s enclosed, above the
floor, in a wooden box, or a casing made of cast or sheet iron, which
should be water-tight.

Since these wheels are usually operated under great heads, the problem
of regulating their water supply requires special consideration. A
gate is always provided at the upper, or intake end, where the water
pipe leaves the flume. Since the pressure reaches 1,000 pounds the
square inch and more, there would be danger of bursting the pipe if
the water were suddenly shut off at the nozzle itself. For this reason
it is necessary to use a needle valve, similar to that in an ordinary
garden hose nozzle; and by such a valve the amount of water may be
regulated to a nicety. Where the head is so great that even such a
valve could not be used safely, provision is made to deflect the
nozzle. These wheels have a speed variation amounting to as much as 25
per cent from no-load to full load, in generating electricity, and
since the speed of the prime mover--the water wheel--is reflected
directly in the voltage or pressure of electricity delivered, the
wheel must be provided with some form of automatic governor. This
consists usually of two centrifugal balls, similar to those used in
governing steam engines; these are connected by means of gears to the
needle valve or the deflector.

As the demand for farm water-powers in our hill sections becomes more
general, the tangential type of water wheel will come into common use
for small plants. At present it is most familiar in the great
commercial installations of the Far West, working under enormous
heads. These wheels are to be had in the market ranging in size from
six inches to six feet and over. Wheels ranging in size from six
inches to twenty-four inches are called water motors, and are to be
had in the market, new, for $30 for the smallest size, and $275 for
the largest. Above three feet in diameter, the list prices will run
from $200 for a 3-foot wheel to $800 for a 6-foot wheel. Where one has
a surplus of water, it is possible to install a multiple nozzle wheel,
under heads of from 10 to 100 feet, the cost for 18-inch wheels of
this pattern running from $150 to $180 list, and for 24-inch wheels
from $200 to $250. A 24-inch wheel, with a 10-foot head would give
1.19 horsepower, enough for lighting the home, and using an electric
iron. Under a 100-foot head this same wheel would provide 25.9
horsepower, to meet the requirements of a bigger-than-average farm
plant.