Think what such an invention means, if practically successful, to the vast stretches of our arid Western land, valueless without water. Spread all over this country of Arizona, New Mexico, Southern California, and other States are thousands of miles of canals to bring in water from the rivers for irrigating the deserts, and there are untold numbers of wind-mills, steam and gasoline pumps which accomplish the same purpose more laboriously. Think what a new source of cheap power will do--making valuable hundreds of acres of desert land, providing homes for thousands of busy Americans. Indeed, a practical solar motor might make habitable even the Sahara Desert. And it can be used in many other ways besides for pumping water. Threshing machines might be run by this power, and, converted into electricity and saved up in storage batteries, it might be used for lighting houses, even for cooking dinners, or in fact for any purpose requiring power. These solar motors can be built at no great expense. I was told that ten-horse-power plants would cost about $200 per horse-power, and one-hundred-horse-power plants about $100 per horse-power. This would include the entire plant, with engine and pump complete. When it is considered that the annual rental of electric power is frequently $50 per horse-power, whether it is used or not, it will be seen that the solar motor means a great deal, especially in connection with irrigation enterprises. [Illustration: The Rear Machinery for Operating the Reflector.] And the time is coming--long-headed inventors saw it many years ago--when some device for the direct utilisation of the sun's heat will be a necessity. The world is now using its coal at a very rapid rate; its wood, for fuel purposes, has already nearly disappeared, so that, within a century or two, new ways of furnishing heat and power must be devised or the human race will perish of cold and hunger. Fortunately there are other sources of power at hand; the waterfalls, the Niagaras, which, converted into electricity, may yet heat our sitting-rooms and cook our dinners. There is also wind-power, now used to a limited extent by means of wind-mills. But greater than either of these sources is the unlimited potentiality of the tides of the sea, which men have sought in vain to harness, and the direct heat of the sun itself. Some time in the future these will be subdued to the purpose of men, perhaps our main dependence for heat and power.