« ZurückWeiter »
(if it took place) I should think would not be omitted in Captain Waddel's account.
I am very much pleased that the explication I sent you, of the crooked direction of lightning, meets with your approbation.
As to your supposition about the source of lightning, the luminous appearance of the sea in the night, and the similitude between the friction of the particles of salt and water, as you considered them in their original separate state, and the friction of the globe and cushion, very naturally led you to the ocean, as the grand source of lightning; but the activity of lightning, or the electric element, and the fitness of water to conduct it, together with the experiments you mention of salt and water, seem to make against it, and to prepare the way for some other hypothesis. Accordingly you propose a new one, which is very curious, and not so liable, I think, to objections as the former. But there is not as yet, I believe, a sufficient variety of experiments to establish any theory, though this seems the most hopeful of any I have heard of.
The effect which the discharge of your four glass jars had upon a fine wire, tied between two strips of glass, puts me in mind of a very similar one of lightning, that I observed at New York, October, 1750, a few days after I Jeft Philadelphia. In company with a number of gentlemen, I went to take a view of the city from the Dutch church steeple, in which is a clock about twenty or twenty-five feet below the bell. From the clock went a wire through two floors, to the clockhammer near the bell, the holes in the floor for the wire being perhaps about a quarter of an inch diameter. We were told, that in the spring of 1750, the lightning struck the clock-hammer, and descended along the wire to the clock, melting in its way several spots of
VOL. V. X
the wire, from three to nine inches long, through one third of its substance, till coming within a few feet of the lower end, it melted the wire quite through, in several places, so that it fell down in several pieces; which spots and pieces we saw. When it got to the end of the wire, it flew off to the hinge of a door, shattered the door, and dissipated. In its passage through the holes of the floors it did not do the least damage, which evidences that wire is a good conductor of lightning (as it is of electricity), provided it be substantial enough, and might, in this case, had it been continued to the earth, have conducted it without damaging the building.*
Your information about your globe's raising the electric fire in greater quantities, by means of a wire extending from the cushion to the- earth, will enable me, I hope, to remedy a great inconvenience I have been under, to collect the fire with the electrifying glass I use, which is fixed in a very dry room, three stories from the ground. When you send your meteorological observations to Dr. Perkins, I hope I shall have the pleasure of seeing them. I am, &,c.
* The wire mentioned in this account was replaced by a small brass chain. In the summer of 1763, the lightning again struck that steeple, and from the clock-hammer near the bell, it pursued the chain as it had before done the wire, went off to the same hinge, and again shattered the same door. In its passage through the same holes of the same floors, it did no damage to the floors, nor to the building during the whole extent of the chain. But the chain itself was destroyed, being partly scattered about in fragments of two or three links, melted and stuck together, and partly blown up or reduced to smoke, and dissipated. [See an account of the same effect of lightning on a wire at Newbury, p. 357.] The steeple, when repaired, was guarded by an iron conductor, or rod, extending from the foot of the vane-spindle, down the outside of the building, into the earth. The newspapers have mentioned, that in 1763, the lightning fell a third time on the same steeple, and was safely conducted by the rod; but the particulars are not come to hand.
FROM JAMES BOWDOIN TO BENJAMIN FRANKLIN.
Remarks on Dr. Colden's Letter respecting the Electricity of the Clouds.
Boston, 1(3 March, 1752.
According to promise in my last, I now return you Dr. Colden's Jetter; for communicating which I am greatly obliged to you. The Doctor, dissenting from you, is of opinion, that sea clouds are less electrified than land clouds, and gives the reasons of his opinion, "that salt, though an electric per se, is never raised in sea vapors; therefore sea clouds are less electrified than land clouds; that, all sulphurs (which mountains especially abound with, from whence thunder-gusts are often observed to rise,) being electrics per se, sulphurous vapors are more electrified than sea vapors." The conclusions from these reasons might be just, if the supposition they are formed upon was just, namely, that vapors, &,c., are more or less electrified according to the quantity of electrics per se they contain. But that seems contrary to experience; for electricity is accumulated upon the conductor without any mixture of the electrics per se (glass or -sulphur), which excited it.
Another reason the Doctor offers is, that electricity forwards vegetation, which makes it probable, he supposes, that vapors from the land and vegetables are more electrified than sea vapors; but, by the same way of reasoning, it is probable that land vapors have a mixture of salt (which the Doctor has denied, and justly, I believe, even of sea vapors), for salt in a suitable proportion, I have heard, promotes vegetation.
I pretend not to say what vapors are most electrified, but only that these reasons do not appear to me to support the Doctor's opinion.
The Doctor hints that he has something in speculation, which will be the means of improving all parts of natural philosophy. If he has communicated his scheme to you, or any new improvement, I shall be obliged, provided it be consistent with the laws of friendship, if you would favor me with some account of it. I have heard, that several gentlemen have desired you to procure them a number of large glass jars suitable for electrical experiments; I take the liberty of adding to your trouble, by asking the favor of you to procure half a dozen of them for me, two of them to be coated and made fit for use, the other four I shall get finished here; for which I shall take care to reimburse you. I am, with much esteem, Sir, yours, &.c.
TO E. KINNERSLEY, AT BOSTON.
Reasons for supposing that the Glass Globe charges positively, and the Sulphur negatively. — Hint respecting a Leather Globe for Experiments when travelling.
Philadelphia, 16 March, 1752.
Sir, Having brought your brimstone globe to work, I tried one of the experiments you proposed, and was agreeably surprised to find, that the glass globe being at one end of the conductor, and the sulphur globe at the other end, both globes in motion, no spark could be obtained from the conductor, unless when one globe turned slower, or was not in so good order as the other; and then the spark was only in proportion to the difference, so that turning equally j or turning that slowest which worked best, would again bring the conductor to afford no spark.
I found also, that the wire of a phial charged by the glass globe, attracted a cork ball that had touched the wire of a phial charged by the brimstone globe, and vice versa, so that the cork continued to play between the two phials, just as when one phial was charged through the wire, the other through the coating, by the glass glo.be alone. And two phials charged, the one by the brimstone globe, the other by the glass globe, would be both discharged by bringing their wires together, and shock the person holding the phials.
From these experiments one may be certain, that your second, third, and fourth proposed experiments would succeed exactly as you suppose, though I have not tried them, wanting time. I imagine it is the glass globe that charges positively, and the sulphur negatively, for these reasons. 1. Though the sulphur globe seems to work equally well with the glass one, yet it can never occasion so large and distant a spark ber tween my knuckle and the conductor, when the sulphur one is working, as when the glass one is used; which, I suppose, is occasioned by this, that bodies of a certain bigness cannot so easily part with a quantity of electrical fluid they have and hold attracted within their substance, as they can receive an additional quantity upon their surface by way of atmosphere. Therefore so much cannot be drawn out of the conductor, as can be thrown on it. 2. I observe, that the stream or brush of fire, appearing at the end of a wire, connected with the conductor, is long, large, and much diverging, when the glass globe is used, and makes a snapping (or rattling) noise; but, when the sulphur one is used,
Vol. v. 36 x*