182 ON THE INTERACTION OF NATURAL FORCES. 



water of the Antilles is carried to the British Isles, and 

 confers upon them a mild uniform warmth, and rich 

 moisture ; while, through similar causes, the floating ice 

 of the North Pole is carried to the coast of Newfoundland 

 and produces raw cold. Further, by the heat of the sun 

 a portion of the water is converted into vapour, which 

 rises in the atmosphere, is condensed to clouds, or falls 

 in rain and snow upon the earth, collects in the form of 

 springs, brooks, and rivers, and finally reaches the sea 

 again, after having gnawed the rocks, carried away light 

 earth, and thus performed its part in the geologic 

 changes of the earth ; perhaps besides all this it has 

 driven our water-mill upon its way. If the heat of the 

 sun were withdrawn, there would remain only a single 

 motion of water, namely, the tides, which are produced 

 by the attraction of the sun and moon. 



How is it, now, with the motions and the work of 

 organic beings ? To the builders of the automata of the 

 last century, men and animals appeared as clockwork 

 which was never wound up, and created the force which 

 they exerted out of nothing. They did not know how 

 to establish a connexion between the nutriment con- 

 sumed and the work generated. Since, however, we 

 have learned to discern in the steam-engine this origin 

 of mechanical force, we must inquire whether something 

 similar does not hold good with regard to men. Indeed, 

 the continuation of life is dependent on the consumption 

 of nutritive materials : these are combustible substances, 

 which, after digestion and being passed into the blood, 

 actually undergo a slow combustion, and finally enter 

 into almost the same combinations with the oxygen of 

 the atmosphere that are produced in an open fire. As 

 the quantity of heat generated by combustion is inde- 

 pendent of the duration of the combustion and the steps 

 iu which it occurs, we can calculate from the mass of the 



