ON FORCE. 289 



the reduction of the carbouic acid cannot be effected, and 

 an amount of sunlight is consumed exactly equivalent to 

 the molecular work done. Thus trees are formed; thus 

 the cotton on which Mr. Bazley discoursed last Friday is 

 produced. I ignite this cotton, and it flames; the oxygen 

 again unites with the carbon; but an amount of heat equal 

 to that produced by its combustion was sacrificed by the 

 sun to form that bit of cotton. 



We cannot, however, stop at vegetable life, for it is the 

 source, mediate or immediate, of all animal life. The sun 

 severs the carbon from its oxygen and builds the vegetable; 

 the animal consumes the vegetable thus formed, a reunion 

 of the severed elements takes place, producing animal 

 heat. The process of building a vegetable is one of wind- 

 ing up; the process of building an animal is one of running 

 down. The warmth of our bodies, and every mechanical 

 energy which we exert, trace their lineage directly to the 

 sun. The fight of a pair of pugilists, the motion of an 

 army, or the lifting of his own body by an Alpine climber 

 up a mountain slope, are all cases of mechanical energy 

 drawn from the sun. A man weighing 150 pounds has 64 

 pounds of muscle; but these, when dried, reduce them- 

 selves to 15 pounds. Doing an ordinary day's work, for 

 eighty days, this mass of muscle would be wholly oxidized. 

 Special organs which do more work would be more quickly 

 consumed: the heart, for example, if entirely unsustained, 

 would be oxidized in about a week. Take the amount of 

 heat due to the direct oxidation of a given weight of food; 

 less heat is developed by the oxidation of the same amount 

 of food in the working animal frame, and the missing 

 quantity is the equivalent of the mechanical work accom- 

 plished by the muscles. 



I might extend these considerations; the work, indeed, 

 is done to rny hand but 1 am warned that you have been 

 already kept too long. To whom then are we indebted for 

 the most striking generalizations of this evening's dis- 

 course? They are the work of a man of whom you have 

 scarcely ever heard the published labors of a German 

 doctor, named Mayer. Without external stimulus, and 

 pursuing his profession as town physician in Heilbronn, 

 this man was the first to raise the conception of the 

 interaction of heat and other natural forces to clearness in 

 his own mind. And yet he is scarcely ever heard of, and 



