Between 1810 and 1830, many important laws governing electrical phenomena were discovered, which tended greatly to render the science more exact, and to give it commercial direction. Oersted, of Denmark, discovered a means of measuring the strength and direction of an electric current. Ampère, of France, discovered the identity of electricity and what had before been called galvanism. Ritchie, of England, made the first machine by which a continuous motion was produced by means of the attractions and repulsions between fixed magnets and electro-magnets. This machine was an early suggestion of the dynamo and motor of the coming years of the century. It meant that electricity was a source of power, as well as of other phenomenal things. In speaking of the electro-magnet in connection with Ritchie’s machine, it is proper to say that the electro-magnet was probably discovered between 1825 and 1830, but precisely by whom is not known. It differs from the natural magnet, or the permanent steel horseshoe magnet, and consists simply of a round piece of soft iron, called a core, around which are wrapped several coils of fine wire. When an electric current is made to pass through this wrapping of wire, called the helix, the iron core becomes magnetized, and has all the power of a permanent magnet. But as soon as the electric current ceases, the magnetic power of the core is lost. Hence it is called an electro-magnet, or a temporary magnet, to distinguish it from a permanent magnet. [Illustration: INDUCTION COIL.] While the discovery of the electro-magnet was very important in the respect that it afforded great magnetic power by the use of a limited or economic galvanic force, or, in other words, by the use of smaller and fewer Voltaic batteries, it was not until Faraday began his splendid series of electrical discoveries, in 1831, that a new and exhaustless wellspring of electricity was found to lay at the door of science. Faraday’s prime discovery was that of the induction of electric currents, or, in other words, of manufacturing electricity directly from magnetism. He began his experiments with what became known as an induction coil, which, though then crude in his hands, is the same in principle to-day. It consists of an iron core wrapped with two coils of insulated wire. One coil is of very lengthy, thin wire, and is called the secondary coil. The other is of short, thick wire, and is called the primary. When a magnetic current is passed through the primary coil, with frequent makes and breaks, it induces an alternating current of very high tension in the secondary coil, thus powerfully increasing its effects. In Faraday’s further study of electric induction, he showed that when a conductor carrying a current was brought near to a second conductor it induced or set up a current in this second. So magnets were found to have a similar effect upon one another. [Illustration: MAGNETIC FIELDS OF FORCE.]