io6 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 con- 

 clusively that the X rays proceed from the anode and not the 

 cathode/ May I point out that I have proved that this is un- 

 doubtedly 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 differ- 

 ent 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. Salvionr's description of the apparatus, which fol- 

 lows, 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, 



