fluorescing power and low absorptivity. This experiment showed that the
best fluorescent materials were not necessarily the salts of the
heaviest metals, like platinum. It is assumed that the reader knows the
difference between phosphorescence and fluorescence, but the dividing
line is so difficult in some cases and the one not being distinguished
from the other by experimenters, that the author has used the same words
as the experimenters, although he admits that fluorescence is often
meant where phosphorescence is stated, and _vice versa_. An anomaly
presented itself as to rock salt, which although transparent to light
yet powerfully absorbed X-rays and was strongly fluoresced thereby.
Again, fluorite which is transparent to light, fluoresced strongly with
the X-rays, and under their action became brighter and brighter and
continued after cutting off the X-rays, the material therefore, being
highly phosphorescent, the light enduring for several minutes. Upon
watching the phosphorescence of fluorite, the same penetrated the plate
very slowly to the depth of one-sixteenth of an inch, but beyond that
depth there was complete darkness. The only other truly phosphorescent
substance noticed was calcic tungstate, especially in thick layers, so
that the shadow of the bones of the hand remained thereon for a minute
or two upon cutting out the discharge tube from the circuit. Some
chemicals, within a dark box and _very close_ to the discharge tube,
phosphoresced by giving spots here and there, but they did not
phosphoresce at a greater distance, and the light was probably not due
to the X-rays. Edison attributed the result directly to the “electrical
discharge.” The list is as follows: ammonium sulphur cyanide, calcic
formate, and nitrate, ferric citrate, argentic nitrate, calcic and iron
citrate, soda, lime, “zinc, cyanide” (perhaps this means cyanide of
zinc), zinc hypermanganate, and zinc valeriate. The salts of the
following metals did not fluoresce under the influence of the X-rays.
Aluminum, antimony, arsenic, boron, beryllium, bismuth, barium,
chromium, cobalt, copper, gold, iridium, magnesium, manganese, nickel,
tin, and titanium.


[Illustration:

  ROENTGEN RAYS AT THE UNIVERSITY OF MINNESOTA.
  1. Watch and chain.
  2. College badges in mahogany box.
  3. Copper coin.
  4. Weights in heavy velvet-lined mahogany box; blank space contains
    aluminum.
  5. Coins in inner pocket of heavy seal purse.
  6 and 7. Colored glass.
  8. Key
  9. Lead-pencil.
  _West. Elect._, Mar. ’96.
]


Edison stated that the following substances were among those which
fluoresced more or less under the action of the X-rays. Mercurous
chloride, mercury diphenyl, cadmic iodide, calcic sulphide, potassic
bromide, plumbic tetrametaphosphate, potassic iodide, plumbic bromide,
plumbic sulphate, fluorite, powdered lead glass, pectolite, sodic
cressotinate, ammonic salicylate, and salicylic acid. Compared with the
above, the following fluoresced less. Powdered German glass, baric,
calcic and sodic fluorides, sodic, mercuric, cadmic, argentic and
plumbic chlorides, plumbic iodide, sodic bromide, cadmic and “cadmium,
lithia bromide, mercury, cadmium sulphate,” uranic sulphate, phosphate,
nitrate, and acetate, molybdic acid, dry potassic silicate, sodic
bromide, wulfenite, orthoclase, andalucite, herdinite, pyromorphite,
apatite, calcite, danburnite, calcic carbonate, strontic acetate, sodic
tartrate, baric sulphobenzoic, calcic iodide, and natural and artificial
ammonium benzoic. Not one of all the 1800 crystals and precipitates
fluoresced through a thick cardboard under the influence of the arc
light, 16 inch spark in air, a vacuum tube so highly exhausted that a 10
inch spark left it dark, nor the direct rays of the sun at noon time. As
calcic tungstate was phosphorescent by friction, he theorized that the
X-ray is a wave due to concussion.

Flame sensitive to X-rays. Edison stated that his assistants submitted
the sensitive flame and the phonographic listening tube to the action of
the X-rays, and found that they were responsive thereto.


133. X-RAYS APPARENTLY PASSED AROUND A CORNER. Referring to the figure
“X-ray Diffusion Fig. 1”, p. 129, it will be noticed that there were
three principal elements. First a discharge tube, then a thick steel
plate and then a sciascope, all arranged in the proportion indicated in
the figure, where the sciascope was within six inches of the edge of the
plate, “well within the shadow” thereof. § 69. Fluorescence was seen
under these conditions. When the sciascope was directly behind the
middle of the plate and opposite the discharge tube, there was no
fluorescence, showing that the plate was thick enough to cut off all the
rays and therefore the energy must have traveled in two directions for
some reason or other.

Prof. Elihu Thomson remarked concerning this experiment that he
considered, in view of some experiments of his own, on diffusion and
opalescence (§ 103), that the sciascope was luminous in view of
reflection (§ 146) of the X-rays from various objects in the room, as
from the walls and floor of the room, tables, metal objects, electrical
apparatus and so on. Theory admits the property of diffraction, which
would cause the rays to turn around the edge of the plate, according to
the principles of diffraction of light, provided the X-rays were due to
transverse or longitudinal or any vibrations. See _Elect. Eng._, N.Y.,
April 15, p. 378.

While Edison generally devotes his energy to actual experiments and
dealings with facts and principles, rather than with theories, yet, in
this instance, he merely suggested that the fluorescence under the
conditions named might indicate that the propagation of X-rays was
similar to that of sound in air, the wave being of exceedingly short
length. He referred to Le Conte’s experiment of ’82 (see _Phil. Mag._,
Feb. ’82), where an experiment of a somewhat similar nature was
performed in connection with the propagation of sound.


[Illustration:

  X-RAY DIFFUSION, FIG. 1, § 133.
]


Prof. William A. Anthony (see _Elect. Eng._, Apr. 3, ’96, p. 378) held
that the Le Conte experiment did not warrant Edison’s conclusion, for
the experiment of Le Conte showed comparatively sharp sound shadows; for
even at a distance of twelve feet there was no apparent penetration
within the geometrical boundary. He referred to Stine’s, § 110. Scribner
and M’Berty’s, § 111, as upholding rectilinear propagation. While he did
not explain what the Edison result was due to, yet he argued that the
cause was other than that ascribed by Edison. In this connection, the
author performed an experiment (_Elect. Eng._, Apr. 22, ’96, p. 409) to
substantiate that X-rays were propagated through such a high vacuum that
it was necessary to have electrodes within 1/8 of an inch of each other,
in order to obtain a discharge with a coil that gave 15 in. spark in
open air. The experiment consisted in casting the shadow of an
_uncharged_ tube upon the screen of a sciascope. The shadows of the wire
forming the electrodes within the vacuum were produced very sharply,
while the glass tube was faintly outlined. Inasmuch as the shadows of
objects _within_ the vacuum tube were obtained, therefore the X-rays
must have passed through the evacuated space. Sound and X-rays are
therefore dissimilar. The shadows were as sharp and as dark as those
made by similar wires in open air. In this connection, see also Lenard’s
experiment, § 72, showing that external cathode rays were also
transmitted by a vacuum in a “dead” tube. Roentgen’s experiment showed
that X-rays from a mass located entirely within the vacuum in the
discharge tube radiated X-rays into the outside atmosphere. § 91. This
experiment would hardly prove, however, that X-rays, after having been
liberated in open air, would pass through a second vacuum space, because
there may have been some X-rays, generated at the surface of the glass
in Roentgen’s experiment, struck by those rays which radiated from the
mass at the centre of the vacuum space. Did not Lenard and Roentgen
experiment with the same radiant energy? The author answers, yes. § 77.


134. PERMEABILITY OF DIFFERENT SUBSTANCES. Lenard § 68. determined the
permeability of several substances to cathode rays. Roentgen also the
same in regard to X-rays. § 82 and 83. Others have made comparisons.
From the sciagraph made by Edison, the following classification is made,
each sheet of material being about 1/32 inch thick. The most opaque were
coin silver, antimony, lead, platinum, bismuth, copper, brass, and iron,
which were about the same as one another. Slate, ivory, glacial
phosphoric acid shellacked, and gutta percha, were about the same as one
another and less than the above. Aluminum, tin, celluloid, hard rubber,
soft rubber, vulcanized fibre, paper, shellac, gelatine, phonographic
cylinder composition, asphalt, stearic acid, rosin, and albumen, were
about the same as one another and less than the above group, as to
permeability.

The accompanying picture, p. 6, marked Terry’s Sciagraph, Fig. 1, is a
sciagraph of pieces of different materials named as in the following
list, taken by Prof. N. M. Terry of the U.S.N.A., see also p. 127. “1,
rock salt, 0.6 inch thick; 2, cork, 0.4 inch thick; 3, quartz, 0.45 inch
thick, cut parallel to optic axis; 4, verre trempe, 0.4 inch thick; 5,
glass, 0.7 inch thick; 6, chalk; 7, Iceland spar; 8, mica, very thin; 9,
quartz, over a square piece of glass; 10, aluminum foil, [_a_] four
thicknesses, [_b_] two thicknesses, [_c_] one thickness; 11, platinum
foil; 12, tourmaline; 13, aragonite; 14, paraffine, 0.4 inch thick. 15,
tin foil, [_a_] one thickness, [_b_] two thicknesses, [_c_] three
thicknesses; 16, rubber insulated wire; 17, electric light carbon; 18,
glass, 0.32 inch thick; 19, alum., 1.4 inch thick; 20, tourmaline; 21,
gas coal; 22, bee’s wax; 23, pocket-book, 10 thicknesses of leather; 24
coin in pocket-book; 25, key in pocket-book; 26, machine oil in ebonite
cup; 27, ebonite, 0.25 inch thick; other samples have given very faint
shadows like wood and leather; this was polished; 28, wood, 0.2 inch
thick; 29, steel key.” _Elect. Eng._, N.Y.


134_a_. HODGES’ EXPERIMENT. ILLUSTRATION OF PENETRATING POWER OF LIGHT.
_Elec. Eng._, N.Y., March 4, ’96. Attention has been invited in the
scientific press to the penetrating power of heat rays and of light rays
of low refrangibility. In conjunction with this, let it be remembered
that the photographic plate has the property of being impressed
practically, only by rays having a higher refrangibility than red. It
would be natural, therefore, to conclude that if the spectrum could be
turned around, the photographic impression might be produced through
opaque bodies. This perhaps, was the kind of reasoning which prompted
Mr. N. D. C. Hodges, formerly editor of _Science_, to perform an
experiment, the gist of which consisted in attesting the permeability of
rays of light which had been passed through fuchsine. Christiansen,
Soret and Kundt performed experiments with an alcoholic solution of this
material and found that the order of the colors in the spectrum was
somewhat reversed, namely, violet was the least refracted, then red, and
then yellow, which was the most refracted. Mr. Hodges used a pocket
kodak, carrying a strip for twelve exposures. This camera was placed in
a closely fitting pasteboard box. Thus protected, some portions of the
film were exposed to sunlight, so far as it could penetrate the end of
the pasteboard box, while other exposures were made with a prism, on the
end of the box, containing an alcoholic solution of fuchsine. The
portions of film exposed to the anomalous rays produced by the fuchsine
solution were fogged, while the control experiments with ordinary light
showed none. The anomalous rays must have penetrated the pasteboard, and
probably the wood and leather of which the camera was made.


135. PENETRATING POWER OF X-RAYS INCREASED BY REDUCTION OF TEMPERATURE.
§ 23 and 72_b_ at end. Among the hundreds of ideas that occured to
Edison in connection with Roentgen ray tests was that concerning what
might happen by cooling the discharge tube to a very low temperature. As
before, he maintained the tube in connection with the air pump so as to
be able to vary the vacuum. The reduction of temperature was obtained by
means of ice water. Of course the bulb could not be placed in the water
itself on account of trouble which would occur from electrolysis,
therefore, the discharge tube was immersed in a vessel of oil, § 13,
which in turn was surrounded by a freezing mixture. The vessel was a
stout battery jar 14 inches high, eight inches in diameter with glass
walls 5/10 of an inch thick. The oil employed was paraffine. The
refrigerating jar was 12 inches high and 12 inches in diameter and the
glass wall thereof, 3/8 inch thick. He tested the difference in the
power of the rays by first noticing the thickness of steel that was not
penetrated by the rays generated from the tube while in air. Crucible
steel 1/16 of an inch thick did not transmit rays sufficiently to
illuminate the sciascope, and yet with the use of oil and reduction of
temperature, and after the rays had passed through two thicknesses of
glass as well as through the oil and ice water, the sciascope was made
luminous by rays after passing through a plate of steel of double the
thickness, __i.e.__ 1/8 in. thick. See in this connection, Tesla’s
experiment, § 135, where powerful rays were obtained by immersing the
discharge tube in oil. Accounts of these two experiments were published
simultaneously. Tesla attributed the idea of this use of oil to Prof.
Trowbridge of Harvard University, who showed that a discharge tube
immersed in oil is adapted to the generation of X-rays of increased
penetrating power. See cut at p. 135.


