396 Prof. Thomson, On the Diffuse [Jan. 24, 



intensity of the rays, the results show that the intensity at M 

 where ^r is small cannot exceed that at N where ty is nearly 7r/2 

 in anything like the ratio of 2 to 1, thus showing that the greater 

 part at any rate of the effect does not arise in the way suggested. 



Some experiments were made to see if there was anything of 

 the nature of selective absorption of these diffusely returned rays. 

 In these a plate in the position M was covered with paper, on this 

 paper two crosses were placed, one of these crosses was made of 

 thin platinum foil, the other by painting red lead on the paper ; 

 the thickness of the layer of red lead was altered until when the 

 diffusely returned rays came from the lead sheet at the bottom of 

 the box the depth of the shadow cast by the red lead was very 

 nearly the same as that cast by the platinum foil. The bottom of 

 the box was then covered by a piece of platinum and photographs 

 again taken : the depth of the shadows seemed to be in the same 

 proportion as when the rays were reflected from lead, showing that 

 there is no marked selective absorption. 



The absence of refraction in these diffusely returned rays was 

 verified by the following experiment. A straight slit parallel to the 

 bottom of the box was cut in the side BO of a lead box, the diffusely 

 returned rays passing through the slit produced a bright line on a 

 photographic plate placed outside the box, a thin wedge of alu- 

 minium was placed between the slit and the photographic plate 

 and photographs were again taken, the line of light on the plate 

 was found unbroken by the prism though faint in the part where 

 the rays were intercepted. The equality of the radiation in differ- 

 ent directions shows that these secondary rays do not originate by 

 the method of which the theory is given above. The primary 

 Rontgen rays ionize the substances through which they pass, and 

 the rapid ionization in an electric field of a molecule consisting of 

 positively and negatively electrified atoms will be accompanied by 

 an electromagnetic disturbance lasting for only a short time. The 

 general character of this disturbance may be represented graphi- 

 cally as in the following figures. In the first stage (a) the 

 Faraday tubes in the external field and that connecting the atom 

 in the molecule are uninfluenced by each other ; in the next stage 

 (6) the tubes bend towards each other, then they run together 

 and break away as in fig. (c), and after this stage the atoms in the 

 molecule are not connected by a Faraday tube and are dissociated. 

 While these changes are in progress we have a very rapid 

 movement of Faraday tubes in a space comparable with that 

 between the atoms in a molecule. This movement of the tubes 

 will give rise to an electromagnetic disturbance which in con- 

 sequence of the intense radiation will be almost dead beat and 

 so equivalent to a pulse of electromagnetic disturbance. The 



