If we cover a non-magnetic piece of iron with a wire coil, and taking a magnet turn it rapidly beneath the wire-bound iron, so that the magnetic poles approach each other alternately, an electrical current will be generated in the wire. The electro-magnetic machine is thus made; but although strong currents may be generated as a source of motive power it is a failure. To Faraday our knowledge of magneto-electricity is due. “He knew” (says Professor Tyndall in his interesting work, “Faraday as a Discoverer”) “that under ordinary circumstances the presence of an electrified body was sufficient to excite by induction an unelectrified body. He knew that the wire which carried an electric current was an electrified body, and still all attempts had failed to make it excite in other wires a state similar to its own.” But while he was making his experiments on the induction of electric currents he noticed that at the time the current was passing from the battery through the coils of wire that no motion was perceptible in the galvanometer. But when the circuit was opened, and when it was closed, there was a slight motion of the needle in the galvanometer, but in different directions. After consideration the philosopher came to the conclusion “that a battery current through one wire induced a similar current through the other, but for an instant only.” Œrsted had already demonstrated that all magnetic effects were attributable to the attraction and repulsion of electric currents; and founding his views upon the theory of Ampère, Faraday came to the conclusion that electricity could be produced from magnetism, or that the electric current could be obtained from magnets. This he succeeded in doing. By inserting a steel magnet about half its length into a coil of wire, Faraday induced a current to pass through the wire in two directions. Thus he proceeded to solve all the mysteries of magneto-electricity, and stated that to produce currents it was only necessary to “cut appropriately the lines of magnetic force.” The application of the magnet to the machines for electric lighting will be shown further on. Very powerful currents are obtained by the induction coil; but the currents would not be of practical service were it not for the apparatus called a Commutator, or key, which reverses the connection of the bobbins, and turns the current at every half revolution. Just as if a current were being sent across and back over a table, and when the current has reached the end, an instantaneous _wheel round_, or pivoting of the table, _sends the current on_, in continuation (but on the table all the time), because of the sudden change of its position. The back rush being on the table, the movement of the latter really makes the line continuous, and by quickly breaking and reversing the current in the commutator, the effect is gained in the machine. [Illustration: Electro-magnets and bobbin, etc. (Clarke’s machine)] CHAPTER XXII.