Electro-positive. The triangular bipyramid, Fig. 3. The pentagonal bipyramid, Fig. 4. The binate molecule, Fig. 14. The equatorial frustular form, Fig. 8. Electro-negative. The quality, intensity, or tension of a body's electricity, then, depends upon its form; but the quantity being determined by the number of unsuppressed facets which it possesses, depends upon the extent of its surface. Thus, the intensity of the electric state of the triangular bipyrainid (Fig. 3.) is much greater than that of the icosædron (Fig 13.), because it is much farther from a state of repose or neutralization: but the quantity of electricity proper to the latter is much greater; and were two bodies isamorphous, but one possessed a greater number of faces than the other, that which had its faces most numerous would have its quantity of electricity, or its electric power, greatest. Thus, as will be afterwards shewn, potassium and sodium are isamorphous; but the surface of potassium is represented by 40, while that of sodium is represented by 30: the former, therefore, is a more powerful electric body. The tetrædron (Fig. 2.) is incapable of entertaining the two electricities in a symmetrical manner, and is wholly passive as to either. It therefore depends for its electric state upon induction, and will be positive or negative, according to the state of the body within whose sphere of action it exists. Some other bodies, again, are almost altogether unipolar, as, for instance, the prismatic frustum, terminated by the negative pyramids (Fig. 8.). The electric state of such a form must be almost wholly negative. 18. The pyramidal (positive) and prismatic (negative) polarities, may sometimes be so far displaced, even in a large mass, that one or other may be developed in excess, in a cer tain region, and, of course, the consecutive one in excess in the consecutive region; and by being introduced into such regions, weaker bodies may be rendered more or less unipolar, or their natural state be more or less changed for a longer or shorter time. Suppose we are in possession of two such bodies as a magnet and a bit of iron. In the latter, when its magnetic equilibrium is not disturbed by induction or rotation, the contiguous particles neutralize each other's polarity, and the whole mass remains quiescent. No free polarity is therefore exhibited; but let one pole of the magnet, as, for instance, the northverse, be brought near the bit of iron, the subtile matter of this pole of the magnet draws up the consecutive matter in the iron formerly in quiescent union with the other, and, at the same time, depresses that other, because both are elastic or impenetrable to each other. Thus a state of polarity is induced upon the iron by the proximity of the polarity of the magnet, the order of the poles always being such, that consecutive poles are contiguous. When the molecules of iron are, to a certain extent, insulated from each other by a certain crystalline state, or admixture of carbon, oxygen, sulphur, phosphorus, &c., the polarity of the mass once induced, may be sustained in a state of free development for an indefinite time, if not altered by a subsequent induction, heat, a rapidly vibratory motion, or like accident. The mass becomes, as it were, one molecule, and it will be afterwards shewn, that a particle of iron is destitute of an axis, or any feature that should give a direction to its polarity naturally one way more than another. Hence, in such a mass, poles may be induced in any positions to which the external form is suitable. It is only the angles of the superficial strata of particles, however, that can be induced into this state of unnatural constraint. In the interior of the mass, the consecutive polarities continue to neutralize each other; and as much free polarity may be induced upon a hollow as upon a solid mass, provided the thickness of the walls do not fall below a certain quantity bearing a relation to the extent of the surface. Again, let two disks of dissimilar substances (that is substances of dissimilar forms, and, consequently, dissimilar electrical states) be taken and brought near each other; each will disturb the electrical equilibrium of the other, a mutual decomposition of their electricities will ensue, and each will become polarized-those aspects fronting each other being expressive of the relative electrical states of the two bodies. Let N (Fig. 16.) be a thin disk, capable of becoming polarized, but not in this state when insulated, and negative in relation to the disk P. When they are brought near each other, the equatorial (negative) fluid of N draws up the pyramidal (positive) fluid of P, coming out at the same time to meet it, while both re-act in pushing before them, towards the most distant or external surfaces, or even expelling a portion of the polarities of nonconsecutive kinds respectively; hence, each of the two disks is in a polarized state by induction; and two polarized axes are developed, one in each thin plate. But when they are brought into perfect contact, the two axes must be confluent into one, and the poles reversed. The disks become one mass, which is (though not more eminently