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XLIV: TO PETER COLLINSON - Benjamin Franklin, The Works of Benjamin Franklin, Vol. II Letters and Misc. Writings 1735-1753 [1904]

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The Works of Benjamin Franklin, including the Private as well as the Official and Scientific Correspondence, together with the Unmutilated and Correct Version of the Autobiography, compiled and edited by John Bigelow (New York: G.P. Putnam’s Sons, 1904). The Federal Edition in 12 volumes. Vol. II (Letters and Misc. Writings 1735-1753).

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XLIV

TO PETER COLLINSON

Philadelphia, 11 July, 1747.

Sir:—

In my last I informed you that in pursuing our electrical inquiries we had observed some particular phenomena which we looked upon to be new, and of which I promised to give you some account, though I apprehended they might not possibly be new to you, as so many hands are daily employed in electrical experiments on your side the water, some or other of which would probably hit on the same observations.

The first is the wonderful effect of pointed bodies, both in drawing off and throwing off the electrical fire. For example:

Place an iron shot of three or four inches diameter on the mouth of a clean, dry glass bottle. By a fine silken thread from the ceiling, right over the mouth of the bottle, suspend a small cork ball about the bigness of a marble, the thread of such a length as that the cork ball may rest against the side of the shot. Electrify the shot, and the ball will be repelled to the distance of four or five inches, more or less, according to the quantity of electricity. When in this state, if you present to the shot the point of a long, slender, sharp bodkin, at six or eight inches’ distance, the repellency is instantly destroyed, and the cork flies to the shot. A blunt body must be brought within an inch and draw a spark to produce the same effect. To prove that the electrical fire is drawn off by the point, if you take the blade of the bodkin out of the wooden handle and fix it in a stick of sealing-wax, and then present it at the distance aforesaid, or if you bring it very near, no such effect follows; but sliding one finger along the wax till you touch the blade, and the ball flies to the shot immediately. If you present the point in the dark you will see, sometimes at a foot distance and more, a light gather upon it, like that of a fire-fly or glow-worm; the less sharp the point the nearer you must bring it to observe the light, and at whatever distance you see the light you may draw off the electrical fire and destroy the repellency. If a cork ball so suspended be repelled by the tube, and a point be presented quick to it, though at a considerable distance, it is surprising to see how suddenly it flies back to the tube. Points of wood will do near as well as those of iron, provided the wood is not dry, for perfectly dry wood will no more conduct electricity than sealing-wax.

To show that points will throw off1 as well as draw off the electrical fire; lay a long sharp needle upon the shot, and you cannot electrize the shot so as to make it repel the cork ball. Or fix a needle to the end of a suspended gun-barrel, or iron rod, so as to point beyond it like a little bayonet,2 and while it remains there, the gun-barrel or rod cannot, by applying the tube to the other end, be electrized so as to give a spark, the fire continually running out silently at the point. In the dark you may see it make the same appearance as it does in the case before mentioned.

The repellency between the cork ball and the shot is likewise destroyed: 1st, by sifting fine sand on it,—this does it gradually; 2dly, by breathing on it; 3dly, by making a smoke about it from burning wood1 ; 4thly, by candle-light, even though the candle is at a foot distance,—these do it suddenly. The light of a bright coal from a wood fire, and the light of a red-hot iron do it likewise, but not at so great a distance. Smoke from dry rosin dropped on hot iron does not destroy the repellency, but is attracted by both shot and cork ball, forming proportionable atmospheres round them, making them look beautifully, somewhat like some of the figures in Burnet’s or Whiston’s Theory of the Earth.

