xix.] SOME OPINIONS. 267 



in behalf of the compound nature of the chemical elements, can 

 these simpler forms be any other than those we detect by means 

 of the spectroscope ? By the conditions of the problem and 

 the absence of knowledge they are not decomposable in the 

 laboratory; if they were they would cease to be elementary 

 bodies at once, and would be wiped out of our tables. Nor do 

 I think it possible that in the present stage of our knowledge 

 they can be revealed to us in any other way than by the spec- 

 troscope. It is unfortunate that none of these chemists who 

 have given us this view have helped us by showing in what way 

 the possibility, which all of them suggest, and which many of 

 them intensely believe in, could be absolutely demonstrated ; but 

 it is obvious that if dissociation is the thing which time out of 

 mind has made compound bodies simpler, in their minds the 

 condition of higher temperature must have been present. The 

 only difficulty was the way in which the effects of that high 

 temperature could be measured and weighed, and I think that 

 if the spectroscope had been introduced earlier they would pro- 

 bably have left some hints behind them which would have been 

 of the greatest value to those who work with that instrument. 



Passing from the chemists to the physicists, there is one, at 

 all events, who has appreciated exactly how this decomposability 

 of the terrestrial elements could be established. I refer to the 

 lamented Clerk Maxwell. In his article on Atoms in the 

 Encyclopaedia Britannica, he says : " The discovery of a 

 particular line in a celestial spectrum which does not coincide 

 with any line in a terrestrial spectrum indicates either that a 

 substance exists in the heavenly body not yet detected by 

 chemistry on the earth, or" (and it is to the "or" I wish to 

 draw attention) " that the temperature of the heavenly body is 

 such that some substance undecomposable by our methods is 

 there split up into components unknown to us in their separate 

 states." Absolutely nothing could be clearer than this. 



But in endeavouring to discuss the question as to how far the 