[Illustration:

  SCIAGRAPH OF RATTLESNAKE BY USE OF STOPS. § 107., p. 101.
  By Leeds and Stokes.
]


 NON-REFLECTION OF X-RAYS. (_Elect. Eng._, Feb. 19, ’96, p. 190.
Apparently extracted from the daily press.)—That the X-rays were only
slightly reflected (Roentgen, § 81., and even when very powerful (Tesla,
§ 146., was determined in a severe manner by Edison. The first
experiment consisted in employing a funnel 8 inches long and 3/4 inch at
the smaller end. The discharge tube was in the larger end, and the
photographic plate across the smaller end. After experiment and
development, the plate showed overlapping circular images, which would
indicate reflection from the inner surface of the funnel. This may have
been due to a jarring vibration of the funnel. Therefore, he carried the
experiment further by using a funnel 9 feet long. The plate did not
indicate any signs of reflection, as it merely became generally fogged.
The material of the tube is not named, but if of brass or other
impermeable metal, it is thought that his experiment would have shown a
result agreeing with that of others herein. Again, the reporter may have
been in error. Also, the rays may have been very weak, as the experiment
was performed when Edison first started to investigate the subject.


136. X-RAYS NOT YET OBTAINABLE FROM OTHER SOURCES THAN DISCHARGE
TUBES.—Edison exposed covered plates to the direct sun-light at noon for
three or four hours; no photographic impression; also to electric sparks
in open air, of twelve or more inches in length; no clouding even of the
photographic plate.

Profs. Rowland et. al., of the Johns Hopkins University, in a
contribution to _Electricity_, Apr. 22, ’96, p. 219, confirmed this
point by stating: “As to other sources of Roentgen rays, we have tried a
torrent of electric sparks in air from a large battery, and have
obtained none. Of course, coins laid on or near the plate, under these
circumstances, produce impressions, but these are, of course, induction
phenomena.” (See Sandford and McKay’s Fig. p. 20). “As to sun-light,
Tyndall, Abney, Graham, Bell and others have shown that some of the rays
penetrate vulcanite and other opaque objects.” Poincaré, at an early
date, advanced the hypothesis that X-rays are due to phosphorescence,
whether produced by electrical or other means. _Elect. World_, Digest.,
Mar. 28, ’96, p. 343, where it is also stated that Chas. Henry thought a
certain experiment of his own was in favor of the hypothesis. The
experiment was performed with a phosphorescent material which had been
exposed to the light and then brought into darkness. Niewengloswski
inferred, from an experiment, that phosphorescent bodies increase the
penetrating power of sun-light. Tesla admitted the possibility of the
radiation of X-rays from the sun. In an article describing important
experiments in the _Elect. Rev._, N.Y., Apr. 22, ’96, p. 207, he stated:
“I infer, therefore, that the sun-light and other sources of radiant
energy must, in a less degree, emit radiations or streamers of matter
similar to those thrown off by an electrode in a highly exhausted
enclosure. This seems to be at this moment still a matter of
controversy.” Roentgen, in his first announcement, showed that the
phosphorescent spot was the source of the X-rays. § § 79 and 80. All the
different opinions and theories, therefore, indicated that
phosphorescence by sun-light might possibly emit X-rays. Probably few
had sufficient belief in the matter, one way or the other, to try the
experiment in an extreme manner. The author was curious to prove the
question, but he only obtained negative results. It cannot be conceived
how the matter could have been more severely tested, for he concentrated
the light of the sun nearly to a focus by a large lens, namely 5 in. in
diameter, together with a reflecting funnel. The maximum phosphorescence
was therefore obtained by placing suitable chemicals at the opening in
the funnel. The sciascope showed absolutely no X-rays present.
Photographic plates were not in the least acted upon, even after hours
of exposure, the same having opaque covers of aluminum. See _Elect.
Eng._, N.Y., Apr. 8, ’96, p. 356. If X-rays are emitted from the sun,
they are all absorbed by the atmosphere of the earth, or are overcome by
some other force.


[Illustration:

  COOLING DISCHARGE TUBE. EDISON. § 135.
]


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




                               CHAPTER XI


137. TESLA’S EXPERIMENTS. _Elec. Rev._, N.Y., March 11, ’96, page 131,
March 18, page 147, April 1, page 171, and April 8, page 183. KIND OF
ELECTRICAL APPARATUS FOR OPERATING DISCHARGE TUBES FOR POWERFUL X-RAYS.
§ 106, 109, 114, 131. The experiments performed by Nikola Tesla were
particularly noteworthy for the magnitude and intensity of the rays
generated by his apparatus, under his skilful manipulation of the
adjustments and circuits particularly as to resonance. The remarkable
results that he obtained are not surprising when we learn that he
employed his well-known system for producing exceedingly enormous
potential and unusually high frequency. § 51. The primary electrical
generator as he indicated and as apparent from his system referred to in
the above section, could be either a direct or alternating current
generator, or other form. If the first is employed, of course an
interrupter is necessary in order that there may be a current induced in
the secondary.


[Illustration:

  SCIAGRAPH OF RAT, TAKEN BY OLIVER B. SHALLENBERGER WITH FOCUS TUBE
  (CUT AT p. 81) AND TESLA SYSTEM. § 137, pp. 136 and 138.
]


Mr. Oliver B. Shallenberger, (_Mem. Amer. Inst. Elec. Eng._) whose
laboratory is in Rochester, Pa., gave some important general
instructions concerning the Tesla system § 51, that he employed in the
production of remarkably clear sciagraphs, in conjunction with the focus
tube, § 91, representing the hand at page 68, and showing a rat shown at
this § 137. (_Elec. World_, N.Y., March 17, ’96.) Even the ligaments
were clearly shown in the sciagraph of the rat, and some of them are
dimly reproduced by the half tone process. As to the apparatus and
operation, which are especially important, it may be stated that the
current was taken from an alternator, of a frequency of 133 periods per
second, and passed through a primary coil of a transformer for
increasing the E. M. F. from 100 volts to from 16 to 25 thousand. The
secondary current was then passed through Leyden jars and a double
cascade of slightly separated brass cylinders, whereby it was changed
into an oscillatory current of an extremely high frequency, which was
then conducted through the primary of a second induction coil having
very few turns of wire, and no iron core and having a ratio of 7 to 1.
By this means the E. M. F. was raised to somewhere between 160,000 volts
to 250,000, and was used to energize the discharge tube for the
generation of X-rays. Caution should be taken, because the current
coming from the first transformer, being of large quantity and very high
E. M. F. is exceedingly dangerous, but the current of the second
secondary has been passed through one’s body without danger, as reported
by Mr. Tesla several years ago, and confirmed by Mr. Shallenberger.


138. PHOSPHORESCENT SPOT MAINTAINED COOL.—In testing the power of the
X-rays in connection with the appearance of the phosphorescent spot,
Tesla noticed that they were most powerful when the cathode rays caused
the glass to appear as if it were in a fluid state. § 61. To prevent
actual puncture, he maintained the spot cool by means of jets of cold
air. It became possible thereby to use bulbs of thin glass at the
location of the generation of the X-rays. § 119. He concluded from
certain results that not only was glass a better material for discharge
tubes than aluminum, but because, by other tests, he found that thin
aluminum cast more shadow with X-rays than thicker glass. There are, of
course, many other reasons, based on mechanical construction, why glass
is preferable, and also why a tube with an aluminum window is not to be
desired. Principally, the latter will soon leak.


139. EXPULSION OF MATERIAL PARTICLES THROUGH THE WALLS OF A DISCHARGE
TUBE.—At quite a low vacuum, and after sealing off the lamp, he attached
its terminal to that of the disruptive coil. After a while, the vacuum
became enormously higher, as indicated by the following steps: First, a
turbid and whitish light existed throughout the bulb. This was the first
principal characteristic. Next, the color changed to red, and the
electrode became very hot, in that case where powerful apparatus was
employed. The precaution should be taken to regulate the E. M. F., to
prevent destruction of the electrode. Gradually, the reddish light
subsided, and white cathode rays, which had begun, grew dimmer and
dimmer until invisible. At the same time, the phosphorescent spot became
brighter and brighter and hotter and hotter, while the electrode cooled,
until the glass adjacent thereto was uncomfortably cold to the touch. At
this stage, the required degree of exhaustion was reached, and yet
without any kind of a pump. He was enabled to hasten the process by
alternate heating and cooling, and by the use of a small electrode. This
whole phenomenon was exhibited with external electrodes as well. He
acknowledged that instead of the disruptive coil, a static machine could
be used, or, in fact, any generator or combination of devices adapted to
produce a very high E. M. F.

The reduction of temperature of the electrode he attributed to its
volatilization. Without actually testing the rays with a fluorescent
screen or photographic plate, he could always know their presence by the
relative temperatures of the phosphorescent spot and the electrode, for
when the latter was at a low temperature and the former at a high
temperature, X-rays were sure to be strong.

From the fact that the vacuum became higher and higher by the means
stated, he was very much inclined to believe that there was an expulsion
of material particles through the walls of the bulb. When these
particles which were passing with very great velocities struck the
sensitive photographic plate they should produce chemical action. He
referred to the great velocity of projected particles within a discharge
tube, pages 46 and 47, and to Lord Kelvin’s estimate upon the same, and
reasoned that with very high potentials, the speed might be 100 km per
second. The phenomenon indicated, he said, that the particles were
projected through the wall of the tube and he entered into an elaborate
discussion on this point. He referred to his own experiment of causing
the rays from an electrode in the open air to pass directly through a
thick glass plate. § 13. He performed an experiment also of producing a
blackening upon a photographic plate apparently by the projected
particles, an electrical screen being employed to prevent the formation
of sparks. § 35. which as well known will cause chemical action upon the
plate. No stronger proof as to the expulsion of material particles could
be desired than an operation in which the eyes can see for themselves
that such an action must have taken place. Usually he was troubled by
the streamers (cathode rays) from the electrode suddenly breaking the
glass of the discharge tube. This occurred when the spot struck was at
or near the point where the same was sealed from the pump. He arranged a
tube in which the streamers did not strike the sealing point, but rather
the side of the tube. It was extraordinary that a visible but fine hole
was made through the wall of the tube, and especially that no air rushed
into the vacuum. On the other hand, the pressure of the air was overcome
by something rushing out of the tube through the hole. The glass around
the hole was not very hot, although if care were not taken, it would
become much hotter, and soften and bulge out, also indicating a pressure
within, § 27. greater than the atmospheric pressure. He maintained the
punctured tube in this condition for some time and the rarefaction
continued to increase. As to the appearances, the streamers were not
only visible within the tube, but could be seen passing through the
hole, but as the vacuum became higher and higher, the streamers became
less and less bright. At a little higher degree of vacuum, the streamers
were still visible at the heated spot, but finally disappeared.

This electrical process of evacuating varies in its rapidity according
to the thinness of the glass. Here again he noted the application of his
theory in that an easier passage was afforded for the ions. § 47. A few
minutes of operation produced through thin glass, a vacuum from very low
to very high, whereas, to obtain the same vacuum through much thicker
glass over 1/2 hour was necessary. Again with a thick electrode the time
required was much greater. The small hole was not always visible and it
was thought that the material went through the pores. The result
obtained by the following experiment tends to uphold Mr. Tesla’s
emission theory.


139_a_. LAFAY’S EXPERIMENT. GIVING TO X-RAYS THE PROPERTY OF BEING
DEFLECTED BY A MAGNET BY PASSING THEM THROUGH A CHARGED SILVER LEAF.
_Comptes Rendus_, March 23, ’96 and April 7, 13, 27, and _L’Ind. Elec._,
April and May ’96. From trans. by Louis M. Pignolet. He placed at about
.5 cm. below a discharge tube, a lead screen pierced by a slit 2 mm.
wide; and 0.04 m. lower, a second lead screen having a slit 5 mm. wide
completely covered by an extremely thin leaf of silver. Opposite the
silver leaf and exactly in the axis of the slit, was fixed a platinum
wire 1.5 mm. diameter. Thus, the rays which passed successively through
the two slits projected a shadow of the wire on a photographic plate
below.

When the silver leaf was connected to the negative pole of the induction
coil that excited the tube, the rays, which had become electrified (§
61_b_, p. 47) bypassing through the leaf, were deflected by a magnetic
field of about 400 L. G. S. units, whose lines of force were parallel to
the slit. The direction of the deflection was determined by the same law
as that of the deflection by a magnetic field of the cathode rays in the
interior of a discharge tube. § 59. When the silver leaf was not
connected to the coil, no deflection was produced. § 79.

To double the apparent deflection, one part of the slit was covered by a
lead plate during the first half of the experiment. The lead plate was
removed and placed over the other part of the slit, and the direction of
the magnetic field reversed during the last half of the experiment. Thus
the distance on the sciagraph between the two parts of the wire, was
double the deflection produced by the magnetic field.

The deflection was in the same direction when the silver leaf was
connected to the negative pole of a static electric machine, but was in
the opposite direction when the leaf was connected to the positive pole
of the machine. The test was criticised in the scientific press, and,
therefore, in order to be certain that the deflections observed were not
due to the combined effects of the electro-magnet which produced the
magnetic field and the electric field of the charged silver leaf, the
experiments were modified. To remove this uncertainty, the electrified
rays were caused to enter a grounded Faraday cylinder (see figure at E.
F. G. H., p. 47), through a small opening, before passing between the
poles of the electro-magnet. The deviations which were recorded on a
photographic plate in the box were the same as before.

Additional experiments showed that the deflections by the magnetic field
took place as well when the rays were electrified, after their passage
through another magnetic field, as before. Lafay continued the
experiments in great detail and by many control tests, and he took
accurate measurements and followed the suggestions of others. It would
be well for those who have facilities to repeat these most interesting
and important researches, to determine for themselves some satisfaction.

It is of interest to note that an American, Paul A. N. Winand, (_Mem.
Amer. Inst. Elect. Engs._), in the absence of facilities for
experimenting, proposed (_Elect. World_, N.Y., June 6, ’96) to interpose
a hollow sphere, which had high potential, in the path of X-rays, and to
learn in what manner, if any, the rays are influenced. He argued that it
would seem natural that, inasmuch as the rays produce a discharge, there
should be a reaction of the charged surface upon the rays.

