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diff --git a/old/63422-0.txt b/old/63422-0.txt deleted file mode 100644 index ffd65f3..0000000 --- a/old/63422-0.txt +++ /dev/null @@ -1,8533 +0,0 @@ -The Project Gutenberg EBook of Roentgen Rays and Phenomena of the Anode -and Cathode., by Edward P. Thompson - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Roentgen Rays and Phenomena of the Anode and Cathode. - -Author: Edward P. Thompson - -Contributor: William A. Anthony - -Release Date: October 9, 2020 [EBook #63422] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK ROENTGEN RAYS AND PHENOMENA *** - - - - -Produced by deaurider, Barry Abrahamsen, and the Online -Distributed Proofreading Team at https://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - ------------------------------------------------------------------------- - - -[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}”. 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