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40. When the air, with its vapors raised from the ocean between the tropics, comes to descend in the polar regions, and to be in contact with the vapors arising there, the electrical fire they brought begins to be communicated, and is seen in clear nights, being first visible where it is first in motion, that is, where the contact begins, or in the most northern part; from thence the streams of light seem to shoot southerly, even up to the zenith of northern countries. But, though the light seems to shoot from the north southerly, the progress of the fire is really from the south northerly, its motion beginning in the north being the reason that it is there seen first.

For the electrical fire is never visible but when in motion, and leaping from body to body, or from particle to particle, through the air. When it passes through dense bodies, it is unseen. When a wire makes part of the circle, in the explosion of the electrical phial, the fire, though in great quantity, passes in the wire invisibly; but, in passing along a chain, it becomes visible as it leaps from link to link. In passing along leaf gilding it is visible; for the leaf gold is full of pores; hold a leaf to the light and it appears like a net, and the fire is seen in its leaping over the vacancies. And, as when a long canal filled with still water is opened at one end, in order to be discharged, the motion of the water begins first near the opened end, and proceeds towards the close end, though the water itself moves from the close towards the opened end; so the electrical fire discharged into the polar regions, perhaps from a thousand leagues length of vaporized air, appears first where it is first in motion, that is, in the most northern part, and the appearance proceeds southward, though the fire really moves northward. This is supposed to account for the aurora borealis.

41. When there is great heat on the land, in a particular region (the sun having shone on it perhaps several days, while the surrounding countries have been screened by clouds), the lower air is rarefied and rises, the cooler, denser air above descends; the clouds in that air meet from all sides, and join over the heated place; and, if some are electrified, others not, lightning and thunder succeed, and showers fall. Hence thundergusts after heats, and cool air after gusts; the water, and the clouds that bring it, coming from a higher and therefore a cooler region.

42. An electrical spark, drawn from an irregular body at some distance, is scarcely ever straight, but shows crooked and waving in the air. So do the flashes of lightning, the clouds being very irregular bodies.

43. As electrified clouds pass over a country, high hills and high trees, lofty towers, spires, masts of ships, chimneys, &c., as so many prominences and points, draw the electrical fire, and the whole cloud discharges there.

44. Dangerous, therefore, is it to take shelter under a tree, during a thunder-gust. It has been fatal to many, both men and beasts. 45. It is safer to be in the open field for another

When the clothes are wet, if a flash in its way to the ground should strike your head, it may run in the water over the surface of your body; whereas, if your clothes were dry, it would go through the body, because the blood and other humors, containing so much water, are more ready conductors.

Hence a wet rat cannot be killed by the exploding electrical bottle, when a dry rat may.

reason.

This was tried with a bottle, containing about a quart It is since thought, that one of the large glass jars, mentioned in these papers, might have killed him, though wet.

46. Common fire is in all bodies, more or less, as well as electrical fire. Perhaps they may be different modifications of the same element; or they may be different elements. The latter is by some suspected.

47. If they are different things, yet they may and do subsist together in the same body.

48. When electrical fire strikes through a body, it acts upon the common fire contained in it, and puts that fire in motion; and, if there be a sufficient quantity of each kind of fire, the body will be inflamed.

49. When the quantity of common fire in the body is small, the quantity of the electrical fire (or the electrical stroke) should be greater; if the quantity of common fire be great, less electrical fire suffices to produce the effect.

50. Thus spirits must be heated before we can fire them by the electrical spark.* If they are much heated, a small spark will do; if not, the spark must be greater.

51. Till lately, we could only fire warm vapors ; but now we can burn hard, dry rosin. And, when we can procure greater electrical sparks, we may be able to fire, not only unwarmed spirits, as lightning does, but even wood, by giving sufficient agitation to the common fire contained in it, as friction we know will do.

52. Sulphureous and inflammable vapors, arising from the earth, are easily kindled by lightning. Besides what arise from the earth, such vapors are sent out by stacks of moist hay, corn, or other vegetables, which heat and reek. Wood, rotting in old trees or buildings, does the same. Such are therefore easily and often fired.

* We have since fired spirits without heating them, when the weather is warm.

A little, poured into the palm of the hand, will be warmed sufficiently by the hand, if the spirit be well rectified. Ether takes fire most readily.

53. Metals are often melted by lightning, though perhaps not from heat in the lightning, nor altogether from agitated fire in the metals. For, as whatever body can insinuate itself between the particles of metal, and overcome the attraction by which they cohere (as sundry menstrua can), will make the solid become a fluid, as well as fire, yet without heating it; so, the electrical fire, or lightning, creating a violent repulsion between the particles of the metal it passes through, the metal is fused.

54. If you would, by a violent fire, melt off the end of a nail, which is half driven into a door, the heat given the whole nail, before a part would melt, must burn the board it sticks in; and the melted part would burn the floor it dropped on. But, if a sword can be melted in the scabbard, and money in a man's pocket by lightning, without burning either, it must be a cold fusion.*

55. Lightning rends some bodies. The electrical spark will strike a hole through a quire of strong paper.

56. If the source of lightning, assigned in this paper, be the true one, there should be little thunder heard at sea far frorn land. And accordingly some old seacaptains, of whom inquiry has been made, do affirm, that the fact agrees perfectly with the hypothesis ; for that, in crossing the great ocean, they seldom meet with thunder till they come into soundings; and that the islands far from the continent have very little of it. And a curious observer, who lived thirteen years at Bermudas, says, there was less thunder there in that whole time, than he has sometimes heard in a month at Carolina.

* These facts, though related in several accounts, are now doubted; since it has been observed, that the parts of a bell-wire which fell on the floor, being broken and partly melted by lightning, did actually burn into the boards. (See “Philosophical Transactions,” Vol. LI. Part I.) And Mr. Kinnersley has found that a fine iron wire, melted by electricity, has had the same effect.

TO PETER COLLINSON.

Accumulation of the Electrical Fire proved to be in the

electrified Glass. - Effect of Lightning on the Needle of Compasses explained. Gunpowder fired by the Electric Flame.

Philadelphia, 27 July, 1750. SIR, Mr. Watson, I believe, wrote his Observations on niy last paper

in haste, without having first well considered the experiments, related § 17,* which still appear to me decisive in the question, Whether the accumulation of the electrical fire be in the electrified glass, or in the non-electric matter connected with the glass ? and to demonstrate that it is really in the glass.

As to the experiment that ingenious gentleman mentions, and which he thinks conclusive on the other side, I persuade myself he will change his opinion of it, when he considers, that, as one person applying the wire of the charged bottle to warm spirits, in a spoon held by another person, both standing on the floor, will fire the spirits, and yet such firing will not determine whether the accumulation was in the glass or the non-electric; so the placing another person between them, standing on wax, with a basin in his hand, into which the water from the phial is poured, while he at the instant of pouring presents a finger of his other hand to the spirits, does not at all alter the case; the stream from the phial,

• See the paper entitled, I arther Experiments, &c.

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