It is evident that if any one repeats these experiments, expert
manipulation is required.


139_b_. GOUY’S EXPERIMENTS. THE PENETRATION OF GASES INTO THE GLASS
WALLS OF DISCHARGE TUBES. _Comptes Rendus_, March 30, ’96. From trans.
by Louis M. Pignolet. From observations with slightly different glass
from four tubes, it seemed that the cathode rays cause the gases in the
tubes to penetrate the glass where they remain occluded until the glass
is nearly softened (after cutting off the current), by heat, whereby
they are set at liberty as minute bubbles visible by the microscope,
which finally partly combine and become visible to the naked eye.


[Illustration:

  HALOS 1 FT. DIAM., IN CLEAR AIR, AROUND INCANDESCENT ELECTRIC LAMPS
  OF USUAL SIZE. CROSS AT CENTER OF EACH HALO. § 140, p. 143.
  Observed by means of a photograph, in 1882, by William J. Hammer.
]


[Illustration:

  MORTIFICATION OF THE ULNA. § 204.
  From sciagraph by Prof Miller.
]


Under the same conditions, tubes which have been used for a long time
exhibit numerous wrinkles, indicating a superficial modification of the
glass. These may exist with or without the bubbles.


140. DISCHARGE TUBE SURROUNDED BY A VIOLET HALO. By means of enormous
potential and high frequency, the tube was surrounded, Tesla stated, by
violet luminosity or halo. § 6. and 74. From the fact that Lenard
obtained a similar appearance in front of the aluminum window, it might
be reasonable to conclude that there is some close relationship between
the two phenomena.

As an illustration of halo by light, may be mentioned the well known
appearance so often occurring in the atmosphere concentrically with the
moon, and sometimes surrounding the sun. Under favorable circumstances,
(in a mist or dust in the air), a halo, at some distance from a flame or
other light is faintly visible. It has generally been assumed that the
reason of a halo by light is based upon the laws of reflection, or
refraction or both, the bending of the rays taking place, through, or
upon the surface of the particles of moisture. Others have held that
particles of ice in the upper atmosphere, are the reflectors or
refractors, or both. More puzzling has been the attempt to explain the
novel appearance reproduced fairly well in the cut, page 140. It is here
represented in print for the first time, but the photograph from which
it was taken, was at various times, shown to different physicists, some
of whom attributed the beautiful effect to the property of interference
of light, and naming Newton’s rings as an analogous production. Prof.
Anthony in an interview expressed himself as well satisfied that
interference could not occur under the circumstances named. He
recognized that there was a curved surface of glass which might be
considered as made up of an infinite number of layers. The author
introduces the matter for the purpose of consideration by others, and
especially because it is so intimately connected with the subject of the
vacuum tube and electricity. The details must be understood for the
purpose of proper appreciation. Mr. William J. Hammer, of New York, had
a photograph taken of the large Concert Hall at the Crystal Palace,
Sydenham, Eng., by the light of the Edison incandescent lamps with which
the Hall was illuminated. This photograph was made in 1882 during the
International Electrical Exhibition held at the Crystal Palace. The
picture shows a small section of the whole photograph and represents
(although probably no one would judge so by looking at the picture) a
festoon of _pear_-shaped incandescent electric lamps, each one hanging
downward, and separated from its neighbor by between _three and four_
feet. They were so far away from the camera that a picture of the lamps
unlighted, would have represented them as mere specks. The bright
circles with the bright central crosses in the centre of the dark spaces
were, therefore, fully one foot in diameter, while the lamp bulbs
themselves were only about two or three inches thick, as usual. Why then
should there be the halos? Why should the crosses appear? And why should
the black area be so large? If the electricity and vacuum have nothing
to do with it, why should not the halos appear when photographs are
taken of flames and other sources of light in the absence of mist and
dust? In order to answer questions which will perhaps be proposed, let
it be stated that there was no visible dust nor moisture in the room,
the photograph being taken early in the evening and at a time when the
Hall was not in use. The halos were not apparent except when reproduced
by a photograph. The lamps had the usual carbon filaments hanging so
that the several filaments were in different planes, and they were of 16
candle power and were connected in parallel circuit, the average E. M.
F. being about 110 volts. The lamps were fed by the Edison direct
current dynamos. The festoon shown, is one of a dozen or more which were
suspended between the columns rising from the gallery and supporting the
roof and were hung about forty feet from the floor. The hall was further
illuminated by a huge electrolier pendant from the centre of the
ceiling. These details were obtained from Mr. Hammer, who planned the
installation.


141. ANÆSTHETIC PROPERTIES OF X-RAYS.—Tesla reported that he and his
assistants tested the action of the rays upon the human system, and
found that upon continued impact and penetration of the head by very
powerful radiations, strange effects were noticed. He was sure that from
this cause a tendency to sleep occurred (§ 84, at end), and the
faculties were benumbed. He said that time seemed to pass quickly. The
general effect was of a soothing nature, and the top of the head seemed
to feel warm under the influence of the rays. Incidentally, he noticed,
as he stated, “When working with highly strained bulbs, I frequently
experienced a sudden and sometimes even painful shock in the eye. Such
shocks may occur so often that the eye gets inflamed, and one cannot be
considered cautious if he abstains from watching the bulb too closely.”

The author calls to mind the reports in the daily press that Edison also
noticed that the eyes were in some way sensitive to the rays. The eye,
it was reported, became fatigued at the time, and yet later, objects
could be more easily distinguished.

In this connection, it should be remembered that there are not only
cathode rays, X-rays, etc., but the electric force that Lenard spoke of
in the neighborhood of the discharge tube, and in testing the effects
upon the eyes, of course, the precaution should be taken to determine
whether cathode rays, X-rays or the electric sparks are answerable for
the peculiar effects. Roentgen reasoned, § 84, that the eyes were not
sensitive, but the rays, in his case, were not strong enough to travel
40 to 60 feet, as in Tesla’s experiments, but only 2 m. (about 7 ft.).


142. SCIAGRAPHS OF HAIR, FUR, HEART, ETC., BY X-RAYS.—Tesla was probably
the first to be at all successful in the representation in sciagraphs of
such objects as hair and cloth and similar easily permeable objects. In
the case of a rabbit, not only was the skeleton visible, but also the
fur. Sciagraphs of birds exhibited the feathers fairly distinctly. The
picture of a foot in a shoe not only represented the bones of the foot,
and nails of the shoe, but every fold of the leather, trowsers,
stockings, etc. His opinion as to the useful application of the rays was
that any metal object, or bony or chalky deposit could be “infallibly
detected in any part of the body.” In obtaining a sciagraph of a skull,
vertebral column, and arm, even the shadows of the hair were clearly
apparent. It was during such an experiment that the anæsthetic qualities
were noticed. The author saw several of the above named sciagraphs.
Furthermore, on the screen he believed he detected the pulsations of the
heart. _Elect. Rev._, N.Y., May, 20, ’96.

Although we do not doubt this report concerning what Mr. Tesla saw, yet
some scientific men are exceedingly dubious concerning the results
obtained by other scientists, unless the same are confirmed by
additional witnesses. It will certainly be of interest to such skeptics
to have corroboratory evidence. In company with Prof. Anthony, Mr. Wm.
J. Hammer and Mr. Price, editor of the _Elect. Rev._, N.Y., the author
visited a laboratory at 31 West 55th street, New York City, for the
purpose of beholding the pulsations of the human heart by means of an
experiment performed by Mr. H. D. Hawkes, of Tarrytown, N.Y. There was
nothing new about his apparatus, the admirable results being due merely
to accurately proportioned electrical and mechanical details and
skillful manipulation. The Tesla system was not used, but merely a large
induction coil and rotary interrupter, and a direct current from the
incandescent lamp circuit of 110 volts, all substantially as Roentgen
himself employed. The sciascope was provided with the Edison calcic
tungstate screen. In order to overcome the sparking between the
terminals on the outside of the tube after a few minutes of use, he
heated the cathode end by means of a Bunsen burner flame. § 139, near
beginning. The utility consisted in the evaporation of condensed
moisture upon the cool end of the discharge tube. The temporary heating
always prevented, for several minutes, any sparking on the outside.
After some preliminary experiments, each person, in turn, pressed the
sciascope upon the breast of another, at the location of the heart,
while the discharge tube was directly at the back of a young man. The
ribs and spinal column were visible, and, projecting from the spine,
appeared a semi-circular area, which expanded and contracted. Any one
viewing such an operation, and knowing that he is looking at the
movements of the heart, cannot but be impressed with weird wonder, and
cannot but credit great honor, not only to Roentgen and Lenard, but to
all those early workers who have gradually but surely, successfully made
discovery after discovery in the department of the science of
discharges, finally culminating in the most wonderful discovery of all.

The author remembers seeing in some medical paper that William J.
Morton, M.D., of New York, had also witnessed the beating of the heart
with the sciascope at an early date. Similar reports are occurring
weekly.

§ 142_a_. Mr. Norton, of Boston (_Elect. World._, N.Y., May 23, ’96)
also stated that the heart could be seen in faint outline, and also its
pulsations. The lungs were very transparent. The liver being quite
opaque, its rise and fall with the diaphragm was plainly followed.
Others have suggested drinking an opaque (to X-rays) liquid, like salt
water, and tracing its path.


143. PROPAGATION OF X-RAYS THROUGH AIR TO DISTANCES OF 60 FT.—In
Roentgen’s first experiments, the maximum distances at which the
fluorescent screen was excited was about 7 ft. Tesla obtained similar
action at a distance of over 40 ft. Photographic plates were found
clouded if left at a distance of 60 ft. for any length of time. This
trouble occurred when some plates were in the floor above and 60 ft.
distant from the discharge tube. He attributed the wonderful increase
largely to the employment of a single electrode discharge tube, because
the same permitted the highest obtainable E. M. F. that could be
desired.


[Illustration:

  SCIAGRAPH OF FOOT IN LACE SHOE. § 204.
  By Prof. Miller.
]


144. X-RAYS WITH POOR VACUUM AND HIGH POTENTIAL.—In the course of
Tesla’s experiments, he observed that the Crookes’ phenomena and X-rays
could be produced without the high degree of vacuum usually considered
necessary, § 118. but by way of compensation, the E. M. F. must be
exceedingly high, and, of course, the tube and electrical apparatus
substantially of those dimensions involved in Tesla’s work. One must be
careful not to over-heat the discharge tube, which is likely to occur by
increase of potential. He gave definite instructions for preventing the
destruction of the tube by heating, by stating that it is only necessary
to reduce the number of impulses, or to lengthen their duration, while
at the same time raising their potential. For this purpose, it is best
to have a rotary circuit interrupter in the primary instead of a
vibrating make and break, for then it becomes convenient to vary the
speed of the interrupter, which may be, evidently, so constructed that
the duration of the impulses may also be varied, for example, by
different sets of contact points arranged on the rotary interrupter, and
made of different widths.


145. DETAIL CONSTRUCTION AND USE OF SINGLE ELECTRODE DISCHARGE TUBES FOR
X-RAYS. He pointed out that with two electrodes in a bulb as previously
employed by nearly all experimenters, or an internal one in combination
with an adjacent external one the E. M. F. applicable was necessarily
greatly limited for the reason that the presence of both, or the
nearness of any conducting object “had the effect of producing the
practicable potential on the cathode.” Consequently he was driven, as he
said, to a discharge tube having a single internal electrode, the other
one being as far away as required. § 9. In view of his ingenious
arrangements of the disruptive coil, and circuits, condensers and static
screens for the bulb, he found it immaterial to pay attention to some
other details followed by experimenters. For example, it made
comparatively little difference in his results whether the electrode was
a flat disk or had a concave surface.


[Illustration:

  TESLA’S FIGS. 1 AND 2, REFLECTION AND TRANSMISSION OF X-RAYS BY
    DIFFERENT SUBSTANCES. § 145 and § 146_a_.
]


The form of tube described by Tesla in full, will hereinafter be alluded
to as exhibited in the several figures accompanying this description,
and it consisted, therefore, of the long tube “_b_” made of very thick
glass except at the end opposite the electrode “_e_”, where it was blown
thin, p. 149. The electrode was an aluminum disk having a diameter only
slightly less than that of the tube and located about one inch beyond
the rather long narrow neck _n_, into which the leading-in wire _c_
entered. It is important that a wrapping _w_ be provided around this
wire, both inside and outside of the tube. The sealing point was on the
side of the neck. An electric screen has been referred to heretofore. It
is lettered _s_, and was formed of a coating of bronze paint applied on
the glass between the electrode and neck _n_. The screen could be made
in other ways, for example, as shown at _s_, Fig. 2, where it consists
of an annular disk behind and parallel to the electrode disk. This ring
_s_ in Fig. 2. must be placed at the right distance back of the
electrode _e_, but just how far can only be determined by experience.
The unique service of the screen was that of an automatic system for
preventing the vacuum from becoming too high by use. The peculiar action
was as follows, namely from time to time, a spark jumped through the
wrapping _w_ within the tube to the screen and liberated just about
enough gas to maintain the vacuum at an approximately constant degree.
Another way in which he was able to guard against too high a vacuum,
consisted in extending the wrapping _w_ to such a distance inside of the
tube, that the same became heated sufficiently to liberate occluded
gases. As to the long length of the leading-in wire within a long neck
behind the cathode, Lenard found the same to be valuable in conjunction
with a wrapping around the wire. With high potential, a spark, at a
certain high degree of vacuum, formed behind the electrode, and
prevented the use of very high potential, but by having the wire extend
far into the tube and providing wrappers, the sparking was much less
likely to occur. By proper adjustment as before intimated, Tesla could
produce just about enough to compensate for the electrical increase of
the vacuum. Another difficulty that presented itself in connection with
high E. M. F. was the undue formation of streamers heretofore referred
to, apparently issuing from the glass, and so often disabling it. He
therefore immersed the discharge tube in oil as pointed out in detail
hereinafter. The walls of the tube served to throw forward to the thin
glass many of those rays that otherwise would have been scattered
laterally. Upon comparing a long thick tube of this kind with a
spherical one, the sensitive plate was acted upon by the rays in 1/4 the
time with the tube. A modification consisted in surrounding a lower
portion of the tube, with an outside terminal _e_, indicated in dotted
lines in Fig. 1. In this way the discharge tube had two terminals. The
greatest advantage probably in using a long tube, was that the longer it
was, within the proper limits, the greater the potential which could be
applied with advantages. As to the aluminum electrode, he noticed that
it was superior, in comparison with one made of platinum which gave
inferior results, and caused the bulb to become disabled in an
inconveniently short period of time.


