��Popular Science Muiil/ili/
��succeeded in developing about one horse- power for every one hundred scjuare feet of reflecting surface he abandoned his jilan in disgust. "The scheme is im- practicable on account of the great cost of the needed apjiaraius," he declared. "The fact is that although the heat is obtained for nothing, so extensi\c, costK' and complc.v is the concentration ap- paratus that solar steam is many times more costly than steam produced l)y burning coal."
Even if much water could be boiled by mirrors, enough, let us suppose, to dex'elop a thousantl horse-power, it docs not necessarih' follow that the sun nK)tor will sujjplant the steam engine, l-actory machinery must sometimes be driven at night. How can the solar motor do that? In the desert of Sahara the sun does not shine at midnight.
Evidently the inventor of a solar power plant must design a storage sys- tem — a piece of apparatus that can be charged with excess power and tapped at will in sunless periods. Ericsson slaved on this phase of the problem as much as he did on the invention of the engine itself. Yet his results were un- satisfactory. Some of his successors ha\e designed machinery to compress air in strong, steel tanks; some ha\e
��planned systems in which a dynamo is made to charge a storage-batter\-; and some ha\'e thought of pum[)ing water into a reservoir from which it could sub- sequently be drawn to turn a water- wheel, ("ompressed air machinery, stor- age-batteries, and pumps cost much me)ne>-, even though the sun's heat may be had for nothing — so much money in fact that a boiler and a steam engine may prove cheaper in the end.
Askance though he might look at a colleague who really believed in substi- tuting sun's heat for coal, an engineer could not den>- that Ericsson had none too \i\idly [lictured the possibilities that await the successful in\'entor in desert lands. After making due allow- ance for the absorption of the atmos- phere, the total energy received b>- the earth in one day from the sun amounts to about 341,600 million million horse- power — eciuivalent to about two hun- dred anil thirt\' million horse-power for e\ery inhabitant.
To obtain these figures some instru- ment for measuring the sun's heat was obviously employed. Ordinarily solar heat is mercifully radiated and carried away as fast as it is received; otherwise the sea would have boiled away long ago, and e\ery li\ing thing on the earth
���The parabolic reflectors which serve to concentrate the sun's hciit upon a trouph of water at their focus move automatically with the sun. This solar plant is capable of RivinR an average of fifty horse power. Were it located farther south, it would yield energy amounting to otx)ut sixty five horse power, making due allowance for the absorption of the atmospheie