April 21, 1916] 



SCIENCE 



569 



All physical phenomena are effects attributed 

 to a universal activity called energy. 



Since energy is conserved, or constant in 

 amount, all of our experimental observations 

 of it are limited to the various effects due to 

 its transfer and transformations. 



The doing of work indicates the transfer of 

 energy ( Maxwell ) . 



All spontaneous natural processes may be made 

 to do work (Nernst). 



Transformations of energy take place ac- 

 companied by, or during, transfer. 



Since writers of text-books and other writers 

 who necessarily depend more upon authority 

 than upon their own investigations and inter- 

 pretations can doubtless quote the necessary 

 "good authority" for their principal state- 

 ments, when such statements are questioned, 

 they will pay but little attention to adverse 

 criticism so long as they have the necessary 

 authority for their statements. This being 

 only natural and reasonable, the foregoing 

 view regarding the use and misuse of the words 

 " work " and " energy " shall also be sup- 

 ported by quoting the necessary " high author- 

 ity," Professor Clerk-Maxwell. All of the fol- 

 lowing quotations will be taken from two of 

 his well-known and justly prized books,- 

 " Theory of Heat," tenth edition, which will 

 be referred to as T. of H., and his " Matter 

 and Motion," which will be referred to as M. 

 and M. In addition to being a scientific in- 

 vestigator and mathematician of the first rank 

 Professor Maxwell possessed a remarkable abil- 

 ity as a scientific writer and expositor. 



The use of the term energy, in a scientific sense, 

 to express the quantity of work a body can do, was 

 introduced by Dr. Young (T. of H.), p. 91. 



Dr. Young wrote at a time when the con- 

 servation of energy was yet imthought of. 

 Hence Professor Maxwell " inherited " the 

 definition — did not originate it. The incon- 

 sistencies in the following excerpts may safely 

 be attributed to the growth of the subject and 

 the failure of the later parts to agree with the 

 older parts. A considerable part of the growth 

 of the subject was due to the labors of Pro- 

 fessor Maxwell himself. 



For the energy of a body may be defined as the 

 capacity it has of doing work, and is measured by 

 the quantity of work it can do (T. of H., p. 90). 



Energy is the capacity of doing work (M. and 

 M., p. 101). 



Perhaps those writers who " define " energy 

 are not so much to blame, after all! They 

 have, at least, " good authority." There could 

 be no exception taken to the first statement if 

 it confined itself to the following : " The 

 energy of a body may often be measured by 

 its capacity of doing work," i. e., to transfer 

 its energy; but there is no warrant for the 

 last sweeping generalization that " energy is 

 the capacity of doing work." It is indeed a 

 striking example of a very common human 

 trait — a tendency to repeat current familiar 

 phrases without critical examination. Every- 

 body does it more or less. All that the facts 

 which he presented warranted him in claiming 

 was that the capacity of doing work is due to 

 enei-gy, or, that one important characteristic 

 of energy is its capacity of doing work, i. e., 

 of bringing about its own transfer. 



Here then we have two sets of quantities, one re- 

 lating to work, the other to heat. . . . 



Of these quantities work and heat are simply 

 two forms of energy (T. of H., p. 194). 



It should be noted here that work is spoken 

 of as a " form of energy." 



The potential energy of a material system is the 

 capacity it has of doing work depending on other 

 circumstances than the motion of the system (M. 

 andM., p. 120). 



The preceding excerpts are sufficient to show 

 the influence of Dr. Toung's definition of 

 energy. Some quite different statements as to 

 the relation of work and energy wiU now be 

 given — evidently the result of Professor Max- 

 well's own study of the subject, but whose fuU 

 significance he did not then realize, or live 

 to complete. 



Work, therefore, is a transference of energy 

 from one system to another; the system which 

 gives out energy is said to do work on the system 

 which receives it, and the amount of energy given 

 out by the first system is always exactly equal to 

 that received by the second (M. and M., p. 104). 



