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].
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.