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return of the tube, they will approach each other till they touch, and then repel as at first. If the tin tube be electrified by wax, or the wire of a charged phial, the balls will be affected in the same manner at the approach of excited wax, or the wire of the phial.
Electrify the cork balls, as in the last experiment, by glass, and at the approach of an excited stick of wax their repulsion will be increased. The effect will be the same, if the excited glass be brought towards them, when they have been electrified by wax.
The bringing the excited glass to the end or edge of the tin tube, in the third experiment, is supposed to electrify it positively, or to add to the electrical fire it before contained; and therefore some will be running off through the balls, and they will repel each other. But, at the approach of excited glass, which likewise emits the electrical fluid, the discharge of it from the balls will be diminished; or part will be driven back, by a force acting in a contrary direction; and they will come nearer together. If the tube be held at such a distance from the balls, that the excess of the density of the fluid round about them, above the common quantity in air, be equal to the excess of the density of that within them, above the common quantity contained in cork, their repulsion will be quite destroyed. But, if the tube be brought nearer, the fluid without being more dense than that within the balls, it will be attracted by them, and they will recede from each other again.
When the apparatus has lost part of its natural share of this fluid, by the approach of excited wax to one end of it, or is electrified negatively, the electrical fire is attracted and imbibed by the balls to supply the deficiency; and that more plentifully at the approach of excited glass, or a body positively electrified, than before ; whence the distance between the balls will be increased, as the fluid surrounding them is augmented. And, in general, whether by the approach or recess of any body, if the difference between the density of the internal and external fluid be increased, or diminished, the repulsion of the balls will be increased, or diminished, accordingly.
When the insulated tin tube is not electrified, bring the excited glass tube towards the middle of it, so as to be nearly at right angles with it, and the balls at the end will repel each other; and the more so, as the excited tube is brought nearer. When it has been held a few seconds, at the distance of about six inches, withdraw it, and the balls will approach each other till they touch; and then, separating again, as the tube is moved farther off, will continue to repel when it is taken quite away. And this repulsion between the balls will be increased by the approach of excited glass, but diminished by excited wax; just as if the apparatus had been electrified by wax, after the manner described in the third experiment.
Insulate two tin tubes, distinguished by A and B, so as to be in a line with each other, and about half an inch apart; and, at the remote end of each, let a pair of cork balls be suspended. Towards the middle of .4, bring the excited glass tube, and holding it a short time, at the distance of a few inches, each pair of balls will be observed to separate; withdraw the tube, and the balls of J1 will come together, and then repel each other again; but those of B. will hardly be affected. By the approach of the excited glass tube, held under the balls of A, their repulsion will be increased; but if the tube be brought, in the same manner, towards the balls of B, their repulsion will be diminished.
In the fifth experiment, the common stock of electrical matter in the tin tube is supposed to be attenuated about the middle, and to be condensed at the ends, by the repelling power of the atmosphere of the excited glass tube, when held near it. And perhaps the tin tube may lose some of its natural quantity of the electrical fluid, before it receives any from the glass; as that fluid will more readily run off from the ends and edges of it, than enter at the middle; and accordingly, when the glass tube is withdrawn, and the fluid is again equally diffused through the apparatus, it is found to be electrified negatively; for excited glass brought under the balls will increase their repulsion.
In the sixth experiment, part of the fluid driven out of one tin tube enters the other; which is found to be electrified positively, by the decreasing of the repulsion of its balls at the approach of excited glass.
Let the tin tube, with a pair of balls at one end, be placed three feet at least from any part of the room, and the air rendered very dry by means of a fire; electrify the apparatus to a considerable degree; then touch the tin tube with a finger, or any other conductor, and the balls will, notwithstanding, continue to repel each other, though not at so great a distance as before.
The air surrounding the apparatus, to the distance of two or three feet, is supposed to contain more or less of the electrical fire, than its common share, as the tin tube is electrified positively or negatively; and, when 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 Auid 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