io Stokes, on the Nature of the Rontgen Rays. 



but not exhausted to the very highest degree that art can 

 obtain. When you get to such tremendous exhaustions 

 as that, you cannot get the discharge to pass through 

 the tube. What did he do ? Previous experiments had 

 shown that certain metals — aluminium especially — are, 

 or appear to be, to a certain extent transparent to these 

 rays. Working on the supposition that an aluminium 

 plate is, to a certain extent, transparent to these rays, 

 Lenard constructed a tube, highly exhausted, but not 

 to the very last degree. Then a window of aluminium 

 foil — a very small aperture for mechanical reasons — was 

 fastened in an air-tight manner at the end of the tube, 

 to lead into a second tube provided with a phosphorescent 

 screen. The cathodic rays produced in the first tube 

 fell upon the aluminium plate and, as Lenard supposed, 

 passed through it as rays of light would pass through 

 glass. And so he got them into the second tube, and 

 it not being necessary to make an electric discharge pass 

 through the second tube, he could exhaust it to the very 

 highest power of skill that he had. It was a work of days 

 and days. The cathodic rays behaved in this very highly 

 exhausted tube like ordinary cathodic rays. We are 

 asked to assume that we are dealing here with a vacuum, 

 and according to Lenard that shows — and no doubt it 

 would if we grant the assumption — that it is no longer a 

 question of matter, but of some process going on in the 

 ether.* And, apparently on the strength of that very 

 elaborate experiment, Rontgen in his first paper seems 

 to have been of the opinion that the cathodic rays were 

 something going on in the ether. But are we justified 

 in assuming that we are here dealing with a perfect 



* Even if the vacuum were perfect, and the result were still the 

 same, that would not disprove the theory that the cathodic rays are 

 streams of molecules, for the molecules might have been obtained from 

 the aluminium window itself. 



