ON THE DISSIPATION OF ENERGY. 463 





 air, but that it acts- in a manner more nearly 



analogous to that of an electric motor working in 

 virtue of energy supplied to it by a voltaic battery. 

 According to either view, however, the mechanical 

 effect achieved by an animal in walking up-hill, or 

 in flying or swimming, or in dragging loads along 

 the ground, or in acting as motor for a horse-mill, 

 or tread-mill, or a crank, or a lever as for pumping, 

 or for any kind of mechanism, is a part equivalent 

 for the oxidation of the food ; the rest of the 

 equivalent being animal heat. Joule estimated 

 that from J to J of the dynamical equivalent of 

 the complete oxidation of all the food consumed 

 by a horse may be produced from day to day 

 in mechanical effect as of weights raised, the 

 remainder, or from f to f , being evolved and given 

 out as heat ; and similar proportions seem to hold 

 for the mechanical work and the development of 

 heat by a healthy vigorous working man. It is, 

 however, conceivable that animal life might have 

 the attribute of using the heat of surrounding 

 matter, at its natural temperature, as a source of 

 energy for mechanical effect, and thus constituting 



