44 Prof. TyndalPs Notes on Scientific History. 



The whole paper of Prof. Thomson, published in the Philoso- 

 phical Magazine for 1852, vol. iv., may be compared with the 

 writings of Dr. Mayer now before the reader. I, however, will 

 limit myself here to the section " On the Power of Animated 

 Creatures over Matter" (p. 258). 



" A principal object of the present communication is to 

 point out the relation of this theory [that of animal heat and 

 motion] to the dynamical theory of heat. It is remarked, in the 

 first place, that both animal heat and weights raised or resistance 

 overcome, are mechanical effects of the chemical forces which act 

 during the combination of food with oxygen. The former is a 

 dynamical mechanical effect, being thermal motions excited; 

 the latter is a mechanical effect of the statical kind. The whole 

 mechanical value of these effects, which are produced by means 

 of the animal mechanism in any time, must be equal to the me- 

 chanical value of the work done by the chemical forces. Hence, 

 when an animal is going up-hill or working against resisting 

 force, there is less heat generated than the amount due to the 

 oxidation of the food, by the thermal equivalent of the mecha- 

 nical effect produced. From an estimate made by Mr. Joule 

 [in 1846, Phil. Mag. vol. xxviii. p. 454], it appears that from 

 i to \ of the mechanical equivalent of the complete oxidation of 

 all the food consumed by a horse may be produced from day to 

 day as weights raised [Mayer published the same result a year 

 previous to Mr. Joule, see 39]. The oxidation of the whole 

 food consumed being, in reality, far from complete [see Mayer, 

 36 to 39], it follows that a less proportion than f, perhaps 

 even less than f of the heat due to the whole chemical action 

 that actually goes on in the body of the animal, is given out 

 as heat. An estimate, according to the same principle, upon 

 very imperfect data, however, is made by the author, regarding 

 the relation between the thermal and the non-thermal mecha- 

 nical effects produced by a man at work [Mayer made the same 

 estimate, see 38] ; by which it appears that probably as much 

 as £ of the whole work of the chemical forces arising from 

 the oxidation of his food during the twenty-four hours may 

 be directed to raising his own weight, by a man walking up-hill 

 for eight hours a day ; and perhaps even as much as \ of the 

 work of the chemical forces may be directed to the overcoming 

 of external resistances by a man exerting himself for six hours 

 a day in such operations as pumping. In the former case there 

 would not be more than |, and in the latter not more than J 

 of the thermal equivalent of the chemical action emitted as 

 animal heat, on the whole, during twenty-four hours, and the 

 quantity of heat emitted during the time of working would bear 

 much smaller proportions respectively than these to the thermal 



