[cox A CALLENDAR] EXPERIMENTS ON THE X-RAYS 179 



intense green fluorescence covering one half of the walls of the tube on 

 the side exposed to the reflection from the platinum plate. The boundaiy 

 of this i>-reea fluorescence was observed to bulge in or out according to 

 the direction in which the magnet was presented, precisely as if caused 

 by rays having the same properties as ordinary kathode rays, although 

 proceeding from the platinum plate, and not direct ft-om the kathode. 

 On making simultaneous observations with the fluoroscope and with the 

 photographic plate, we found that the boundary of the X-radiation out- 

 side the tube, which under ordinary conditions coincides exactly with the 

 plane of the platinum plate, was also deflected by the magnet, but in the 

 opposite direction to the boundary of the green fluorescence. This efl'ect 

 was verified on several occasions in various ways, the deflection amounting 

 in some cases to half an inch on the photographic plate at a distance of 

 eight inches from the tube. 



We conclude from those observations that the rays causing the 

 brilliant green fluoi'escence of the glass, were probably identical with 

 ordinary kathode rays, and were reflected by the platinum according to 

 the same law of diffuse reflection as the X-rays. This observation is of 

 some interest as establishing a point of similarity between the X-rays 

 and kathode rays. The other observation would however appear to show 

 that the two are distinct. The fact that the boundary of the X-radi- 

 ation appeared to be deflected, is probably to be explained by a slight 

 shift of the focus point on the platinum plate, which was not perfectly 

 plane. This explanation receives support from the fact that the shadow 

 of the magnet itself as seen in the same photographs, is not perceptibly 

 double. Further, the sharpness of the boundary both before and after 

 deflection in each case, would appear to lend support to the view that the 

 kathode and X-rays are of two distinct kinds, sharply separated in 

 properties, rather than rays of the same kind, ditfering only in degree, 

 and connected by a continuous series possessing intermediate projierties 

 in the way of penetration and magnetic refrangibiiity. We,might, there- 

 fore, still suppose the kathode rays to l»e streams of radiant atoms, even 

 if the X-rays were proved to be of the nature of a wave motion in the 

 a'ther. 



Action of X-Rays on Seleniuvi. — Among the negative results which 

 we obtained, there are some perhaps which deserve mention. A selenium 

 cell was prepai-ed by Professor Cox, consisting of copper wire wound 

 on a plate of mica, and annealed in the tisual waj^. The resistance of 

 the film, when measured with a megohm and a Thomson -Varley slide box, 

 was found to be nearly ten megohms. This somewhat high valtie was 

 probably due to the thickness and small size of the selenitim film. It 

 proved, however, to be very fairly sensitive to ordinary light, and, what 

 was more important, to have an extremely constant resistance, and to 

 return very qtiickly to the original value when the disturbing influence 



