The rapid entrance and exit of the steel magnet in the helix of copper wire would be insufficient to produce any quantity of electricity, and the ingenuity of man has been taxed to arrange a method by which a magnet may be suddenly formed and destroyed inside a coil of insulated copper wire. The difficulty, however, has been surmounted by several ingenious contrivances, based on the principles first discovered by Faraday; and the one especially to be noticed is the revolution of a coil of copper wire enclosing a piece of soft iron, called the _armature_, before the poles of a powerful magnet. The first machine was invented [Page 243] by M. Hypolyte Pixii, of Paris, and in 1833, Mr. Saxton improved upon this machine, and three years afterwards, Mr. E. M. Clarke described a very ingenious modification of the electro-magnetic machine, which is depicted at page 241 of this chapter. In this picture, the letter A is the permanent fixed horse-shoe magnets, which are very appropriately termed the _battery_ magnets, because they take the position that would otherwise be occupied by a voltaic battery, and they are indeed the prime source of the electrical power that is evoked. D is the intensity _armature_ which screws into a brass mandril seated between the poles of the magnets A, motion being communicated to it by the multiplying wheel, E. This armature or _inductor_ has two coils of fine insulated copper wire of 1500 yards in length, coiled on its cylinders, the commencement of each coil being soldered to the bar D, from which projects a brass stem, also soldered into D, carrying the break-piece H, which is made fast in any position by a small binding-screw in a hollow brass cylinder to which the other terminations of the coils, F F, are soldered, these being insulated by a piece of hard wood attached to the brass stem. O is an iron wire spring pressing against one end of the hollow brass cylinder; P is a square brass pillar; Q is a metal spring that rubs gently on the break-piece H; T is a copper wire for connecting the brass pieces with the wood L between them, and out of which P and O pass; R R are two handles of brass with metallic wires, the end of one being inserted into either of the brass pieces connected with P and O, and the other into the brass stem that carries the break-piece H, delivers a most severe shock directly the wheel is set in motion.