------------------------------------------------------------------------
[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.
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