436 FRAGMENTS OF SCIENCE. 



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 as- 

 suredly far in advance of all living men. 



Mayer grasped the mechanical theory of heat with 

 commanding power, illustrating it and applying it in 

 the most diverse domains. He began, as we have seen, 

 with physical principles; he determined the numerical 

 relation between heat and work; he revealed the source 

 of the energies 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 vege- 

 table, 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 atten- 

 tion 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 falling body in 

 weight, 17,356 C. He also found, in 1845, that the 

 gravitating force between the earth and sun was com' 

 petent to generate an amount of heat equal to that ob- 

 tainable from the combustion of 6,000 times the weight 

 of the earth of solid coal. With the quickness of 

 genius he saw that we had here a power sufficient to 

 produce the enormous temperature of the sun, and 

 also to account for the primal molten condition of our 

 own planet. Mayer shows the utter inadequacy of 

 chemical forces, as we know them, to produce or main- 

 tain the solar temperature. He shows that were the 

 sun a lump of coal it would be utterly consumed in 



