Abbildungen der Seite

my sulphur globe, and the cushion belonging to it, and make the trial; but must caution you not to use chalk on the cushion; some fine powdered sulphur will do better. If, as I expect, you should find the globes to charge the prime conductor differently, I hope you will be able to discover some method of determining which it is that charges positively. I am, &c.



Probable Cause of the different Attractions and Repulsions of the two Electrified Globes mentioned in the preceding Letter.

Philadelphia, 2 March, 1752.


I thank you for the experiments communicated. I sent immediately for your brimstone globe, in order to make the trials you desired, but found it wanted centres, which I have not time now to supply; but, the first leisure, I will get it fitted for use, try the experiments, and acquaint you with the result.

In the mean time I suspect, that the different attractions and repulsions you observed, proceeded rather from the greater or smaller quantities of the fire you obtained from different bodies, than from its being of a different kind, or having a different direction. In haste, I am, &c.


*The Reverend Ebenezer Kinnersley was a professor in the College of Philadelphia. - EDITOR,


Effect of Lightning on Captain Waddel's Compass, and on the Dutch Church at New York.



Boston, 2 March, 1752.

I have received your favor of the 24th of January past, enclosing an extract from your letter to Mr. Collinson, and Dr. Colden's letter to yourself, which I have read with a great deal of pleasure, and am much obliged to you for. Your extract confirms a correction Mr. Kinnersley made, a few days ago, of a mistake I was under respecting the polarity given to needles by the electrical fire, "that the end which receives the fire always points north;" and "that the needle, being situated east and west, will not have a polar direction.” You find, however, the polarity strongest when the needle is shocked lying north and south; weakest when lying east and west; which makes it probable that the communicated magnetism is less, as the needle varies from a north and south situation. As to the needle of Captain Waddel's compass, if its polarity was reversed by the lightning, the effect of lightning and electricity, in regard of that, seems dissimilar; for a magnetic needle in a north and south situation (as the compass needle was), instead of having its power reversed, or even diminished, would have it confirmed or increased by the electric fire. But perhaps the lightning communicated to some nails in the binacle (where the compass is placed) the magnetic virtue, which might disturb the compass.

This I have heard was the case; if so, the seeming dissimilarity vanishes; but this remarkable circumstance

(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 left 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



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 1765, 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.


Remarks on Dr. Colden's Letter respecting the Electricity of the Clouds.

Boston, 16 March, 1752.


According to promise in my last, I now return you Dr. Colden's letter; 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,

« ZurückWeiter »