He tested the source of the X-rays by means of the following arrangement of the apparatus: It will be noticed that the lead diaphragm is quite close to the fluorescent spot. Upon holding the sciascope on the opposite side, and pointing it toward the spot, the luminous area of the fluorescent screen was about the same as that of the opening in the diaphragm, but the size grew rapidly upon receding from the diaphragm. If the rays had come from the cathode, however, the fluorescent spot on the screen would not have increased in size so rapidly during recession, and, therefore, the rays must have come from the spot on the glass struck by the cathode rays. § 113, 116, 117. 107_a_. LEEDS’ AND STOKES’ EXPERIMENT. USE OF STOPS IN SCIAGRAPHY. _Western Electrician_, Mar. 14, ’96.—In order to obtain clear definitions of the shadows, Messrs. M. E. Leeds and J. B. Stokes provided lead plates with holes, varying in size from 1/4 inch to an inch between the discharge tube on one side and the object and photographic plate on the other. In this manner they obtained excellent sciagraphs of animals having very fine skeletons. See the picture of the rattlesnake at § 135 and of a fish on page 63. See also the frog taken abroad page 90. 107_b_. MACFARLANE, MORTON, KLINK, WEBB AND CLARK’S EXPERIMENT. X-RAYS FROM TWO PHOSPHORESCENT SPOTS. _Elect. World_, Mar. 14, ’96.—By means of nails projecting vertically from a board (similar to the process carried out by Dr. William J. Morton, _Elect. Eng._, N.Y., Mar. 5, ’96), they proved, undoubtedly, that the source of the X-rays was at the surface of the glass directly opposite the cathode. By modification, which acted as further proof, a tube was provided with a cathode at the centre. There was a phosphorescent spot at each end. One board was placed laterally to the tube, and two shadows of each of certain nails were cast, which were caused as proved by measurement, by a double source of X-rays. This experiment illustrates the importance of preventing double shadows. The plate should be perpendicular to the line joining the two sources of the X-rays when there are two such sources. Even with the focus tube Dr. Philip M. Jones, of San Francisco, determined that there were two phosphorescent spots. These should be taken into account in all cases and attempts made to produce but one strong focus upon the platinum. _Elect. World_, N.Y., May 23, ’96. [Illustration: STINE’S EXPERIMENT. FIG. 1, § 108, p. 104. ] [Illustration: STINE’S EXPERIMENT. FIG. 2, § 108, p. 104. ]