N. B.—This experiment should be made in a closet where the air is very still, or it will be apt to fail.

The light of the sun thrown strongly on both cork and shot by a looking-glass, for a long time together, does not impair the repellency in the least. This difference between fire-light and sun-light is another thing that seems new and extraordinary to us.1

We had for some time been of opinion that the electrical fire was not created by friction, but collected, being really an element diffused among, and attracted by other matter, particularly by water and metals. We had even discovered and demonstrated its afflux to the electrical sphere, as well as its efflux, by means of little, light windmill-wheels made of stiff paper vanes fixed obliquely, and turning freely on fine wire axes; also by little wheels of the same matter, but formed like water-wheels. Of the disposition and application of which wheels, and the various phenomena resulting, I could, if I had time, fill you a sheet.2 The impossibility of electrizing one’s self (though standing on wax) by rubbing the tube, and drawing the fire from it; and the manner of doing it by passing the tube near a person or thing standing on the floor, &c., had also occurred to us some months before Mr. Watson’s ingenious Sequel came to hand; and these were some of the new things I intended to have communicated to you. But now I need only mention some particulars not hinted in that piece, with our reasonings thereupon; though perhaps the latter might well enough be spared.

1. A person standing on wax and rubbing the tube, and another person on wax drawing the fire, they will both of them (provided they do not stand so as to touch one another) appear to be electrized to a person standing on the floor; that is, he will perceive a spark on approaching each of them with his knuckle.

2. But if the persons on wax touch one another during the exciting of the tube, neither of them will appear to be electrized.

3. If they touch one another after exciting the tube, and drawing the fire as aforesaid, there will be a stronger spark between them than was between either of them and the person on the floor.

4. After such strong spark neither of them discover any electricity.

These appearances we attempt to account for thus: We suppose, as aforesaid, that electrical fire is a common element, of which every one of the three persons above mentioned has his equal share, before any operation is begun with the tube. A, who stands on wax and rubs the tube, collects the electrical fire from himself into the glass; and, his communication with the common stock being cut off by the wax, his body is not again immediately supplied. B (who stands on wax likewise), passing his knuckle along near the tube, receives the fire which was collected by the glass from A; and his communication with the common stock being likewise cut off, he retains the additional quantity received. To C, standing on the floor, both appear to be electrized; for he, having only the middle quantity of electrical fire, receives a spark upon approaching B, who has an over quantity; but gives one to A, who has an under quantity. If A and B approach to touch each other, the spark is stronger, because the difference between them is greater. After such touch there is no spark between either of them and C, because the electrical fire in all is reduced to the original equality. If they touch while electrizing, the equality is never destroyed, the fire only circulating. Hence have arisen some new terms among us: we say B (and bodies like circumstanced) is electrized positively; A, negatively. Or rather, B is electrized plus; A, minus. And we daily in our experiments electrize bodies plus or minus, as we think proper. To electrize plus or minus, no more needs to be known than this, that the parts of the tube or sphere that are rubbed, do, in the instant of the friction, attract the electrical fire, and therefore take it from the thing rubbing; the same parts immediately, as the friction upon them ceases, are disposed to give the fire they have received to any body that has less. Thus you may circulate it as Mr. Watson has shown; you may also accumulate or subtract it, upon or from any body, as you connect that body with the rubber, or with the receiver, the communication with the common stock being cut off. We think that ingenious gentleman was deceived when he imagined (in his Sequel) that the electrical fire came down the wire from the ceiling to the gun-barrel, thence to the sphere, and so electrized the machine and the man turning the wheel, &c. We suppose it was driven off, and not brought on through that wire; and that the machine and man, &c., were electrized minus—that is, had less electrical fire in them than things in common.

