570 



SCIENCE 



[N. S. Vol. XLHI. No. 1112 



Now it is evident as soon as the attention is 

 called to it that work can not, at the same 

 time, be both energy and the transference of 

 energy. If two statements are inconsistent, 

 one, at least, must be abandoned. Let ns see 

 which. 



A similar inconsistency, or contradiction, 

 is found in two recent, excellent, test-books, 

 both by the same author, who quotes freely from 

 Maxwell. In one book we find that " energy 

 is the capacity for doing worh" while in the 

 other book it is stated that " work may now 

 be defined as the act of transferring energy 

 from one body or system to another." If we 

 combine these two statements in one we find 

 that energy is the capacity for transferring 

 energy ! 



The conflict evidently arises from retaining 

 the old definition of Dr. Young which was in- 

 troduced before the principle of conservation 

 was recognized. It should be abandoned as 

 no longer applicable. (See discussion of 

 Joule's experiment given above, and the con- 

 clusion derived from it.) 



In order to show that the last excerpt from 

 Maxwell is not a mere slip of the pen but a 

 conclusion based on evidence two additional 

 excerpts will be given. 



The process by which stress produces change of 

 motion is called work, and, as we have already 

 shown, work may be considered as the transfer- 

 ance of energy from one body or system to another 

 (M. and M., p. 164). 



The transactions of the material universe appear 

 to be conducted, as it were, on a system of credit. 

 Each transaction consists of the transfer of so 

 much credit or energy from one body to another. 

 This act of transfer or payment is called work. 

 The energy so transferred does not retain any 

 character by which it can be identified when it 

 passes from one form to another (M. and M., p. 

 166). 



We have, then, a conflict of authority from 

 the same source and we must, perforce, decide 

 from the evidence and not on the authority, 

 and that is decidedly in favor of the later and 

 consistent view that work is a transference of 

 energy and not a " form of energy." The au- 

 thors of text-books have just as good author- 



ity, if they care to use it, for defining work as 

 a process of transference of energy as they 

 have for defining energy as "the capacity of 

 doing work " ; and by so doing can place them- 

 selves more nearly in touch with recent de- 

 velopments as to what constitutes the relation 

 between work and energy. 



We have had one " definition " of energy ; 

 the following statement, by way of contrast, 

 might also be used as another. 



Hence, as we have said, we are acquainted with 

 matter only as that which may have energy com- 

 municated to it from other matter, and which may, 

 in its turn, communicate energy to other matter. 



Energy, on the other hand, we know only as that 

 which in all natural phenomena is continually pass- 

 ing from one portion of matter to another (M. and 

 M., p. 165). 



This latter, and later, conception of energy 

 seems, to my mind, a long step in advance over 

 the conception of energy as the " capacity of 

 doing work." In addition, it is in full accord 

 with the later developments of our knowledge 

 of energy and with the general principle of 

 conservation. 



If we accept the conservation of energy as 

 an established principle, then we must accept 

 the legitimate deductions from it or abandon 

 it as a principle. It is plain that neither the 

 view that energy is a capacity of doing work, 

 nor the view that makes work a " form of 

 energy " is consistent with considering work a 

 transference of energy; and also that while 

 the last view is consistent with the principle 

 of conservation the other two are not. The 

 consistent view, and to that extent at least, 

 the true view is, so far as my knowledge goes, 

 the personal contribution of Professor Max- 

 well. No earlier, or contemporary writer, so 

 far as I know, and they are not numerous, 

 makes such defixiite and specific generalized 

 statements. His treatment of energy in 

 " Matter and Motion " is a distinct advance 

 over his treatment of it in his " Theory of 

 Heat." No doubt that if he had lived a few 

 years longer he would have renewed his study 

 of energy and cleared up his apparent incon- 

 sistencies. His later years were devoted 



