gine that can deliver even 15 per cent;
a steam engine, on the other hand, uses about 17 per cent of the
energy in the coal under its boilers and passes the rest up the
chimney as waste heat and smoke.

There is still another advantage possessed by water-power over its two
rivals, steam and gas: It gives the most even flow of power. A gas
engine "kicks" a wheel round in a circle, by means of successive
explosions in its cylinders. A reciprocating steam engine "kicks" a
wheel round in a circle by means of steam expanding first in one
direction, then in another. A water wheel, on the other hand, is made
to revolve by means of the pressure of water--by the constant force of
gravity, itself--weight. Weight is something that does not vary from
minute to minute, or from one fraction of a second to another. It is
always the same. A square inch of water pressing on the blades of a
water wheel weights ten, twenty, a hundred pounds, according to the
height of the pipe conveying that water from the source of supply, to
the wheel. So long as this column of water is maintained at a fixed
height, the power it delivers to the wheel does not vary by so much as
the weight of a feather.

This property of falling water makes it the ideal power for generating
electricity. Electricity generated from mechanical power depends on
constant speed for steady pressure--since the electric current, when
analyzed, is merely a succession of pulsations through a wire, like
waves beating against a sea wall. Water-power delivers these waves at
a constant speed, so that electric lights made from water-power do not
flicker and jump like the flame of a lantern in a gusty wind. On the
other hand, to accomplish the same thing with steam or gasoline
requires an especially constructed engine.

_The Simple Weir_

Since a steady flow of water, and a constant head, bring about this
ideal condition in the water wheel, the first problem that faces the
farmer prospector is to determine the amount of water which his stream
is capable of delivering. This is always measured, for convenience,
in _cubic feet per minute_. (A cubic foot of water weighs 62.5 pounds,
and contains 7-1/2 gallons.) This measurement is obtained in several
ways, among which probably the use of a weir is the simplest and most
accurate, for small streams.

A weir is, in effect, merely a temporary dam set across the stream in
such a manner as to form a small pond; and to enable one to measure