employed inftead of the rope. When this weight, which had, above, been in equilibrio with that in the oppofite bason, had been thus brought 170 feet nearer the furface of the earth; the equilibrium, we are told, was deftroyed, and, instead of preponderating, in confequence of its fituation, it rofe; fo that it was neceffary to add to the weight in this lower fcale. We observe, however, that one ounce and fix drachms were found sufficient to restore the equilibrium; and that the balance might be made to incline either to the one fide or the other, on the addition of another ounce to either of the basons.

The Reader is not to confider this particular experiment as one of the most favourable to the cause of the Anti-attractionaires. We relate it chiefly to fhew the grounds on which they found their objections to the Newtonian fyftem of attraction, and the method by which they endeavour to fupport them; obferving only, that in the many other experiments of the fame kind, related in this and other numbers of M. Rozier's work, the refults have been, at different times, more or lefs favourable to their hypothefis. We shall next attend to the experiments and reasonings of the oppofite party, who fupport the doctrine of attraction, principally collected from the following article.

A Memoir, indicating the different Caufes which may accidentally change the apparent Effects of the Gravity of Bodies, placed at unequal Heights: read before the Academy of Dijon.

The balance that was used in the experiments related in this Memoir, would carry 250 pounds in each bafon; and was fo fenfible, that when it was loaded with this weight, it would turn on the addition of half a drachm. The experiments were made in the tower of a church, at the height of 120 feet. They were conducted nearly in the fame manner as the preceding, and with a fcrupulous attention to every circumstance that might influence the refults. Barometers and thermometers, in particular, were placed both above and below. In the first experiment, the balance, containing on each fide 200 pounds, including the weight of a long rope in one of the bafons, being in perfect equilibrium; this laft mentioned bafon was let down 120 feet below its former ftation, fufpended by the rope abovementioned. At first, the equilibrium was fomewhat difturbed by the ofcillations of this lower bafon; fo that it was found neceffary to add two drachms to the upper weight, to render the balance even. This motion, however, at length ceafing, it was found requifite to take out this fmall additional weight; and then the fuperior and inferior weights were obferved to equiponderate, in the fame manner as when they had both been fufpended at the fuperior ftation.

As the density of the air is greater near the furface of the earth than at different heights above it, the Author of this memoir calculates, from data furnished by other experiments here menREV. Feb. 1776.

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tioned, the quantity of the effect which this difference muft produce in the apparent gravity of the upper and lower weights; which were each of caft iron, and equal to two-fifths of a cubic foot. From his calculations it appears that, in confequence of the difference between the denfity, or weight, of two-fifths of a cubic foot of air at the earth's furface, difplaced by the lower weight, and that of an equal bulk of the fame Auid difplaced by the upper weights, the lower weight ought to weigh, 52 grains and three-fifths less than the upper. On the other hand, he calculates the increase of gravity which, according to the Newtonian fyftem, the lower weight ought to have acquired, in confequence of its greater proximity to the furface: Eftimating the femidiameter of the earth to be 3,268,965 toises, he obferves, that the force with which the lower weights were attracted, is to that which acted on the upper ones, placed 20 toifes higher, and confequently diftant 3,268,985 toiles from the earth's centre, as the fquare of the last number is to that of the firft; and finds that, on this account, the lower weights ought to have acquired an increase of gravity equal only to 22/ grains.

As the lower weights therefore ought to have loft 52 grains and three-fifths, in confequence of the density of the air; and, on the contrary, to have acquired 22 grains, in confequence of attraction; there remains only a difference of 30 grains and one-tenth, which is too inconfiderable a quantity to be rendered fenfible in a balance loaded with 500 weight.

