THE ADVANCE OF SCIENCE 69 



ever in human history as that in which new chemical 

 elements, not of an ordinary type, but possessed of 

 truly astounding properties, were made known with 

 extraordinary rapidity and sureness of demonstration. 

 Interesting as the others are, it is the discovery of radio- 

 activity and of the element radium which so far exceeds 

 all others in importance that we may well account it a 

 supreme privilege that it has fallen to our lot to live 

 in the days of this discovery. No single discovery ever 

 made by the searchers of nature even approaches that 

 of radio-activity in respect of the novelty of the 

 properties of matter suddenly revealed by it. A new 

 conception of the structure of matter is necessitated 

 and demonstrated by it, and yet, so far from being 

 destructive and disconcerting, the new conception fits 

 in with, grows out of, and justifies the older schemes 

 which our previous knowledge has formulated. 



Before saying more of radio-activity, which is apt to 

 eclipse in interest every other topic of discourse, I must 

 recall to you the discovery of the five inert gaseous 

 elements by Rayleigh and Ramsay, which belongs to 

 the period on which we are looking back. It was found 

 that nitrogen obtained from the atmosphere invariably 

 differed in weight from nitrogen obtained from one of 

 its chemical combinations ; and thus the conclusion 

 was arrived at by Rayleigh that a distinct gas is present 

 in the atmosphere, to the extent of i per cent., which 

 had hitherto passed for nitrogen. This gas was 

 separated, and to it the name argon (the lazy one) was 

 given, on account of its incapacity to combine with 

 any other element. Subsequently this argon was found 

 by Ramsay to be itself impure, and from it he obtained 

 three other gaseous elements equally inert : namely 

 neon, krypton, and xenon. These were all distinguished 



