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and could communicate those signs to metals and water. Afterwards it was found, that rubbing of glass would not produce the electric matter, unless a communication was preserved between the rubber and the floor; and subsequent experiments proved, that the electric matter was really drawn from those bodies that at first were thought to have none in them. Then it was doubted whether glass, and other bodies called electrics per se, had really any electric matter in them, since they apparently afforded none but what they first extracted from those which had been called non-electrics. But some of my experiments show, that glass contains it in great quantity, and I now suspect it to be pretty equally diffused in all the matter of this terraqueous globe. If so, the terms electric per se and non-electric should be laid aside as improper; and (the only difference being this, that some bodies will conduct electric matter, and others will not,) the terms conductor and non-conductor may supply their place. If any portion of electric matter is applied to a piece of conducting matter, it penetrates and flows through it, or spreads equally on its surface; if applied to a piece of non-conducting matter, it will do neither. Perfect conductors of electric matter are only metals and water; other bodies conducting only as they contain a mixture of those, without more or less of which they will not conduct at all.* This (by the way) shows a new relation between metals and water heretofore unknown.
To illustrate this by a comparison, which, however, can only give a faint resemblance. Electric matter passes through conductors, as water passes through a porous stone, or spreads on their surfaces as water spreads on a wet stone; but, when applied to nonconductors, it is like water dropped on a greasy stone, it neither penetrates, passes through, nor spreads on the surface, but remains in drops where it falls. See farther on this head, in my last printed piece, entitled Opinions and Conjectures, &c. 1749.
* This proposition is since found to be too general ; Mr. Wilson having discovered, that melted wax and rosin will also conduct.
Query. What are the effects of air in electrical experiments ?
Answer. All I have hitherto observed are these. Moist air receives and conducts the electrical matter in proportion to its moisture, quite dry air not at all; air is therefore to be classed with the non-conductors.
Dry air assists in confining the electrical atmosphere to the body it surrounds, and prevents its dissipating; for in vacuo it quits easily, and points operate stronger, that is, they throw off or attract the electrical matter more freely, and at greater distances; so that air intervening obstructs its passage from body to body in some degree. A clean electrical phial and wire, containing air instead of water, will not be charged, nor give a shock, any more than if it was filled with powder of glass; but exhausted of air, it operates as well as if filled with water. Yet an electric atmosphere and air do not seem to exclude each other, for we breathe freely in such an atmosphere, and dry air will blow through it without displacing or driving it away. I question whether the strongest dry north-wester* would dissipate it. I once electrified a large cork ball at the end of a silk thread three feet long, the other end of which I held in my fingers, and whirled it round, like a sling, one hundred times in the air, with the swiftest motion I could possibly give it; yet it retained its electric atmosphere, though it must have passed through eight hundred yards of air, allowing my arm in giving the motion to add a foot to the semidiameter of the circle. By quite dry air, I mean the dryest we have; for perhaps we never have any perfectly free from moisture. An electrical atmosphere raised round a thick wire, inserted in a phial of air, drives out none of the air, nor on withdrawing that atmosphere will any air rush in, as I have found by a curious experiment a curious experiment * accurately made,
* A cold dry wind of North America.
, whence we concluded that the air's elasticity was not affected thereby An Experiment towards discovering more of the Qual
ities of the Electric Fluid. From the prime conductor, hang a bullet by a wire hook; under the bullet, at half an inch distance, place a bright piece of silver to receive the sparks; then let the wheel be turned, and in a few minutes (if the repeated sparks continually strike in the same spot) the silver will receive a blue stain, nearly the color of a watch-spring.
* The experiment here mentioned was thus made. An empty phial was stopped with a cork. Through the cork passed a thick wire, as usual in the Leyden experiment, which wire almost reached the bottom. Through another part of the cork passed one leg of a small glass siphon, the other leg on the outside came down almost to the bottom of the phial. This phial was first held a short time in the hand, which, warming and of course rarefying the air within, drove a small part of it out through the siphon. Then a little red ink in a tea-spoon was applied to the opening of the outer leg of the siphon; so that as the air within cooled, a little of the ink might rise in that leg. When the air within the bottle came to be of the same temperature of that without, the drop of red ink would rest in a certain part of the leg. But the warmth of a finger applied to the phial would cause that drop to descend, as the least outward coolness applied would make it ascend. When it had found its situation, and was at rest, the wire was electrified by a communication from the prime conductor. This was supposed to give an electric atmosphere to the wire within the bottle, which might likewise rarefy the included air, and of course depress the drop of ink in the siphon. But no such effect followed.
A bright piece of iron will also be spotted, but not with that color; it rather seems corroded.
On gold, brass, or tin, I have not perceived it makes any impression. But the spots on the silver or iron will be the same, whether the bullet be lead, brass, gold, or silver.
On a silver bullet there will also appear a small spot, as well as on the plate below it.
FROM JAMES BOWDOIN TO BENJAMIN FRANKLIN.
On the Causes of the crooked Direction of Lightning.
Objections to the Hypothesis that the Sea is the Source of Lightning. - On the Swiftness of the Electrical Fire.
Boston, 21 December, 1751. SIR, The experiments Mr. Kinnersley has exhibited here, have been greatly pleasing to all sorts of people, that have seen them; and I hope, by the time he returns to Philadelphia, his tour this way will turn to good ac
His experiments are very curious, and I think prove most effectually your doctrine of electricity ; that it is a real element annexed to, and diffused among, all bodies we are acquainted with ; that it differs in nothing from lightning, the effects of both being similar, and their properties, so far as they are known, the same.
The remarkable effect of lightning on iron lately discovered in giving it the magnetic virtue, and the same effect produced on small needles by the electrical fire, are a further and convincing proof that they are both the same element; but, which is very unaccountable, Mr. Kinnersley tells me it is necessary, to produce this effect, that the direction of the needle and the electrical fire should be north and south, from either to the other; and that, just so far as they deviate therefrom, the magnetic power in the needle is less, till, their direction being at right angles with north and south, the effect entirely ceases.
We made at Faneuil Hall, where Mr. Kinnersley's apparatus is, several experiments to give some small needles the magnetic virtue, previously examining, by putting them in water, on which they will be supported, whether or not they had any of that virtue; and I think we found all of them to have some small degree of it, their points turning to the north. We had nothing to do then, but to invert the poles, which accordingly was done by sending through them the charge of two large glass jars; the eye of the needle turning to the north, as the point before had done. That end of the needle, which the fire is thrown upon, Mr. Kinnersley tells me, always points to the north.
The electrical fire, passing through the air, has the same crooked direction as lightning. * This
This appearance I endeavour to account for thus. Air is an electric per se; therefore there must be a mutual repulsion between air and the electrical fire. A column or cylinder of air, having the diameter of its base equal to the diameter of the electrical spark, intervenes between that part of the body which the spark is drawn from and that of the body it aims at. The spark acts upon this column, and is acted upon by it, more strongly than any other neighbouring portion of air. The column, being thus acted upon, becomes more dense, and, being more dense, repels the spark more strongly; its repellency being in proportion to its density. Having acquired, by
This is most easily observed in large strong sparks, taken at some inches distance.