{ 2 THE POPULAR SCIENCE MONTHLY. 



ally recognized ; and this process, too, will apparently go on till th& 

 earth ceases to rotate on its axis, and presents one face constantly to 

 the sun. 



Thus we see that the destruction of the land by the sea, so inter- 

 esting in a geological point of view, is partly due to the sun's action. 

 Not only is he the source of the light and heat we enjoy, but he aids 

 in forming the vast sedimentary beds that form so large a part of the 

 crust of the earth, mixing the ingredients of our fields, and moulding 

 our globe. 



By heating the air, the sun produces winds, and some of the labor 

 thus expended is made use of by man in turning his windmills, and 

 carrying his wares across the sea. But there is another expenditure 

 of the sun's heat more immediately useful to man. By evaporating 

 the sea and other bodies of water, he loads the air with moisture, 

 which, when in contact with cold mountain-peaks or cold masses of air, 

 loses its heat, and, being condensed, falls as rain or snow. Thus the 

 rivers are replenished, which for a long time supplied the greater part 

 of the labor employed in manufactures, though the invention of the 

 steam-engine is fast reducing relatively the value of this supply of 

 labor. 



But vast as the sun's power thus exerted is, and useful as it is to 

 man, it is surpassed in importance by his labor exerted through organ- 

 ized beings. The above-named agents have one defect : on the whole, 

 they are incapable of being stored up to any great degree ; we must em- 

 ploy them as Nature gives them to us. Organized existence, however, 

 possesses the power of storing up labor to a very high degree. The 

 means it adopts are not mechanical, but chemical. The formation of 

 chemical compounds is attended with the giving out of heat, which, 

 as we have said before, is equivalent to labor, and, if of sufficient 

 intensity, can by us be made available as labor, as in the steam-engine. 

 Now, we take iron-ore, consisting of iron in combination with other 

 substances. By means of great heat, the iron is set free in the smelt- 

 ing-furnace. The iron, then, in its change of form has, as it were, 

 taken in all this heat. If, now, we take this iron, and, keeping it from 

 the influence of the air, reduce it to very fine powder, and then sud- 

 denly expose it to the air, by the force of natural affinity, it will absorb 

 the oxygen of the air, and in so doing give out the heat before required 

 to set it free from the oxygen ; and if the iron be in small enough por 

 tions, so that the process is sufficiently rapid, we may see the iron grow 

 red-hot with the heat thus disengaged. 



Now, plants and trees, by the aid of the solar light and heat, re 

 move various substances, carbon especially, from what seem to be theii 

 more natural combinations, and in other combinations store them up 

 in their structures. Take a young oak-tree with its first tender leaves ; 

 if deprived of the sun's light and heat, its growth would be stayed, 

 and its life die out. But, with the aid of the sun's rays, it absorbs 



