A WHEWELLITE ESSAY ON MARS. 135 



lightning, and probably, also, to terrestrial magnetism 

 and the aurora. By their vivifying action vegetables 

 are enabled to draw support from organic matter ; and 

 become in their turn the support of animals and man, 

 and the source of those great deposits of dynamical 

 efficiency which are laid up for human use in our coal 

 strata. By them the waters of the sea are made to cir- 

 culate in vapour through the air, and irrigate the land, 

 producing springs and rivers. By them are produced 

 all disturbances of the chemical equilibrium of the 

 elements of nature, which, by a series of compositions 

 and decompositions, give rise to new products, and 

 originate a transfer of materials. Even the slow degra- 

 dation of the solid constituents of the surface in which 

 its chief geological change consists, is almost entirely 

 due, on the one hand, to the abrasion of wind or 

 rain and the alteration of heat and frost, on the other, 

 to the continual beating of sea-waves agitated by winds, 

 the results of solar radiation.' 



What would happen if the source of all these pro- 

 cesses, of every form, in fact, of force existing and 

 acting on the earth were to lose more than one-half of 

 its power? We can answer this question best by 

 another. What would happen if the engine working 

 a mighty system of machinery were deprived of more 

 than one-half of its due supply of fuel ? The engine 

 might continue to work, but it would no longer work 

 efficiently. The machinery would no longer serve its pur- 

 pose. And in like manner the great machinery which is 

 maintained by solar action on the earth, would no longer 