146. PERCENTAGE OF REFLECTED X-RAYS. He performed some preliminary
experiments, testing roughly as to whether any appreciable amount of
radiation could be reflected or not from any given surface. Within 45
minutes he was enabled to obtain clear and sharp sciagraphs of metal
objects, and the same could have been obtained only by the reflected
rays, because he screened the direct rays by means of very thick copper.
By a rough calculation he found that the percentage of the total amount
of rays reflected was somewhere in the neighborhood of 2 per cent.

Prof. Rood, of Columbia University, N.Y., (_Sci._, Mar. 27, ’96.) by
means of an experiment with platinum foil, § 80, concluded that the per
centage was about .005, the incident angle being 45 degrees. He regarded
this figure as the mere first approximation. Judging from Roentgen, §
85, Tesla, Rood and others, therefore, it seems to be established that
the percentage of X-rays reflected is very small.

Prof. Mayer, of Stevens Institute, (_Science_, May 8, ’96,) is of the
opinion that there is a regular or specular reflection, having witnessed
some experiments obtained by Prof. Rood, of Columbia Univ., N.Y. Prof.
Mayer reported that the original negatives were taken in such a way as
to substantiate regular reflection, and were carefully examined by six
eminent physicists at the _National Acad. of Sci._ at Washington, April
23, ’96, and none had the slightest doubt concerning the completeness of
the demonstration. The material employed for reflecting was platinum
foil. § 103_a_.

DIFFERENCE BETWEEN DIFFUSION AND REFLECTION. Judging from the
experiments above related, as well as those considered in § 103_a_,
there might at first appear to be contradictory results, reported by
different authorities. Experts, it is thought will, without argument,
discover the harmonious agreement, and will commend the work of
scientists, who, in different parts of the world, and at about the same
time, made similar experiments, which now being considered jointly, are
found to agree so wonderfully closely. Upon reading the above sections
and those referred to, there can be no doubt whatever but that X-rays,
upon striking a body are, to a certain per cent. scattered, or thrown
back, or bent from their straight course, and sent in a backward and
different direction, at one angle or another. The only apparent absolute
contradiction to this is that of Perrin, § 103_a_, _near the end_. But
his is a case of one witness against scores, and, therefore, evidence
based upon his experiments, must be counted out. The error was either
due to some oversight of his own, or more probably the mistake is merely
a typographical one, for often a mistake creeps in between a man’s
dictation and the printed work. It is difficult to accuse Perrin of a
mistake, for he is a great French authority in such matters. Assuming
that no error has occured, let it be noticed that he does not pronounce
non-reflection from all substances, but only from steel p. 154, l. 9,
and flint, which have been so polished as to form a mirror-like surface,
whereas all other experimenters, with scarcely an exception, have not
employed such surfaces. The difficult point to believe is that, after
six hours, no energy from the mirror could be collected. If we accept
Perrin’s results it must be only in regard to those two particular
materials, polished steel and flint. Another feature which is on the
edge of conjecture, is that of true or specular reflection, referred to
by Prof. Mayer, § 146. Many attempts have been undertaken to prove
whether the rays were thrown backward on the principle of reflection as
light from a mirror, or of diffusion as light from chalk. Let the
student notice that the evidence is overwhelming in favor of the turning
back of the rays to a very small per cent. upon striking any object. As
to specular reflection, which means similar to the reflection of light
from a polished mirror, it is practically the same as diffusion, the
difference being substantially of a technical nature. This allegation is
based upon the detail distinction between reflection and diffusion given
by P. G. Tait, professor of natural philosophy, Univ. of Edinburgh, who
states, in _Encyclo. Brit._, vol. 141, p. 586:—

“It is by scattered light that non-luminous objects are, in general,
made visible. Contrast, for instance, the effect when a ray of sunlight
in a dark room falls upon a piece of polished silver, and when it falls
on a piece of chalk. Unless there be dust or scratches on the silver,
you cannot see it, because no light is given from it from surrounding
bodies except in one definite direction, into which (practically) the
whole ray of sunlight is diverted. But the chalk sends light to all
surrounding bodies, from which any part of its illuminated sides can be
seen; and there is no special direction in which it sends a more
powerful ray than in others. It is probable that if we could, with
sufficient closeness, examine the surface of the chalk, we should find
its behavior to be in the nature of reflection, but reflection due to
_little mirrors_ inclined to all conceivable aspects, and to all
conceivable angles to the incident light. _Thus scattering may be looked
upon as ultimately due to reflection._ When the sea is perfectly calm,
we see it in one intolerably bright image of the sun only. But when it
is continuously covered with slight ripples, the definite image is
broken up, and we have a large surface of the water shining by what is
virtually scattered light, though it is really made up of parts each of
which is as truly reflected as it was when the surface was flat.”


146_a_. REFLECTED AND TRANSMITTED X-RAYS COMPARED.—In order to carry on
a series of investigations, Mr. Tesla constructed a complete special
apparatus represented in Fig. 2, p. 149, and embodied in it also an idea
which he attributed to Prof. William A. Anthony, which consisted in
arranging for sciagraphs to be produced by the rays transmitted through
the reflecting substance as well as by the reflected rays themselves.
The figure serves to show at a glance the construction and, therefore,
the explanation need be but brief. It consisted of a _T_ tube, having
three openings, those at the base and side being closed by photographic
plates in their opaque holders, which carried on the outside the objects
_o_ and _o´_ to be sciagraphed. At an angle to both plates, and
centrally located, was a reflecting plate, _r_, which could be replaced
by plates of different materials. At the upper opening of the plate _B_
was a discharge tube, _b_, placed in a heavy Bohemian glass tube, _t_,
to direct the scattered rays downward as much as possible from the
electrode, _e_, to and through the thin end of the discharge tube. The
objects to be sciagraphed, namely _o_ and _o´_, were exact duplicates of
each other. No statement could be found as to the thickness of the
tested plates, _r_, except that they were all of equal size. The
distance from the bottom of the discharge tube to the reflecting plate,
_r_, was 13 inches, and from the latter to each photographic plate about
7 inches, so that both pencils of rays had to travel 20 inches in each
instance. One hour was taken as the time of exposure. After a series of
experiments with a great many different kinds of metals, they arranged
themselves as to their reflecting power, in an order corresponding to
Volta’s electric contact series in air. § 153. The most electro-positive
metal was the best reflector, and so on. For exhaustive investigations
upon the discovery of Volta, see _“Experimental Researches” of
Kohlrausch, Pogg. Ann., ’53_, and Gerland, _Pogg. Ann., ’68_. The metals
Tesla tested were zinc, lead, tin, copper and silver, which were, in
their order, less and less reflecting, and the order is the same in the
electro-positive series, zinc being the most positive, and the others
less and less so, in the order named. For a complete list of the metals
arranged by the Volta series, see any standard electrical text-book. He
could not notice much difference between the reflecting powers of tin
and lead, but he attributed this to an error in the observation.

He tried other metals, but they were either alloys or impure. Those
named in the list above were the pure metals. However, he carried on
experiments with sheets of many different substances, and arrived at the
following table, which shows particularly the relative transmitting and
reflecting powers of the various substances in the rough.


                   Impression by        Impression by
      Reflecting     Transmitted Rays.    Reflected Rays.
      Body

      Brass        Strong               Fairly good

      Toolsteel    Barely perceptible   Very feeble

      Zinc         None                 Very strong

      Aluminum     Very strong          None

      Copper       None                 Fairly strong but much
                                          less than zinc

      Lead         None                 Very strong but a little
                                          weaker than zinc

      Silver       Strong, a thin plate Weaker than copper
                     being used

      Tin          None                 Very strong about like
                                          lead

      Nickel       None                 About like copper

      Lead-glass   Very strong          Feeble

      Mica         Very strong          Very strong about like
                                          lead

      Ebonite      Strong               About like copper.


By comparing, as in previous experiments, the intensity of the
photographic impression by reflected rays with an equivalent impression
due to a direct exposure of the same bulb and at the same distance, that
is, by calculations from the times of exposure under assumption that the
action upon the plate was proportionate to the time, the following
approximate results were obtained:


                               Impression
                    Reflecting     by     Impression
                    Body         Direct   by
                                 Action   Reflected
                                          Rays.

                    Brass         100     2

                    Tool steel    100     0.5

                    Zinc          100     3

                    Aluminum      100     0

                    Copper        100     2

                    Lead          100     2.5

                    Silver        100     1.75

                    Tin           100     2.5

                    Nickel        100     2

                    Lead-glass    100     1

                    Mica          100     2.5

                    Ebonite       100     2


He stated that while these figures can be but rough approximations,
there is, nevertheless a fair probability that they are correct, in so
far as the relative values of the sciagraphic impressions of the various
objects by reflected rays are concerned.

In order to devise means for testing the comparative reflecting power in
a more decided manner, he laid pieces of different metals side by side
upon a lead plate. Consequently the reflecting surface was formed of two
parts corresponding to the two metals. § 80. The vertically
perpendicular partition of lead served to prevent the mingling of the
rays from the two metals. Ingenious precautions were taken; as for
example, so arranging matters that upon equal areas of the two plates,
equal amounts of X-rays impinged. § 80. He undertook to determine the
position of iron in the series by thus comparing it with copper. It was
impossible to be sure which metal reflected better. The same regarding
tin and lead and also in reference to magnesium and zinc. Here, a
difference was noticed, namely that the magnesium was a better
reflector.

He has made practical application of the power of the substances to
reflect a certain per cent. of the rays by employing reflectors for the
purpose of reducing the time required for exposure of the photographic
plates. It admits, he stated, of the use of reflectors in combination
with a whole set of discharge tubes, whereby rays which would be
otherwise scattered in all directions are brought more nearly to a
single direction of propagation.


[Illustration:

  FROM SCIAGRAPH OF KNEE-JOINT. STRAIGHT, FRONT VIEW.
  By Prof. Goodspeed. _Photo. Times_, July, ’96.
]


It might be argued, that in as much as zinc would reflect only about
three per cent. of the incident rays, no practical gain would ensue in
sciagraphy by the use of a reflector. He pointed out the falsity of such
an argument. In the first place, the angle employed in these tests was
45°. With greater angles, the proportion of reflected rays would be
greater assuming that the law of reflection is the same as that of
light. By mathematical calculation and tests, he showed that there was
no doubt whatever about the advantage of using reflectors. He obtained a
sciagraph, on a single plate, of the ribs, arms and shoulder, clearly
represented. He stated the details as follows. “A funnel shaped zinc
reflector two feet high, with an opening of five inches at the bottom
and 23 inches at the top, was used in the experiment. A tube similar in
every respect to those previously described, was suspended in the
funnel, so that only the static screen of the tube was above the former.
The exact distance from the electrode to the sensitive plate was four
and one-half feet.”


147. DISCHARGE TUBE PLACED IN OIL.—When the E. M. F. was increased, by
having the discharge tube, as usual, in open air, sparks formed behind
the electrode, and within the vacuum, and endangered the life of the
discharge tube. He obviated this difficulty partly by having the
electrode located well within the evacuated space, so that the wire
leading to it was unusually long. By excessive E. M. F., also, streamers
broke out at the end of the tube. To overcome all difficulties in
connection with sparking and breaking of the tube, he followed the
proposition of Prof. Trowbridge, and submerged the discharge tube in
oil, § 11, at end, and § 13, which was continually renewed by flowing
into and out of the vessel in which the discharge tube was contained,
all as shown in the accompanying figure, p. 157, “Discharge Tube
Immersed in Oil.” The discharge tube, _t_, may be recognized by its
shape, and it is located horizontally in a cylindrical tube lying
sidewise upon a table. To regulate the flow of the oil, the reservoir
may be raised and lowered by a bracket, s. The X-rays enter the outside
atmosphere by passing first through glass, then oil, and then through a
diaphragm of “pergament” forming the right hand end of the oil vessel.
When the results were compared with those obtained by Roentgen in his
first experiments, the rays were found so powerful that it is not
surprising that Tesla was able to obtain more definitely a closer
knowledge of the properties of the rays. Roentgen obtained, with his
tube and a screen of barium platino cyanide, a shadow picture of the
bones of the hand at a distance of less than 7 ft., while Tesla obtained
a similar picture with a screen of calcic tungstate, and with his tube
immersed in oil at a distance of 45 ft. Tesla also made sciagraphs with
but a few minutes’ exposure at a distance of 40 ft., by the help of
Prof. Henry’s method, __i.e.__, with the assistance of a fluorescent
powder. § 151. He referred also to Salvioni’s suggestion of a
fluorescent emulsion. He attributed to Mr. E. R. Hewitt the conjecture
that the sharpness of the sciagraphs might be increased by a thin
aluminum sheet having parallel groves. Several experiments were made,
therefore, with wire gauze, as well as with a screen formed of a mixture
of fluorescent and iron-fluorescent powders. With the strong power of
the rays as obtained by Tesla in combination with such adjuncts, the
shadows were sharper, although the radiation, of course, was weakened by
the obstruction. § 107_b_.


