Hypotheses of Dynamics. 257 



latest paper (p. 30), " amounts to just this, that whatever 

 energy appears in a bounded region must necessarily have 

 passed through the boundary/' It is quite obvious that the 

 assumption of contact-action together with the law of the 

 conservation of energy do justify this proposition. It is 

 equally obvious that, with the ordinary conception of energy, 

 this proposition cannot be asserted. It may hold, but we 

 cannot assert that it does. Why this difference ? Not 

 because the law of conservation is more precise or definite in 

 the one case than in the other, but because we have a more 

 complete conception of transference. With the ordinary 

 conception of energy the only source of knowledge of trans- 

 ference is the third law of motion. With the other conception, 

 we have both the third law and the axiom of contact-action *; 

 and it is because of the greater definiteness which this latter 

 axiom gives to our conception of transference, that it enables 

 us to assert that if energy appears within a bounded region, 

 it must have been either conveyed or transferred across the 

 boundary f. 



The above proposition seems to Prof. Lodge " to confer 

 upon energy the same kind of identity or continuous exist- 

 ence (or, if you please, objectivity) as matter possesses." 

 What kind of identity or continuous existence matter is 

 supposed to possess (we need not refer to anything so meta- 

 physical as objectivity) may be gathered from the earlier of the 

 two statements referred to above, viz. : — " On the new plan we 

 may label a bit of energy and trace its motion and change of 

 form, just as we may ticket a piece of matter so as to identify 

 it in other places under other conditions ; and the route of 

 the energy may be discussed with the same certainty that its 

 existence was continuous as would be felt in discussing the 



* It should be noted that according to these two conceptions the third 

 law, though expressed in the same words, is not the same law. In the 

 one case it applies to all material bodies, whether in contact or at a 

 distance. In the other it applies to all bodies in contact, whether they 

 are material bodies or elements of the medium. 



t It should be noted, however, that the law of conservation during 

 transference which, notwithstanding the reiteration of his old claim, is all 

 that Prof. Lodge now considers himself to have deduced, does not of 

 itself, as he seems to suppose, justify the assertion of the above proposi- 

 tion. For it is consistent with this law that energy may, as he says, 

 " ]eak away in some silent unobtrusive fashion." If it may thus leak 

 out of observation, it may also leak into observation. Since, then, some of 

 the energy which appears within a bounded region may have got there 

 by this process of unobtrusive leakage, and since the above law can tell 

 us nothing as to how it got there, this law cannot of itself justify the 

 above proposition. It cannot therefore even in this first sense be called a 

 law of identity. 



