How to Place the Detector.—If the detector is placed north and south, as shown by the two markings, N and S (Fig. [37]), the magnet bar will point north and south, being affected by the earth's magnetism; but when a current of electricity flows through the coil (B), the magnet will be deflected to the right or to the left, so that the pointer (O) will then show the direction in which the[p. 55] current is flowing through the wire (R) which you are testing.
The next step of importance is to measure the current, that is, to determine its strength or intensity, as well as the flow or quantity.
Different Ways of Measuring a Current.—There are several ways to measure the properties of a current, which may be defined as follows:
1. The Sulphuric Acid Voltameter.—By means of an electrolytic action, whereby the current decomposes an acidulated solution—that is, water which has in it a small amount of sulphuric acid—and then measuring the gas generated by the current.
2. The Copper Voltameter.—By electro-chemical means, in which the current passes through plates immersed in a solution of copper sulphate.
3. The Galvanoscope.—By having a coil of insulated wire, with a magnet suspended so as to turn freely within the coil, forming what is called a galvanoscope.
4. Electro-magnetic Method.—By using a pair of magnets and sending a current through the coils, and then measuring the pull on the armature.
5. The Power or Speed Method.—By using an electric fan, and noting the revolutions produced by the current