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) The cover image was created by the transcriber and is placed in the public domain. ROENTGEN RAYS AND PHENOMENA OF THE ANODE AND CATHODE. 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. § 72a. 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 i ii iii 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 (§ § 63a, 84, 99, 101a, 103a, 112a, 124a, 128, at end, 139a, 154, 155, 156, 157, 158, and 159); to Mr. N. D. C. Hodges, formerly editor and proprietor of Science, who obtained some pertinent accounts, (§ 97a, 97b, 99A, B, C, D, to 99T, 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. iv v CONTENTS. CHAPTER I. § 1. Secondary Current by Induction. No Increased E. M. F. Faraday 2. Electric Spark and Increased E. M. F. by Induced Current. Page 3. Spark in Secondary Increased by Condenser in Primary. Fizeau 4. Atmosphere around an Incandescent Live Wire. Vincintini 5. Magnetizing Radiations from an Electric Spark. Henry 6. Arcing Metals at Low Voltage. Faraday 7. Non-arcing Metals at High Voltage. Practical Application. Wurts 8. Duration of Spark Measured. Wheatstone 8a. Discharge—Intermittent, Constant, and Oscillatory—by Variation of Resistance. Feddersen 9. Musical Note by Discharge with Small Ball Electrodes. Invisible Discharge. Faraday 9a. Pitch of Sound Changed by Approach of Conductor Connected to Earth. Faraday and Mayer 10. Brush Discharge. Color. Striæ. Nitrogen Best Transmitter of a Spark, and its Practical Bearing in Atmospheric Lightning. Cathode Brushes in Different Gases. Faraday 11. Glow by Discharge. Glow Changed to Spark. Motion of Air. Apparent Continuous Discharge during Glow. Faraday 12. Spark. Solids Perforated. Lullin 13. Spark. Glass Perforated. Holes Close Together. Practical Application for Porous Glass. Fage 14 and 14a. Spark. Penetrating Power. Conducting Power of Gas. Relation of E. M. F. to Pressure of Gases. Discharge through Hydrogen Vacuum Continued with Less Current than that Required to Start it. Knochenhaurer, Boltzmann, Thomson (Kelvin), Maxwell, Varley, Harris, and Masson 15. Dust Particles or Rust on the Electrodes Hasten Discharge. Gordon 16. Where the Distance is Greater, the Dielectric Strength is Smaller, Both Distances Being Minute. Thomson (Kelvin) 17. Discharge through Gases under Very High Pressures. Increased Dielectric Strength. Cailletet 18. Discharges in Different Chemical Gases Variably Resisted. Faraday 19. Gas as a Conductor. Molecule for Molecule, its Conductivity Greater than that for Gases. Thomson, J. J. 20. Relation of Light to Electricity. The Square Root of the Dielectric Capacity Equal to the Refractive Index. Boltzmann, Gibson, Barclay, Hopkinson, and Gladstone 21. Hermetically Sealed Discharge Tubes with Platinum Leading-in Wires. Plücker and Geissler 22. Luminosity of Discharge Tubes Produced by Rubbing. Increased by Low Temperature. Geissler 23. Different Vacua Needed for Luminosity by Friction and by Discharge. Alvergniat 24. Phenomena of Discharge around the Edges of an Insulating Sheet. Steinmetz 25. Highest Possible Vacuum Considered as a Non-conductor. Morgan 26. Constant Potential at the Terminals of a Discharge Tube. De La Rue and Müller 26a. Polarity of Discharge-tube Terminals in Secondary of Ruhmkorff Coil. Mathematical Deductions. Klingenberg 27. Pressure in Discharge Tube Produced by a Spark. Kinnersley, Harris, and Riess CHAPTER II. vi vii 28. Actions of Magnetism upon the Arc and Flame. Davy, Bancalari, and Quet 29. Rotation of Luminous Discharge by a Magnet. Application in Explaining Aurora Borealis. De La Rive 30. Action of Magnet on the Cathode Light. Relations Different according to the Position Relatively to the Magnetic Lines of Force. Plücker and Hittorf 31. Discharge Retarded Across, and Accelerated Along, the Lines of Magnetic Force. Thomson, J. J. 32. Resistance of Luminosity of the Discharge Afforded by a Thin Diaphragm. Thomson, J. J. 33. Forcing Effect of the Striæ at a Perforated Diaphragm. Solomons CHAPTER III. 34. Electric Images. Riess 35. Electrographs on Photographic Plate by Discharge. Sanford and McKay 36. Positive and Negative Dust Pictures upon Lines Drawn by Electrodes. Lichtenberg 36a. Photo-electric Dust Figures. Hammer 36b. Dust Portrait. Hammer 37. Electrical Images by Discharge Developed by Condensed Moisture. Karsten 37a. Magnetographs. McKay 38. Bas-relief Facsimiles by Electric Discharge. Piltchikoff 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. Striæ. Least E. M. F. Required. Gassiot 42. Current Interrupted Inside of Discharge Tube instead of Outside. Poggendorff 43. Source of Striæ at the Anode. Color Changed by Change of Current. De La Rue and Müller 44. Dark Bands by Small Discharges Disappear on Increase of Current, and Appear Again by Further Increase. Solomons 45. Motion of Striæ. Method of Obtaining Motion when Desired and of Stopping the Same. Spottiswoode 46. Motion of Striæ Checked at the Cathode. Tube, 50 ft. Long. The Anode the Starting-point. Thomson, J. J. 