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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 90a) that feeble X-rays were emitted after the current was cut off from the discharge tube. (From trans. by Mr. Pignolet.)

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.

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.”

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.

124a. 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.

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.

128a. 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.

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.

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.

134a. 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 72b 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.

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.