instrument, to follow an absolutely accurate plan in
constructing each part, in every detail, and great care must be
exercised, particularly in winding. It is necessary also to be very
careful in selecting the sizes of wire used and in the number of turns
made in the coils.

This is equally true of the fourth method, using the electro-magnet,
because the magnetic pull is dependent upon the size of wire from which
the coils are made and the number of turns of wire.

OBJECTIONS TO THE CALORIMETER.--The calorimeter, or sixth method, has
the same objection. The galvanoscope and electro-magnet do not respond
equally to all currents, and this is also true, even to a greater
extent, with the calorimeter.

CHAPTER VI

VOLTS, AMPERES, OHMS AND WATTS

UNDERSTANDING TERMS.--We must now try to ascertain the meaning of some
of the terms so frequently used in connection with electricity. If you
intended to sell or measure produce or goods of any kind, it would be
essential to know how many pints or quarts are contained in a gallon, or
in a bushel, or how many inches there are in a yard, and you also ought
to know just what the quantity term _bushel_ or the measurement _yard_
means.

INTENSITY AND QUANTITY.--Electricity, while it has no weight, is capable
of being measured by means of its intensity, or by its quantity. Light
may be measured or tested by its brilliancy. If one light is of less
intensity than another and both of them receive their impulses from the
same source, there must be something which interferes with that light
which shows the least brilliancy. Electricity can also be interfered
with, and this interference is called _resistance_.

VOLTAGE.--Water may be made to flow with greater or less force, or
velocity, through a pipe, the degree of same depending upon the height
of the water which supplies the pipe. So with electricity. It may pass
over a wire with greater or less force under one condition than another.
This force is called voltage. If we have a large pipe, a much greater
quantity of water will flow through it than will pass through a small
pipe, providing the pressure in each case is alike. This quantity in
electricity is called _amperage_.

In the case of water, a column 1" x 1", 28 inches in height, weighs 1
pound; so that if a pipe 1 inch square draws water from the bottom it
flows with a pressure of 1 pound. If the pipe has a measurement of 2
square inches, double the quantity of water w