ill flow therefrom, at the
same pressure.

AMPERAGE.--If, on the other hand, we have a pipe 1 inch square, and
there is a depth of 56 inches of water in the reservoir, we shall get as
much water from the reservoir as though we had a pipe of 2 square inches
drawing water from a reservoir which is 28 inches deep.

MEANING OF WATTS.--It is obvious, therefore, that if we multiply the
height of the water in inches with the area of the pipe, we shall obtain
a factor which will show how much water is flowing.

Here are two examples:

1. 28 inches = height of the water in the reservoir.

2 square inches = size of the pipe.
Multiply 28 x 2 = 56.

2. 56 = height of the water in the reservoir.
1 square inch = size of the pipe.
Multiply 56 x 1 = 56.

Thus the two problems are equal.

A KILOWATT.--Now, in electricity, remembering that the height of the
water corresponds with _voltage_ in electricity, and the size of the
pipe with _amperage_, if we multiply volts by amperes, or amperes by
volts, we get a result which is indicated by the term _watts_. One
thousand of these watts make a kilowatt, and the latter is the standard
of measurement by which a dynamo or motor is judged or rated.

Thus, if we have 5 amperes and 110 volts, the result of multiplying them
would be 550 watts, or 5 volts and 110 amperes would produce 550 watts.

A STANDARD OF MEASUREMENT.--But with all this we must have some
standard. A bushel measure is of a certain size, and a foot has a
definite length, so in electricity there is a recognized force and
quantity which are determined as follows:

THE AMPERE STANDARD.--It is necessary, first, to determine what an
ampere is. For this purpose a standard solution of nitrate of silver is
used, and a current of electricity is passed through this solution. In
doing so the current deposits silver at the rate of 0.001118 grains per
second for each ampere.

THE VOLTAGE STANDARD.--In order to determine the voltage we must know
something of _resistance_. Different metals do not transmit a current
with equal ease. The size of a conductor, also, is an important factor
in the passage of a current. A large conductor will transmit a current
much better than a small conductor. We must therefore have a standard
for the _ohm_, which is the measure of resistance.

THE OHM.--It is calculated in this way: There are several standards, but
the one most generally employed is the _International Ohm_. To determine
it, by thi