MAGNETIC NEEDLE.
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.