unds of work
per second, or 11,045 H.P. Such a stream would be very valuable for
the running of machinery.

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