which ascend, in a given space, from the surface of the earth. "By means of a little bees wax," fays he, "I fastened a half-crown very near, but "not quite contiguous to the fide of the glafs, "and fetting the glafs, with its mouth down"wards, on the grafs, it presently became "covered with vapour, except that part of it, "which was near to the half-crown. Not only "the half-crown itself, was free from vapour, "but it had hindered any from fettling on the

glass, which was near it, for there was a little ring of glass furrounding the half-crown, to "the distance of a quarter of an inch, which "was quite dry, as well as that part of the glass, "which was immediately under the half-crown; "it feemed as if the filver had repelled the water "to that distance. A large red wafer had the "fame effect as the half-crown; it was neither "wetted itself, nor was the ring of glass, contiguous to it, wetted. A circle of white paper produced the fame effect, fo did feveral other "fubftances, which it would be tedious to "enumerate.”*

Do not the inftances of repulfion, here adduced, with various others, which may perhaps be recollected and noticed by the Gentlemen prefent, warrant us to conclude, that this principle is a powerful agent, in the operations of nature? To this caufe, the air we breathe owes, pro

Watfon's Chemical Effays, vol. III. p. 64.

bably,

bably, its existence and elafticity; the light, which illuminates our globe, its rapid motions and diverfified inflections; and fire, its genial, expanfile, and animating energy. Is it, therefore, confiftent with analogy, to exclude repulfion from that branch of phyfics, which chemistry comprehends? The fubject certainly merits further investigation: And I fhall ftate, to my friend Dr. Wall, the facts and queries, which I have now laid before this Society; that he may communicate to us, fuch limitations or confirmations of his doctrine, as an attentive review of it may fuggeft, to his ingenuous and philofophic mind.

EXTRACTS of Two LETTERS from Dr. WALL of OXFORD, to Dr. PERCIVAL, in Reply to the foregoing QUERIES concerning ATTRACTION and REPULSION; communicated to the LITERARY and PHILOSOPHICAL SOCIETY. Read January, 12, 1785.

I

DEAR SIR,

T gives me great pleasure to think that my paper on oil, &c. was fo far approved, as to be thought worthy of a place in your Memoirs. I am by no means pofitive, that my hypothefis

will abfolutely ftand the teft of examination, fo far as to prove, that there is no principle of repulfion in chemistry: but I think ftill, notwithstanding your very ingenious obfervations, that, in moft cafes, APPARENT REPULSION may be refolved into ELECTIVE ATTRACTION. The experiment, which you first adduce, made with a mixture of oil and water agitated in a glass veffel, if I understand it right, appears to me not to affect the point in queftion. I think that the commotion, which the water undergoes while the oil remains tranquil, depends upon the different fpecific gravity of the two fluids (whereby they receive the force of the impulfe in unequal proportions) and upon the difpofition of the oil, from its fuperior levity, to preferve its place, upon the top of the water, whatever agitation the water beneath may be fubjected to. In the boiling of brine, I admit that the agitation of the water must have a confiderable effect in breaking down the crystals of falts, and thus preventing their regular and complete formation: but this cannot be all that takes place, when an oily fubftance is put into the brine; because, if it were, the fame effect would refult from boiling the brine only without the addition of any oily or refinous matter.

Forgive me, in the fecond place, if I fhould not agree with you in explaining the conflict, which is felt in the lungs, upon the inspiration of the fumes of burnt oil, in the fame manner

as

as you do. I think your theory too fubtile. What is the primary action of atmospheric air, received into the lungs; and what appears to be the operation it performs there, before it is refpired? Do not the late obfervations of innumerable chemifts fhew, that it is in part converted into fixed air in that procefs, and in part phlogisticated, by carrying off the phlogiston, separated from the blood in the circulation, and discharged by the lungs? The more perfectly the air inspired is dephlogisticated, it answers the demand of nature more entirely; but when it is either largely mixed with fixed air, or loaded with phlogistic particles, such as the empyreumatic vapours from burnt oil, it is rendered unfit for these important purposes, and, inftead of carrying off noxious matters, it conveys into the lungs a new cause of offence; and thus produces a fenfe of conflict and uneafiness in a two-fold manner; by not carrying off the load from which the conftitution is ufually freed by the process of respiration; and by superadding a ftimulus ab extra.

I cannot admit the application of the laws of mechanical attraction, much less the properties of algebraic quantities, to the phænomena of chemistry. It was well obferved by the late excellent Dr. Lewis, of Kingston, in his Philosophical Commerce of Arts, "that it is of great importance, that these two orders or forms of "attraction

"attraction (the mechanical, and the chemical) "fhould be properly diftinguished and separated "from each other, as many errors have arifen, " from applying to one, fuch laws only as obtain " in the other."

Your illustration of repulfion, from the beautiful appearance of the drops of water on colewort leaves, feems, at firft view, to prefent a moft forcible objection to my fyftem; and yet perhaps upon more mature confideration, that fact may be affumed as a confirmation of it. For water, from the ftrong attraction of its particles to each other, efpecially when the quantity is inconfiderable, and is allowed to fall upon an inclined surface, does not adhere to that furface, but forms itself into globules, and runs off, till by the breaking of fome of the drops, or the accidental remora of others, that furface becomes wetted, and then the drops no longer exhibit the property above-mentioned. And this is fometimes remarkable, even when the water falls upon fubftances, which in other circumstances are much disposed to imbibe it, and to unite with it; as when water is let fall from a height on a furface covered with duft, with flour, &c. And a fimilar ftate may obtain upon colewort, and fome other large leaves, which are smooth, and are liable, after a dry feafon, to become covered with the fine duft that floats in the air; or poffibly, there exfudes on the furface of fuch