THE ORIGIN OF MOTIVE POWER. 431 



charged by an electrical machine. The luminous 

 heat generated in the last-mentioned case was the 

 complement to a deficiency of heat of friction in 

 the plate-glass and rubber of the machine, which a 

 perfect determination, and comparison with the 

 amount of work spent in turning the machine, 

 would certainly have detected. 



The application of mechanical principles to the 

 mechanical actions of living creatures was pointed 

 out. It appears certain, from the most careful 

 physiological researches, that a living animal has 

 not the power of originating mechanical energy ; 

 and that all the work done by a living animal in 

 the course of its life, and all the heat that has been 

 emitted from it, together with the heat that would 

 be obtained by burning the combustible matter 

 which has been lost from its body during its life, 

 and by burning its body after death, make up 

 together an exact equivalent to the heat that 

 would be obtained by burning as much food as it 

 has used during its life, and an amount of fuel 

 that would generate as much heat as its body 

 if burned immediately after birth. 



