Prof. William A. Anthony (see _Elect. Eng._, Apr. 3, ’96, p. 378) held that the Le Conte experiment did not warrant Edison’s conclusion, for the experiment of Le Conte showed comparatively sharp sound shadows; for even at a distance of twelve feet there was no apparent penetration within the geometrical boundary. He referred to Stine’s, § 110. Scribner and M’Berty’s, § 111, as upholding rectilinear propagation. While he did not explain what the Edison result was due to, yet he argued that the cause was other than that ascribed by Edison. In this connection, the author performed an experiment (_Elect. Eng._, Apr. 22, ’96, p. 409) to substantiate that X-rays were propagated through such a high vacuum that it was necessary to have electrodes within 1/8 of an inch of each other, in order to obtain a discharge with a coil that gave 15 in. spark in open air. The experiment consisted in casting the shadow of an _uncharged_ tube upon the screen of a sciascope. The shadows of the wire forming the electrodes within the vacuum were produced very sharply, while the glass tube was faintly outlined. Inasmuch as the shadows of objects _within_ the vacuum tube were obtained, therefore the X-rays must have passed through the evacuated space. Sound and X-rays are therefore dissimilar. The shadows were as sharp and as dark as those made by similar wires in open air. In this connection, see also Lenard’s experiment, § 72, showing that external cathode rays were also transmitted by a vacuum in a “dead” tube. Roentgen’s experiment showed that X-rays from a mass located entirely within the vacuum in the discharge tube radiated X-rays into the outside atmosphere. § 91. This experiment would hardly prove, however, that X-rays, after having been liberated in open air, would pass through a second vacuum space, because there may have been some X-rays, generated at the surface of the glass in Roentgen’s experiment, struck by those rays which radiated from the mass at the centre of the vacuum space. Did not Lenard and Roentgen experiment with the same radiant energy? The author answers, yes. § 77. 134. PERMEABILITY OF DIFFERENT SUBSTANCES. Lenard § 68. determined the permeability of several substances to cathode rays. Roentgen also the same in regard to X-rays. § 82 and 83. Others have made comparisons. From the sciagraph made by Edison, the following classification is made, each sheet of material being about 1/32 inch thick. The most opaque were coin silver, antimony, lead, platinum, bismuth, copper, brass, and iron, which were about the same as one another. Slate, ivory, glacial phosphoric acid shellacked, and gutta percha, were about the same as one another and less than the above. Aluminum, tin, celluloid, hard rubber, soft rubber, vulcanized fibre, paper, shellac, gelatine, phonographic cylinder composition, asphalt, stearic acid, rosin, and albumen, were about the same as one another and less than the above group, as to permeability.