sepower, or
even a thousand horsepower, according to the conditions under which
it is used. With a given supply of water, the head, in feet,
determines the size of wheel necessary. The farther a stream of water
falls, the smaller the pipe necessary to carry a given number of
gallons past a given point in a given time.

A small wheel, under 10 x 13.5 ft. head, would give the same power
with the above 376 cubic feet of water a minute, as a large wheel
would with 10 x 376 cubic feet, under a 13.5 foot head.

This is due to the _acceleration of gravity_ on falling bodies. A
rifle bullet shot into the air with a muzzle velocity of 3,000 feet a
second begins to diminish its speed instantly on leaving the muzzle,
and continues to diminish in speed at the fixed rate of 32.16 feet a
second, until it finally comes to a stop, and starts to descend. Then,
again, its speed accelerates at the rate of 32.16 feet a second, until
on striking the earth it has attained the velocity at which it left
the muzzle of the rifle, less loss due to friction.

The acceleration of gravity affects falling water in the same manner
as it affects a falling bullet. At any one second, during its course
of fall, it is traveling at a rate 32.16 feet a second in excess of
its speed the previous second.

In figuring the size wheel necessary under given conditions or to
determine the power of water with a given nozzle opening, it is
necessary to take this into account. The table on page 51 gives
velocity per second of falling water, ignoring the friction of the
pipe, in heads from 5 to 1000 feet.

The scientific formula from which the table is computed is expressed
as follows, for those of a mathematical turn of mind:

Velocity (ft. per sec.) = sqrt(2gh); or, velocity is equal to the
square root of the product (g = 32.16,--times head in feet, multiplied
by 2).

SPOUTING VELOCITY OF WATER, IN FEET PER SECOND, IN HEADS
OF FROM 5 TO 1,000 FEET

Head Velocity

5 17.9
6 19.7
7 21.2
8 22.7
9 24.1
10 25.4
11 26.6
11.5 27.2
12 27.8
12.5 28.4
13 28.9
13.5 29.5
14 30.0
14.5 30.5
15 31.3
15.5 31.6
16 32.1
16.5 32.6
17 33.1
17.5 33.6
18 34.0
18.5 34.5
19 35.0