THE SOURCES OF POWER Importance of Power.—In the present Age of Steel and Electricity all sources of power have assumed a new and increasing importance. The manufacturer needs power to drive his machinery, to bring raw materials, and to carry his finished products to market. The mer chant needs power to run his elevator, and supply him with light. The farmer needs it to plow his fields, saw his wood, sharpen his scythes, churn his butter, and carry his crops to market. You your self need power to light your home, to carry you on journeys, and to bring you letters and supplies. It is clear, therefore, that everyone in a civilized community uses power either directly or indirectly. Farms, transportation systems, and factories, however, are the greatest users of power. Hence in this chapter we shall think particularly of their needs in considering the seven great sources of power (1) man's own body, (2) animals, (3) wind, (4) water, (5) wood, (6) coal, and (7) petroleum.
Kinds of Power.—(1) Man.—The oldest and most common source of power is the energy of man's body. He uses it to raise food, build houses, carry loads, and wield the ax. He also uses it for manu factures such as the woolen rugs of the Khirghiz and the carved toys of the Swiss.
In tropical countries man's strength is the chief source of power. For instance in India, Africa, and tropical South America long lines of coolies trudge hundreds of miles through jungle and swamp weighed down with heavy loads on their heads or backs. In China some device like a wheelbarrow is usually used to aid man's strength in carrying both goods and people; and in Japan the jinrikisha serves the same purpose to better effect. In the most advanced countries, although millions of men furnish power for transportation, unlike the coolie, they transport their loads only short distances, as in carrying bricks and mortar, loading boxes into wagons, and lifting leather into cutting machines. In our own country man's bodily power is used less than anywhere else, since its place is taken by so many devices such as elevators and electric trucks.
(2) Animals.—Since man's own strength is not sufficient to ac complish all his ambitious plans, he long ago obtained other sources of power by taming the horse, donkey, ox, camel, water buffalo, ele phant, yak, llama, and reindeer. His use of one or another of these
animals, quite unlike his use of his own strength, is least in tropical countries and greatest in the most advanced parts of the world.
In tropical countries animals are little used for two chief reasons: (a) The people are not energetic and intelligent enough to take good care of their animals. (b) The most useful animals like the horse and ox do not thrive in tropical countries because of the poor grass and pestering insects. The fine animals introduced by the United States into the Philippines deteriorate rapidly if left to the care of the natives.
In countries like Japan and eastern China horses and other beasts of burden are also rare. The climate is not favorable to grass, and the places where food for animals might be raised are needed to sup ply food for the dense human population. In dry, grassy regions like the steppes of Central Asia and our own Western States, horses and cattle are numerous, for there is much land that is good for grazing and not for agriculture. Nevertheless, animals are not used for power nearly so much there as in the great agricultural regions like the eastern United States, especially Illinois and its neighbors; or north western Europe, especially northern France and the Low Countries. In such places horses are so valuable for farm work that their number is increasing in spite of the increased use of automobiles.
(3) How Wind Furnishes Power.—The sources of power thus far considered demand little or no mechanical skill. The use of wind, however, demands that people shall be inventive and able to construct machinery. Hence windmills are unknown within the tropics except where Europeans or Americans have introduced them. The steady trade winds, however, are almost ideal for wind-power. Hence in tropical towns like Merida in Yucatan, a regular forest of windmills may be seen, since most of the 65,000 people use water pumped from caverns and streams deep down in the porous limestone. The chief development of windmills, however, is in the energetic temperate zone. In level open regions like Holland, Wisconsin, and Iowa, where the wind blows freely and steadily, they are used in large num bers to pump water into tanks, and to cut wood and fodder.