1877. If to a wire, connecting the poles of a galvanic battery, iron filings are applied, each ferruginous particle becomes a little magnet, and displays exactly the same disposition to unite in filaments as has been represented to take place when they are exposed upon a sheet of paper, to the influence of a magnet supporting it. But while this affection is thus identical with that induced by the steel magnet, it differs therefrom, in its being as transient as the galvanic discharges to which it owes its existence. These, at the lowest estimate, are sufficiently rapid to go round the globe in two seconds; whence it may be conceived that the time taken to percur a few inches of wire must be almost infinitely brief. Hence, although the filings continue in a state of magnetization so long as the action of the battery is sustained, and the wire kept in due contact with the poles of the battery, it is only by a rapid reiteration of discharges, that this result is effected.
1878. As the relative position of the particles composing the steel magnet has been inferred to be indicated by that of the movable filings which they influence, we may suppose the position of the particles composing the wire, to be indicated by that which the filings take by which it is encircled. These are situated always as if forming tangents to the circumference of the wire, and hence it may be perceived that the metallic particles, forming the wire, have been shifted from their normal position, parallel to the axis, so as to take that tangential direction which the magnetization evinces.
1879. On one end of the wire being in communication with one pole of a voltaic series, on touching the other pole of the series with the other end of the wire, filaments of the particles previously situated parallel to the axis, are jerked out of the normal position with an inconceivable quickness, the discharge, however, not affecting successive parts of the length absolutely at once, but successively; so that there is a time required for the process, however inconceivably minute it may appear to us. The effect upon the filaments of filings, at the different ends of the wire, are perfectly simultaneous, and the effect analogous, but different in this respect, that the positive poles are presented externally at one end, the negative at the other, so that, when the polarizing affections meet at an intermediate point within the wire, neutrality ensues.
1880. Thus it will be perceived that no current passes through the wire, any more than the water which is seen to form a wave, on one side of a lake, passes with the wave which is seen apparently to proceed to the other side. Notoriously, in this case, nothing passes but the momentum, which is successively imparted to successive portions of the intervening water; so, in the galvanic discharge, successive portions of the intervening wire are affected by the original disturbing jerks, of which the power passes from each portion to that next beyond it, just as the momentum in the case of the aqueous wave.
1881. Upon these considerations I hold myself as warranted in calling the affections of the wire, as described, waves of polarization, not that the affection of the wire has the smallest similitude to that with which water produces waves, but that, in both cases, there is a successive communication of a property. It is well known that there is this analogy in the two cases; in either, opposite waves, on due meeting, produce reciprocal neutrality.
1882. The neutralization of the electro-polarity induced upon the charged conductors ([1867]) by touching both at the same time by a conducting rod, is effected in some degree analogously to the process in the voltaic discharge; since waves of opposite polarization are produced at each extremity, and, rushing toward an intermediate point, are neutralized by meeting. But the polarization in the case of the conductors, as has been stated, ([1874],) is superficial, and extends not only to the surfaces of the conductors, but likewise to the surrounding ether and air, and does not affect the ponderable atoms of the wire unless the charge be too great to pass in this superficial manner. In that case, being condensed upon the wire to a state of great intensity, it causes a polarization of the atoms composing it, similar to that of the voltaic discharge, though less durable.
1883. From the preceding exposition it follows that the conduction and insulation of that species of electricity which is excited by an electrical machine or other frictional processes, exists upon the superficies of insulated masses, or that of the circumambient particles of the air or ether. This frictional electricity likewise passes preferably over the surfaces of conductors, so that the moistened surface of glass, or other non-conductors, conveys it with enormous facility. It is notorious, that when the air is moist, electrical machines are paralyzed. But this cannot be in consequence of the moist air acting as a conductor. Agreeably to some experiments which I made, a fog from hot water does not act as a conductor. Evidently, were a fog or a cloud a conductor, the air and moisture forming a thunder cloud could not be electrified, so as to give the discharges which constitute lightning.
1884. It is well known that a tube will carry more lightning than a rod, of which the sectional area should comprise the same quantity of metal. Yet, when the wire is too small to carry a charge outside, it is acted upon intestinally and may be explosively deflagrated. But while the existence of a film of moisture upon the glass legs of an electrical machine, may paralyze its power, to a powerful galvanic battery moisture is well known to be essential.
1885. If the poles of a powerful voltaic series, while highly charged, were severally to have a conducting communication with the conductors of an electrical machine, it would discharge them so rapidly, that the most active working would not enable them to give a spark; yet at the poles of the same series there might be charges accumulated which would, in effecting chemical decomposition, heating, deflagrating wire, or inducing magnetism, be immensely superior to that created by a machine.