weighed at intervals, when it had been in the fcale fix hours, and had then loft fo much of its heat, as to be only blood warm, was found to be acquiring weight in the proportion of seven grains in the space of an hour*. But, when weighed the day following, at the expiration of twenty-four hours after the commencement of the experiment, it had acquired a ftill further addition of two pennyweights and seventeen grains, which, according to the above. progreffion, it would have required at least nine hours and a half, nay, most probably, even a longer time, to accomplish. If to these nine hours and a half, we add the preceding fix, we obtain fifteen hours and a half; a period long before the expiration of which, the mafs of iron must have taken the temperature of the furrounding bodies, fince the first fix of these were fufficient to reduce it, from the welding point, down to blood heat.

I will not trefpafs longer on the time of the Society, but will conclude by obferving, that metals, which are the only bodies hitherto employed to determine this point, are certainly, from the changes they undergo by the action

During the two firft hours of its expofure in the scale, the increase of weight had proceeded with much more rapidity; in the third hour it proceeded lefs quickly, and continued to diminish gradually in celerity to the expiration of the fixth.

of

of heat, very ill adapted to the purpofe; and that to arrive at any degree of certainty, it will perhaps be neceffary to weigh the body in vacuo, or at least in a veffel fo confined, as that any current of air through it fhall be prevented; and that the beam of the fcales fhall be formed of materials less liable to expanfion by heat, than metals in general are.

REMARKS on the FLOATING of CORK BALLS in WATER; by Mr. BANKS, Lecturer in Natural Philofophy. Communicated by the Rev. THOMAS BARNES, D. D. Fellow of the American Philofophical Society, bolden at Philadelphia.

PER

READ DECEMBER 6, 1786.

ERHAPS no fimple appearance seems fo generally mifunderstood as that of Cork Balls, &c. on Water; and as one falfe principle, adopted, is often productive of more, a few obfervations on fo fimple a phenomenon, perhaps, may not be thought below the notice of the learned, although perfectly acquainted with the true caufe. That clean bubbles of glafs or pieces of cork, left to fwim in water, contained in clean veffels of glafs or china, and at the distance

diftance of about one inch from the fide, will approach that fide is certain; and it appears that this and fimilar experiments have frequently been made by philofophers, to prove the attraction of these bodies. To this I cannot affent, for different reafons; which I prefume are fupported by the following experiments.

The experiments are made in a veffel of glass or earthen ware five or fix inches in diameter.

EXPERIMENT I. If a clean cork be wet and placed about one inch from the fide of the containing veffel, it will approach the fide with an accelerated motion.

EXPERIMENT II. If two corks be placed about an inch from each other, and at a fufficient distance from the fide, they approach each other in the fame manner.

EXPERIMENT III. Pour water into the veffel till it is rather higher than the brim; place the cork close by the fide, and it recedes with a retarded motion.

EXPERIMENT IV. Sink a piece of metal in the center of the veffel, fo that the top thereof may be above the furface of the water, the cork, placed at a proper diftance, will approach it.

EXPERIMENT V. Raife the water until the metal is covered, and the cork will remain at reft at any distance from the metal.

In all the experiments, the water which furrounds the balls is elevated by capillary attraction, as alfo by the fide of the containing veffel, except in experiment III.

EXPERIMENT VI. Pieces of dry cork, or painted balls, placed gently on water, and near each other, also approach each other; but if one is placed near the fide of the containing veffel, adjoining to which the water is elevated, it will recede.

In this experiment the furrounding fluid is depreffed.

Whether thefe bodies attract each other, or not, I prefume is not to be determined by these experiments; however they are not intended to difprove any attraction, but rather to prove that there is fome other more powerful caufe on which the phenomena depend: if not, why does the ball in the third experiment leave the fide, to which it adhered in the firft; or how fhall we account for the univerfal recefs of balls around which the fluid is depreffed, from thofe around which it is elevated; and why are they not attracted by bodies exceedingly near, when thefe bodies are perfectly covered with water?

Thefe experiments I know are not of fufficient weight with fome who rank high amongst the literati, to prove that the phenomena are not owing to attraction; yet I prefume the true cause has long fince been explained upon hydro

ftatical

ftatical principles by Dr. W. J. Gravesande, &c. for, as every body which fwims impreffes the fupporting fluid with a force equal to its own weight, the fluid reacts and preffes the fupported body with the fame force. The fides of the body are also preffed by the furrounding fluid with forces which are as the depth: and if the encompaffing water be raised by capillary attraction, the pressure will still be the fame, or equal on oppofite fides, fo that without force the body cannot move; but if it be placed fo near the fide that the water elevated by it joins that elevated by the fide of the veffel, or by another ball, the preffure on that fide is diminished, while that on the other fide, remaining the fame, will cause it to approach the fide or other ball and in the fame manner, if the fluid is depreffed, when the cavities meet, the preffure on that fide will be diminished, and the bodies of confequence approach each other or the fide of the veffel; and the recefs in the third experiment is evidently owing to the preffure being fuperior on that fide neareft to the glafs, when the fluid is elevated above it, and the elevation round the ball joins the declining furface near the edge. Some indeed have drawn directly the contrary conclufion; but when the elevated water which furrounds the ball, and is fupported by it, is caufed with one fide to join the declining furface of the fupporting fluid, it must then gra