[Illustration:

  DISCHARGE TUBE IMMERSED IN OIL, § 147, PAGE 156.
]


With the apparatus involving the discharge tube in oil, and with
tremendously high potential, he obtained what may be called wonderful
results; for with the sciascope he obtained shadow pictures of the
vertebral column, outline of the hip bones, the location of the heart
(and later detected its pulsations), ribs and shorter bones, and,
without the least difficulty, the bones of all the limbs. More than
this, a sciagraph of the skeleton of the hand was perceived through
copper, iron or brass very nearly 1/4 inch thick, while glass 1/2 inch
thick scarcely dimmed the fluorescence. The skull of the head of an
assistant acted likewise, while at a distance of three feet from the
discharge tube. The motion of the hand was detected upon the screen
although the rays first passed through one’s body. In making
observations with the screen, he advised that experimenters should
surround the oil box closely, except at the end, with thick metal
plates, to prevent X-rays from coming in undesired directions by
reflection from different objects in the room. Obviously the shadows
will be sharper.


148. BODIES NOT MADE CONDUCTORS BY X-RAYS. Tesla referred to Prof. J. J.
Thomson as having announced some time ago “that all bodies traversed by
Roentgen radiations become conductors of electricity.” The author has
witnessed other similar expressions giving credit to Thomson in this
respect, but he understands that Prof. Thomson, having discovered that
X-rays discharge both negatively and positively charged bodies,
conjectured or drew a corallary as to the probability of the bodies
therefore becoming conductors. Tesla, nevertheless, seems to have proved
that the corallary does not hold. In the first place he employed the
very powerful rays, and next, he let the oil be the substance traversed
by the rays. Besides this, he applied a sensitive resonance test. See
detail treatment of his experiments on this subject in _Elect. Rev._,
N.Y., June 24, ’93, p. 228. In brief “a secondary not in very close
inductive relation to the primary circuit, was connected to the latter
and to the ground, and the vibration through the primary was so adjusted
that true resonance took place. As the secondary had a considerable
number of turns, very small bodies attached to the free terminal
produced considerable variations of potential of the latter. Placing a
tube in a box of wood filled with oil and attaching it to the terminal,
I adjusted the vibration through the primary so that resonance took
place without the bulb radiating Roentgen rays to any appreciable
extent. I then changed the conditions so that the bulb became very
active in the production of the rays.”

According to the corallary above referred to, the oil should be, with
such an environment and under such subjection, a conductor of
electricity, but it was not. He emphasized his satisfaction in the
results by saying “the method I followed is so delicate that a mistake
is almost an impossibility.”

Prof. W. C. Peckham, _Elect. World_, N.Y., May 30, ’96, reasoned that
the oscillating electro-static action upon the outside of the tube, is
concerned in the production of fluorescence, and other properties of
X-rays. “These oscillations are certainly synchronous with the
vibrations of the cathode rays in the tube, which in turn synchronize
with the oscillation in the induction coil. If the vibrations of the
tube cannot keep time with those of its coil, few or no X-rays will be
given out. The cause seems to be similar to that of sympathetic
vibrations in sound. In a word, the discharge tube is a resonator for
its coil, and when the coil and tube are properly attuned, the maximum
effect is obtained.


149. APPLEYARD’S EXPERIMENT. NON-CONDUCTORS MADE CONDUCTORS BY CURRENT.
_Proc. Phil. So._, May 11, _Nature_, Lon., May 24, ’64, p. 93. A piece
of celluloid was pressed between two metal plates serving as terminals.
A galvanometer was employed to indicate the diminution of resistance by
time, and it also showed that the electrification was negative. When
mercury was one of the metals, the abnormal results did not occur,
except to a very small extent. When the celluloid was replaced by gutta
percha tissue, the electrification was normal. Many non-metals were
employed, and several were lowered in resistance.


149_a_. RESISTANCE SOMEWHAT INDEPENDENT OF METAL PARTICLES.—Through a
mixture of conducting and non-conducting materials, like a sheet of
gutta percha, having brass filings imbedded therein,—with 750 volts, no
current passed, and this held true until the proportion in weight of the
metal to the gutta percha was 2 to 1. Let it be remembered, also, that
selenium is reduced as to resistance under the influence of light.


150. MINCHIN’S EXPERIMENT. RESISTANCE LOWERED BY ELECTRO-MAGNETIC WAVES.
_Nature_, Lon., May 24, ’94, p. 93.—Referring to Appleyard’s experiment,
it will be noticed that he found that mixtures of certain limited per
cents. of metallic particles and insulators were exceedingly high in
resistance. Prof. G. M. Minchin found that such materials became
conductors under the influence of powerful electro-magnetic
disturbances, and that after the current was conducted, its resistance
remained greatly lowered in behalf of very weak impulses, although,
before the experiment, the resistance was so high. § 14_a_. But after
the current was interrupted by moving the terminal away from the
mixture, the high resisting power returned slowly, at a rate somewhat in
proportion to the hardness of the mixture. The film employed consisted
of shellac or gelatine or sealing wax, while among the metals was
pulverized tin. In the latter case, the resistance was reduced by the
electro-magnetic waves from apparent infinity to 130 ohms, the
electrodes being displaced by 1 cm.


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




                              CHAPTER XII

               MISCELLANEOUS RESEARCHES ON ROENTGEN RAYS.


                                -------

151. PUPIN AND SWINTON’S EXPERIMENT. SCIAGRAPHIC PLATES COMBINED WITH
FLUORESCENT SALTS. _The Elect._, Lon., Apr. 24, ’96.—Prof. Pupin, of
Columbia College (_Electricity_, N.Y., Feb. 12, ’96—the author saw him
use it Feb. 7, ’96—), was among the first, and probably actually the
first, to lessen the time of exposure by a fluorescent screen. Prof.
Salvioni also worked in this direction at an early date. Prof. Swinton
reported some details in the matter, and he was able to obtain a
sciagraph of the bones of the hand in less than 10 seconds, with a
moderately excited discharge tube, whereas, without the screen the time
was two minutes. He experimented first with barium platino cyanide, but
the results referred to were obtained with calcic tungstate, finely
ground, and made up into paste by means of gum, and dried. He spread the
same upon a celluloid sheet which was placed with the celluloid side
against the photographic film. The difficulty experienced first was in
the formation of spots on the negative, because some of the crystals
fluoresced more than others. Such a defect, however, showed that the
fluorescent salt increased the rapidity of the action upon the
photographic film. The result of this experiment, as well as that of
others, has sufficiently established the fact that the fluorescent
screen is of great importance in connection with the art of rapid
sciagraphy.

Phosphor sulphide of zinc is among those which hasten photographic
action. (Chas. Henry, in _Comptes Rendus_, Feb. 10, ’96.) Dr. W. J.
Morton employed the screen in taking the sciagraph of the thorax, p. 61.
The advantageous use is also confirmed by BASILEWSKI (_Comptes Rendus_,
March 23, ’96. From trans. by Louis M. Pignolet).—The photographic plate
was covered with a sheet of paper coated with barium and platino
cyanide, so that the two prepared surfaces were in contact, and the
fluorescent paper was between the object and the plate.


[Illustration:

  THORAX. § 206.
  By W. J. Morton, M.D. Fluorescent screen used (§ 151).
]


[Illustration:

  NORMAL ELBOW. § 204.
  By Prof. Miller.
]


J. W. Gifford, (_Nature_, May 21, ’96) tried a great variety of
fluorescent bodies in combination with the photographic plate, and found
that potassium platino cyanide was decidedly the best.


152. THOMPSON’S (S. P.) EXPERIMENT. PENETRATING POWER OF X-RAYS VARIES
WITH THE VACUUM. _Comptes Rendus._ CXIII., p. 809. _The Elect._, Lon.,
April 24, ’96, p. 866. In a communication to the Académie des Sciences
Prof. Sylvanus P. Thompson of the University College of Liverpool,
argued that by one kind of X-rays the bones of the hand were more easily
penetrated than by another kind. The two varieties were produced by
different vacua. § 75 and 76. Let the vacuum be supposed to become
higher and higher. At the first generation of the X-rays, the
fluorescent screen showed that the bones of the hand cast very dark
shadows. With increase of the vacuum, the shadows of the bones were very
faint. This result is also obtained by reduction of temperature. §
152_a_.


152_a_. BLEEKRODE’S EXPERIMENT. PERMEABILITY AT LOW TEMPERATURES
INCREASED. _Elect. Rev._, Lon., June 12, ’96.—Experiments performed by
him confirmed those of Edison. § 135. An experiment by Prof. Dewar
strongly confirmed the results. They noticed the same peculiarity that
Edison did, namely, that the shadow of the finger exhibited the flesh
and bones as if they were equally transparent. Varied tests showed that
the reduction of the temperature of glass increased its permeability.


153. MURRAY’S EXPERIMENT. REDUCTION OF THE CONTACT POTENTIAL OF METALS
BY X-RAYS. _Trans. R. So._, Mar. 19, ’96. _The Elect._, Lon., Apr. 24,
’96, p. 857. J. R. E. Murray of the Cavendish Laboratory, at the
suggestion of Prof. J. J. Thomson, carried on a long series of careful
experiments, to find whether the contact potential of a pair of plates
of different metals was, in any way, affected by the passage of X-rays
between the plates. All the ordinary precautions were taken. The contact
potential was measured by Thomson’s (Kelvin) method, see _Trans. Brit.
Asso._, 1880. The important result obtained, was that “the air through
which the rays pass, § 90, is temporarily converted into an electrolyte,
§ 47, and when in this condition forms a connection between the plates,
which has the same properties as a drop of acidulated water, namely, it
rapidly reduces the potential between the opposing surfaces of the
plates to zero, and may even reverse it to a small extent.”


154. NODON’S EXPERIMENT. TRANSPARENCY OF DIFFERENTLY COLORED MEDIA TO
THE X-RAYS. _Comptes Rendus_, Feb. 3, ’96. From trans. by Louis M.
Pignolet. The rays were passed through two openings in a thick metal
diaphragm, one of which was covered by an uncolored piece of gelatine
and the other by a piece tinted with the color to be tested. The two
images were received on the same plate. The various colors tested were
traversed with equal facility by the rays, § 68 and 82.

The investigation described above was made by Albert Nodon at the
Laboratoire des Recherches Physiques à la Sorbonne.

This agrees with Bleunard who found that colors seemed to have no
influence on the passage of the rays as water colored with various
aniline colors offered no more resistance than when pure. From trans. by
L. M. P. _Comptes Rendus_, March, ’96.

A. and L. Lumière (_Comptes Rendus_, Feb. 17, ’96,) observed that the
X-rays act in the same manner upon colored photographic plates rendered
sensitive to various regions of the spectrum. Thus, plates sensitive to
red, yellow and green gave exactly the same impression, provided they
had the same general sensibility to white light. While this may not be
accurately so, it illustrates that materials are penetrated by X-rays
independently of the laws of color.


155. MESLANS. CHLORINE, IODINE, SULPHUR, PHOSPHORUS, COMBINED WITH
CERTAIN COMPOUNDS, INCREASE OPACITY TO THE X-RAYS (_Comptes Rendus_,
Feb. 10, ’96. From trans. by Louis M. Pignolet.)—Carbon in its various
forms was found to be very transparent, also organic substances
containing, besides carbon, only the gaseous elements hydrogen, oxygen
and nitrogen; but this transparency was far from uniform. Organic
substances,—ethers, acids, nitrogenized compounds (_corps azotes_),—were
easily traversed by the rays; but the introduction of an inorganic
element, as particularly, chlorine, sulphur, phosphorus, and, above all,
iodine, renders them opaque. § 82. This occurs also with sulphates of
the alkaloids. Iodoform, the alkaloids, picric acid, fuchsine and urea
are very transparent. Metallic salts are very opaque, but this varies
with the metal and the acid. Bleunard went further into details. The
opacity of solutions of salts increased with the atomic weight of the
metal and of the metalloid. Water was easily traversed by the rays.
Solutions of bromide of potassium, chloride of antimony, bichromate of
potash offered considerable opposition to the passage of the rays.
Solutions of borate of soda, permanganate of potassium were easily
traversed. The liquids were held in paper boxes. The experiments above
related were conducted by Maurice Meslans at l’École de Pharmacie de
Nancy.


[Illustration:

  FROM SCIAGRAPH OF PENCIL, KEY, FOUNTAIN-PEN, AND COIN. § 161.
  By Prof. McKay, Packer Institute.
]


[Illustration:

  FROM SCIAGRAPH BY PROF. MILLER. § 156.
  1. Real diamond.
  2. Paste.
  3. Glass.
  4. Real diamond mounted in gold ring.
]


156. BUQUET & GASCARD’S EXPERIMENTS. ACTION OF THE X-RAYS UPON THE
DIAMOND AND ITS IMITATIONS; ALSO UPON JET. _Comptes Rendus_, Feb. 24,
96. From trans. by Louis M. Pignolet.—Sciagraphs taken by the X-rays
showed that diamonds became transparent, and their shadows disappeared
with long exposures; but imitation diamonds remained opaque under the
same conditions. Jet was distinguished from its imitations by the same
method. The diamond and jet cast clearer shadows on a fluorescent screen
than their imitations.

