The figure on page 242 shows a magnetic compass needle. This is used
to test the direction of an electric current flowing through a wire or
cable conductor. The plus sign, +, is the positive and the minus, -,
sign is the negative end or pole. _A continuous current always flows
from the positive to the negative end or pole_, hence the north end or
pole, N, is the positive end of the needle and the south pole, S, is
the south pole of the needle.
When one of these devices is held in close proximity to a conductor
of electricity _it immediately assumes a parallel position to the
conductor_ and indicates the direction in which the current is flowing.
The long, upper arrow, as shown in the figure, tells the direction of
the flow. A small pocket compass may be used in place of this device
and is often carried in the pocket of electricians for the purpose of
indicating the direction of the current.