Page:Popular Science Monthly Volume 1.djvu/52

42 recognized; and this process, too, will apparently go on till the 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 interesting 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 organized beings. The above-named agents have one defect: on the whole, they are incapable of being stored up to any great degree; we must employ 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 smelting-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 suddenly 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 portions, 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, remove various substances, carbon especially, from what seem to be their 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