PAPERS PRESENTED AT GENERAL SESSIONS 101 



pie of conservation of energy means that the total amount 

 of ''motion" in the universe, or system, ''remains ever 

 the same." But a little further reading shows that the 

 meaning is not settled by such expressions. The same 

 book reads: "All forms of energy may be regarded as 

 motion", and there is a "species of energy-, named po- 

 tential energy, in which nothing is moving." The Cen- 

 tury Dictionary defines kinetic energy as "energy in 

 the form of motion", and potential energy as "energy 

 existing in a positional form, not as motion". 



The most universal illustration of potential energy is 

 a raised weight. The reader may happen to have seen the 

 quotation from Crabb, in the New Revised Encyclopaedic 

 Dictionary: "With energy is comiected the idea of activ- 

 ity." If so, he will be sure to ask himself what the activ- 

 ity is doing in the weight while remaining raised, and 

 will be disappointed by not being able to find in the book 

 which gave the illustration, or in any other, either an 

 answer — which perhaps he would not expect — or so much 

 as an intimation that such a question might arise. 



Another frequent illustration of potential energy is a 

 coiled watch spring. It is familiar knowledge that if a 

 spring is of gas or rubber, heat is developed in the com- 

 pression and absorbed upon the release. The reader who 

 has no laboratory, but only books, would be much better 

 satisfied with the illustration if it were accompanied by 

 information as to whether similar heat phenomena at- 

 tend the use of a metallic spring ; also whether, in either 

 case, the heat is adequate to the work. But nowhere is 

 this cpiestion referred to. 



Conservation of energy is the technical name of the 

 generalization, or principle, that the amount of energy- 

 in an isolated system remains the same, that is, never 

 changes in quantity. Carl Snyder ("The World Ma- 

 chine," 1907) says that "gravitation is a standing nega- 

 tion of such a concept". The raised weight illustration 

 certainly induces the question: "Where does gravita- 

 tion come in?" And if potential energy does not exist 

 "as motion", the question arises whether a clear concept 

 of potential energy* can be consistent with an equally clear 

 concept of the conservation of energy. The phrase per- 



