Hypotheses of Dynamics. 259 



mind they must get mixed. Yet, before we can be said to 

 follow a bit of energy as we do a labelled portmanteau, 

 we must either have some means of making this distinction, 

 or we must frame our hypothesis of acting mechanism in 

 such a way as to exclude the possibility of two bits of energy 

 getting into the same body at the same time. 



Prof. Lodge refers to Prof. Poynting's paper on the 

 "Transfer of Energy in the Electromagnetic Field"* as an 

 illustration of the power which the contact-action hypothesis 

 gives us of labelling and following bits of energy. Prof. 

 Poynting's results, however, were based not only on the 

 assumption of contact-action, but on other hypotheses as well, 

 which made his axiom of acting mechanism, if not complete, 

 at any rate much more complete than contact-action alone 

 would have made it ; and, moreover, if I understand him 

 aright, he did not profess to label and follow the bits of 

 energy distributed in the fields which he investigated. 



(7) The complete Transformation of Energy during 

 Transference. 

 Id the present paper Prof. Lodge gives a formal demon- 

 stration, and a discussion of illustrative instances, of his pro- 

 position that, according to the contact-action conception, 

 " energy cannot be transferred without being transformed"!. 

 I need not enter into a detailed criticism of the demonstration. 

 It is sufficient for my purpose to draw attention to two points: — 

 (1) The demonstration itself admits the possibility that a body 

 may act as " a mere transmitter, not itself active, only passing 

 on what it receives/' and applies to bodies not acting in this 

 way. But a body cannot pass on the energy it receives with- 

 out the energy being first transferred to it and subsequently 

 transferred by it. The demonstration, therefore, admits that 

 energy may in certain circumstances be transferred without 

 being transformed, excludes such cases from consideration, 

 and restricts itself to other cases J. (2) The demonstration is 

 entirely qualitative. It is shown that in these other cases of 

 action between two bodies, if one body lose, or gain, kinetic 



* Phil. Trans. 1884, pt. ii. p. 343. 



t Phil. Mag. [5] vol. xix. p. 486. The formal statement of the pro- 

 position in the present paper is much less precise than in the paper just 

 cited. He says, " My proposition was that the change of form is always 

 from kinetic to potential or vice versa" though he certainly would not 

 have set himself to prove anything so obvious. The context, quoted 

 below, shows that it is the complete transformation of energy during 

 transference that the demonstration is held to prove. 



X It should he noted, however, that on p. 33 Prof. Lodge speaks of the 

 treatment of potential energy as being " conveyed elsewhere as a simple 

 flux without transfer or transformation," as " blindfold treatment " which 

 " does not exhaust the matter."' 



