spent, and the water only remained. In the morning I observed, that though the motion of the ship continued the same, the water was now quiet, and its surface as tranquil as that of the oil had been the evening before. At night again, when oil was put upon it, the water resumed its irregular motions, rising in high waves almost to the surface of the oil, but without disturbing the smooth level of that surface. And this was repeated every day during the voyage.

third part of the tumbler,

Since my arrival in America, I have repeated the experiment frequently thus. I have put a pack-thread round a tumbler, with strings of the same, from each side, meeting above it in a knot at about a foot distance from the top of the tumbler. Then putting in as much water as would fill about one I lifted it up by the knot, and swung it to and fro in the air; when the water appeared to keep its place in the tumbler as steadily as if it had been ice. But pouring gently in upon the water about as much oil, and then again swinging it in the air as before, the tranquillity before possessed by the water was transferred to the surface of the oil, and the water under it was agitated with the same commotions as at sea.

I have shown this experiment to a number of ingenious persons. Those who are but slightly acquainted with the principles of hydrostatics, &c. are apt to fancy immediately that they understand it, and readily attempt to explain it; but their explanations have been different, and to me not very intelligible. Others, more deeply skilled in those principles, seem to wonder at it, and promise to consider it. And I think it is worth considering; for a new appearance, if it cannot be explained by our old principles, may afford us new ones, of use perhaps in explaining some other obscure parts of natural knowledge. I am, &c.

B. FRANKLIN.

Congelation of Quicksilver.·

-Cold produced by Evap

oration.*

Perth Amboy, 26 February, 1763.

THE most remarkable discovery that has been made within these three years is, that quicksilver is in reality a melted metal, with this character only, that of all others it requires the least heat to melt it. The Academy of Sciences at Petersburg have found, that by dipping a mercurial thermometer into repeated cooling mixtures, and so taking from the mercury the heat that was in it, they have brought it down some hundred degrees (the exact number I cannot remember) below the freezing point, when the mercury became solid and would sink no longer; and then the glass being broke, it came out in the form of a silver bullet adhering to a wire, which was the slender part that had been in the tube. Upon trial it was found malleable and was hammered out to the bigness of a half-crown, but soon after on receiving a small degree of warmth it returned gradually to its fluid state again. This experiment was repeated by several members of that Academy two winters successively, and an authentic account of it transmitted to our Royal Society.

I suppose you have seen, in the second volume of the new Philosophical Essays of the Edinburgh Society, an account of some experiments to produce cold by evaporation made by Dr. Cullen, who mentions the like having been before made at Petersburg. I think it is but lately, that our European philosophers have known or acknowledged any thing of such a power in

*This is a fragment of a letter in the handwriting of Franklin, a part of which only has been found. It is not known to whom it was written. - EDITOR.

nature. But I find it has been long known in the east. Bernier, in the account of his travels into India, written above a hundred years since, mentions the custom of travellers carrying their water in flasks covered with wet wrappers, and hung to the pommels of their saddles, so as that the wind might act upon them, and so cool the water. I have also seen a kind of jar for cooling water, made of potter's earth glazed, and so porous that the water gradually oozed through to the surface, supplying water just sufficient for a constant evaporation. I tried it and found the water within much cooler in a few hours. This jar was brought from Egypt.

FROM JOHN CANTON TO B. FRANKLIN.*

*

The Melting of Metals by Lightning not a cold Fusion. - Compressibility of Water and other Fluids.

London, 29 June, 1764.

DEAR SIR, Your favor of the 14th of March came to my hands the 15th of May last, and gave me great pleasure. The first experiment of Mr. Kinnersley's, which you mention, is, as you observe, a beautiful one to see; and,

* Mr. Canton was a very ingenious experimental philosopher, and for many years an active and valuable member of the Royal Society. His papers in the Philosophical Transactions, and other publications, contributed much to the improvement of science. His fondness for electricity was the cause of an intimate friendship between him and Dr. Franklin, which continued till the death of Mr. Canton, on the 22d of March, 1772, in the fifty-fourth year of his age. His most important discovery was that of the compressibility of water, in opposition to the received opinion formed on the celebrated Florentine experiment. For this discovery he was honored by the Royal Society with the Copley Medal, in November, 1765.-EDITOR.

I think, fully proves that the fusion of metals by lightning is not a cold fusion. I have myself several times melted small brass wire by a stroke from your case of bottles, which left a mark where it lay upon the table, and some balls of twice or three times its diameter near the mark, but no part of the wire could be found. At the time of the stroke a great number of sparks, like those from a flint and steel, fly upward and laterally from the place where the wire was laid, and lose their light in the daytime, at the distance of about two or three inches. The diameter of a piece of Mr. Kinnersley's wire, which you were so kind as to send me with the balls, I found to be one part in one hundred and eighty-two of an inch; mine was but one part in three hundred and thirty.

The second of Mr. Kinnersley's experiments, which you relate, and which seems to be a very extraordinary one, I have several times endeavoured to make, but without success. The air with you must certainly be much drier than in England; for I have never observed the enclosed pith-balls to separate by the electrized air of a room, without having first heated the phial, notwithstanding which, they always came together in the phial, before the outward air had lost its electricity, as appears by their separating again when taken out of it. I once electrified the air of my largest room to a considerable degree, and by opening the windows and doors suffered the wind to blow through for about five minutes. I then shut them and examined the air in the room, but found no sign of electricity remaining. This air I electrified to about the same degree as before, and, leaving it confined, it retained a sensible degree of its electricity for more than three quarters of an hour. Hence I entirely agree with you, that the glass in Mr. Kinnersley's

experiment received some degree of electricity from the electrized air, and so kept the balls separated after that air was blown away.

I have put your ingenious friend Mr. Bowdoin's telescope into Mr. Nairne's hands, who is making a pedestal for it, which I think will be an improvement of that which Mr. Bowdoin has described in his last

letter to me, which you saw. You may depend on my taking all possible care to get it well executed and soon. I find the fitting Dollond's micrometer to the telescope is impracticable.

Since the publication of a short paper in the Transactions, which contains an account of experiments to prove that water is not incompressible, I have discovered a remarkable property belonging to that fluid, which is new to me, though perhaps it may not be so to you. The property I mean is, its being less compressible in summer than in winter. This is contrary to what I find in spirit of wine and oil of olives, which are (as one would expect water to be) more compressible when expanded by heat, and less so when contracted by cold. For, when Fahrenheit's thermometer is at thirty-four degrees and the barometer at twenty⚫nine and a half, water is compressed by the weight of the atmosphere forty-nine parts in a million of its whole bulk, and spirit of wine sixty of the same parts. When the thermometer is at fifty degrees, water is compressed forty-six parts and spirit of wine sixty-six parts in a million by the same weight; and, when the thermometer is at sixty-four degrees, this weight will compress water no more than forty-four parts, but it will compress spirit of wine seventy-one of these parts.

As I am not able at present to account for this difference in the compressibility of water myself, I should be very glad to have your thoughts upon it.