How Power May be Obtained in the Future.—In spite of all possible economies and inventions the time will surely come when new sources of power will be needed. Man-power and animal-power have long been insufficient. The space available for raising wood decreases as the world's population becomes more dense. Coal and petroleum are rapidly being exhausted. Among the sources of power now used only the wind and running water can be counted on as permanent sources of abundant power. It is estimated that when proper dams and reservoirs are built the streams of the United States may possibly supply more than 100,000,000 horse-power. At present our factories and transportation systems use about 30,000,000 horse-power; the heat used in houses, and the power used on farms, in automobiles, and for all manner of minor purposes probably brings the total up to 50,000,000. Thus if the water-power could all be utilized it would suffice for the present, but our population is growing with great rapidity, and the amount of power needed per individual is also increasing by leaps and bounds. Hence if we have 200,000,000 people in 1970, we shall probably need much more than 100,000,000 horse-power for all purposes including heat and light. Similar con ditions will probably prevail in other countries. Thus even when all the water-power has been harnessed, the world will ultimately need much additional power to heat its houses, cook food, carry on indus tries, and keep transportation systems in operation.
Part of this can perhaps be obtained from the wind, but the greatest source of power is the sun. In the drier part of Texas, where the sky is usually cloudless, any two average counties among the 245 in the State receive from the sun enough power to run all the factories and transportation systems in the whole of the United States. If we
can devise means of using sun-power directly and cheaply, one of the world's greatest problems will be solved. To-day steam can be made in solar steam engines whose boilers are heated by concentrating the sun's rays upon them by means of mirrors. Such engines, however, are too expensive to be practicable, and can be used only in places where the sun is rarely clouded. The engineer who invents a solar engine that is practical and cheap, and that has sufficient storage to carry it through cloudy days, will do mankind a most wonderful service. When that is accomplished, we may hope at last to get rid of our strike-breeding coal mines except as places from which material for dyes, medicines, and so forth is extracted. We might also get rid of the factory chimneys that pollute the air of our cities. Per haps our factory towns will be as clean and wholesome as are those in Switzerland and elsewhere that now use hydro-electric power. We may be able to extract aluminum cheaply and in enormous quantities and thus conserve less abundant metals such as iron and copper. We may perhaps pump water for irrigation so cheaply as to cultivate many dry regions that now are almost uninhabited. We may be able to heat our houses electrically with as much ease as we now light them. Think of the work and dirt that would be saved in that one way! The cost of transportation and of manufactured goods will be lessened, for now one of the largest items, especially in transportation, is the cost of coal. In short, if ever solar energy should become cheaply and easily available, life might be revolutionized almost as much as it has been by the invention of the steam engine, and the change would in most respects be beneficial.