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very dry, may not part with its overplus, or have its deficiency supplied so suddenly, as the tin ; but may continue to be electrified, after that has been touched for a considerable time.
Having made the Torricellian vacuum about five feet long, after the manner described in the Philosophical Transactions, Vol. XLVII. p. 370, if the excited tube be brought within a small distance of it, a light will be seen through more than half its length; which soon vanishes, if the tube be not brought nearer; but will appear again, as that is moved farther off. This may be repeated several times, without exciting the tube afresh.
This experiment may be considered as a kind of ocular demonstration of the truth of Mr. Franklin's hypothesis; that, when the electrical fluid is condensed on one side of thin glass, it will be repelled from the other, if it meets with no resistance. According to which, at the approach of the excited tube, the fire is supposed to be repelled from the inside of the glass surrounding the vacuum, and to be carried off through the columns of mercury; but, as the tube is withdrawn, the fire is supposed to return.
Let an excited stick of wax, of two feet and a half in length, and about an inch in diameter, be held near its middle. Excite the glass tube, and draw it over one half of it; then, turning it a little about its axis, let the tube be excited again, and drawn over the same half; and let this operation be repeated several times; then will that half destroy the repelling power of balls electrified by glass, and the other half will increase it. By this experiment it appears, that wax also may be electrified positively and negatively. And it is probable, that all bodies whatsoever may have the quantity they contain of the electrical fluid increased or diminished. The clouds, I have observed, by a great number of experiments, to be some in a positive, and others in a negative, state of electricity. For the cork balls, electrified by them, will sometimes close at the approach of excited glass; and at other times be separated to a greater distance. And this change I have known to happen five or six times in less than half an hour; the balls coming together each time and remaining in contact a few seconds, before they repel each other again. It may likewise easily be discovered, by a charged phial, whether the electrical fire be drawn out of the apparatus by a negative cloud, or forced into it by a positive one; and by whichsoever it be electrified, should that cloud either part with its overplus, or have its deficiency supplied suddenly, the apparatus will lose its electricity; which is frequently observed to be the case, immediately after a flash of lightning. Yet, when the air is very dry, the apparatus will continue to be electrized for ten minutes, or a quarter of an hour, after the clouds have passed the zenith; and sometimes till they appear more than half-way towards the horizon. Rain, especially when the drops are large, generally brings down the electrical fire; and hail, in summer, I believe never fails.
When the apparatus was last electrified, it was by the fall of thawing snow, which happened so lately as on the 12th of November; that being the twenty-sixth day and sixty-first time it has been electrified, since it was first set up, which was about the middle of May. And, as Fahrenheit's thermometer was but seven degrees above freezing, it is supposed the winter will not entirely put a stop to observations of this sort. At London, no more than two thunder-storms have happened during the whole summer; and the apparatus was sometimes so strongly electrified in one of them, that the bells, which have been frequently rung by the clouds, so loud as to be heard in every room of the house (the doors being open), were silenced by the almost constant stream of dense electrical fire, between each bell and the brass ball, which would not suffer it to strike.
I shall conclude this paper, already too long, with the following queries.
1. May not air, suddenly rarefied, give electrical fire to, and air, suddenly condensed, receive electrical fire from, clouds and vapors passing through it ?
2. Is not the aurora borealis the flashing of electrical fire from positive towards negative clouds, at a great distance, through the upper part of the atmosphere, where the resistance is least?
TO JAMES BOWDOIN.
Concerning the Light emitted by Salt Water. — The
Abbé Nollet's Letters on Electricity.
Philadelphia, 13 December, 1753. DEAR SIR, I received your favor of the 12th ultimo, with the law of your province for regulating the Indian trade, for which I thank you, and for the remarks that accompany it, which clearly evince the usefulness of the law, and I hope will be sufficient to induce our Assembly to follow your example,
I have yet received no particulars of the unhappy gentleman's death at Petersburg, (whose fate I lament.)
One of the papers says, that all the letters from thence confirm the account, and mentions his name, (Professor Richmann,) but nothing farther. No doubt we shall have a minute account of the accident with all its circumstances, in some of the magazines or the Transactions of the Royal Society.*
The observation you made of the sea water emitting more and less light, in different tracts passed through by your boat, is new; and your manner of accounting for it ingenious. It is indeed very possible, that an extremely small animalcule, too small to be visible even by the best glasses, may yet give a visible light. I remember to have taken notice, in a drop of kennel water, magnified by the solar microscope to the bigness of a cart-wheel, there were numbers of visible animalcules of various sizes swimming about; but I was sure there were likewise some which I could not see, even with that magnifier; for the wake they made in swimming to and fro was very visible, though the body that made it was not so. Now, if I could see the wake of an invisible animalcule, I imagine I might much more easily see its light, if it were of the luminous kind. For how small is the extent of a ship's wake, compared with that of the light of her lantern.
My barometer will not show the luminous appearance by agitating the mercury in the dark, but I think yours does. Please to try whether it will, when agitated, attract a fine thread hung near the top of the tube.
As to the answer to Nollet, if I were going on with it, I should be extremely glad of your peeping into it (as you say) now and then, that I might correct it by your advice. The materials in short hints have been long collected and methodized; they only want to be clothed with expression. But, soon after my return from New England, I received the enclosed from Monsieur Dalibard, wherein he tells me, that he is preparing an answer, not only to the Abbé, but. to some others that have wrote against my doctrine, which will be published the beginning of this winter. This, with a good deal of business, and a little natural indolence, has made me neglect finishing my answer, till I shall see what is done by him. Perhaps it may then
* Professor Richmann was killed at Petersburg, on the 26th of July, 1753, while repeating Franklin's experiment for bringing electricity from the clouds. He received a shock, which caused instantaneous death. A full account of the circumstances attending his death is contained in the Philosophical Transactions, Vol. XLVIII. p. 765; and Vol. XLIX. p. 61. - Editor.
appear unnecessary for me to do any thing farther in it. And will not one's vanity be more gratified in seeing one's adversary confuted by a disciple, than even by one's self? I am, however, a little concerned for Dalibard, when I find by his letter, that he has been so far imposed on by the Abbé's confident assertion, that a charged bottle placed on an electric per se loses its electricity, as to attempt to account for it, when the thing is absolutely not fact. I have in answer wrote him my sentiments on that and some other particul of the Abbé's book, which I hope will get to hand before his answer is published. I am, with the greatest esteem and regard, Dear Sir, your most obliged humble servant,