The above tests were made by Albert Buquet and Albert Gascard, at the
Cabinet de Physique de l’École des Sciences de Rouen.

The half-tone on lower half of adjacent page, 164, was taken from a
sciagraph by Prof. Dayton C. Miller, of Case School of Applied Science.
The differences of opacity are proved, because all were of same
thickness and exposed simultaneously.

Prof. Sylvanus P. Thompson (_The Elect._, Lon., May 18, ’96) confirmed
the above, and also found that, although the diamond is more transparent
than glass, it is more opaque than block carbon or graphite.

Mineralogists are thus enabled to submit minerals to the X-ray test in
making analyses.


157. DUFOUR’S EXPERIMENT. INACTIVE DISCHARGE TUBES MADE LUMINOUS BY
X-RAYS. _Comptes Rendus_, Feb. 24, ’96. From trans. by Mr. Pignolet.—He
observed that very small and sensitive Geissler tubes phosphoresced when
exposed to X-rays. § § 22, 23.


158. BEAULARD’S EXPERIMENTS. NON-REFRACTION OF X-RAYS IN A VACUUM.
_Comptes Rendus_, Mar. 30, ’96. From trans. by Louis M. Pignolet. With
prisms of ebonite, F. Beaulard held that no decided deviation could be
observed within the vacuum.


159. CARPENTIER’S EXPERIMENT. SCIAGRAPH SHOWING THE PARTS IN RELIEF ON A
COIN. _Comptes Rendus_, Mar. 2, ’96. From trans. by Louis M. Pignolet.
An imprint of a coin stamped upon a thin piece of well annealed aluminum
by pressing the coin against the aluminum, was reproduced in a
sciagraph. The raised parts of the coin were scarcely 8/100 of a
millimeter high. The aluminum was 5/10 millimeter thick. This result is
admirably represented by the sciagraph of an aluminum medal on page 166,
taken by Prof. Dayton C. Miller, of Case School of Applied Science,
_Elect. World_, N.Y., Mar. 21, ’96, who also made a sciagraph of a
copper plate 1/4 inch thick having blow holes which appeared in the
picture, but they could not be detected by light, serving to illustrate
an application of the new discovery in testing the homogeneity of
metals.


160. WUILLOMENET’S EXPERIMENTS. TRANSPARENCY OF THE EYE TO THE X-RAYS
DETERMINED BY SCIAGRAPH OF BULLET THEREIN. _Comptes Rendus_, Mar. 23,
’96. A sciagraph taken with an exposure of _three hours_ showed
perfectly a lead shot introduced into the vitreous media of the eye of a
full grown rabbit. Therefore the opacity of the media of the eye was not
absolute.

In a second series of experiments by Dr. Wuillomenet a human head was
used, but the results were negative in spite of a great intensity of the
rays and a long exposure, § 82.


161. FERNAND RANWEZ’S EXPERIMENTS. APPLICATION OF THE X-RAYS TO ANALYSIS
OF VEGETABLE MATTER. _Comptes Rendus_, Apr. 13, ’96. From trans. by
Louis M. Pignolet. Sciagraphy can render valuable services in analytical
researches and specially in the analysis of vegetable foods where they
will show the most usual adulterations consisting of mineral substances.


[Illustration:

  BAS-RELIEF SCIAGRAPH, § 159, BY PROF. DAYTON C. MILLER.
]


This method offers several advantages for small samples of the
substances can be examined. The samples are not chemically changed. A
great number of tests can be made in a short time. Lastly, the sciagraph
obtained affords a permanent record.

The tests were made on samples of adulterated saffron composed of
mixtures of pure saffron and saffron coated with sulphate of barium. A
sciagraph taken with an exposure of three minutes showed scarcely
visible imprints of the pure but strong impressions of the adulterated.
See sciagraph of pen, (mineral) in holder, (vegetable), in cut at upper
part of p. 164, which also shows the graphite in a wooden pencil.


162. ERRERA’S EXPERIMENT. ACTION OF THE X-RAYS ON PHYCOMYCES. HERTZ
WAVES AND ROENTGEN RAYS NOT IDENTICAL. _Comptes Rendus_, March 30, ’96.
From trans. by Louis M. Pignolet.—_Phycomyces Nitens_, when submitted to
the asymmetrical action of Hertz electric waves, became curved,
according to Hegler. Errera found a Phycomyces was not affected by the
X-rays, thus denoting an absence of Hertz waves in the rays. Credit for
the above result is due to L. Errera, from experiments made at the
Laboratoire Physique and the l’Institut Solvay (Université de
Bruxelles).


163. GOSSART, CHEVALLIER, FOUTANA AND URUANNI’S EXPERIMENT, IN
CONJUNCTION WITH J. R. RYDBERG. NO MECHANICAL ACTION OF X-RAYS. _Comptes
Rendus_, Feb. 10, Mar. 23, Apr. 13, ’96. From trans. by Louis M.
Pignolet.—The former party alleged that radiations from a discharge tube
caused a cessation of the rotation of the vane of the radiometer. J. A.
Rydberg was not inclined to confirm such action. A. Foutana and A.
Uruanni made experiments and concluded that the action was due to an
electro-static force, having noticed that a Leyden jar would also
produce such effect. The author made some experiments to determine the
matter in reference to X-rays at a distance outside of the
electro-static field. The rays would neither stop the vanes nor cause
them to rotate. He made some other experiments to detect whether there
was any direct mechanical power possessed by the rays; but if any, it
was exceedingly feeble.

T. C. Porter made some experiments at Eton College, (_Nature_, June 18,
’96,) which confirmed the above results, finding that the radiometer is
entirely inert to the Roentgen rays, whether they be from a properly
electrically screened hot or cold tube. He distinguished between the
caloric conditions, for he found that, not only will reduction of
temperature vary the penetrating power of the rays, § 135 and 152_a_,
but also will an increase of temperature.


164. BATTELLI’S EXPERIMENT. X-RAYS WITHIN DISCHARGE TUBE. _Nuovo
Cimento_, Apr., ’96, p. 193; _Elect. Rev._, Lon., June 12, ’96.—Shortly
after the announcement of the discoveries of Lenard and Roentgen, it
would have been considered strange to assert that X-rays may exist
inside of the discharge tube. Battelli certainly correctly infers, that
inasmuch as X-rays apparently originate from the point where a material
object is struck by the cathode rays, § 115, it would follow that when
the said object is within the vacuum space, X-rays are propagated before
they reach the glass wall of the discharge tube. It has already been
noted (DeMetz, § 63_a_) that photographic action may be produced within
the discharge tube. Battelli has confirmed this, not by a crude
experiment, like that (failure) of some authority in England, but by a
series of severe tests, leaving no doubt as to the production of
photographic action. He discovered in connection with several
subordinate phenomena that among the rays capable of producing a
photographic impression within the discharge tube, some were deflected
by a magnet and others were not, from which he concluded that X-rays may
exist inside the tube, in conjunction with cathode rays, before
collision with the anti-cathode. The experiment consisted in deflecting
the rays by a magnet, the film being in the path that the rays would
have had without a magnet. There was also a film in the path of the
deflected rays. Photographic action was produced upon both. He varied
the vacuum. Photographic action began at 3-10 mm., had its maximum at
1-70 mm., after which it remained constant. No photographic action was
obtained upon a film placed within the tube opposite the anode, except
in one case where it was exceedingly weak. Lenard continually inferred
that there must be two kinds of cathode rays. § 75. Battelli has
certainly sifted the two rays apart and thus proved Lenard’s
conjectures. § 61_b_, p. 47. _The Elect. Rev._, Lon., pays tribute to
Battelli, by offering the following opinion: “We have no hesitation in
saying that Battelli, by means of interesting and ingenious experiments,
has made the greatest advances in the theory of the X-rays since their
discovery by Roentgen.”

In many cases the author has omitted stating, in taking sciagraphs, that
the films were protected from ordinary light by opaque material. This,
as a matter of course, has always been understood. Battelli also had the
films wrapped in material opaque to ordinary light. Experimenters
should, if possible, always employ aluminum for this purpose, because
the author has always noticed that black paper or cloth permits a great
deal of light to come through, even when in double thickness.

Prof. Sylvanus P. Thompson (_The Electr._, Lon., June 26, ’96) located a
wire in a focus tube in the path of the rays between the platinum
reflector and the wall of the tube. Not only was there a sciagraph of
this wire produced in the sciascope, but also the Crookesian shadow of
the wire on the wall of the bulb. For this experiment the exhaustion
must be quite high. “At no state of exhaustion did the platinum
reflector convert all the internal cathode rays into X-rays.” Both
shadows were cast by the platinum reflector as the origin. More or less
of the rays between the reflector and the glass were sensitive to a
magnet.


[Illustration:

  BLEYER’S EXPERIMENT. § 165.
  Combined camera and sciascope at the left: and showing induction coil
    and discharge-tube at the right.
]


165. BLEYER’S EXPERIMENT. COMBINED CAMERA AND SCIASCOPE. _Elect. Eng._,
July 1, ’96; _Royal Acad. Med. & Sur._, of Naples, Italy.—As early as
April 7, J. Mount Bleyer, M.D., of Naples, constructed and used the
apparatus shown in the adjacent cut, p. 169. The picture is
self-explanatory. Attached to an ordinary camera is a flaring sciascope,
for receiving the temporary sciagraph of the hand, for example. The
X-rays are converted into luminous rays by the fluorescent screen, and,
therefore, the camera will serve to take a picture by means of the
luminous rays from the sciagraph of the hand. The cut represents also an
induction coil and a discharge tube. Soon afterwards, it was reported by
an English paper that Dr. Levy, of Berlin, and others of England, had
also made similar tests with success. In order to illustrate the
applicability of the combination, Dr. Bleyer took many sciagraphs with
the camera. He calls it the photofluoroscope, which, however, will
probably not meet with favor for the name does not suggest the nature of
the instrument. When two radically different devices are combined into
one, it is difficult to formulate an acceptable single word, and,
therefore, the instrument will probably always be called by some of the
following terms: A camera with sciascopic adjustment, or combined
sciascope and camera, or corresponding combinations with the word
fluoroscope.

From the time that Roentgen’s discovery was announced, scientists
throughout the world have made careful experiments, up to date, in all
possible directions, and the time has now come when the number of
experiments is rapidly decreasing, only one or two being noted now and
then in the scientific press, and consisting mostly in repetition, with
occasionally a slight departure, involving a radically new subordinate
discovery; but in view of the great number of scientists, and of their
high standing as careful experimenters, and because also of their desire
to be correct in their inferences, there might seem to be little else to
be investigated. Time only will tell. Before passing to the final
chapters relating to other matters, a few more experiments are related
in the briefest manner.


166. Prof. Sylvanus P. Thompson confirmed non-polarization, (_Phil.
So._, June 12, ’96, and _The Electr._, Lon., June 26, ’96.)

Dr. John Macintyre (_Nature_, June 24, ’96) carried on a long series of
experiments with tourmaline, and also arrived at the conclusion that
polarization of X-rays is practically impossible, § 97, at end.


[Illustration:

  FROM SCIAGRAPH BY PROF. GOODSPEED, SHOWING CURVATURE OF THE RADIUS,
    DUE TO ARRESTED DEVELOPMENT OF THE ULNA AT ITS DISTAL EPIPHYSIS. ONE
    BONE SHOWN THROUGH ANOTHER.
]


167. In the same paper Prof. Thompson showed conclusively that there is
a diffuse reflection of X-rays. § 81 and 103. A curious experiment
consisted in his obtaining dust figures, § 36. by the discharge of an
electrified body by X-rays. In another experiment he caused reflection
of the rays from the surface of sodium located in a vacuum. The amount
reflected was a minimum for normal incidence and increased at oblique
incidence.


168. Prof. Oliver J. Lodge, F.R.S., reported in _The Electr._, Lon.,
June 5, ’96, further detail experiments in the line set out in § 113. He
proved conclusively, as stated by the editorial in _The Electrician_,
that a positive charge has increasing effect upon the ray-emitting power
of the surface exposed to the cathodic radiation.


169. At Eton College, T. C. Porter (_Nature_, June 18, ’96) confirmed
the experiments of others by showing that the blackened face of the
thermopile connected with a very sensitive galvanometer was not
influenced in any manner by X-rays.


170. Prof. William F. Magie, of Princeton, N. J., made a careful
experiment in relation to diffraction. _Princeton College Bulletin_,
May, ’96. The experiment would certainly prove that if X-rays are due to
vibrations, the latter are of a different order from those occurring in
light rays, for the slits exhibited light diffraction very well, but
there was no evidence, by a widening of the image on the plate, that
X-rays had been diffracted in the slightest degree. § 110 and 110_a_.


171. Prof. Haga, of Groningen University, at the suggestion of Mr. J. W.
Giltay, (_Nature_, June 4, ’96,) made some very crucial tests, with
numerous precautions, in reference to the action of X-rays upon
selenium, and the results were so positive that they thought that a
practical application could be made by using selenium for detecting
X-rays, both qualitatively and quantitatively. In repeating the
experiments, it must be borne in mind that one half hour or so is
required for selenium to return to its former degree of ohmic resistance
after being struck by light or heat or X-rays.