As the vessel is just upon sailing, I cannot give you so large an account of American electricity as I intended; I shall only mention a few particulars more. We find granulated lead better to fill the phial with than water, being easily warmed, and keeping warm and dry in damp air. We fire spirits with the wire of the phial. We light candles, just blown out, by drawing a spark among the smoke between the wire and snuffers. We represent lightning by passing the wire in the dark over a China plate that has gilt flowers, or applying it to gilt frames of looking glasses, &c. We electrize a person twenty or more times running, with a touch of the finger on the wire, thus: He stands on wax. Give him the electrized bottle in his hand. Touch the wire with your finger and then touch his hand or face; there are sparks every time.1 We increase the force of the electrical kiss vastly, thus: Let A and B stand on wax, or A on wax and B on the floor; give one of them the electrized phial in hand; let the other take hold of the wire; there will be a small spark; but when their lips approach they will be struck and shocked. The same if another gentleman and lady, C and D, standing also on wax, and joining hands with A and B, salute or shake hands. We suspend by fine silk thread a counterfeit spider made of a small piece of burnt cork, with legs of linen thread, and a grain or two of lead stuck in him to give him more weight. Upon the table, over which he hangs, we stick a wire upright, as high as the phial and wire, four or five inches from the spider; then we animate him by setting the electrified phial at the same distance on the other side of him; he will immediately fly to the wire of the phial, bend his legs in touching it, then spring off and fly to the wire in the table, thence again to the wire of the phial, playing with his legs against both, in a very entertaining manner, appearing perfectly alive to persons unacquainted. He will continue this motion an hour or more in dry weather. We electrify, upon wax in the dark, a book that has a double line of gold round upon the covers, and then apply a knuckle to the gilding; the fire appears everywhere upon the gold like a flash of lightning; not upon the leather, nor if you touch the leather instead of the gold. We rub our tubes with buckskin and observe always to keep the same side to the tube and never to sully the tube by handling; thus they work readily and easily without the least fatigue, especially if kept in tight pasteboard cases lined with flannel, and sitting close to the tube.1 This I mention because the European papers on electricity frequently speak of rubbing the tubes as a fatiguing exercise. Our spheres are fixed on iron axes which pass through them. At one end of the axis there is a small handle with which you turn the sphere like a common grindstone. This we find very commodious, as the machine takes up but little room, is portable, and may be enclosed in a tight box when not in use. It is true the sphere does not turn so swift as when the great wheel is used; but swiftness we think of little importance, since a few turns will charge the phial, &c., sufficiently.1

I am, &c.,

B. Franklin.

[1 ]This power of points to throw off the electrical fire was first communicated to me by my ingenious friend, Mr. Thomas Hopkinson, since deceased, whose virtue and integrity, in every station of life, public and private, will ever make his memory dear to those who knew him, and knew how to value him.—F.

[2 ]This was Mr. Hopkinson’s experiment, made with an expectation of drawing a more sharp and powerful spark from the point, as from a kind of focus, and he was surprised to find little or none.—F.

[1 ]We suppose every particle of sand, moisture, or smoke, being first attracted and then repelled, carries off with it a portion of the electrical fire; but that the same still subsists in those particles till they communicate it to something else, and that it is never really destroyed. So, when water is thrown on common fire, we do not imagine the element is thereby destroyed or annihilated, but only dispersed, each particle of water carrying off in vapor its portion of the fire which it had attracted and attached to itself.—F.

[1 ]This different effect probably did not arise from any difference in the light, but rather from the particles separated from the candle, being first attracted and then repelled, carrying off the electric matter with them; and from the rarefying the air, between the glowing coal or red-hot iron and the electrized shot, through which rarefied air, the electric fluid could more readily pass.—F.

[2 ]These experiments with the wheels were made and communicated to me by my worthy and ingenious friend, Mr. Philip Syng; but we afterwards discovered that the motion of those wheels was not owing to any afflux or efflux of the electric fluid, but to various circumstances of attraction and repulsion. 1750.—F.

[1 ]By taking a spark from the wire, the electricity within the bottle is diminished, the outside of the bottle then draws some from the person holding it, and leaves him in a negative state. Then when his hand or face is touched, an equal quantity is restored to him from the person touching.—F.

[1 ]Our tubes are made here of green glass, twenty-seven or thirty inches long, as big as can be grasped.—F.

[1 ]This simple, easily-made machine was a contrivance of Mr. Syng’s.—F.