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Page:Popular Science Monthly Volume 49.djvu/118

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POPULAR SCIENCE MONTHLY.

and which always has some anodic properties. From each point of such a surface rays start in all directions; this is proved by the shadows they cast of slits, holes, and wires."

Prof. S. P. Thompson takes exception to the term anodic, as applied to the X rays. He says: "Is it quite correct, as Prof. Lodge puts it, to call the X rays anodic, because they start from a point opposite the cathode? It may be true that a surface upon which the cathodic discharges are being directed acquires thereby some properties common to the anode, but it is not an actual anode; . . . hence I submit that anti-cathodic would be a more correct term to use in describing them."

Prof. A. W. Porter, of University College, London, in a letter to Nature, says: "In your last issue, in the account of the work in the Comptes Rendus, you state that M. de Heen 'proves conclusively that the X rays proceed from the anode and not the cathode.' May I point out that I have proved that this is undoubtedly true for the bulb I have been using throughout my experiments on the X radiation? The bulb is one in which the negative electrode is concave, and the negative stream is thereby focused to a point on the anode, which is a platinic disk placed near the center of the bulb. By measuring the positions of different parts of a radiograph of a series of concentric zones of tin foil placed in a measured position, I have shown that the actinic rays diverge from the anode disk."

It was announced from Rome that Prof. Salvioni, of Perugia, had discovered a means by which these radiations could be made to so far assist the eye as to enable it to see through all objects which the rays could penetrate, so that the contents of a closed space were revealed.

From Prof. Salvioni's description of the apparatus, which follows, it will be seen that he has made no new discovery, and that it is quite incorrect to say that the observer actually sees the objects. He simply sees the shadows on the phosphorescent screen. The fluorescent light affects the retina like ordinary light, and is quite distinct from the X rays. What is really seen is a shadow picture of the object.

The apparatus is very simple, and is thus described by Prof. Salvioni: "This cryptoscope consists of a small cardboard tube about eight centimetres high. One end is closed by a sheet of black paper, on which is spread a layer of fish glue and calcium sulphide; this substance I have found to be very phosphorescent under the action of Rontgen rays. Within the cardboard tube, at the other end, at which the eye is placed, is fixed a lens, giving a clear image of the phosphorescent paper. On looking through this cryptoscope one can see, even in a light room, the shape and position of metallic bodies inclosed in boxes of cardboard, wood.