              _Total number of_ § § _to this place, 199._


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




                              CHAPTER XIII

  A FEW TYPICAL APPLICATIONS OF X-RAYS IN ANATOMY, SURGERY, DIAGNOSIS,
                                  ETC.


                                -------

200. HOGARTH’S EXPERIMENT. NEEDLE LOCATED BY X-RAYS AND REMOVED. _The
Lancet_, Lon., Mar. 28, ’96.—Dr. Hogarth is the medical officer of the
general hospital, Nottingham. A young woman was suffering with a pain in
her hand near the metacarpal bone of the ring finger. A slight swelling
existed. Ten weeks before, a needle had entered the palm while washing
the floor. It had entered at the base of the fifth metacarpal bone.
Chloroform had been given and an incision made, but no needle found and
its presence doubted. A sciagraph was taken and the needle was
accurately located and the next day removed.


201. SAVARY’S EXPERIMENT. NEEDLE LOCATED BY SCIASCOPE AND REMOVED. _The
Lancet_, Mar. 28, ’96.—Dr. Savary located a needle by a sciascope
although efforts by all other methods had failed. A line was drawn
between two points intersecting the needle at right angles. About half
an inch below the surface of the skin of the wrist the blade of the
scalpel impinged upon the needle, which was removed without difficulty.


202. RENTON & SOMERVILLE’S EXPERIMENT. DIAGNOSIS. _The Lancet_, Lon.,
Apr. 4, ’96.—A writer for the _Lancet_ reported that Drs. Renton and
Somerville made a diagnosis with the assistance of the screen. In one,
the suspected case of unreduced dislocation of the phalanx, they saw
that the parts were in the proper position. He showed to medical men an
old fracture of the forearm where the fragments of the bones were
distinct as to the shadows.


[Illustration:

  FROM SCIAGRAPH OF “COLLES’ FRACTURE” IN THE RIGHT WRIST, BY A FALL ON
    THE SIDEWALK. § 207.
  By William J. Morton, M.D.
]


203. MILLER’S EXPERIMENTS. LOCATION OF BULLETS. _Elect. World_, Mar. 21,
’96.—Bullets were clearly located in the hands of two different men by
Prof. Dayton C. Miller, of the Case School of Applied Science. In one,
the bullet had been lodged for 14 years and had always been thought to
lie between the bones of the forearm, but two sciagraphs from different
directions located the ball at the base of the little finger. By means
of five sciagraphs from different directions, the ball in the other hand
was located at the base of the thumb.


204. INJURIES BY ACCIDENT AND MISCELLANEOUS CASES. _The Integral_,
Cleveland, Ohio, ’96.—Many fingers and hands were examined by Prof.
Miller that had been injured by planing machines, cog-wheels, base
balls, pistols, etc., and in each case the nature of the injuries was
determined. Several cases of fractured arms were studied—some through
splints and bandages. Some sciagraphs indicated that the ends of the
broken bones had not been placed in apposition. Subsequently, an
operation was performed to remedy the setting. In one case, he
sciagraphed the arm from which a piece of the ulna had been removed five
years previously. The necrosis had increased. Two sciagraphs at right
angles to each other clearly exhibited the nature of the disease. The
permanent set of the toes by wearing pointed shoes was clearly exhibited
(p. 30.) The figure on page 147 is the side view of a foot in a laced
shoe. The outlines of the bones can be traced, also the eyelets and the
pegs in the heel, while the uppers scarcely appear. In Fig. 1
(introduction) is shown a head, only the skull being clearly reproduced.
In the negative, the teeth appear and places whence the teeth have been
extracted, also the jaw bones, nasal cavities and the ragged junction of
the bones and cartilage. The varying thickness is represented in the
cut, at the temples and ears. Fig. 2 (introduction) shows that a broken
bone was badly set, the ends overlapping each other instead of meeting
end to end. A sciagraph of an elbow is shown on p. 161. The flesh is
scarcely visible. Fig. 3 (introduction) is a picture which reproduced
the mere indication of the spine and ribs. In the original negative the
collar bones, pelvis, clavicles, buckle of clothing and location of the
heart and stomach were faintly outlined. Fig. 4 (introduction) is a
representation of the knee of a boy 15 years old, in knickerbockers,
showing the buttons clearly, and dimly a 32 caliber bullet which is
imbedded in the end of the femur.


204_a_. NECROSIS. Mortification of the ulna is represented on p. 142.
Necrosis of the bone corresponds to gangrene of the soft parts; life is
extinct.


205. MORTON’S EXPERIMENT. DIAGNOSIS. _Elect. Eng._, N.Y., June 17, ’96.
Lect. before _Odontological So._, N.Y., Apr. 24, ’96; repeated in
_Dental Cosmos_, June, ’96.—Dr. William J. Morton, of New York, made
several important examinations of the human system by the use of X-rays.

In regard to application in dentistry, he stated:—“Each errant fang is
distinctly placed, however deeply imbedded within its alveolar socket;
teeth before their eruption stand forth in plain view; an unsuspected
exostosis is revealed; a pocket of necrosis, of suppuration, or of
tuberculosis is revealed in its exact outlines; the extent and area and
location of metallic fillings are sharply delineated, whether above or
below the alveolar line. Most interesting is the fact that the
pulp-chamber is beautifully outlined, and that erosions and enlargements
may be readily detected.”


206. The author saw one of Dr. Morton’s original photographed sciagraphs
of the thorax, 15 inches by 11 inches, not at all creditably reproduced
at page 161. In the original, to the surgeon’s eye: “The acromion and
coracoid processes of the shoulder blade are clearly shown in their
relations to the head of the humerus, or arm bone, and also the end of
the clavicle, or collar bone, is shown in its relations to the shoulder
joint. We have, in short, an inner inspection in a living person of this
rather complicated joint, the shoulder, and there can be no doubt that
in defined pictures of this nature even very slight deformities and
diseases would be detected. It is noticeable that the front portions of
the ribs are not shown, only the posterior portions lying nearest to the
sensitized plate appear; also the breastbone was sufficiently dense to
almost entirely obstruct the X-rays. A collar button at the back of the
neck is taken through the backbone. In some of my negatives the dark
outline of the heart and liver is shown as well as the outlines of
tumors in the brain; but this is evidently for purposes of demonstrating
the location of organs, an over-exposure, and does not, therefore,
indicate the outlines of the heart.”

The time of exposure was reduced by the use of a fluorescent screen in
conjunction with the photographic plate.


207. A woman was troubled with a stiffened wrist. Dr. Morton took a
single sciagraph of both wrists side by side as shown at page 174, (the
photographic print being presented for this book by E. B. Meyrowitz, 104
East 23d Street, N.Y.) The injured wrist in the picture exhibited the
Colles’ Fracture—the ulna and radius bones being telescoped into their
fractured ends by a fall upon the sidewalk a year before. By knowing the
cause, the manner of cure became evident, and, accordingly, the patient
is expected to bend the wrist backward and forward and laterally several
times a day.


[Illustration:

  From sciagraph of club foot of child by Prof. Goodspeed. Copyright,
    ’96, by William Beverley Harison, Pub. of X-ray pictures, New York.
    This linograph (woodcut), engraved and donated by Stephen J. Cox,
    Downing Building, 108 Fulton St., New York, affords an exact
    likeness of the sciagraph,—well-nigh impossible by an untouched
    half-tone.
]


Dr. Morton, in a lecture before the Medical Society of the County of New
York, to be printed in the _Medical Record_, related that another
promising field of research and application is in the detection of
calcareous infiltrations involving, for instance, the arteries, or
occurring in the lungs and other tissues. Calculi in kidneys, in the
bladder, in the salivary ducts have already been successfully located.
The stages of ossification, and the epiphyseal relations of the osseous
structure in children may be pictured as is demonstrated in the picture
of the entire skeleton of an infant five months of age. The sciagraph
shows plainly that it will be possible to detect spinal diseases, either
in children or in adults. (_Not reproduced._)


208. NORTON’S EXPERIMENT. DIAGNOSIS. _Elect. World_, N.Y., May 23,
’96.—In conjunction with Dr. Francis H. Williams, Dr. Norton examined
several patients from the city hospital to determine how an X-ray
diagnosis would agree with that previously made by the hospital staff.
(See also § 142, at end.) The outline of an enlarged liver, 7 inches in
diameter, was easily distinguished, the two outlines, one by percussion
and one by X-rays, agreeing better in favor of the latter by 1/2 inch.
An enlarged spleen was perfectly outlined. The tuberculosis of one lung
caused it to be more opaque than the sound lung. It was found necessary
to take into account the seams of clothing, buttons, buckles, etc. A
bullet was found exactly under the spot which they marked as being over
the bullet. A foreign metallic body can be easily detected in the
œsophagus, because the latter is quite transparent. They could see the
shadows of the cartilaginous rings in the trachea, glottis, and
epiglottis. Younger persons, up to 10 years of age, are more transparent
than older.


209. LANNELONGUE, BARTHELEMY AND OUDIN’S EXPERIMENTS. OSTEOMYELITIS
DISTINGUISHED FROM PERIOSTITIS. _Elec. Rev._, Lon., Feb. 14, ’96.—In a
sciagraph of a person diseased with the former, the surface of the bone
was proved to be intact, while the internal parts were destroyed. In the
latter disease the changes proceed from the surface to the interior.

The art of sciagraphy, more nearly, as every month passes, becomes
developed by means of improved apparatus, screens, photographic plates
and other elements which at present are only dimly predicted.
Nevertheless, how can a better sciagraph of bones, showing their
thickness and porosity, be desired than that reproduced on page 177, and
taken by Prof. Arthur W. Goodspeed, and representing a club foot of a
child? In the race to excel in this new art, no one, to the author’s
knowledge, has surpassed Prof. Goodspeed, of the University of Penn.,
considered jointly from the standpoints of _priority_, _superiority_,
_quantity_ and _variety_. Dr. Keen, L.L.D., Professor in the Jefferson
Medical College, of Philadelphia, stated (_Inter. Nat. Med. Mag._, June,
’96) that Prof. Goodspeed “has far eclipsed all others in these most
beautifully clear sciagraphs.”


210. A book could be filled with the numerous cases of diagnosis by
X-rays showing the utility. In closing this chapter, let it suffice to
mention some of the sources of literature relating to this subject
directly or indirectly: location of shot (by Dr. Ashhurst, Phila.) in
lady’s wrist, not located by other means. Dr. Packard’s case of
acromegaly; Dr. Muller’s (Germantown) location of needle in boy’s foot;
cause of pain not before known; needle subsequently removed; a perfect
thorax, or trunk, by Prof. Arthur W. Goodspeed, University of
Pennsylvania; Thomas G. Morton’s (M. D. Pres. Acad. Surg., Phila.)
application to painful affection of the foot, called metatarsaligia. All
of the above noticed in _Inter. Med. Mag._, June, 1896. Case of a burned
hand with anchylosis of the fingers, by W. W. Keen, M.D., L.L.D.
Bacteria not killed by X-rays. Normal and abnormal phalanx
distinguished. Fracture and dislocation sometimes differentiated by
X-rays. _Amer. Jour. Med. Sci._, Mar., ’96.


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




                              CHAPTER XIV

                      THEORETICAL CONSIDERATIONS.


                                -------

Before attempting to discuss the facts now known in regard to the
Roentgen phenomena, it is well to review briefly the known ways in which
radiant energy may be transmitted.

By radiant energy is, of course, meant energy proceeding outward from a
source and producing effects at some distant point. There are two well
understood ways in which energy may be transmitted,—first, by an actual
transfer to the distant point of matter to which the energy has been
imparted from the source, as in the flight of a common ball, a bullet,
or a charge of shot. In this mode of transmission, it is evident that
the flying particles, assuming that they are subject to no forces on the
way, will move in straight lines from the source to the distant point.
They constitute real rays, diverging from the source; an obstacle in
their path, would, if the radiations proceeded from a point, cast a
shadow with sharply defined edges.

Second,—by a transfer of the energy from part to part of an intervening
medium, each part as it receives the energy, transmitting it at once to
the parts around it, no part undergoing more than a slight displacement
from its normal position. This mode of transmission constitutes wave
motion. The source imparts its energy to the particles of the medium
near it. Each of those particles transfers its energy to the particles
all around it. Each of these particles in turn transfers its energy to
the particles around it, and so on through the medium. It is plain that
there are here no such things as genuine rays. As the energy is
transferred from particle to particle, each in turn becomes a centre of
disturbance transmitting its motion in all directions. It is only
because the movements transmitted from different points annul one
another except along certain lines, that we have apparent straight lines
of transmission, and, therefore, fairly sharp shadows. But shadows
produced by wave transmissions are never absolutely sharp. The wave
movement is always propagated to some extent within the boundary of the
geometrical shadow, less as the wave lengths are shorter. With sound
waves whose lengths are measured in inches or feet, the penetration into
the shadow is considerable. With light waves 1/37000 to 1/70000 of an
inch in length, the penetration into the shadow is very small and
requires specially arranged apparatus to show that it exists.

This penetration into the geometrical shadow is characteristic of energy
propagated by wave motion, and if the fact of such penetration can be
demonstrated, it is conclusive proof of propagation by waves.

Another characteristic of wave motion is found in the phenomena of
_interference_. This is the mutual effect of two wave systems, which,
when meeting at a given point, may strengthen or annul each other
according to the conditions under which they meet. Either of those
characteristics should enable us to distinguish between propagation by
wave motion and by projected particles. But when wave lengths are very
short and radiations feeble, the tests are not easy to apply.

