95 



and wire-lengths are properly adjusted, so that the X-rays 

 arrive at B at the same moment as the derived impulse, elec- 

 trons are liberated at B by the rays, and guided by the im- 

 pulse into the cylinder, F, and thence to the electrometer. If 

 now the distance of the X-ray bulb from B is altered, say, by 

 an increase of 10 cm., the wire from ]) to B has to be length- 

 ened by 10 cm. Thus, according to Marx, the X-rays travel 

 with the same velocity as the impulse in the wire, and there- 

 fore with the velocity of light. 



But it is to be remembered that the electrons which are 

 liberated by X-rays have an initial velocity averaging about 

 5 X 10^ per sec, i.e., a speed due to thousands of volts, and 

 are scattered in all directions from the surface on which the 

 rays fall. Neither the weak impulse applied to B by the wave 

 coming along the wire, DB, nor the peculiar form of the sur- 

 face, B, could have any sensible effect in the way of guiding 

 these fast-moving electrons into the cylinder, F. Only slow- 

 moving electrons or 8 rays could be guided by such means. It 

 is no doubt true that X-rays do liberate a certain number 

 of h rays, but it is clear that the experiment of Marx is 

 quite consistent with the hypothesis that the X-rays are com- 

 plex, and consist in part of ether pulses travelling with the 

 velocity of light, and producing 8 rays, and in part of mate- 

 rial particles, or pairs, travelling at a speed as yet undeter- 

 mined, and exciting high-speed cathode rays. 



This being the case, it is desirable to consider the material- 

 nature hypothesis more in detail, and to contrast it with 

 that of the ether pulse. 



In the first place, either theory can readily account for 

 the great penetration of the X-ray, for the absence of true 

 reflection and refraction, for the absence of deviation in 

 electric or magnetic fields, and for polarization of a type some- 

 what different from that of light, and agreeing with experi- 

 ment. I have discussed these points in the previous paper. 



It seems to me that the material-nature hypothesis shows 

 to advantage when we consider the secondary radiation of the 

 X-rays. The rays cause the emission of cathode rays whose 

 speed averages about 5 x 10^ (Dorn). We have no experience 

 of any ether wave causing the emission of any but 8 rays, 

 i.e., electrons with a speed of about 10^. It can hardly be 

 said that differences in intensity of the ether pulse can ac- 

 count for this remarkable contrast. For the speed of the 

 8 rays caused by ultra-violet light has been shown by Lenard 

 to be independent of the intensity of the light; and thp 

 velocity of the X-ray secondary radiation does not depend on 

 the intensity of the X-rays. It may be argued that the 

 breadth of the pulse is the prime factor, on the grounds that 