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. Telephone Used to Prove Intermissions. Spottiswoode and Moulton 49a. Cause of Sensitive State Detected by Telephone. Spottiswoode and Moulton 50. Sensitive State Illustrated by a Flexible Conductor within the Discharge Tube. Reitlinger and Urbanitzky 51. System of Operating Discharge Tubes. Excessively High Potential and Enormous Frequency. Tesla 52. Discharge-tube Phenomena by Self-induced Currents. Moore CHAPTER V. 53. Dark Space around the Cathode. Crookes 54. Relation of Vacuum to Phosphorescence. Crookes 55. Phosphorescence of Objects within Discharge Tube. Crookes 56. Darkness and Luminosity in the Arms of a V Tube. Crookes 57. Cathode Rays Rectilinear within the Discharge Tube. Crookes 58. Shadow Cast within the Discharge Tube. Crookes 58a. Mechanical Force of Cathode Rays. Wheel Caused to Rotate. Crookes viii 59. Action of Magnet upon Cathode Rays in Discharge Tube. Crookes 60. Mutual Repulsion of Cathode Rays in Discharge Tube. Crookes 61. Heat of Phosphorescent Spot. Crookes 61a. Theoretical Considerations of Thomson (Kelvin). 61b, page 46. Velocity of Cathode Rays. Thomson, J. J. 61b, page 47. Cathode Rays Charged with Negative Electricity. Perrin 61c, Zeugen’s Photograph of Mt. Blanc Not Due to Cathode Rays. 62. Phosphorescence of Particular Chemicals by Cathode Rays. Goldstein 63. Spectrum of Post-phosphorescence of Discharge Tube Compared with that of Red-hot Metals. Kirn 63a. Chemical Action on Photographic Plate by Cathode Rays Inside of Discharge Tube. De Metz 63b. The Passage of Cathode Rays through Thin Metal Plates within the Discharge Tube (no. § 64). Hertz CHAPTER VI § 65, top of page 53. Cathode Rays Outside of the Discharge Tube whose Exit is an Aluminum Window. A Glow Outside of the Window. Lenard 65., end of page 53. Properties of Cathode Rays in Open Air. Lenard 66. Phosphorescence by Cathode Rays Outside of the Discharge Tube. Lenard 66a. Transmission Tested by Phosphorescence. 67. The Aluminum Window a Diffuser of Cathode Rays. Lenard 68. Transmission of External Cathode Rays through Aluminum and Thinly Blown Glass. Lenard 69. Propagation of External Cathode Rays. Turbidity of Air. Lenard 70. Photographic Action by External Cathode 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. Lenard 71. External Cathode Rays and the Electric Spark Distinguished. Aluminum Window Not a Secondary Cathode. Lenard 72. Cathode Rays Propagated, but Not Generated, in the Highest Possible Vacuum. Air Less Turbid when Rarefied. Lenard 72a. Cathode Rays, while Traversing the Exhausted Observing Tube, Deflected by a Magnet. No Turbidity in a Very High Vacuum. Lenard 72b. An Observing Tube for Receiving the Rays and Adapted to be Exhausted. Lenard 73. Phenomena of Cathode Rays in an Observing Tube Containing Successively Different Gases at Different Pressures. Phosphorescent Screen Employed for Making the Test. Lenard 74. Cause of the Glow Outside of the 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. Lenard 75. External Cathode Rays of Different Kinds Variably Diffused. Theoretical Observations. Lenard 76. Law of Propagation of External Cathode Rays. Lenard 77. Charged Bodies Discharged by External Cathode Rays. Discharge at Greater Distances than Phosphorescence. Not Certain as to the Discharge Being Directly Due to Intermediate Air. Lenard ix 78. Source, Propagation, and Direction of Cathode Rays. General Conclusions. De Kowalskie CHAPTER VII. 79. X-rays Uninfluenced by a Magnet. Source of X-rays Determined by Magnetic Transposition of Phosphorescent Spot. Roentgen 80. Source of X-rays may be at Points within the Vacuum Space. Different Materials Radiate Different Quantities of X-rays. Roentgen 81. Reflection of X-rays. Roentgen 82. Examples of Penetrating Power of X-rays. Roentgen 83. Permeability of Solids to X-rays Increases Much More Rapidly than the Thickness Decreases. Roentgen 84. X-rays Characterized. Fluorescence and Chemical Action. Roentgen 85. Non-refraction of X-rays Determined by Opaque and Other Prisms. Refraction, if Any, Exceedingly Slight. Roentgen 86. Velocity of X-rays Inferred to be the Same in All Bodies. Roentgen 87. Non-double Refraction Proved by Iceland Spar and Other