r a riveted
steel pipe, purchased at the regular price. This pipe, leading from
the pond, or forebay, to the water wheel, should be kept as short as
possible; at the same time, the fall should not be too sharp. An angle
of 30 deg. will be found very satisfactory, although pipe is frequently
laid at angles up to 50 deg.

_Other Types of Impulse Wheels_

In recent years more efficient forms of the old-fashioned overshoot,
pitch-back breast, and undershoot wheels have been developed, by
substituting steel or other metal for wood, and altering the shape of
the buckets to make better use of the power of falling water.

In some forms of overshoot wheels, an efficiency of over 90 per cent
is claimed by manufacturers; and this type offers the additional
advantage of utilizing small quantities of water, as well as being
efficient under varying quantities of water. They utilize the falling
weight of water, although by giving the water momentum at the point of
delivery, by means of the proper fall, impulse too is utilized in some
measure. The modern steel overshoot wheel receives water in its
buckets from a spout set a few degrees back of dead center; and its
buckets are so shaped that the water is retained a full
half-revolution of the wheel. The old-style overshoot wheel was
inefficient principally because the buckets began emptying themselves
at the end of a quarter-revolution. Another advantage claimed for
these wheels over the old style is that, being made of thin metal,
their buckets attain the temperature of the water itself, thus
reducing the danger of freezing to a minimum. They are manufactured in
sizes from 6 feet in diameter to upwards of fifty feet; and with
buckets of from 6 inches to 10 feet in width. In practice it is usual
to deliver water to the buckets by means of a trough or pipe, through
a suitable spout and gate, at a point two feet above the crown of the
wheel. For this reason, the diameter of the wheel corresponds very
closely to the head in feet.

_The Reaction Turbine_

The reaction turbine is best adapted to low heads, with a large supply
of water. It is not advisable, under ordinary circumstances, to use it
under heads exceeding 100 feet, as its speed is then excessive. It
may be used under falls as low as two feet. Five thousand cubic feet
of water a minute would give approximately 14 actual horsepower under
such a head. A sluggish creek that flows in large volume could thus be
utilized for