354 SECTIONMECHANICS. 



of blasting, but for actuating prime-movers in the ordinary sense of the 

 word. 



Again, we may have the heat of the sun applied through the agency 

 of the expansion of gases to the production of power as in the sun 

 pumps of Salomon de Cans, and of Belidor, to the production of 

 power through the generation of steam as in the sun engine of 

 Ericsson ; or, finally, we may have it applied direct, as in the radio- 

 meter of Mr. Crooks. 



A consideration of the foregoing heads under which prime-movers 

 range themselves, will speedily bring us to the conclusion that the 

 main source of all mechanical force on this earth is the sun. If the 

 prime-movers be urged by water, that water has attained the elevation 

 from which it falls, and thus has been made competent to give out 

 power, by reason of its having been evaporated and raised by the 

 heat of the sun. If the power of the water be derived from the tidal 

 influence, that influence is due to the joint action of the sun and its 

 assistant the moon. If the prime-mover depend upon the wind 

 for its force, either directly, as in windmills, or indirectly, as in 

 machines worked by the waves, then that wind is caused to 

 blow by variations of temperature due to the action of the sun. 

 If the prime-mover depend upon light or upon solar heat, as in the 

 case of the radiometer and of the Sun engine, then the connexion 

 is obvious ; and if the heat be due to combustion, then the fuel 

 which supports that combustion is, after all, but the sun's rays 

 stored up. If the fuel be, as is now sometimes the case, straw 

 or cotton stalks, we feel that there we have the growth of the 

 one season's effect of the sun's rays ; if the fuel be wood, it is equally 

 true that the wood is the growth of a few seasons' exercise of the 

 sun's rays ; but if it be the more potent and more general fuel 

 coal then, although the fact is not an obvious one, we know that coal 

 also is merely the stored-up result of many years of the exercise of the 

 sun's rays. 



And even in the case of electrical prime-movers these depend on the 

 slow oxidation that is, burning of metal which has been brought into 

 the metallic or unburnt state from the burnt condition (or that of ore) 

 by the aid of heat generated by the combustion of fuel. 



The interesting lecture-room experiment with glass tubes charged 



