ON MATTER AND FORCE. 69 



active and latent energy which goes in, ought 

 exactly to balance the quantity which comes 

 out, deducting that which remains latent in 

 the chemical substances, or becomes active in 

 the actual warmth of the body itself. 



The chemical changes in the matter within 

 the body (that is, the decrease of potential 

 energy or tension) give rise to different forms 

 of motion. These motions appear as the func- 

 tions or work of the body. 



Two chief kinds may be distinguished first, 

 motion in great masses, as mechanical work, etc. ; 

 secondly, motion in little masses, or molecular 

 motion, as heat, electricity, nutrition, etc. A 

 little mass of carbon and of oxygen contains a 

 certain amount of tendency to move ; that is, of 

 potential energy. These molecules, as soon as 

 they can, move together, and the motion pro- 

 duced must continue in some form until a state 

 of tension or potential energy again results. 



The latent force of the nourishment is most 

 easily measured by determining the amount of 

 latent heat which the food contains. In order 

 to do this a known amount of substance is 

 burnt, and the amount of heat produced is 

 determined ; and as the mechanical equivalent 



