THE X-RAYS. 149 



The result of these experiments is that the radiation upon an imagi- 

 nary hemisphere constructed upon the platinum plate as a center is 

 nearly uniform almost to the borders of this hemisphere. I could detect 

 a slight diminution of intensity at an emanation angle of 80 degrees, 

 but this diminution is relatively small, so that the principal part of the 

 change in intensity occurs between 89 and 90 degrees. I was not able 

 to detect any difference in kind between rays emitted at different 

 angles. 



In consequence of the distribution of intensity of X-rays, just 

 described, it follows that images of the platinum plate formed in the 

 pinhole camera, whether upon the photographic plate or the fluorescent 

 screen, will be more intense the greater the angle which is made by the 

 platinum plate with the screen or photographic film, providing this 

 angle does not exceed 80 degrees. By appropriate arrangements which 

 enabled me to make a comparison between images formed simultane- 

 ously by radiations from the same tube on screens at various angles 

 this result was confirmed. A similar case of intensity distribution is 

 •found in optics in connection with fluorescence. If a few drops of a 

 solution of fluorescein be allowed to fall into a square trough of water, 

 and the trough be illuminated by white or violet light, it will be noticed 

 that the brightest fluorescent light goes out from the edges of the 

 slowly sinking column of fluorescein, or, in other words, from the places 

 where the angle of emanation of the fluorescent light is the greatest. 

 As Stokes has remarked, referring to a similar experiment, tliis appear- 

 ance depends upon the fact that the light exciting the fluorescence is 

 considerably more absorbed by the fluorescein solution than is the fluo- 

 rescent light. It is worth mentioning that the cathode rays which 

 generate the X-rays are much more strongly absorbed by platinum 

 than the X-rays, and it may therefore be surmised that there-exists a 

 similarity between these two processes, the conversion of light into 

 fluorescent . light and the conversion of cathode rays into X-rays. 

 There is as yet, however, no firm ground on which to rest such a 

 conclusion. 



With reference to practical applications, the observation of the dis- 

 tribution of intensity of the rays proceeding from the platinum jilate 

 has some value in connection with the formation of shadow pictures 

 by means of X-rays. In accordance with the observations above 

 recorded it is to be recommended that the discharge tube be so arranged 

 that the rays employed for formation of pictures be those making 

 a large angle, though not much exceeding 80 degrees, with the plati- 

 num plate. In this way the sharpest possible delineation will be 

 obtained, and if the platinum plate is flat and the construction of the 

 tube such that the rays proceeding obliquely pass through not much 

 greater thickness of glass than those going out at right angles to the 

 platinum plate, then no material loss in intensity will be exi^erienced 

 in this arrangement. 



4. In my first communication I designated as the transmissibility of 



