328 FRAGMENTS OF SCIENCE. 



paper. He goes fully through the calculation of the 

 mechanical equivalent of heat. He calculates the perform- 

 ances 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 converted into work. He determines the use- 

 ful 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 manufac- 

 tory, and calculates the equivalent 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 

 degrees 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 after- 

 ward. He also points to the almost exclusive efficacy 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 come their 

 heat, and the work producible by that heat? From the 

 immeasurable reservoir of the sun. Nature has proposed 

 to herself the task of storing up the light which streams 

 earthward from the sun, and of casting into a permanent 

 form the most fugitive of all powers. To this end she has 

 overspread the earth with organisms which, while living, 

 take in the solar light, and by its consumption generate 

 forces of another kind. These organisms are plants. The 

 vegetable world, indeed, constitutes the instrument where- 



