ON FORGE. 289 
the reduction of the carbonic 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 I 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 
