102. PROPOSED DOUBLE CATHODE TUBE. See also _Elect. Rev._, N.Y., Apr. 15, p. 191.—The nature of this will be apparent immediately from the cut which is herewith presented and entitled “Standard X-Ray Tube.” With unidirectional currents the concave electrodes in the opposite ends may each be a permanent cathode, while the upper terminal connected to the angular sheet of platinum may be the anode. Cathode rays, therefore, will be sent out from each concave disk, and striking upon the platinum will be converted into X-rays, assuming that the platinum is the surface upon which the transformation from one kind of ray to another takes place. § 63, at end. This is called a standard tube, because it may be employed with efficiency with any kind of generator. § 8_a_, 26_a_, 115, 116 and 145. It is interesting to notice a confirmation of the efficiency of such a tube, for Mr. Swinton, in a communication to the _Wurz Phys. Med. So._ (see _The Elect._, Lon., and _Elect. Eng._, N.Y., June 3,) showed and described a picture of an exactly similar tube. By an experiment, the tube operated as expected. First proposed by Prof. Elihu Thomson, who is an author also of the following experiment: [Illustration: STANDARD X-RAY TUBE. ] 103. X-RAYS. OPALESCENCE AND DIFFUSION. _Elect. World_, Apr. 25, ’96.—He alluded to opal glass and milk to illustrate that light is reflected not only at the surface of a body, but from points, or molecules, or particles, located underneath the surface. By some experiments with X-rays, he found that they had a similar property only not to such a large per cent., but on the other hand by the way of contrast, there are many more substances opalescent to X-rays than there are to light, for the reason that the former will penetrate more substances and to greater distances. He made many observations with a modified sciascope, § 105, by pointing it away from the discharge tube and towards different substances struck by X-rays. To all appearances, such substances became the sources of the X-rays. He alluded to Mr. Tesla’s experiments on reflection, § 146, but noticed that there was a slight difference between reflection and diffusion and he was satisfied that reflection took place from the interior of the substances as well as from the surface. Metal plates, he said, gave apparently little diffusive effect, appearing to reflect feebly at angles equal to the incident angles. He alluded to Edison’s experiment also, § 133, with a large thick plate cutting off the X-rays and attributed the luminosity of his modified sciascope to rays both reflected and diffused from surrounding objects, which generally as a matter of course, are more of non-metallic objects than metallic, such as floor, ceiling, walls, tables, chairs and so on. Evidently, the interior of one’s hand causes diffusion; very little, however, for a sciagraph by means of a focus tube gives wonderfully clear outlines, and yet the rays do not come from a mathematical point. § 88.