99_T_. BRANLY’S EXPERIMENT. LOSS OF ELECTRIC CHARGE IN DIFFUSE LIGHT AND IN THE DARK. _C. R._, CXVI., pp. 741 to 744. ’93.—A polished aluminum sheet was attached to the terminal of an electroscope properly surrounded by a metal screen. After a few days, the plate acted like any other metal plate polished or unpolished; it lost its charge very slowly, positive or negative alike, independently of the illumination. If it is then again polished, as for example, with emery paper and turpentine, it loses its charge rapidly in diffused light, which has passed through a pane of window glass, for example. Therefore, the ultra-violet rays are not alone effective, although most effective. The longer the time elapsing, after polishing, the slower the discharge takes place. Zinc behaved likewise, only more slowly. Other metals were tried. Bismuth acted differently from most metals. Whether charged positively or negatively, they exhibited rapid loss in the dark, in dry air under a metal bell, independently of the state of the polish. ------------------------------------------------------------------------ CHAPTER IX ------- 100. THOMSON’S EXPERIMENTS. _Elect. Eng._, N.Y., Mar. 11, Apr. 8 and Apr. 22, ’96. _Elect. Rev._, N.Y., Apr. 8, ’96, p. 183. STEREOSCOPIC SCIAGRAPHS. _Elect. World_, N.Y., Mar. 14, ’96.—Prof. Elihu Thomson, of the Thomson-Houston Electric Company, described experiments to determine the practicability of making stereoscopic pictures by X-rays. A solid object may be considered as composed of points which are at different distances from the eye. By monocular vision, the solidity of an object is not assured. However, by the use of both eyes, the objects appear less flat. The experimenter used, as the different objects, a mouse, also metal wires twisted together, and, again, a block of wood having projecting nails. In order to produce a stereoscopic picture with X-rays, he took a sciagraph in the ordinary way. He then caused the relative displacement of the discharge-tube and the object, and took another sciagraph. By mounting the two sciagraphs in a stereoscope, he found that the effect was as expected, and in the case especially of the skeleton of the mouse, it was very curious,—less like a shadow picture and more like the real object. The picture was more realistic, as in the well-known stereoscope for viewing photographs. [Illustration: MULTIPLE SCIAGRAPHS. FIG. 1, § 101, p. 95. ] [Illustration: MULTIPLE SCIAGRAPHS. FIG. 2, § 101, p. 95. ]