38 Prof. TyndalFs Notes on Scientific History, 



animal consumes combustible substances belonging to the vege- 

 table world, and causes them to reunite with the oxygen of the 

 atmosphere. Parallel to this process runs the work done by 

 animals. This work is the end and aim of animal existence. 

 Plants certainly produce mechanical effects, but it is evident 

 that for equal masses and times the sum of the effects produced 

 by a plant is vanishingly small, compared with those produced 

 by an animal. While, then, in the plant the production of 

 mechanical effects plays quite a subordinate part, the conversion 

 of chemical tensions into useful mechanical effect is the charac- 

 teristic sign of animal life. 



32. In the animal body chemical forces are perpetually 

 expended. Ternary and quaternary compounds undergo during 

 the life of the animal the most important changes, and are, for 

 the most part, given off in the form of binary compounds — as 

 burnt substances. The magnitude of these forces, with re- 

 ference to the heat developed in these processes, is by no means 

 determined with sufficient accuracy; but here, where our object 

 is simply the establishment of a principle, it will be sufficient to 

 take into account the heat of combustion of the pure carbon. 

 When additional data have been obtained, it will be easy to 

 modify our numerical calculations so as to render them accordant 

 with the new facts. 



33. The heat of combustion of carbon I assume with Dulong 

 to be 8550°. The mechanical work which corresponds to the 

 combustion of one unit of weight of coal corresponds to the 

 raising of 9,670,000 units to a height of 1 foot. 



If we express by a weight of carbon the quantity of chemical 

 force which a horse must expend to perform the above amount 

 of work, we find that the animal in one day must apply 1*34 lb. ; 

 in an hour 0*167 lb. ; and in a minute 0*0028 lb. of carbon to 

 the production of mechanical effect. 



According to current estimates, the work of a strong labourer 

 is fth of that of a horse. A man who in one day lifts l,850,0001bs. 

 to a height of a foot must consume in the work 0*19 lb. of 

 carbon. This for an hour (the day reckoned at eight hours) 

 amounts to 0*024 lb. ; for a minute it amounts to 0*0004 lb. = 3*2 

 grains of carbon. A bowler who throws an 8-lb. ball with a 

 velocity of 30' consumes in this effort j^th of a grain of carbon. 

 A man who lifts his own weight (150 lbs.) 8 feet high, consumes 

 in the act 1 grain of carbon. In climbing a mountain 10,000 

 feet high, the consumption (not taking into account the heat 

 generated by the inelastic shock of the feet against the earth) 

 is 0*155 lb. = 2 ozs. 4drs. 50grs. of carbon. 



34. If the animal organism applied the disposable com- 

 bustible material solely to the performance of work, the quan- 



