Oersted’s discovery of the production of magnetism by electricity naturally suggested the possibility of producing electricity from magnetism. In the year 1831 one of the most brilliant of our British scientists, Michael Faraday, discovered that a current of electricity could be induced in a coil of wire either by moving the coil towards or away from a magnet, or by moving a magnet towards or away from the coil. This may be shown in a simple way by connecting the ends of a coil of insulated wire to a galvanometer, and moving a bar magnet in and out of the coil; when the galvanometer shows that a current is induced in the coil on the insertion of the magnet, and again on its withdrawal. We have seen that a magnet is surrounded by a field of magnetic force, and Faraday found that the current was induced when the lines of force were cut across. Utilizing this discovery Faraday constructed the first dynamo, which consisted of a copper plate or disc rotated between the poles of a powerful horse-shoe magnet, so as to cut the lines of force. The current flowed either from the shaft to the rim, or _vice versa_, according to the direction of rotation; and it was conducted away by means of two wires with spring contacts, one pressing against the shaft, and the other against the circumference of the disc. This machine was miserably inefficient, but it was the very first dynamo, and from it have been slowly evolved the mighty dynamos used to-day in electric power stations throughout the world. There is a little story told of Faraday which is worth repeating even if it is not true. Speaking of his discovery that a magnet could be made to produce an electric current, a lady once said to him, “This is all very interesting, but what is the use of it?” “Madam,” replied Faraday, “what is the use of a baby?” In Faraday’s “baby” dynamo, as in all others, some kind of power must be used to produce the necessary motion, so that all dynamos are really machines for converting mechanical energy into electrical energy. The copper disc in this first dynamo did not prove satisfactory, and Faraday soon substituted for it rotating coils of wire. In 1832 a dynamo was constructed in which a length of insulated wire was wound upon two bobbins having soft iron cores, and a powerful horse-shoe magnet was fixed to a rotating spindle in such a position that its poles faced the cores of the bobbins. This machine gave a fair current, but it was found that the magnet gradually lost its magnetism on account of the vibration caused by its rotation. The next step was to make the magnet a fixture, and to rotate the bobbins of wire. This was a great improvement, and the power of machines built on this principle was much increased by having a number of rotating coils and several magnets. One such machine had 64 separate coils rotating between the poles of 40 large magnets. Finally, permanent magnets were superseded by electro-magnets, which gave a much more powerful field of force.