THE COPLEY MEDALIST OF 1871 459 



Thus, in baldest outline, I have sought to give some 

 notion of the first half of this marvellous essay. The 

 second half is so exclusively physiological that I do not 

 wish to meddle with it. I will only add the illustration 

 employed by Mayer to explain the action of the nerves 

 upon the muscles. As an engineer, by the motion of his 

 finger in opening a valve or loosing a detent, can liberate 

 an amount of mechanical motion almost infinite compared 

 with its exciting cause, so the nerves, acting upon the 

 muscles, can unlock an amount of activity wholly out of 

 proportion to the work done by the nerves themselves. 



As regards these questions of weightiest import to the 

 science of physiology, Dr. Mayer, in 1845, was assuredly 

 far in advance of all living men. 



Mayer grasped the mechanical theory of heat with com- 

 manding power, illustrating it and applying it in the most 

 diverse domains. He began, as we have seen, with phys- 

 ical principles; he determined the numerical relation be- 

 tween heat and work; he revealed the source of the ener- 

 gies of the vegetable world, and showed the relationship 

 of the heat of our fires to solar heat. He followed the 

 energies which were potential in the vegetable up to their 

 local exhaustion in the animal. But, in 1845, a new 

 thought was forced upon him by his calculations. He 

 then, for the first time, drew attention to the astounding 

 amount of heat generated by gravity where the force has 

 sufficient distance to act through. He proved, as I have 

 before stated, the heat of collision of a body falling from 

 an infinite distance to the earth to be sufficient to raise 

 the temperature of a quantity of water, equal to the fall- 

 ing body in weight, 17,356 C. He also found, in 1845, 

 that the gravitating force between the earth and sun was 



