134 ANNUAL OF SCIENTIFIC DISCOVERT. 



creases the temperature of the surface only about one thirtieth of a degree 

 centigrade ; so that the remnant of the old store of force which is enclosed 

 as heat within the bowels of the earth, has a sensible influence upon the pro- 

 cesses at the earth's surface, only through the instrumentality of volcanic 

 phenomena. These processes owe, their power almost wholly to the action of 

 other heavenly bodies, particularly to the light and heat of the sun, and partly 

 also, in the case of the tides, to the attraction of the sun and moon. 



Most varied and numerous arc the changes which we owe to the light and 

 heat of the sun. The sun heats our atmosphere irregularly, the warm rare- 

 fied air ascends, while fresh cool air flows from the sides to supply its place : 

 in this way Avinds are generated. This action is most powerful at the equa- 

 tor, the warm air of which incessantly flows in the upper regions of the at- 

 mosphere towards the poles : while just as persistently, at the earth's sur- 

 face, the trade wind carries new and cool air to the equator. Without the 

 heat of the sun all winds must, of necessity, cease. Similar currents are 

 produced by the same cause in the waters of the sea. Their power may be 

 inferred from the influence which in some cases they exert upon climate. 

 By them the warm water of the Antilles is carried to the British Isles, a 

 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 cold. Further, by the heat of the sun, 

 a portion of the water is converted into vapor, 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 the light earth, and thus per- 

 formed 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 withdrawn, there would remain only a single motion of water, namely, the 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 connection 

 between the nutriment consumed 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 con- 

 sumption of nutritive materials : these arc combustible substances, which, 

 after digestion and being passed into the blood, actually undergo a slow com- 

 bustion, 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 independent of the duration of the com- 

 bustion and the steps in which it occurs, we can calculate from the mass of 

 the consumed material how much heat, or its equivalent work is thereby 

 generated in an animal body. Unfortunately, the difficulty of the experi- 

 ments is still very great; but wirliin those limits of accuracy which have 

 been as yet attainable, the experiments show that the heat generated in the 



