Near Cairo, Egypt, there is a plant erected by an American inventor, Mr. Frank Shuman, which develops about fifty horsepower. This consists of a series of five huge trough-shaped mirrors that focus the sun’s rays upon boilers and thus generate low pressure steam. The mirrors measure 13 feet in width and 304 feet in length and these are mounted on a light steel framework with their axes running north and south so that they may be turned from east to west to follow the course of the sun across the sky. In order to prevent the mirrors from shading each other in the early morning and late afternoon they are set twenty-five feet apart. Mirrors are made of thin sheets of window glass, silvered at the back. The troughs are parabolic in cross section and at the focus of each is hung a tubular boiler painted black to absorb the heat rays. The five boilers feed a common steam reservoir from which steam is fed to a pump. This pump raises about 6,000 gallons of water per minute, which is used for irrigating purposes. Of course at night the supply of energy is cut off and on cloudy or rainy days no steam is generated, but such days are few in the region of Cairo, and continuous operation is not essential to the operation of irrigating systems. There are localities in Africa, Asia Minor, and even in the United States where the lack of water and the pitiless rays of the sun have turned vast regions into deserts. Here the very rays which have parched vegetation may be utilized to pump water over the thirsty lands and convert them into rich agricultural regions. There is another mighty source of power in the internal heat of the earth. Here and there all over the earth are vent holes through which the pent-up energy makes its escape in the form of steam, gases, or molten lava. There is no question as to the enormous stores of energy in active volcanoes, and as we appreciate the value of heat energy our eyes turn covetously to these great chimneys of the subterranean furnaces. HARNESSING VOLCANOES