Again, a wave is in general propagated with different velocities in
different media. This causes a deflection or deformation of the wave as
it passes from one medium into another, and results in _refraction_, as
in the cases of light and sound. Absence of refraction would be strong
though not conclusive evidence against a wave theory of propagation.

In wave propagation, each particle of the medium suffers a small
displacement from its equilibrium position and performs a periodic
motion about that position. This displacement may be in the line of
propagation—longitudinal vibration—or it may be in a plane at right
angles to that line—transverse vibration. All the phenomena mentioned
above, diffraction, interference, refraction, and also reflection,
belong equally to either mode of wave propagation. Other phenomena must
be made use of to distinguish between these.

When the vibrations are transverse they may all be brought into one
plane through the line of propagation. They may be _polarized_, when the
ray will present different phenomena upon different sides. When the
vibrations are longitudinal, no such phenomena can be produced.
Polarization, then, serves to distinguish between longitudinal and
transverse vibrations.

Now let us consider briefly the Roentgen ray phenomena that bear upon
the question of the nature of the propagation.


[Illustration:

  FROM SCIAGRAPH OF NORMAL ELBOW-JOINT; STRAIGHT, IN POSITION OF
    SUPINATION.
  By A. W. Goodspeed. _Phot. Times_, July, ’96.
  Copyright, 1896, by William Beverley Harrison, Publisher of “X-ray”
    Pictures, New York.
]


It seems to be settled beyond question that the origin of the Roentgen
rays is the fluorescent spot in the discharge tube. § § 107, 108, 111.
The evidence seems overwhelming that within the tube, the phenomena are
the result of streams of electrified particles of the residual matter,
shot off from the cathode in straight lines, perpendicular to its
surface. § 57. This was Crookes’ original theory, § 53, _near centre_,
and it seems to have stood well the test of scientific criticism. These
flying particles falling upon anything in their path, give rise to
X-rays. It is preferable, but not essential, that the bombarded surface
should be connected electrically with the anode. § § 113, and 116. The
best results are obtained by using a concave cathode, and placing at its
centre the surface which is to receive the bombardment, thereby
concentrating the effect upon a small area.

Nearly all experimenters agree in locating the origin of the X-rays at
this bombarded spot. The energy here undergoes a transformation, and the
X-rays represent one of the forms of energy developed.

What are the characteristics of this particular form of radiant energy?

It causes certain salts to fluoresce, § § 66, 84, and 132, and it
affects the photographic plate. § § 70 and 84. In these respects, it is
like the short wave length radiations from a luminous source. It is,
however, totally unlike these in its power of penetrating numerous
substances entirely opaque to light, such as wood, paper, hard rubber,
flesh, etc. In passing through hard rubber and some other opaque
insulators, X-rays are like the long wave length radiations from heated
bodies, but X-rays penetrate many substances that are opaque to these
long wave length radiations, and they are especially distinguished from
all forms of radiant energy previously recognized, in their relative
penetrating power for flesh and bones which makes it possible to obtain
the remarkable shadow pictures which have become within three or four
months, so familiar to all the world.

But these phenomena, although they serve to distinguish the X-rays from
all other forms of radiant energy, do not furnish any clew to the nature
of the X-rays themselves.

In attempting to formulate a theory of X-rays, the idea that first
naturally presents itself is that they are due to some form of wave
motion.


[Illustration:

  FROM SCIAGRAPH OF KNEE-JOINT, STRAIGHT, SIDE VIEW, SHOWING PATELLA, OR
    KNEE-CAP.
  By Prof. Goodspeed. _Phot. Times_, July, ’96.
]


The characteristics of wave motion are diffraction and interference
phenomena. So far, no positive evidence of diffraction, § 110, nor
interference, § 89, have been recognized, although experiments, have
been tried that would have shown plainly, diffraction phenomena, had
light been used in place of the Roentgen radiations. § 170. We must,
therefore, conclude, either that the Roentgen radiations in the
experiments were too feeble to produce a record of the diffraction
effects, or, that they are not due to wave motion at all, unless of a
wave length very small even when compared with waves of light. The
absence of refraction is also opposed to any wave theory of the Roentgen
radiations, for it is difficult to believe that waves of any kind could
travel with the same velocity through all media, which they must do if
they suffer no deviation. § 86.

The next supposition naturally is, that the phenomena are due to streams
of particles. It has been suggested that the rays may be streams of
_material_ particles, but this theory cannot be maintained in view of
the fact that the rays proceed, without hindrance, through the highest
vacuum. § § 72_b_ and 133, _near end_. Neither is it consistent with the
high velocity of propagation. Molecules of gas could not be propelled
_through air_ with any such velocity or to any such distance as X-rays
are propagated. Tesla has claimed § 139, that the residual gases are
driven out through the glass of the vacuum bulb by the high potential
that he employs. This has not been confirmed by other experimenters. It
has been observed that the vacuum may be greatly improved by working the
bulb, § 121, that is, sending the discharge through it, but
experimenters generally have found that heating the bulb impairs the
vacuum and restores the original condition. The gases, were, therefore,
occluded during the electrical discharge, to be again set free by
heating the bulb. § 139_b_. The rays may be ether streams, perhaps in
the form of moving vortices, but of such streams we have no independent
knowledge, and can only determine by mathematical analysis, what their
characteristics should be. They would not suffer refraction, and would
not produce interference nor diffraction phenomena. Whether they would
_do_ what the X-rays do, go through the flesh and not through bone,
through wood and not through metal, excite fluorescence, or affect the
photographic plate, cannot be said. There is evidence that there are at
least two kinds of X-rays, § 152, differing in penetrating power, though
perhaps not differing in other respects.


[Illustration:

  FROM SCIAGRAPH OF NORMAL KNEE-JOINT, FLEXED.
  _Phot. Times_, July, 96.
  Copyright, 1896, by William Beverley Harison, Publisher of “X-ray”
    Pictures, New York.
]


X-rays have their origin only in electrical discharges in high vacua.
They are absent from sun-light and from light of the electric arc, and
other sources of artificial illumination, § 136. Proceeding from the
bombarded spot, they are not deflected by a magnet, except in an
evacuated observing tube, as proved by Lenard, § 72_a_, and show no
evidence of carrying an electric charge like cathode rays, § 61_b_, p.
47. On the contrary, they will discharge either a negatively or
positively charged body in their path. The evidence seems conclusive
(Chap. VIII.) that the ultra-violet rays from an illuminating source
also discharge charged conductors. In this respect, therefore, there is
a similarity between the X-rays and ultra-violet light.

The action of the waves of light upon a cell formed of selenium lowers
the resistance of the latter and herein is circumstantial evidence at
least, concerning the similarity of the properties of X-rays and light,
because the former are also found to increase the conducting power of
selenium. § 171.

The experiments of Roentgen, § 90, seem to show that the discharging
effect of X-rays is due to the air through which the rays have passed.

It is certain that the discharge of electrified bodies by light occurs
more generally for negatively than for positively charged bodies, § §
99_B_, 99_I_, and 99_S_, that it depends upon the nature, § 97_b_, and
density, § 97_a_, of the gas surrounding the body, and also upon the
material of the charged body itself. § 98. The discharge would,
therefore, seem to be connected with a chemical action, § 153, _near
end_, which is promoted by the rays. This seems all the more probable,
since it was found, § 98, that the more electro-positive the metal, the
longer the wave length that would influence the discharge. In this
connection, it is well to note that Tesla found, § 146_a_, that in their
power of reflecting (or diffusing X-rays), the different metals stand in
the same order as in the electric contact series in air, the most
electro-positive being the best reflectors. It would be interesting to
know whether connecting the reflecting plate to earth, would, in any
way, vary its reflecting power.

The X-rays seem to discharge some bodies, when positively charged, and
other bodies when negatively charged. They will also give to some bodies
a positive, and to others a negative charge (§ 90_c_). Is the order here
also that of the electrical contact series in air? Are not all the
phenomena of electrical charge and discharge, of reflection or
diffusion, and of X-rays, connected with chemical action, as the
apparent difference of potential, due to contact, undoubtedly is? § 153.

An experiment by La Fay (§ 139_a_) seems to show that X-rays, in air,
after passing through a charged silver leaf, acquire the property of
being deflected by a magnet, as are the cathode rays inside the
generating or exhausted observing tube, § 72_a_. If this is confirmed,
it would go far to support the theory that these rays are streams of
_something_.


[Illustration:

  FROM SCIAGRAPH OF HEAD BY PROF. GOODSPEED. NASAL BONES APPEAR LIKE
    EYELASHES.
  _Inter. Med. Mag._, June, ’96.
  The cervical vertebræ are distinguishable in the original, but barely
    so in the half-tone. Fillings are located.
]


The burden of proof, up to the present, seems to be against any wave
theory of the X-rays, for, although they are like the ultra-violet rays
in producing fluorescence and in affecting the photographic plate, and
have some points of similarity to these rays in their effect upon
charged bodies, the X-rays are totally unlike the ultra-violet, in
respect to diffraction and interference phenomena. In fact, the absence
of such phenomena, if they are really absent, is conclusive proof that
the X-rays cannot be wave motions, unless of a wave length extremely
short even as compared to waves of light.

Since writing the above, I have seen an account of experiments in
relation to diffraction of X-rays, presented to the French Academy by
MM. L. Calmette and G. T. Huillier, in which the authors claim to have
obtained evidence that diffraction occurs. The following translation of
MM. Calmette and Huillier’s paper is taken from the _Electrical
Engineer_, N.Y., for July 22, 1896.

“We have the honor of submitting to the Academy some photographic proofs
obtained with the Röntgen rays by means of the following arrangement.”

“Very near the Crookes tube there is a screen “E” (_diagram omitted_),
of brass, perforated by a slit, the width of which has rarely reached a
half mm. A second metal screen, E´, is formed of a plate provided with
two slits or pierced with a window in which is fixed a metal rod of 1
mm. in diameter. This screen is placed at the distance, _a_, behind the
former. Lastly, a photographic plate, enfolded in two leaves of black
paper, is placed at the distance, _b_, behind the second screen, E´.”

“The following table indicates, for each proof, what is the screen E´
used, and the value of _a_ and _b_ + _a_:


                                  E´.

                 No.                       _a_   _b_ +
                                           Cm.   _a_
                                                 Cm.

                  1.  Rod of 1 mm. in      5     19.5
                        diameter

                  3.  Rod of 1 mm. in      5.5   20
                        diameter

                  5.  Rod of 1 mm. in      8.9   30
                        diameter

                  7.  Two narrow slits,    ?     ?
                        separated by a
                        cylindrical rod of
                        1 mm. in diameter


“On the proofs 1, 3, 5 the shadow thrown by the metallic rod is bordered
on each side by a light band which shows a maximum of intensity. Within
this shade we observe a zone less dark, which seems to indicate that the
Röntgen rays penetrate into the geometrical shadow. Lastly, in proofs 3
and 5 we see, in like manner, a maximum of intensity along the margins
of the window in which the rod is placed.”

“In the proof No. 7 we perceive, in the middle of the two white bands, a
fine dark ray, while in the shadow of the rod which separates the two
slits there is seen a light ray.”

“If we compare these results with those obtained with light in the same
conditions, the slit being relatively wide and the intensity weak, it
seems difficult not to ascribe them to the diffraction of the Röntgen
rays.”

“The proofs obtained in these experiments—which we propose to
continue—are not yet so distinct that we can measure the wave length
with any precision. But we are still led to believe that this wave
length is greater than that of the luminous rays.—_Comptes Rendus._” Of
course, if diffraction phenomena can be demonstrated, the question as to
the radiations being wave propagations, is settled, though the question
whether the vibrations are longitudinal or transverse, is still open.

Before accepting any stream or vortex motion theory, we need to know
more about the X-ray phenomena, and more about stream and vortex motion.


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




 ● Transcriber’s Notes:
    ○ Since this is a collection of articles by different scientists,
      there may be differences in spelling and usage.
    ○ There is no experiment 64. There last experiment on page 51 is
      number 63_b_, and the first experiment page 52 is 65. (A note
      attached to the 63_b_ table of contents entry says that there is
      no experiment 64.)
    ○ The missing entries in the Table of Contents for experiments
      128_a_ and 149_a_ were added.
    ○ There are two experiments labeled 61_b_, page 46 (Thomson’s
      Experiment) and 47 (Perrin’s Experiment). The instance on page 47
      was relabeled 61_c_.
    ○ There are two experiments numbered 159 in the Table of Contents.
      The first follows entry 110_a_ and the other is in order, after
      experiment 158. The first instance was changed to 159a.
    ○ Missing or obscured punctuation was silently corrected.
    ○ Typographical errors were silently corrected.
    ○ Inconsistent spelling and hyphenation were made consistent only
      when a predominant form was found in this book.
    ○ Text that was in italics is enclosed by underscores (_italics_);
      text that was bold by “equal” signs (=bold=).
    ○ The use of a caret (^) before a letter, or letters, shows that the
      following letter or letters was intended to be a superscript, as
      in S^t Bartholomew or 10^{th} Century.
    ○ Superscripts are used to indicate numbers raised to a power. In
      this plain text document, they are represented by characters like
      this: “P^3” or “10^{18}”, _i.e._ P cubed or 10 to the 18th power.
    ○ Variables in formulæ sometimes use subscripts, which look like
      this: “A_{0}”. This would be read “A sub 0”.