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.