ENERGY AND ITS TRANSFORMATIONS. 3 



been admitted as applicable to physical energy since 

 the doctrines of the correlation of forces and the per- 

 sistence of energy became accepted by men of science ; 

 and we are gradually progressing towards the establish- 

 ment of a law of persistence of all existence, whether 

 of matter, of force and energy, or of organic vitality, 

 and perhaps even to its extension until it includes in- 

 tellectual and soul life. 



We see that in the beginning there entered upon 

 an existence of indefinite duration a great universe 

 of matter endowed with its characterizing attributes 

 — the forces. These forces, acting upon a definite 

 quantity of matter with definite intensity, give origin 

 to a fixed amount of actual energy, and become capa- 

 ble of producing another fixed quantity of what is now 

 potential energy. Energy thus brought into exist- 

 ence remains constant in total amount as the quantity 

 of created matter remains constant. 



The action of these forces upon this matter has given 

 rise to every phenomenon which has come, or which 

 can come, within the range of scientific inquiry. 



2. Forces are Classified, according to their methods 

 of affecting matter, into three great classes : 



(1) Those forces with which we are able to make 

 ourselves so readily and thoroughly familiar that we find 

 no difficulty in assigning to each of them its proper 

 place in the scheme of scientific systematization, and 

 which we have found it comparatively easy to distin- 

 guish by their peculiar and readily observed effects. 

 These include the familiar physical forces, as gravita- 

 tion, electrical, chemical, and mechanical forces. 



(2) The vital forces — those which are preservative of 

 all life, which produce and promote the growth of or- 



