113 



III. Solid matter found in elevated positions. 



IV. The natural motions of water and air. 



V. Natural combustibles (as wood, coal, coal-gas, oils, marsh gas, 

 diamond, native sulphur, native metals, meteoric iron.) 

 VI. ArtiScial combustibles (as smelted or electrolytically-deposited 

 metals, hydrogen, phosphorus.) 

 In the present communication, known facts in natural history and 

 physical science, with reference to the sources from which these 

 stores have derived their mechanical energies, are adduced to establish 

 the following general conclusions : — 



1. Heat radiated from the sun (sunlight being included in this 

 term) is the 'principal source of mechanical effect available to man.^ 

 From it is derived the whole mechanical effect obtained by means 

 of animals working, v/ater-wheels worked by rivers, steam-engines, 

 and galvanic engines, and part at least of the mechanical effect ob- 

 tained by means of windmills and the sails of ships not driven by 

 the trade- winds. 



2. The motions of the earth, moon, and sun, and their mutual 

 attractions, constitute an important source of available mechanical 

 effect. From them all, but chiefly, no doubt, from the earth's 

 motion of rotation, is derived the mechanical effect of water-wheels 

 driven by the tides. The mechanical effect so largely used in the 

 sailing of ships by the trade-winds is derived partly, perhaps prin- 

 cipally, from the earth's motion of rotation, and partly from solar heat. 



3. The other known sources of mechanical effect available to man 

 are either terrestrial — that is, belonging to the earth, and available 

 without the influence of any external body, — or meteoric, — that is, 

 belonging to bodies deposited on the earth from external space. 

 Terrestrial sources, including mountain quarries and mines, the heat 

 of hot springs, and the combustion of native sulphur, perhaps also 

 the combustion of all inorganic native combustibles, are actually used, 

 but the mechanical effect obtained from them is very inconsiderable, 

 compared with that which is obtained from sources belonging to the 

 two classes mentioned above. Meteoric sources, including only the 

 heat of newly-fallen meteoric bodies, and the combustion of meteoric 

 iron, need not be reckoned among those available to man for practical 

 purposes. 



* A general conclusion equivalent to this was published by Sir John Herschel 

 in 1833.— See his Astronomy, edit. 1849, § (399.) 



