204 Professor W, Thomson, on Motive Power. [Feb. 29, 



rubber of the machine, which a perfect determination, and com- 

 parison 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. 



On the other hand, the dynamical energy of luminiferous vibra- 

 tions was referred to as the mechanical power allotted to plants 

 (not mushrooms or funguses, which can grow in the dark, are 

 nourished by organic food like animals, and like animals absorb 

 oxygen and exhale carbonic acid,) to enable them to draw carbon 

 from carbonic acid, and hydrogen from water. 



In conclusion, the sources available to man for the production 

 of mechanical effect were examined and traced to the sun's heat and 

 the rotation of the earth round its axis. 



Published speculations* were referred to, by which it is shown to 

 be possible that the motions of the earth and of the heavenly bodies, 

 and the heat of the sun, may all be due to gravitation ; or, that the 

 potential energy of gravitation may he in reality the ultimate created 

 antecedent of all motion, heat, and light at present existing in the 

 universe,* 



[W. T.] 



* Trans. Roy. Soc. Edinburgh, April 1854 (Professor W. Thomson, " On 

 the Mechanical Energies of the Solar System"). Also British Association 

 Report, Liverpool, Sept. 1854 (" On the Mechanical Antecedents of Motion, 

 Heat, and Light). 



