July 28, 1916] 



SCIENCE 



133 



assumes that his statement is a generalized 

 one and offers it as a " definition " of energy 

 and not as a mere statement of the meaning he 

 wishes to have attached to a term, he lays 

 himself open to criticism. For it is not true 

 as a general definition. The quoted statement 

 from Maxwell to which I gave my approval, 

 but which he condemns, shows a Maxwellian 

 conception of energy. Professor Kent, him- 

 self, shows the futility of attempting to throw 

 the Maxwellian conception into the form of 

 a " definition." Professor Kent rejects the 

 idea, or conception, of Maxwell because he can 

 not throw it into the form of a " definition " ; 

 on the contrary, I reject the " definition " be- 

 cause it does not in any adequate way repre- 

 sent Maxwell's conception. Professor Kent 

 seems to think that the statement which I 

 quoted from Maxwell and which met my ap- 

 proval does not rise to the dignity of a con- 

 ception because it does not fit his (Kent's) 

 definition. 



Further on, referring to matter and energy, 

 Professor Kent declares : 



But there is a necessity for definitions of "both 

 these terms. The users of my book demand them. 



The naivete of this statement is delightful. 

 I thought I was discussing a question of sci- 

 ence and logic; Professor Kent seems to con- 

 sider it one of " commerce and finance." How- 

 ever, in the opening paragraph, above, I have 

 shown how he can " define " to his heart's con- 

 tent by merely specifically stating that such 

 and such are the meanings that he wishes to 

 have attached to the terms he uses and then 

 use them consistently himself. When, how- 

 ever, he invades the fields of science and logic 

 he must expect to be judged by the canons that 

 hold in those fields. That is to say, other 

 writers also use the terms matter and energy, 

 but in a more general sense than is customary, 

 or necessary, with the engineer. Professor 

 Kent can not justly deny to others (Maxwell, 

 for instance) a freedom which he claims for 

 himself. It thus happens, of course, that dif- 

 ferent writers may use the same term in dif- 

 ferent senses, but that is a small thing com- 

 pared to what happens when one and the same 

 writer uses a term in two or more senses with- 



out perceiving that he is " mixing things up." 

 It was not " definitions " per se to which I was 

 objecting in my former communication, but to 

 lop-sided, inadequate, or misleading statements 

 intended as definitions, but which can result 

 only in confusion and contradictions.. Every 

 writer is, and should be, free to " define " all 

 the terms he pleases, provided only that so 

 long as he continues to use a term he uses it 

 consistently. Then the "survival of the 

 fittest " will ultimately decide whether they 

 survive or perish. 



As regards the term " energy," in addition 

 to its figurative meaning in literature it has 

 developed two distinct technical meanings, the 

 engineer's and the physicist's. This would 

 not cause any great difficulty if the two tech- 

 nical meanings were distinctly recognized and 

 indicated as is done with the " pound " in use 

 as a unit in engineering practise. Professor 

 Kent claims priority of use for the engineer's 

 definition of energy. Granted, but priority in 

 use can not justify a claim that the thing 

 which he defines is the same thing as that 

 which the physicist claims is conserved. Such 

 a claim is exactly what I meant when I spoke 

 of "mixing things up," or using the same 

 term for two distinctly different things with- 

 out recognizing that they were different. That 

 Professor Kent's definition is consistent with 

 the doctrine of the conservation of energy can 

 not be admitted for a moment by any one who 

 comprehends the meaning of the term con- 

 servation. " The capacity for performing 

 work " always diminishes with the doing of 

 work, for it always depends upon some exist- 

 ing differences, such as difference in tempera- 

 ture, difference in pressure, difference of level, 

 difference in direction of motion, difference in 

 direction of stresses, or even difference in 

 molecular distribution as in the osmotic cell, 

 which difference disappears when the possible 

 work due to it is done. (Compare with 

 3STernst's law.) The capacity for doing work 

 may disappear entirely without diminishing 

 the total energy of a system one particle. 

 Hence, to claim that the capacity for doing 

 work is conserved is tantamount to claiming 

 that a perpetual motion machine is possible; 



