1858. It is to the existence of the power by which these effects are caused, at opposite terminations, that bodies, in congealing or freezing from the state of liquidity, shoot into prismatic, oblong, regular forms, called crystals. This is illustrated in the formation of ice, which is seen to shoot into such prismatic crystals.
1859. When a pane of glass is so situated as to have the focus of a solar microscope thrown upon any spot, so that the glass thus affected may be between the eye of an observer and the microscope, any small crystals formed are greatly magnified. Hence if the focal space be moistened with a solution of certain salts, the solvent evaporating, crystallization ensues, and is seen to form appropriate figures for each salt employed. It is owing to this property that when certain solutions of various substances are evaporated, the soluble solid, as it is deposited from the solvent, arranges itself longitudinally; one atom attaching itself to the pole of another, until it creeps over the sides of the vessel in great quantity. The appearance of arborescence in certain minerals is thus accounted for. When an amalgam of mercury with silver is hung by a platina wire within a bottle of a solution of silver in nitric acid, there is formed a beautiful branching of silver filaments. These are longer, though more slowly formed, as the solution is more dilute. In very dilute solutions I have seen prisms of silver of more than an inch in length, so delicate, that but for the brilliancy of the surface they could not have been detected by the eye.
1860. Farraday distinguished two kinds of polarity—ferro-magnetic and dia-magnetic. That above described as taking place between steel magnets is designated as ferro-magnetic. Dia-magnetic particles under magnetic influence take position at right angles to that which would ensue from ferro-magnetism.
1861. This explanation being premised to enable the student to comprehend what is meant by polarity, I will proceed to explain electric phenomena, according to the theory which I hold.
1862. It is expected that the preceding discussions have prepared the reader to conceive that the atoms of all ponderable matter are endowed with two analogous but opposite polar powers, which we term polarity. That in any two atoms the dissimilar polar powers tend to make them unite, the similar powers having the opposite tendency. That in any inert mass the opposite powers or polarities are in contact, and thus reciprocally neutralized.
1863. It will be also understood that the ethereal fluid which pervades the universe as the means of illumination is assumed to consist in like manner of atoms or particles which are endowed with polarity, so that when the opposite poles are in proximity, there is neutralization: repulsion, and disturbance, when similar poles are approximated. This being premised, the allegation may be intelligible, that when bodies are electrified, the poles of the component atoms or particles are conceived to be deranged from their natural position of reciprocal neutralization, so that they react with exterior bodies, disturbing the poles of their constituent particles, and thus electrifying them by induction.
1864. This abnormal state of disturbance, is conceived to be produced on glass or resin, or any electric, when duly subjected to friction.
1865. Thus when in an electric machine a vitreous surface is rubbed by a leather cushion, the particles both of the leather and glass surfaces are deranged from their natural state of reciprocal neutralization, and present their poles in an active state, and the glass surface, moving through the ethereal medium, ([812]) polarizes it as it passes, the ether resuming its normal state till the ethereal atmosphere over the conductor is reached. To that it imparts durable polarity; the metallic superficies of the conductor taking the opposite state, so that the charge is retained until the glass goes to and returns from the cushion, with a farther supply of polarity.
1866. The charges of polarization received by the plates at each succeeding revolution of the plate or cylinder, is divided with the ethereal atmosphere over the conductor, and this process is reiterated till the frictional power has accomplished its maximum effect. Then the conductor is said to be charged positively, according to the theory of one fluid, and vitreously, according to that of Dufay, or the theory of two fluids. Meanwhile, if the cushion communicates duly with an insulated conductor, a process perfectly analogous to that just described has been charging that conductor, pari passu, with the one first mentioned. By these means we have two excited or charged conductors.
1867. If, before charging these conquerors, two scalps of hair be severally situated on them, it will be perceived that, as the charging proceeds, the hairs on each of the scalps rise, and endeavour to keep away from each other. But, meanwhile, the whole of the hair on either is attracted by that on the other conductor. Moreover, on touching both conductors with any metallic rod, simultaneously, the whole of the excitement disappears, and the hairs assume their normal position.