this fire to other bodies; so are pitch and rosin, excrements, as it were, of trees. To these we may add glass, amber, brimstone, dry earth, and a few other bodies. These have frequently been stiled, electric per se, as if they alone contained the electric fire; an eminently improbable title, founded on a palpable mistake. From the same mistake, all other bodies which easily receive and readily convey it, were termed non electrics, on a supposition, that they contained no electric fire, the contrary of which is now allowed by all. That this fire is inconceivably subtle, appears from its penetrating even the densest metals, and that with such ease, as to receive no perceptible resistance. If any one doubt whether it pass through the substance, or only along the surface of bodies, a strong shock taken through his own body, will prevent his doubting any longer. It differs from all other matter in this, that the particles of it repel, not attract each other; and hence is the manifest divergency in a stream of electrical effluvia But though the particles of it repel each other, yet are they attracted by all other matter. And from these three, the extreme subtlety of this fire, the mutual repulsion of its parts, and the strong attraction of them by other matter, arises this effect, that if a quantity of electric fire be applied to a mass of common matter of any bigness or length, which has not already got its quantity, it is immediately diffused through

the whole It seems, this globe of earth and water, with its plants, animals, and buildings, have diffused through their whole substance, just as much of this fire as they will contain; and this we may term their natural quantity. But this is not the same in all kinds of matter; neither in the same kind of matter in all circumstances. A solid foot of one kind of matter, as glass, contains more of it than a solid foot of another kind; and a pound weight of the same kind of matter, when rarified, contains more than it did before. We know that this fire is in common matter, because we can pump it out by the globe or tube? we know that common matter has near as much of it as it can contain; because if we add a little more to any portion of it, the additional quantity does not enter, but forms a kind of atmosphere round it. On the other hand, we know that common matter has not more of it than it can contain ; otherwise all loose portions of it would repel each other; as they constantly do, when they have such atmospheres. Had the earth, for instance, as much electric fire, in proportion, as we can give to a globe of iron or wood, the particles of dust, and other light matter, would not only repel each other, but be continually repelled from the earth hence the air being constantly loaded therewith, would be unfit for respiration. Here we see another occasion to adore that wisdom,

which has made all things by weight and measure. The form of every electric atmosphere is that of the body which it surrounds; because it is attracted by every part of the surface, though it cannot enter the substance already replete. Without this attraction, it would not remain round the body, but dissipate into the air. The atmosphere of an electrified sphere is not more easily drawn off from any one part of it than from the other, because it is equally attracted by every part: but it is not so with bodies of other figures. From a cube it is more easily drawn off at the corners than the sides; and so from the corners of any bodies of any other form, and most easily from the sharpest corners: for the force with which an electrified body retains its atmosphere, is proportioned to the surface on which that atmosphere rests. So a surface four inches square retains its atmosphere with sixteen times the force than one of an inch square does. As in pulling the hair from an horse's tail, a force insufficient to pull off an handful at once, could easily pull it off hair by hair: so though a blunt body cannot draw off all the atmosphere at once, a pointed one can easily draw it off, particle by particle. If you would have a sensible proof, how wonderfully pointed bodies draw off the electric fire, place an iron shot of four inches diameter, on the mouth of a dry bottle; suspend over it a small cork ball by a silken

thread, just so as to rest against the side of the shot; electrify the shot, and the ball will be repelled four or five inches from it; then present to the shot, six or eight inches off, the point of a sharp bodkin; the fire is instantly drawn off, so the repulsion ceases, and the ball flies to the shot. But a blunt body will not produce this effect, till it is brought within an inch of the shot. If you present the point of the bodkin in the dark, you may see sometimes at a foot distance a light gather upon it like a glow-worm, which is manifestly the fire it extracts from the shot. The less sharp the point is, the nearer it must be brought before you can see the light; and at whatever distance you see the light, you may draw off the electric fire. To be convinced that pointed bodies throw off, as well as draw off the fire, you may lay a long sharp needle on the shot: it cannot then be electrified, so as to repel the ball, because the fire thrown upon it continually runs off at the point of the needle; from which in the dark you may see such a stream of light, as in the preceding instance. While the electric fire, which is in all bodies, is left to itself, undisturbed by any external violence, it is more or less dense, according to the nature of the body which it is in. In dense bodies it is more rare; in rare bodies it is more dense: accordingly every body contains such a quantity of it, rare or dense, as is suitable to its nature.

And there is some resistance to every endeavour of altering its density, in the whole of any body, or in any part of it; for all bodies resist either the increase or diminution of their natural quantity and on the other hand, when it has been either increased or diminished, there is a resistance to its return to its natural state. With regard to the different resistance made by different bodies, in either of these cases it is an invariable rule, that glass, wax, rosin, brimstone, silk, hair, and such bodies, resist the most; and next to these, the air, provided it be dry, and in a sufficient quantity; that this resistance is least in metals, minerals, water, quicksilver, animals, and vegetables, which we may rank together, because the difference in their resistance is very inconsiderable; and that in these bodies the resistance is greater, when their surfaces polished, and extended in length, than when their surfaces are rough and short, or end in sharp points. When a body has more electric fire forced into it than it has naturally, it is said to be electrified positively. When part of the natural quantity is taken away, it is said to be electrified negatively. Now when an iron bar is negatively electrified, the fire drawn out does not go in again as soon as the experiment is over, but forms an atmosphere round it, because of the resistance it finds in its endeavour to dilate itself, either into the air or into the bar: and when it is elec