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For many centuries wind has been used in the countries of the old world as a motive power. In some of the low lying lands of Central Europe the lumbering old windmill is still one of the characteristic features of the landscape. In this country the windmill has of late years been greatly improved and brought extensively into lise. It is estimated there .are over half a million windmills now running, and the annual increase in sales is estimated to be upward of 50,000. They are mainly used for pumping the domestic water supply; in many of the Western States a farm is scarcely considered to be complete unless it can boast of its windmill pump. In some cases the mills are put to such work as cutting feed for stock, grinding corn, and the various lighter mechanical work of a farm. The success of the improved windmill in America has encouraged the manufacturers to push the trade in European countries and there is today a growing demand in the old world for these very useful and economical machines. The chief drawback to the use of wind-driven motors is that the power is intermittent and uncertain. It has often been proposed to store up this power, so that the supply can be drawn upon in calm weather. This can undoubtedly be done ; but whether such storage can be accomplished with economical results is open to question. Water might be raised a certain height and stored in tanks prepared for the purpose. But on the basis that one horse power would require the lifting of 33,000 pounds one foot in one minute, it is evident that it would require large storage tanks and much time to lift enough water to provide a supply of any practical value. To this must be added the cost and care of a water motor to utilize this stored-up energy. A simple calculation shows that to furnish a constant supply of one horse power for a day of ten hours would require the daily storage of 47,000 gallons of water at a height of 50 feet. To accommodate this would require a tank 20 feet square and 16 feet high. fo the expense of such a tank must be added the cost of the strong tower which would have to be built to carry at sucb a height this load of nearly 200 tons. The cost of receivers and motors for the utilization and storage of compressed air would in like manner largely neutralize any apparent utility of such device. To store up sufficient electrical energy to run a one horse power motor foraday of ten hours would require a set of cells whose weight would be from 1,600 to 1,700 pounds. They would occupy some 20 cubic feet of space; and with the motor, belting, shafting and general fittings complete, the plant would cost about $500. There would be a certain amount of drawback to the use of this system in the fact that the handling of a battery necessitates some technical knowledge and skill; a consideration that must necessarily limit the range of its application. Of the three systems of storage, the last mentioned would seem to be the best; and with further improvements in the way of automatic devices for regulating the charging and discharge of the batteries, we may look for a more extended use of this system in the future.
