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. [§ 66a]. The same was true with reference to a pine board 2 or 3 cm. thick. They passed also through aluminum 15 mm. thick. [63b]. Glass was comparatively opaque, [§ 66a], 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. [§ 63b].
THICKNESS. | RELATIVE THICKNESS. | DENSITY. | |
|---|---|---|---|
| Platinum | .018 mm. | 1 | 21.5 |
| Lead | .050 mm. | 3 | 11.3 |
| Zinc | .100 mm. | 6 | 7.1 |
| Aluminum | 3.500 mm. | 200 | 2.6 |
He concluded from these data that the permeability increased much more rapidly than the thickness decreased.
84. Fluorescence and Chemical Action. [§ 70] and [63a].—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.
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.