EVOLUTION THE MASTER-KEY 



have attempted briefly to indicate the problems 

 upon which all physicists are now engaged, since 

 they realize that the last few years have given 

 us a modicum of truth and a first step onward, 

 beside which all previous inquiry into the nature of 

 matter may be regarded as nugatory and stationary. 

 The late Professor Tait, joint-author with Lord 

 Kelvin of the leading work on physics in any 

 language, was fond, as one who had the honor of 

 sitting at his feet remembers, of styling the law 

 of the conservation of energy "this grand prin- 

 ciple." He never showed the same enthusiasm 

 for the law of the conservation of matter, though 

 there was no reason, at that time, why he should 

 not regard the two as peers. But Tait had the 

 insight which many a most distinguished and 

 useful servant of science does not possess. I 

 fancy this partiality of his, which has often been 

 remarked upon, was due to what we may perhaps 

 call an intuitive perception that the two laws are 

 not peers; in short, that the law of the conserva- 

 tion of energy would ultimately be found to in- 

 clude the other. And so it has turned out. While 

 no one can now regard matter as other than a 

 phase of the cosmic activity, yet no physicist is one 

 whit disturbed in his belief that the power of 

 which matter is an expression is eternal and un- 

 creatable. Atoms may come and atoms may go, 

 "and leave not a wrack behind," but assuredly 

 this power goes on forever. The last problem of 

 all philosophy is the relation of this power or energy 

 44 



