THE COPLEY MEDALIST OF 1871. 485 



brief paper. He goes fully through the calculation of 

 the mechanical equivalent of heat. He calculates the 

 performances of steam-engines, and finds that 100 Ibs. 

 of coal, in a good working engine, produce only the 

 same amount of heat as 95 Ibs. in an un working one ; 

 the 5 missing Ibs. having been converted into work* 

 He determines the useful effect of gunpowder, and finds 

 nine per cent, of the force of the consumed charcoal in- 

 vested on the moving ball. He records observations on 

 the heat generated in water agitated by the pulping- 

 engine of a paper manufactory, and calculates the equi- 

 valent of that heat in horse-power. He compares 

 chemical combination with mechanical combination 

 the union of atoms with the union of falling bodies with 

 the earth. He calculates the velocity with which a 

 body starting at an infinite distance would strike the 

 earth's surface, and finds that the heat generated by its 

 collision would raise an equal weight of water 17,356 

 C. in temperature. He then determines the thermal 

 effect which would be produced by the earth itself falling 

 into the sun. So that here, in 1845, we have the germ 

 of that meteoric theory of the sun's heat which Mayer 

 developed with such extraordinary ability three years 

 afterwards. He also points to the almost exclusive effi- 

 cacy of the sun's heat in producing mechanical motions 

 upon the earth, winding up with the profound remark, 

 that the heat developed by friction in the wheels of our 

 wind and water mills comes from the sun in the form 

 of vibratory motion ; while the heat produced by mills 

 driven by tidal action is generated at the expense of the 

 earth's axial rotation. 



Having thus, with firm step, passed through the 

 powers of inorganic nature, his next object is to bring 

 his principles to bear upon the phenomena of vegetable 

 and animal life. Wood and coal can burn : whence 



