Hypotheses of Dynamics. 263 



which they act on one another is massless and elastic*. But 

 even with this axiom of acting mechanism his thesis as to 

 complete transformation during transference holds only for 

 transferences between particles and elements of the medium, 

 and not for transferences from element to element of the 

 medium. 



(8) The Complete Transference of Energy during 

 Transformation. 



Besides the proposition just considered, Prof. Lodge, in the 

 paper referred to above, asserted also that u energy cannot be 

 transformed without being transferred. v Although I called 

 this proposition in question also, no reference is made to it in 

 the present paper beyond a reiteration of the assertion (p. 16). 

 In a synopsis of the paper, however, published by Prof. Lodge 

 himself f, the admission is made that the assertion is incapable 

 of proof. For we find it laid down, as the fifth axiom of 

 dynamics, that " energy which is not being actively trans- 

 ferred from one body to another remains unaltered in quantity 

 and form." 



Prof. Lodge's right to enunciate this proposition as an axiom 

 may be judged by his own standard. According to him 

 (p. 3 of his paper), in setting forth an axiom, (1) regard must 

 be had to the experience of the human race, (2) hundreds of 

 instances should be adduced in which it holds, (3) a few 

 special cases should be critically examined and in no case- 

 found to fail, and (4) u contrary instances " should be called 

 for. Most of these regulations, which are obviously intended 

 to prevent people from carelessly and thoughtlessly enunciat- 

 ing axioms, are admirable. With the exception, perhaps, of 

 the appeal to the experience of the race, such formulators of 

 axioms as Galilei, Newton, and D'Alembert followed them, 

 especially as to the critical examination of special cases. 

 But Prof. Lodge, in the present instance, ignores them all- 

 He does not show how the proposition in question appeals to 

 the race ; he gives no instances in which it holds ; he examines 

 no special cases critically ; and he makes no reference to a 

 contrary instance which I ventured to bring forward in my 

 paper (p. 141). We are forced, therefore, to conclude that 

 according to his own regulations he is not yet in a position to 

 enunciate this proposition as an axiom. 



* On p. 21 he speaks of "the potential energy of the particles of a 

 spring," thus assuming its particles to be elastic, but this occurs in a 

 paragraph which is "true in one sense but not a final or complete 

 statement." 



t ' Nature,' vol. xlviii. p. 62. 