In the fecond experiment the refults were fimilar, as likewife in a third, in which iron wire was substituted for the rope. In a fourth, on using a counterpoife, confifting of dry wooders billets, instead of the metal weights, and which were first perfectly poised above; the billets evidently loft weight, on being let down to within a fmall distance from the pavement; fo that it was found neceffary to take away feven drachms from the upper bafon to reftore the equilibrium. This experiment is prefented as offering an equivocal proof of the influence of the fuperior denfity of the air, at the lower ftation, in diminishing the relative gravity of bodies weighed in it. In fact, it appears from calculation, that the voluminous wooden counterpoife abovementioned ought to have loft nearly this quantity of its weight; in confequence of the fuperior denfity of the medium in which it was fufpended, independent any other cause.

of

Experiments on the Weight of Bodies at different Diflances from the Centre of the Earth, made in the Mines of Montrelay in Britany. By the Chevalier de Dolomieu, &c.

These experiments, which likewife relate to the preceding queftion, were made in a different order. The fcales were fixed on the furface of the earth, and after procuring an exact

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equilibrium between the oppofite weights in that situation, those contained in one of the bafons were let down, to the depths of 114 and 1go yards, into a coal mine. Sometimes the undermoft weight preponderated, but more frequently the fuperior. The quantity however, in either cafe, was fo fmall, that the Author very properly concludes, from the refults both of his own and the many other experiments that have lately been made on this fubject, that they are infufficient to deter mine the queftion. In this opinion we readily concur with him; nor fhould we have taken fo much notice of the fubject, were not the question itself of great importance, and had it not likewife been fo very extenfively and warmly litigated, of late, among our neighbours on the Continent. The experiments which have been produced in fupport of the theory of gravitation have indeed the merit of evincing the feeblenefs of this late attack upon it; but nothing further is or can be determined from them: nor does the Newtonian fyftem ftand in need of fuch feeble supports.-Non tali auxilio, nec defenforibus iftis, &c.

CHEMISTRY.

Though the prefent volume contains feveral excellent papers on different branches of this fcience, we fhall confine ourfelvés to two or three articles relative to AIR, and its different fpecies:-a fubject which at prefent juftly engages the attention of the philofophical world; and which must doubtless be still further excited towards it, by the important difcoveries made in this part of philofophical chemistry :-an account of the most material of thefe is given in the prefent Number of our Review.

In the first of thefe articles we shall exhibit, merely as a matter of curiofity, a lucky hit made by an ancient French phyfician on this fubject, almoft in the very infancy of experimental philofophy.

A Letter to the Editor, on the additional Weight acquired by Metals in the Act of Calcination. By M. Bayer, Apothecary-Major in the Army, &c.

In this letter M. Bayen gives an account of a curious and very rare book written at the beginning of the laft century, by Jean Rey, a physician at Perigord, and containing an inquiry into the cause of the increase of weight which certain metals acquire in calcination. The cause of this phenomenon, which has not till very lately been fatisfactorily explained, appears to have been difcovered, or rather happily conjectured, by this ancient phyfician, who feems to have been a very inquifitive and fagacious philofopher. His work is divided into 28 chapters. From the following titles of fome of them the Reader will infer that Jean Rey was at least an ingenious speculator:

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Chap.

Chap. I. Every thing material under the whole compafs of the heavens [foubs le pourpris des cieux] has weight. II. There is nothing light in nature. III. There is no motion upwards that is natural. IV. Air and fire are heavy, and naturally move downwards. VI. Gravity is fo ftrictly annexed to the first matter of all the elements, that even on their tranfmutation into each other, they always preferve the fame weight. X. Air is rendered heavy by the compreffion of its particles. XIV. Fire can thicken or condenfe [efpeffer] the air.'

In the 16th chapter the Author having paved the way to the folution of the difficulty, relates the circumstance which gave occafion to his inquiry.

