1868. In producing this discharge, iron is not more effective than any other metal. It is, in fact, known to be less competent for this species of conduction, than copper, silver, or gold.
1869. When the conductors are excited they have a powerful effect upon gold leaves, suspended as in the electrometer.
1870. The state of the conductors, when excited, as described here, is said to be static. Such a state of excitement is distinguished as a statical charge of electricity.
1871. In the next place, if we procure a horse-shoe magnet, lay it on a table, cover it with a sheet of paper, and then sift over it iron filings, we shall see the shape of the magnet delineated upon the paper, by the filings arranging themselves above its corners in preference. But as the sifting proceeds, the filings will be seen to extend themselves in filaments, so as very much to resemble the electrified hair above described. A tuft of the ferruginous filaments will be formed upon each pole of the magnet, each filament avoiding its neighbours, as far as possible. But while each filament, in either tuft, avoids every other in its appropriate tuft, the whole of the filaments in one, are attracted by those in the other. Thus, the charges of polarity which cause each similarly polarized filament to avoid those in the same state, induce those polarized by one of the poles of the magnet, to attract such as are polarized by the other pole of the magnet.
1872. Here is, so far, a great analogy between the phenomena of the polarization of filings and the polarization of the hair, above described. But then there is this difference: excepting iron, cobalt, and nickel, there is no metal which can, by contact with the poles of a magnet, neutralize the polarity by which the iron filings are affected; and even these metals produce this result by a process, the inverse of that by which charges of statical electricity are neutralized. In fact, the magnetic metal, far from acting as a discharger, acts as a keeper; and a piece of iron, of a suitable shape, applied to the terminations of a horse-shoe magnet, prevents the gradual diminution of the magnetism, which otherwise ensues. Hence the name keeper is applied to it, as well as armature, derived from the French.
1873. It will be perceived that, in a steel magnet, the charges are sustained at the terminations of a conductor, which, as estimated by Cavendish, conducts electricity with a velocity two hundred thousand times as great as water.
1874. The charge of the conductor of the machine is superficial, a gilt globe of glass holding as good a charge as a solid globe of metal; and, moreover, in this superficial charge, the ether and the air participate, undergoing a polar affection, analogous to that of the filings exposed to the influence of the magnet.
1875. On the other hand, in the use of the steel magnet, the charge is internal, and, other things being equal, increases with the quantity of iron charged; neither the air nor the ether participate in this magnetic charge. There is no mode in which the charges of the poles of a magnet can be made to pass from one to the other, through any interposed conducting mass.
1876. The retention of the charge seems to be dependent upon a state of the particles in which they are capable of being deranged from their normal position with a certain degree of extraneous influence, and can only resume their natural relative position by a contrary application of a similar agent. Although steel differs from iron only in containing, as an ingredient, one-fiftieth of carbon, this gives it the highly valuable property of hardening, when suddenly refrigerated; a result which may be accounted for by supposing that, in consequence of the sudden exposure to a powerful conducting medium, there is a sort of a jerk by which the particles loose from their midst an undue portion of their ethereal constituents, and cannot recover their normal arrangement after the refrigeration. When this effect is reached to a maximum, the steel is so brittle as sometimes to fly into two or more pieces when left to itself. When soft iron is subjected to the magnetizing process, it exchanges one polarity for the other with such speed, that, in some electro-magnetic instruments, this reversal is effected more than one hundred times in a second; but precisely in proportion as the magnetism is readily received, it is more readily lost. On the other side, when hardened to a maximum, steel can scarcely be magnetized at all. Thus, to have a permanent magnet, we must employ the metal in a state of induration between the extremes. These facts tend to corroborate the inference that magnetism is dependent on the relative position of the ferruginous particles. It is presumed that the ferruginous particles of which the filings consist indicate, by their direction, as seen externally, the direction in which the constituent particles of the magnet are situated beneath the metallic surface.[42]