Although liquid air is not found in nature, and is therefore called an artificial product, it is produced by taking advantage of natural law. Without the intellect of man it never would have been seen upon this earth; and the same may be said concerning many things in our world, both animate and inanimate. The genius of man is God-like. He lifts the veil that shrouds the mysteries of nature, and here he comes in very touch with the mind of the Infinite. Man interprets this thought through the medium of natural law, and lo, a new product!
How much life would have been robbed of its charm and interest if all these things had been worked out for us from the beginning! For there is no interest so absorbing and no pleasure so keen as that of pursuit when the pursuer is reaching out after the hidden things that are locked up in Nature's great storehouse. From time to time she yields up her secrets, little by little, to encourage those who love her and are willing to work, not only for the pleasure of the getting, but for the highest and best good of their fellows.
WATER.
CHAPTER XIX.
RIVERS AND FLOODS.
Water covers such a large proportion of the earth's surface and is such an important factor in the economy of nature that it becomes a matter of interest to study the process of its distribution. Water is to our globe what blood is to our bodies. A constant circulation must be kept up or all animal and vegetable life would suffer. Here, as in every other operation of nature, the sun is the great heart and motive power that is active in the distribution of moisture over the face of the globe.
The total annual rainfall on the whole surface of the earth amounts to about 28,000 cubic miles of water. Only about one-fourth of this amount ever reaches the ocean, but it is either absorbed for a time by animal and vegetable life or lifted through the process of evaporation into the air as invisible moisture, when it is carried over the region of rainfall and there condensed into water and falls back upon the earth—only to go through the same operation again. The whole surface of the earth is divided into drainage areas that lead either directly through rivulets and rivers to the ocean, or into some land-locked basin, where it either finds an outlet under ground or is kept within bounds through the process of evaporation, the same as is the case with our great oceans. In North America the amount of drainage area that has no outlet to the ocean amounts to about 3 per cent. of the whole surface. In other countries the percentage of inland drainage is much larger. The great Salt Lake in Utah is an instance where there is no outlet for the water except through the medium of evaporation. Inasmuch as all rivers and streams contain a certain proportion of salt,—especially in such strongly alkaline land regions as the Great Basin of the North American continent,—these inland lakes in time become saturated with this and other mineral substances.