Mr. Brun, apothecary at Bergerac, had informed him that having put two pounds fix ounces of fine tin into an iron veffel, exposed to a violent heat during fix hours, he found that it was converted into a calx, which weighed feven ounces more than the tin originally employed.-Jean Rey answers, and boldly maintaineth that this increase of weight proceeds from the air, which has been thickened [efpeffi], rendered heavy, and in fome degree adhefive, by the vehement and long continued heat of the furnace; which air mixes with the calx, and attaches itself to its minutest particles, in the fame manner as water adheres, and adds weight, to thofe of fand.'-This air, he elsewhere affirms, is no otherwife changed than in being deprived of its fluidity [defpouillé de cette fubtilité quide] which rendered it incapable of adhering to any fubftance; and in the present case is made more grofs, heavy, and adhesive.'

Chemical Effays, or Experiments made on certain Mercurial Precipitates, with a View to difcover their Nature. By the fame. Part III.

Though we have not feen the Author's two preceding effays, we are induced, by the interefting nature of the fubject, and of the conclufions deducible from it, to extract the fubftance of fome of the proceffes given in this memoir, as they bear likewife a near relation to the recent difcoveries made with respect to the analyfis and conftitution of The Air, related in the prefent Number of our work.

We find that the Author had before fhewn, in the fecond part of these effays, published in the Number for April, 1774, that mercury, first diffolved in the nitrous acid, and then precipitated by fixed alcalis, was reducible per fe, or without the addition of charcoal, or any other fubftance containing phlegifton. The following are fome of the principal refults of one of the Author's proceffes, of a fimilar nature, made with mercury fublimate, or a combination of that fluid with the marine acid.

Having

Having procured a precipitate of this mercurial falt, by the. addition of fixed alcali, which he afterwards reduced to the state of a pure metallic calx, he put an ounce of it into a small glafs retort, to which he adapted a Chemico-pneumatic apparatus*, before defcribed. Having continued the fire as long as was ne ceflary, he found by the bulk of the water that had been depreffed in the receiver, that 41 ounces of claffic fluid + had been expelled from the mercurial calx. Within the retort he found 7 drachms II grains of mercury revivified. This experiment which, the Author obferves, was frequently repeated with dif ferent alcalis, and with the fame fuccefs, proves that the mercurial calx, thus precipitated from marine acid, is reducible into running mercury, without addition; as is alfo that precipitated from the nitrous acid. It is found likewife that both owed the increase of weight which, we should have obferved, they had acquired during the preceding part of the procefs, to the elastic fluid which difplaced the water in the receiver.

The Author next relates his experiments on the red precipitate, as it is called, of mercury; and fhews that it likewife is reducible, or capable of being restored to a metallic state, without the addition of phlogiften. But we fhall dwell more particularly on his last procefs, in which he relates his experiments on the Mercurius calcinatus per fe; or on mercury reduced to the ftate of a calx (merely by being a long time expofed to a great heat, in a glafs veffel with a narrow aperture, and) without the intervention of any other media than fire and the air.

He put an ounce of this fubftance into a small coated glass retort, to the neck of which was adapted an apparatus of the fame kind with that above hinted at. A violent red heat was applied, fo that the retort was flattened by it. At the end of the process, forty-five ounces of water were found to be difplaced in the recipient, by an equal quantity of elastic fluid expelled, by fire, from the mercurial calx. The reduction was complete; for the calx was changed almost wholly into running mercury, which weighed 7 drachms 18 grains: the 54 grains deficient answering nearly to what may be eftimated to be

By this term, we fuppofe that the Author means an Apparatus, contrived to catch the fixed air, or other elaftic vapours expelled from certain fubttances; particularly, by receiving and detaining them in an inverted vessel previously filled with water, in the manner practifed by Dr. Hales, and Dr. Priestley.

This phrafe has been pretty univerfally, and properly enough, adopted by the French philofophers, to exprefs, in general, that unknown elastic matter, whether air or vapour, that is expelled from various fubitances, in the proceffes of calcination, fermentation, eftervefcence, &c.; and to which we have given, perhaps ftill more properly, the appellation of air.

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