432 FEAGMENTS OF SCIENCE. 



ture.' The title of his second great essay was, ' Organic 

 Motion in its Connection with Nutrition/ In it he 

 expands and illustrates the physical principles laid 

 down in his first 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 

 unworking one; the 5 missing Ibs. having been con- 

 verted into work. He determines the useful effect of 

 gunpowder, and finds nine per cent, of the force of the 

 consumed charcoal invested 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 equivalent of that heat in horse- 

 power. He compares chemical combination with me- 

 chanical 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 ex- 

 traordinary ability three years afterwards. He also 

 points to the almost exclusive efficacy of the sun's heat 

 in producing mechanical motions upon the earth, wind- 

 ing up with the profound remark, that the heat devel- 

 oped by friction in the wheels of our wind and water 

 mills comes from the sun in the form of vibratory mo- 

 tion; while the heat produced by mills driven by tidal 

 action is generated at the expense of the earth's axial 

 rotation. 