than previous to justa-position, nor perhaps even so much so) positive and negative, on opposite aspects, according as one or other is most proper to the substance of that surface, and the region of union is neutral, being the neutral plane of an axis. On separating them after contact, the disk N consequently contains neutral subtile matter + negative, and is therefore negative; the disk P contains neutral matter + positive, and is consequently positive-the state of coercion existing for a longer or shorter time, for minutes, hours, or days, according to circumstances. The re-union of the neutral and the pure positive or negative states re-establishes the original condition. To develope these phenomena in a symmetrical manner, it is necessary that the quantity of electricity in both disks be the same, and the one as far from a perfect neutrality, by excess of positive electricity, as the other is by excess of negative. Hence it follows, that there is a certain relative magnitude between particles when their union, in consequence of difference in electrical state, takes place with most effect. Thus, perhaps, the triangular bipyramid (Fig. 3.) is much more highly positive than the compound form (Fig. 15.) is negative; and the intensity of the one is just neutralized by the quantity of the other, so that a vigorous union may take place between them, and the compound particle resulting (Fig. 17.) be destitute of the properties of both, and exhibit only that which is proper to its own form, considered as one. Hence the electrical power of a particle is expressed by quantity its intensity. In experiments on compound masses, whose polarity is excited by artificial means, the phenomena of induction make the same power act the part both of attraction and repulsion. Thus, light bodies, not charged with the same electricity, are attracted to such as are charged, and a similar polarity being induced upon them by their vicinity, or contact, they are then repelled, because there remains no force to retain them united; but when one particle is drawn to another, in virtue of a dissimilar electric state, they are attached by the attractions of their angles; and even though a similar electric state be induced, there is no departure; hence a molecule does not throw off spontaneously those parts which are in the same electric state. For, relieving it of such parts, it is necessary to make it hot, which weakens the intensity of the cohering force, and strengthens the existing electric repulsion at the same time. Dissimilarity of substance is not necessary, however, to the development of a polarized electric axis. Dissimilarity of state in the same sort of substance, in different regions, produces the same effect. It is, in fact, equivalent to a dissimilarity of substance. Many bodies, when in the aëriform, liquid, or red hot state, are more different from themselves when solid and cold, than they are, in either state, from many other bodies. Hence, if on one extremity or aspect a body is heated, or is passing off as a liquid or a gas, the mass will be (within the limits of distance always to be considered) in the state of a polarized axis; and in such cases, it is to be observed that the region of activity is naturally the positive pole. Thus, let a bit of charcoal, burning at one end, be held so that the fumes passing off from the burning part shall not interfere with it, and it will be found that the hot end is positive, the cold end negative. Again, let it be held so that the fumes, as they pass off, may sweep along the surface of the mass; charged, as they are, with the positive fluid, they give it off to that region which would otherwise be negative, restore the equilibrium, and prevent the development of an axis. These facts, though explained in a different manner, have lately been observed by M. Pouillet. The same phenomena are beautifully exhibited in flames, as will afterwards be shewn. This motility of subtile matter induces us to believe that the quantity investing any given particle is not invariably the same, but becomes excessive or exhausted, more or less, according to the phases through which the body has lately passed. It is most reasonable to believe, that, in certain cases of contact, or union, the electrical state of a body is so far affected, that, when it is set free, its condition as to subtile matter is not the same as it was previous to contact; and that it will require exposure to some bodies having abundance or deficiency of subtile matter, a relatively positive or negative state, to restore it speedily to that proper to its form. Many electrical experiments are most easily explained, on the supposition that there is an actual transference of the subtile principle; and it seems very credible that in many cases it is so. The grand means of restoring subtile matter to a body which has been deprived of it, is exposure to the sunbeam, which is not to be wondered at, when we consider its structure, afterwards to be described. All substances are not capable of developing polarized axes. This is true, however, of most bodies in a somewhat neutral and natural state, in which they are, of course, well |