ning water. But when
the infant nursed by Watt and Stephenson had grown into a giant, both of
these natural agents were deposed from the important position they once
held. Windmills in a state of decay crown many of our hilltops, and the
water-wheel which formerly brought wealth to the miller now rots in its
mountings at the end of the dam. Except for pumping and moving boats and
ships, wind-power finds its occupation gone. It is too uncertain in
quantity and quality to find a place in modern economics. Water-power,
on the other hand, has received a fresh lease of life through the
invention of machinery so scientifically designed as to use much more of
the water's energy than was possible with the old-fashioned wheel.

[Illustration: FIG. 187.--A Pelton wheel which develops 5,000
horse-power. Observe the shape of the double buckets.]

The _turbine_, of which we have already spoken in our third chapter, is
now the favourite hydraulic engine. Some water-turbines work on much the
same principle as the Parsons steam-turbine; others resemble the De
Laval. Among the latter the Pelton wheel takes the first place. By the
courtesy of the manufacturers we are able to give some interesting
details and illustrations of this device.

[Illustration: FIG. 188.--Pelton wheel mounted, with nozzle in
position.]

The wheel, which may be of any diameter from six inches to ten feet, has
buckets set at regular intervals round the circumference, sticking
outwards. Each bucket, as will be gathered from our illustration of an
enormous 5,000 h.p. wheel (Fig. 187), is composed of two cups. A nozzle
is so arranged as to direct water on the buckets just as they reach the
lowest point of a revolution (see Fig. 188). The water strikes the
bucket on the partition between the two cups, which turns it right and
left round the inside of the cups. The change of direction transfers the
energy of the water to the wheel.

[Illustration: FIG. 189.--Speed regulator for Pelton wheel.]

The speed of the wheel may be automatically regulated by a deflecting
nozzle (Fig. 189), which has a ball and socket joint to permit of its
being raised or lowered by a centrifugal governor, thus throwing the
stream on or off the buckets. The power of the wheel is consequently
increased or diminished to meet the change of load, and a constant speed
is maintained. When it is necessary to waste as little water as
possible, a concentric tapered needle may be fitted inside the