am combines both in one apparatus. It is a self-acting pump of
the impulse type, in which force is suddenly applied and discontinued,
these periodical applications resulting in the lifting of water.
Single-acting rams pump the water which operates them; double-acting
rams utilize an impure supply to lift a pure supply from a different
source.

The advantages of the ram are: it works continuously, day and night,
summer and winter, with but very little attendance; no lubrication is
required, repairs are few, the first cost of installation is small.
Frost protection, however, is essential. The disadvantages are that a
ram can be used only where a large volume of water is available. The
correct setting up is important, also the proper proportioning in size
and length of drive and discharge pipes. The continual jarring tends
to strain the pipes, joints, and valves; hence, heavy piping and
fittings are necessary. A ram of the improved type raises water from
twenty-five to thirty feet for every foot of fall in the drive pipe,
and its efficiency is from seventy to eighty per cent.

Running water is a most convenient and cheap power, which is often
utilized in water wheels and turbines. These supply power to run a
pump; the water to be raised may come from any source, and the pump
may be placed at some distance from the water wheel. Where sufficient
fall is available--at least three feet--the overshot wheel is used. In
California and some other Western States an impulse water wheel is
much used, which is especially adapted to high heads.

_Windmills Used for Driving Pumps_

The power of the wind applied to a windmill is much used for driving
pumps. It is a long step forward from the ancient and picturesque
Dutch form of windmill, consisting of only four arms with cloth sails,
to the modern improved forms of wheels constructed in wood and in
iron, with a large number of impulse blades, and provided with devices
regulating the speed, turning the wheel out of the wind during a gale,
and stopping it automatically when the storage tank is filled. The
useful power developed by windmills when pumping water in a moderate
wind, say of sixteen miles an hour velocity, is not very high, ranging
from one twenty-fifth horse-power for an eight and one-half foot wheel
to one and one-half horse-power for a twenty-five foot wheel. The
claims of some makers of windmills as to the power developed should be
accepted with caution.

The chief