Page:Popular Science Monthly Volume 15.djvu/312

 been made public, it appears that the Ericsson sun-engine is composed of three distinct parts—the engine proper, that is, the working mechanism, the steam-generator, and the concentrating apparatus, by means of which last the feeble intensity of the sun's rays is augmented to the degree that will suffice to produce steam at a practical working pressure.

He claims that this concentrating apparatus will abstract on the average, for all latitudes between 45° north and 45° south, fully 3$1⁄2$ heat-units for every square foot presented vertically to the sun's rays. With 100 square feet of surface in his concentrating apparatus, therefore, he believes it will be possible to continuously develop from the sun's rays 8·2 horse-power during nine hours within the above-named range of latitude.

Mouchot, who, so far as the practical construction of the solar engine is concerned, has progressed further even than Ericsson, exhibited at the late Exposition at Paris a working sun-engine upon substantially the same general principle of construction as that above described, and which, from its novelty and the importance of the principle it illustrated, received universal popular attention and a most encouraging and flattering report of the judges of awards.

Not to over-estimate the capabilities of the new system, Ericsson, in his consideration of the practical side of the subject, assumes that a sun-engine of one horse-power will demand the concentration of heat from one hundred square feet; and on this estimate he proceeds to show that in all reasonable probability those regions of the earth that now suffer from an excess of heat will some day derive such benefits from their unlimited command of motive power as to vastly overbalance their climatic disadvantages. He proposes the sun-engine only for those regions where there is steady sunshine, and has mapped out extensive tracts of land aggregating no less than 9,000 miles in length and 1,000 miles in breadth, including therein the southern coast of the Mediterranean, Upper Egypt, much of the Red Sea region, the greater part of Persia and Arabia, and portions of China, Thibet, and Mongolia, in the Eastern Hemisphere; and Lower California, the Mexican plateau, Guatemala, and the west coast of South America for a distance of 2,000 miles, as the field of the solar empire of the future. As an evidence of the sincerity of his belief in the realization of these ideas, let me quote you the following enthusiastic passage from one of his numerous essays upon this subject: “The time will come,” asserts Ericsson, “when Europe must stop her mills and factories for want of coal. Upper Egypt then, with her never-ceasing sun-power, will invite the European manufacturer to remove his machinery and erect his mills on the firm ground along the sides of the alluvial plain of the Nile, where sufficient power can be obtained to enable him to run more spindles than a hundred Manchesters.”

For centuries past the wind has been put to work with very good