Abbildungen der Seite
PDF
EPUB

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 from 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

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.

Bermudas, says, there was less thunder there in that whole time, than he has sometimes heard in a month at Carolina.

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 my 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 ane 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, the side of the basin, with the arms and body of the person on the wax, being altogether but as one long wire, reaching from the internal surface of the phial to the spirits.

* See the paper entitled, Farther Experiments, &c.

June 29th, 1751. In Captain Waddell's account of the effects of lightning on his ship, I could not but take notice of the large comazants (as he calls them), that settled on the spintles at the top-mast heads, and burned like very large torches (before the stroke). According to my opinion, the electrical fire was then drawing off, as by points, from the cloud; the largeness of the flame betokening the great quantity of electricity in the cloud ; and, had there been a good wire communication from the spintle heads to the sea, that could have conducted more freely than tarred ropes, or masts of turpentine wood, I imagine there would either have been no stroke, or, if a stroke, the wire would have conducted it all into the sea without damage to the ship

His: compasses lost the virtue of the loadstone, or the poles were reversed, the north point turning to the south. By electricity we have (here at Philadelphia) frequently given polarity to needles, and reversed it at pleasure. Mr. Wilson, at London, tried it on too large masses, and with too small force.

A shock from four large glass jars, sent through a fine sewing-needle, gives it polarity, and it will traverse when laid on water. If the needle, when struck, lies east and west, the end entered by the electric blast points north. If it lies north and south, the end that lay towards the north will continue to point north when placed on water, whether the fire entered at that end, or at the contrary end.

The polarity given is strongest when the needle is struck lying north and south ; weakest, when lying east

« ZurückWeiter »