270 



Essay on Motion and Force. 



of motion appears in other matter. There is, then, no 

 such property in matter as tendency to remain at rest. 

 No^manLever perceived matter in that state. The term 

 inertia, as implying something which is at best negative 

 and hypothetical, should be discarded ; and if the term is 

 to be used as meaning the tendency of motion to continue, 

 it is certainly a most unfortunate selection of a name for 

 that property. It would be easy to fix upon a term which 

 would convey the idea of the perpetuity of motion, but it 

 is not my province to do this. 



And here I cannot forbear noticing a theory which has 

 for its foundation the law of Carnot, and which I think 

 was first put forth by William Thompson, and since 

 assented to by Helmholtz, who states the law in 

 the following general terms: "Only when heat passes 

 from a warmer to a colder body, and then only partially 

 can it be converted into mechanical work. I cannot give 

 this theory in a more condensed form than it is given 

 by Helmholtz, in the words which follow. "At each 

 motion of a terrestrial body, " a portion of mechanical 

 force passes by friction or collision into heat, of which 

 only a part can be converted back again into mechanical 

 force. This is also generally the case in every electrical 

 and chemical process. From this it follows that the first 

 portion of the store of force, the unchangeable heat, 

 is augmented by every natural process, while the second 

 portion, mechanical, electrical, and chemical force, 

 must be diminished ; so that if the universe be delivered 

 over to the undisturbed action of its physical processes, 

 all force will finally pass into the form of heat, and all 

 heat come into a state of equilibrium. Then all possi- 

 bility of a further change would be at an end, and the 

 complete cessation of all natural processes must set in. 

 The life of men, animals, and plants, could not of course 

 continue if the sun had lost its high temperature and 

 with it his light, if all the components of the earth's sur- 

 face had closed those combinations which their affinities 



