Fig. 235.
a b. Coil of copper wire. c. Permanent bar magnet placed inside the coil, when the galvanometer needle, d, is deflected.
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 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 below. 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.
In Saxton's electro-magnetic machine, the permanent steel magnets are placed horizontally instead of perpendicularly, and are composed of six or more horse-shoe-shaped pieces of steel. The armatures, or inductors, or electro-magnets (for they consist of pieces of soft round iron with wire wound round them), are two in number, and are adapted to exhibit either quantity or intensity effects. The quantity armature is constructed of stout iron, and covered with thick insulating wire. The intensity armature is made of slighter iron, and covered with from one thousand to two thousand yards of fine copper wire coated with silk. The quantity armature is intended for the exhibition of results similar to those which are procurable from a voltaic battery, such as the magnetic spark, inducing magnetism in soft iron, heating platinum wire. The intensity armature is employed for the chemical decomposition of water and other bodies, and likewise for the administration of those terrible blows to the nervous system which cause strong men of the mildest deportment to become painfully excited, and to make those ejaculations which are so peculiar to the genus John Bull.
EXPERIMENTS WITH THE MAGNETO-ELECTRIC MACHINE.
First Experiment.
The decomposition of water by the passage of electricity from one platinum plate to another, has already been illustrated at [page 198]. The same fact may likewise be displayed by the following arrangement of the machine. (Fig. 236.)
Fig. 236.