113. LODGE’S EXPERIMENT. X-RAYS MOST POWERFUL WHEN THE ANODE IS THE PART STRUCK BY THE CATHODE RAYS. PIN-HOLE PICTURES BY X-RAYS TO DETERMINE SOURCE OF X-RAYS, AND PIN-HOLE IMAGES UPON GLASS COMPARED. _The Elect._, Lon. Apr. 10, ’96, p. 784.—The object of the experiment was to confirm, if possible, by a modified construction, the source of the X-rays, as being the surface struck by cathode rays, whether the surface is that of glass or any other substance. He had constructed, for this purpose, a discharge tube, as illustrated in the diagram, which may be seen, at a glance, to contain a concave electrode at one end, and a flat electrode at the other. Between them, and connected to the concave electrode, is an inclined sheet of aluminum, shading both electrodes. The wires leading to the aluminum sheet are well protected by glass. He arranged matters so that either the concave or the flat electrode could be made positive or negative. The operation consisted first in taking through a pin hole, 1/4 of an inch in diameter, X-ray pictures on photographic plates, from different points, at measured distances. After these were taken, glass plates received the luminous images at the positions of the sensitive plate. Pencil drawings were then made, and compared with the X-ray pictures. The experiment involved also the repetition of this operation, except that the polarity of the terminals was changed. “When the small flat disk was cathode, every part of the complicated anode appeared strongly and quickly on the plate, especially the tilted and first bombarded portion on a photographic plate placed above the tube. The cathode disk itself did not show at all. On a plate placed below the bulb, the anode cup appeared strong, but the tilted disk did not appear. On the other hand, … its focus spot acted as a feeble point source, by reason of a few rays reflected back on to it from the cup. “When the current was _reversed_, the small disk anode showed faintly, being excited by rays which had penetrated the interposed tilted disk, but again the cathode hardly showed at all, not even the tilted portion on a plate placed below the bulb. This is confirmed by J. Perrin. In no case could an image of the cathode be obtained. (_Comptes Rendus_) Mar. 23, ’96. From trans. by L. M. P.) By giving a very long exposure (two hours), some impression was obtained by Dr. Lodge about equal to that from the shaded anode disk; but, of course, if the tilted plate had been under these circumstances an anode, it is well known that a few minutes would have sufficed to show it strong upon the plate beneath. “Hence, undoubtedly, the X-rays do not start from the cathode _or from anything attached to the cathode_ but do start from a surface upon which the cathode rays strike, whether it be an actual anode or only an ‘anti-cathodic’ surface. Best, however, if it be an actual anode. (Independently discovered by Rowland, § 116. and Roentgen, § 91.”)