102 ILLINOIS STATE ACADEMY OF SCIENCE 



petual motion would seem to be one that ''everybody" 

 would understand more easily than conservation of en- 

 ergy. It certainly would have been less likely to result 

 in the difficulties attending kinetic and potential. It has 

 been buried in derision, however, because connoting a 

 machine designed to thwart a fundamental method of na- 

 ture. But when used so as to include the smallest parti- 

 cles, as well as masses, it cannot be negatived — unless by 

 gravitation, the nature of which, though the subject of 

 a great amount of speculation, remains as much a mys- 

 tery as ever. Professor Tyndall's description of heat as 

 a "mode of motion" seems better adapted to a clear con- 

 cept than the modern expression "form of energy". 



Exception is not taken to the term potential energy in 

 a school book. The pupil who really cares will become 

 scholar enough to understand. The objection is only to 

 its use without the support of explanation or reference 

 in books intended for the general public. It seems to be 

 responsible for stored energy. Possibly, also, it may mis- 

 lead some who are educated in branches of science that 

 do not involve general physics. An eminent, and gen- 

 uinely scientific author, in such a branch, published the 

 following : 



"In animals the final products of broken down proto- 

 plasm are carbon dioxide, water, and a nitrogenous sub- 

 stance called urea. These products are called excretory 

 products. The animal machine is unable to utilize the 

 energy tvliich exists in the form of potential energy in 

 these substances, and they are removed from the body." 

 (Italics mine.) 



The italicized words are unnecessary. They are of the 

 ij\)Q termed, in legal phraseology, obiter. It was sug- 

 gested to the author that they be omitted from later 

 editions. They reappeared, however, though, to save his 

 life, he could not have proved them, nor cited anything 

 put forth as proof. 



Stored energy is the present subject. By its mention 

 the writer is forcibly reminded of the memorable words 

 of the famous philosopher, Mrs. Prig: "I don't believe 

 there's no sich a person." 



