558 THE POPULAR SCIENCE MONTHLY. 



economy. Still, nothing conld be plainer than this. In our day, 

 when it is probable that force, motion, gravity, heat, light, electricity, 

 magnetism, are simply modifications of one and the same agent, and 

 the effect of the vibrations of that impalpable and invisible fluid known 

 as ether, the assertion that the sun is the only fuel, the only force, 

 must not call forth anywhere the smile of incredulity. All fuels, all 

 forces, are to be regarded as only parts of the sun's heat. What is 

 coal ? Fossil carbon. And was not this carbon fixed in plants by the 

 sun's heat, of which it is the equivalent? Under the action of solar 

 radiations the carbonic acid in the atmosphere is decomposed on con- 

 tact with plants ; the carbon is fixed in the plant, and the oxygen 

 goes back into the air to serve for the respiration of animals. Hence, 

 no sun, no vegetation ; no vegetation, no carbon ; no carbon, no coal. 

 Coal, in burning, gives up the solar heat which was stored up in it, 

 and therefore it was that, on seeing a locomotive engine move, Ste- 

 phenson said : " It is not the coal that drives this engine, it is the sun's 

 heat stored up in the coal thousands of ages ago ; locomotives are but 

 the horses of the sun." We might make a like comparison with re- 

 spect to wine and the alcohol it contains ; and the Boi'delais use no 

 mere figure of speech when they speak of their admirable Sauterne 

 wine as being " bottled sunshine." 



When water rises in the shape of vapor, what is it that causes it 

 to ascend ? The heat of the sun. If it comes down as rain, forming 

 torrents and brooks which feed our mill-races and drive our mills, 

 what is it that turns the wheel ? The sun, for it was the sun that in 

 the first place raised the water. When the wind blows upon the 

 sails of a windmill, or on the sails of a ship, what is it that drives the 

 mill or propels the ship? The sun, for wind is simply an atmospheric 

 current produced by the heating of a stratum of air which, being 

 dilated by the sun, tends to an equilibrium with strata of the same 

 density, and hence rises, while a volume of cooler air takes its place. 

 And what are the tides, the propulsive power of which there is some 

 thought of utilizing, whether directly by means of water-wheels, or 

 indirectly by compressing air and so producing a constant supply of 

 force ? They are a portion of the heat of the sun, for the seas are 

 formed by the coming together of all those torrents and rivers which 

 descend into their common reservoir, the ocean. Then, too, the tides 

 are the result of the combined attraction of sun and moon upon the 

 earth. Thus we find that the sun is always and everywhere active. 



It is, therefore, no paradox to regard the sun as the one source of 

 fuel in the future, and as the reservoir of foi'ce to which generations 

 to come will at no distant day have recourse. Hence it is that savants 

 and great engineers, as Euclid, Archimedes, Hero, Salomon de Cans, 

 Buffon, Saussure, Belidor, Evans, Herschel, Pouillet, Ericsson, have in 

 every age put to themselves the question how it might be possible to 

 take from the sun a part of its heat for the benefit of this poor globe. 







