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I flatter myself, that this short account of these matters will not be disagreeable to you; and am,

With the most profound respect,

Your most obedient humble servant,

W. WATSON.

TO JAMES BOWDOIN.

On the Mode of coating Electrical Jars.

SIR,

Philadelphia, 12 April, 1753.

I have shipped eighteen glass jars in casks well packed, on board Captain Branscombe for Boston; six of them are for you, the rest I understand are for the College. Leaf tin, such as they use in silvering lookingglasses, is best to coat them with; they should be coated to within about four or five inches of the brim. Cut the tin into pieces of the form here represented, and they will comply better with the bellying of the glass; one piece only should be round to cover the bottom; the same shapes will serve the inside. I had not conveniency to coat

them for you, and feared to trust anybody else, Mr. Kinnersley being abroad in the West Indies. To make the pieces comply the better, they may be cut in two where the cross lines are. They reach from the top to the edge of the round piece which covers the bottom. I place them in loose rims of scabboard, something like a small sieve, in which they stand very well. If you charge more than one or two together, pray take care how you expose your head to an accidental stroke; for, I can assure you from experience, one is

sufficient to knock a stout man down; and I believe a stroke from two or three, in the head, would kill him. Has Dr. Colden's new book reached you in Boston? If not, I will send it to you.

With great respect, I am, Sir,

Your most humble servant,

B. FRANKLIN.

P. S. The glass-maker being from home, I cannot now get the account. The tin is laid on with common paste, made of flour and water boiled together, and the pieces may lap over each other a little.

TO PETER COLLINSON.

Hypothesis of the Sea being the grand Source of Lightning retracted.-Positive, and sometimes negative, Electricity of the Clouds discovered. - New Experiments and Conjectures in Support of this Discovery. Observations recommended for ascertaining the Direction of the Electric Fluid.-Size of Rods for Conductors to Buildings. - Appearance of a Thun

der-cloud described.

SIR,

Philadelphia, September, 1753.

In my former paper on this subject, written first in 1747, enlarged and sent to England in 1749, I considered the sea as the grand source of lightning, imagining its luminous appearance to be owing to electric fire, produced by friction between the particles of water and those of salt. Living far from the sea, I had then no opportunity of making experiments on the sea water, and so embraced this opinion too hastily.

For, in 1750 and 1751, being occasionally on the

seacoast, I found, by experiments, that sea water in a bottle, though at first it would by agitation appear luminous, yet in a few hours it lost that virtue; hence and from this, that I could not by agitating a solution of sea salt in water produce any light, I first began to doubt of my former hypothesis, and to suspect, that the luminous appearance in sea water must be owing to some other principles.

I then considered whether it were not possible, that the particles of air, being electrics per se, might, in hard gales of wind, by their friction against trees, hills, buildings, &c., as so many minute electric globes, rubbing against non-electric cushions, draw the electric fire from the earth, and that the rising vapors might receive that fire from the air, and by such means the clouds become electrified.

If this were so, I imagined that by forcing a constant violent stream of air against my prime conductor, by bellows, I should electrify it negatively; the rubbing particles of air drawing from it part of its natural quantity of the electric fluid. I accordingly made the experiment, but it did not succeed.

In September, 1752, I erected an iron rod to draw the lightning down into my house, in order to make some experiments on it, with two bells to give notice when the rod should be electrified; a contrivance obvious to every electrician.

I found the bells rang sometimes when there was no lightning or thunder, but only a dark cloud over the rod; that sometimes, after a flash of lightning, they would suddenly stop; and at other times, when they had not rung before, they would, after a flash, suddenly begin to ring; that the electricity was sometimes very faint, so that, when a small spark was obtained, another could not be got for some time after; at other

times the sparks would follow extremely quick, and once I had a continual stream from bell to bell, the size of a crow-quill; even during the same gust there were considerable variations.

In the winter following I conceived an experiment, to try whether the clouds were electrified positively or negatively; but my pointed rod, with its apparatus, becoming out of order, I did not refit it till towards the spring, when I expected the warm weather would bring on more frequent thunder-clouds.

The experiment was this; to take two phials; charge one of them with lightning from the iron rod, and give the other an equal charge by the electric glass globe, through the prime conductor; when charged, to place them on a table within three or four inches of each other, a small cork ball being suspended by a fine silk thread from the ceiling, so as it might play between the wires. If both bottles then were electrified positively, the ball, being attracted and repelled by one, must be also repelled by the other. If the one positively, and the other negatively, then the ball would be attracted and repelled alternately by each, and continue to play between them as long as any considerable charge remained.

Being very intent on making this experiment, it was no small mortification to me, that I happened to be abroad during two of the greatest thunder-storms we had early in the spring; and, though I had given orders in the family, that, if the bells rang when I was from home, they should catch some of the lightning for me in electrical phials, and they did so, yet it was mostly dissipated before my return; and, in some of the other gusts, the quantity of lightning I was able to obtain was so small, and the charge so weak, that I could not satisfy myself; yet I sometimes saw what heightened my suspicions, and inflamed my curiosity.

At last, on the 12th of April, 1753, there being a smart gust of some continuance, I charged one phial pretty well with lightning, and the other equally, as near as I could judge, with electricity from my glass globe; and, having placed them properly, I beheld, with great surprise and pleasure, the cork ball play briskly between them, and was convinced, that one bottle was electrized negatively.

I repeated this experiment several times during the gust, and in eight succeeding gusts, always with the same success; and being of opinion (for reasons I formerly gave in my letter to Mr. Kinnersley, since printed in London), that the glass globe electrizes positively, I concluded, that the clouds are always electrized negatively, or have always in them less than their natural quantity of the electric fluid.

Yet, notwithstanding so many experiments, it seems I concluded too soon; for at last, June the 6th, in a gust which continued from five o'clock, P. M., to seven, I met with one cloud that was electrized positively, though several that passed over my rod before, during the same gust, were in the negative state. This was thus discovered.

I had another concurring experiment, which I often repeated, to prove the negative state of the clouds, viz., while the bells were ringing, I took the phial, charged from the glass globe, and applied its wire to the erected rod, considering, that if the clouds were electrized positively, the rod, which received its electricity from them, must be so too; and then the additional positive electricity of the phial would make the bells ring faster; but, if the clouds were in a negative state, they must exhaust the electric fluid from my rod, and bring that into the same negative state with themselves, and then the wire of a positively charged phial,

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