THE RONTGEN KAY AND ITS RELATION TO PHYSICS 579 



the polarization. If they were very small waves, transverse waves, like 

 light, we ought to be able to polarize them. Becquerel, by exposing 

 certain phosphorescent substances to the sun, obtained from them cer- 

 tain rays which penetrated objects like aluminium,. etc. But these rays 

 were evidently small rays of light, because he could polarize them, and 

 he could refract them, and they were probably very short waves of ultra 

 violet light. But we never have been able to discover that there was 

 any such effect in a Rontgen ray. Some persons have claimed that they 

 got polarization; but if there ever was any polarization, it is very small, 

 indeed. One of the principal advances in respect to these rays is that 

 made by J. J. Thomson, in considering the electric discharge of bodies. 

 He has published most valuable results with regard to the effect of 

 these rays upon gases. When the rays fall upon a gas, they affect the 

 gas in some way so that it becomes a conductor. Now, you can subject 

 the gas to these rays and allow the gas to go through a tube off into 

 another vessel, so that it will discharge an electrified body in that vessel. 

 But he has found the most interesting result that it will not continue 

 long to affect these bodies. After one has allowed a certain amount 

 of electricity to pass through it, it then becomes an insulator again. 

 It only allows a certain amount of electricity to go through it. That is 

 easily explained or you can explain it by the Rontgen rays liberating 

 the ions, and only a certain amount of them. Just as soon as these 

 are used up in the conduction of the gas, then it ceases to conduct. So 

 that a certain amount of gas will conduct a certain amount of electricity, 

 and then it stops conducting. That is a most interesting result. It is 

 one of the great advances we have made since Rontgen's discovery. 

 Rontgen knew nearly all we know now about these rays. We have 

 discovered very little indeed; but that point I think we have at least 

 discovered. 



Then it is said that these rays affect a selenite cell in the same way 

 that light affects it it changes the resistance of the selenite cell. 



Of course, we are only considering the theory to-night; at least I 

 am, and we do not have to consider the bones, and so on. I have had 

 some students at work in my laboratory, and it was with the utmost 

 difficulty that I kept them from photographing bones. Bones seemed 

 to be the principal object to be photographed by the Rontgen rays when 

 they were first discovered, and I suppose it is the same now. Most 

 people connect Rontgen rays with bones; but I do not intend to say very 

 much about them. 



Now, one important point with respect to these rays is as to whether 



