Page:Popular Science Monthly Volume 76.djvu/532

528 Bureau. So the measurements are preparing the way for such control of the rain that this gift of the heavens will be made an unmixed benefit instead of a partial evil. Of the entire rainfall, only about a third flows through rivers into the sea (chiefly in floods), while it is estimated that fully half is evaporated, thereby returning to the air to affect the weather and temper the climate; and measurements of evaporation have begun, and will doubtless open means of exercising some control over the water in the air, no less than that on the surface and within the soil. Meantime it is estimated that less than a sixth of the mean annual rainfall is actually utilized in life and growth and other useful processes connected with the soil and its productions; and it is becoming clear that larger and better uses of the elemental water are possible through progressive redirection of the natural processes and powers. In the beginning, men bowed to the storm and fled the flood; later they predicted in order to seek shelter before the storm arrived; now they seek control at least of the storm waters in order that their volume and strength may be directed to welfare.

The four elements interact through organisms, of which the substance is mainly from the soil and water and their products; their circulatory medium and chief constituent is water, their force is from the sun, and their functions are maintained by air. During the ages the native flora adjusted itself to soil and earth-shaping agencies so closely that each type produced a surface to fit its needs—forests developing deep and friable soils and steeper slopes, grasses developing thinner soils and flatter slopes, and mosses producing spongy soils lining basins, each according to its kind and its capacity as conditioned by climate. A quarter of the area of the United States was too arid to sustain a full floral mantle, a third was wooded and more than a third was grassed when settlement began; for wherever the water supply suffices, vitality overspreads the surface and dominates the inorganic earth. Without water, vitality fails; there is neither assimilation nor germination, nor yet metabolism, in the absence of liquid, while transpiration and respiration depend largely on the passage of water from liquid to vapor. With water, the primarily organic circulation extends from the plant to the soil below and the air above and passes into still more complicated interrelations in animal bodies; and the locus of most effective energizing on the planet is the infinitely complex surface—the soil with its extensions in stem, leaf, flower, fruit and other organic bodies—at which water is continually passing from one form to another, absorbing or yielding latent heat, and mechanically interacting with the sun in seizing and storing and transferring molecular action. This is the complex in which vitality attains dominance over lower nature; and through it investigators are attaining control over the vital powers for the welfare of men and nations.