524 



SCIENCE 



[N. S. Vol. XXXI. No. 797 



cation to have no personal or individual 

 traits which we need take into account. 

 Without this postulate we should be un- 

 able to generalize our phj^sieal laws so as 

 to include many new phenomena— phe- 

 nomena unknown at the time of the form- 

 ulation of the law. The tenacity with 

 which the experimentalist holds to his as- 

 sumption of a simple law is well illustrated 

 by two papers read before the last meeting 

 of this society: papers which illustrate 

 how complex nature is becoming as re- 

 search goes on. I refer to the work of 

 Professor H. W. Morse and Professor E. 

 B. Rosa on electrolysis. Each investiga- 

 tion dealt with slight deviations from one 

 of Faraday's fundamental laws: and 

 each investigation apparently assumed its 

 truth: in any event assumed an equally 

 simple law. Thousands of engineering 

 results obtained each day in the week con- 

 vince us that there are no accidents in 

 history and allow us to believe that no 

 postulate was ever better justified by its 

 success. 



The behavior of nature in this respect 

 always reminds me of a remark, really a 

 new formulation, once made by Professor 

 Michelson in describing the labor of sev- 

 eral years in locating and eliminating the 

 errors in a certain steel rod upon which 

 he was cutting an accurate screw. ' ' I felt, ' ' 

 he said, "as if matched in a game against 

 an opponent: bid my antagonist always 

 played fair." 



II. ENERGY POSTULATE 



Passing now to the consideration of 

 energy, it is not yet three score years and 

 ten, since Poggendorff and Magnus re- 

 fused space, in the Ann. d. Physik., to 

 Hehnholtz's little tract, "Die Erhaltung 

 der Kraft, ' ' on the ground that it was too 

 metaphysical. But thanks partly to the 

 clear vision of Helmholtz, partly to the 



clever analysis of H. Poincare, and largely 

 to the experimental success of the prin- 

 ciple, the time has now come, I believe, 

 when we can say that the conservation of 

 energy is so useful, as a postulate, that 

 present-day science can not successfully 

 accomplish its work without it. Experi- 

 ment has been able to demonstrate it as a 

 law only for particular cases and only ap- 

 proximately: but experiments have been 

 so numerous and compelling, as to have 

 created a new attitude of mind in the 

 present generation, leading us to believe 

 that everywhere in the physical universe 

 there is some constant quantity, corre- 

 sponding to a certain constant of integra- 

 tion, called "energy." 



The most recent illustration of the man- 

 ner in which the physicist assumes this 

 constancy is, of course, the case of the 

 steady heat production in radium. No 

 sooner had Curie and Laborde made this 

 remarkable discovery, in 1903, than men 

 began, not to doubt the validity of the law 

 of the conservation of energy, but to look 

 about for the energy which was thus being 

 transformed into heat. Accordingly Ruth- 

 erford and Barnes succeeded, in the follow- 

 ing year, in showing that 23 per cent, of 

 this intra-atomic energy was due to radium 

 itself, 32 per cent, to radium C and 45 per 

 cent, to the emanation and radium A to- 

 gether. In saying that the time has come 

 when the Law of the Conservation of 

 Energy may properly be regarded as one 

 of the presuppositions of physics, it is to be 

 carefully noticed that this statement does 

 not include the Law of the Dissipation of 

 Energy. 



III. CAUSAL POSTULATE 



The infinite regress involved in the 

 search after causes and the vanity of at- 

 tempting to follow a series of causes to its 

 end are, at least, as old as the Greeks. 



