176.  Windmills.  Those of us who have spent our vacation days in the country know that there is no ready-made water supply there as in the cities, but that as a rule the farmhouses obtain their drinking water from springs and wells.  In poorer houses, water is laboriously carried in buckets from the spring or is lifted from the well by the windlass.  In more prosperous houses, pumps are installed; this is an improvement over the original methods, but the quantity of water consumed by the average family is so great as to make the task of pumping an arduous one.

The average amount of water used per day by one person is 25 gallons.  This includes water for drinking, cooking, dish washing, bathing, laundry.  For a family of five, therefore, the daily consumption would be 125 gallons; if to this be added the water for a single horse, cow, and pig, the total amount needed will be approximately 150 gallons per day.  A strong man can pump that amount from an ordinary well in about one hour, but if the well is deep, more time and strength are required.

The invention of the windmill was a great boon to country folks because it eliminated from their always busy life one task in which labor and time were consumed.

177.  The Principle of the Windmill.  The toy pin wheel is a windmill in miniature.  The wind strikes the sails, and causes rotation; and the stronger the wind blows, the faster will the wheel rotate.  In windmills, the sails are of wood or steel, instead of paper, but the principle is identical.

[Illustration:  FIG. 124.—­The toy pin wheel is a miniature windmill.]

As the wheel rotates, its motion is communicated to a mechanical device which makes use of it to raise and lower a plunger, and hence as long as the wind turns the windmill, water is raised.  The water thus raised empties into a large tank, built either in the windmill tower or in the garret of the house, and from the tank the water flows through pipes to the different parts of the house.  On very windy days the wheel rotates rapidly, and the tank fills quickly; in order to guard against an overflow from the tank a mechanical device is installed which stops rotation of the wheel when the tank is nearly full.  The supply tank is usually large enough to hold a supply of water sufficient for several days, and hence a continuous calm of a day or two does not materially affect the house flow.  When once built, a windmill practically takes care of itself, except for oiling, and is an efficient and cheap domestic possession.

[Illustration:  FIG. 125.—­The windmill pumps water into the tank.]

178.  Steam as a Working Power.  If a delicate vane is held at an opening from which steam issues, the pressure of the steam will cause rotation of the vane (Fig. 126), and if the vane is connected with a machine, work can be obtained from the steam.