Materials. Roentgen and Mayer 88. Rectilinear Propagation of X-rays Indicated by Pin-hole Camera and Sharpness of Sciagraphs. Roentgen 89. Interference Uncertain Because X-rays Tested were Weak. Roentgen 90. Electrified Bodies, whether Conductors or Insulators, or Positive or Negative, Discharged by X-rays. Hydrogen, etc., as the Intermediate Agency. Roentgen 90a. Application of Principle of Discharge by X-rays. Roentgen 90A, b, c, d. Supplementary Experiments on Charge and Discharge by X-rays. Minchin, Righi, Benoist, Hurmuzescu, and Borgmann 91. Focus Tube. Roentgen, Shallenberger, et al. 91a. Tribute to the Tesla Apparatus. Roentgen 92. X-rays and Longitudinal Vibrations. Roentgen 93. Longitudinal Waves in Luminiferous Ether by Electrical Means Early Predicted by Thomson (Kelvin) 94. Theory as to X-rays Being of a Different Order of Magnitude from those so far Known. Schuster 95. Longitudinal Waves Exist in a Medium Containing Charged Ions. Theoretical. Thomson, J. J. 96. Practical Application of X-rays Foreshadowed. Boltzmann 97. The Sciascope. Magie, Salvioni, et al. CHAPTER VIII. 97a. Electrified Bodies Discharged by Light of a Spark, and the Establishment of a Radical Discovery. Hertz 97b. Above Results Confirmed and More Specific Tests. Wiedemann and Ebert 98. Negatively Charged Bodies Discharged by Light. Discharge from Earth’s Surface Explained by Inference and Experiment. Elster and Geitel 99. Relation between Light and Electricity. Cathode of Discharge Tube Acted upon by Polarized Light and Apparently Made a Conductor Because of the Discharging Effect. Elster and Geitel 99A to 99T. Briefs Regarding Action between Electric Charge and Light. Schuster, Righi, Stolstow, Branly, Borgmann, Mebius, et al. CHAPTER IX. 100. Stereoscopic Sciagraphs. Thomson, E. x 101. Obtaining Manifold Sciagraphs 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. Thomson, E. 101a. Sciagraph Produced through 150 Sheets of Photographic Paper. Lumière. 102. Discharge Tube Adapted for Both Unidirectional and Alternating Currents. Thomson, E., and Swinton 103. X-rays. Opalescence and Diffusion. Thomson, E., Pupin, and Lafay 103a. Diffusion and Reflection in Relation to Polish. Imbert, et al. 104. Fluorometer. Fluorescing Power of Different Discharge Tubes Compared. Thomson, E. 105. Modified Sciascope for Locating the Source and Direction of X-rays. Phosphorescence Not an Essential Accompaniment in Production of X-rays. Thomson, E. 106. X-rays from Discharge Tube Excited by Wimshurst Machine. Full Details Given of the Electrical Features. Rice, Pupin, and Morton 107. Source of X-rays Determined by Projection through a Small Hole upon Fluorescent Screen Adjustable to Different Positions. Rice 107a. Use of Stops in Sciagraphy. Leeds and Stokes 107b. X-rays from Two Phosphorescent Spots. Macfarlane, Klink, Webb, Clark, Jones, and Morton 108. Source of X-rays Determined by Shadows of Short Tubes. Stine 109. Instructions Concerning Electrical Apparatus for Generating X-rays. Stine 110. Apparent Diffraction Really Due to Penumbral Shadows. Stine 110a. Non-diffraction. Perrin 159a. Non-Refraction 111. Source of X-rays Tested by Interceptance of Assumed Rectilinear Rays from the Cathode. Scribner and M’Berty 112. Source of X-rays on the Inner Surface of the Glass Tube Determined by Pin-hole Images. Scribner and M’Berty, Perrin 112a. Anode Thought to be the Source. Cause of Error Suggested. De Heen 113. Pin-hole Pictures by X-rays Compared 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. Lodge 114. Valuable Points Concerning Electrical Apparatus Employed. Lodge 115. X-rays Equally Strong during Fatigue of Glass by Phosphorescence. Lodge 116. Area Struck by Cathode Rays Only an Efficient Source when Positively Electrified. Rowland, Carmichael, and Briggs 117. Transposition of Phosphorescent Spot and of Cathode Rays without a Magnet. Salvioni, Elster, Geitel, and Tesla 117a. 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 Thick. Edison 120. To Prevent Puncture of Discharge Tube by Spark. Edison 121. Variation of Vacuum by Discharge and by Rest. Edison 122. External Electrodes Cause Discharge through a Higher Vacuum than Internal. Edison 123. Profuse Invisible Deposit from Aluminum Cathode. Edison and Miller 124. Possible Application of X-rays. Fluorescent Lamp. Edison and Ferranti 124a. Greater (?) Emission of X-rays by Easily Phosphorescent Materials. Piltchikoff 125. Electrodes of Carborundum. Edison 126. Chemical Decomposition of the Glass of the Discharge Tube Detected by the Spectroscope. Edison 127. Sciagraphs. Duration of Exposure Dependent upon Distances. Edison xi xii