thefe ofcillations, which depends on the motion of the nodes of the lunar orbit, may be very confiderable. These large ofcillations, however, are caufed by the refiftances which the fea meets with in its motion; in confequence of thefe refiftances, it happens that thefe ofcillations are nearly the fame as if the flood were brought at every inftant in equilibrio, under the luminary which attracts it. The general expreffion is given for the tides, in the cafe of nature, in which the fun and moon move in orbits inclined to the equator, occafioning ofcillations of the fecond kind. The heights of the tide near the fyzygies are mentioned. The abfolute mean height of a tide for a day is half of the fum of the heights of the morning and evening tides; and the whole, or total tide, is the excess of that half fum above the medium bafe of the fea. After thefe definitions, are given expreffions for the fame times, for any day near the fyzygies; alfo near the equinoxes and the folftices; with a determination of the interval of the highest tide after the fyzvgies; which interval at Breft is nearly one day and a half. The variation of the distances of the fun from the earth has a fmall influence on the tides, as appears both by theory and obfervations. The increafe of the total tide near the quadratures, after the minimum, is equal to the fquare of the time, multiplied by the coefficient 0.2272 of a metre, agreeably both to theory and obfervations. In the quadratures of the equinoxes, this coefficient is 0.3123, and in the quadratures of the follices 0.1421 the evening tides, at Brett, exceed the morning tides, near the quadratures of the vernal equinox; but the contrary circumftance takes place near the quadro ures of the autumnal equinox: the retardations of the tides at the quadratures vary with the distance of the moon from the carth; but three times lefs than in the fyzygies, both hy theory and obfervations. A formula is added for determining the greateft total tides, which ought to happen in our ports.

In the fifth book, the author treats of the motions of the celeftial bodies round their own centres of gravity, in three chapters, viz. the motions of the earth round its centre of gravity; the motions of the a son round her centre of graVity; and thofe of Saturn's rings round their centres of gra vity. The chief particulars of thefe chapters are, a research into the momentum of the earth's inertia, relatively to its three principal axes; an attempt to prove that the fphere is not the only fold in which all the momenta of inertia may be equal; cxprcfions for the perturbating forces of the earth's motion round its centre of gravity; expreffions for the motion of the equinoxe, and the nutation of the terrestrial axis; arguments tending to prove that the action of the fun and moon, on the terreftrial spheroid, confiderably change the variations

I

I

304

in the obliquity of the ecliptic, and the length of the year; that the variations of the motion of the earth's rotation are infenfible; that the variations of the mean length of a day are likewife infenfible; that the earth's motions are not at all affected by the ofcillations of the fea, or by the irregularities in its depth, or by the refiftances which it ineets with, or by the currents, waves, winds, or earthquakes. We alfo find numeral expreflions for the inclination of the earth's axis, and the polition of the equinoxes; formulæ for the variation. of the ftars in declination and right afcenfion, &c. From phænomena compared with theory, it appears, that the earth is not a homogeneous or uniform mafs; and that the flattening of the earth, as deduced from obfervations on pendulums, is expreffed by agreeing nearly with drawn from " 321 obfervations on the nutation and preceffion, and alfo on the tides. In the aftronomical theory of the moon's libration, it is shown, that the mean motion of her rotation is exactly equal to that of her revolution about the earth; and that it partakes of the fame fecular inequalities, by virtue of the ter reftrial attraction on the lunar fpheroid; that the mean motion of the nodes of the inclination of the lunar equator to the true ecliptic is equal to that of the nodes of the lunar orbit; that the defcending node of the lunar equator always coincides with the afcending node of the orbit; and that the mean inclination of the lunar equator to the true ecliptic is conftant. Thefe refults remain unaltered by the fecular motions of the ecliptic; and the action of the fun, on the lunar fphervid, does not fenfibly influence the motions of this fpheroid about its centre of gravity. Without the rotation, and the flattening of the figure of Saturn, his rings, by virtue of the attraction of the fun and of the laft fatellite, would not continue in the fame plane; but the action of Saturn always preferves them nearly in the plane of the equator, as well as the orbits of the first fix fatellies. As the fatellites of Uranus, or the new planet, revolve in the fame plane, it follows that this is the plane of the equator of that planct, and that it turns rapidly about its axis.

Annales de Chymic. Vols. XXIII. et XXIV.

Annals of Chemifiry. (Continued from Vol. XXVI. New Arr. p. 512.)

As we approach nearer the prefent day, thefe volumes are more interefting, fince they are more new; and we may add,

that the two which are now before us contain many important articles.

In the first paper, a curious and useful instrument is defcribed, under the appellation of a stereometer, calculated to afcertain the specific gravity of folids which cannot be plunged: into water. The ufual method of afcertaining specific gravities is, to weigh the bodies in water and in air; and, from the difference of weight in these media, to determine their peculiar denfity. To avoid the inconvenience which muft refult from plunging fome bodies in water, M. Sage propofes to weigh them in air of different denfities, and has defcribed. an useful inftrument for this purpose. He condenfes the common air; but a rarefaction of it would, we think, be more useful. His inftrument he does not confider as perfect: indeed, it is far from being perfect. The means of correcting the obfervations, however, are added; and the formulæ appear to be very accurate.

The abbe Fortis, in 1783, gave an account of a mine of faltpetre at Pulo. The quantity of falt which it afforded was, confiderable; and it feemed to increase daily. M. Klaproth, of Berlin, examined this falt, and found it very pure, containing nearly one half of true nitre. The queftion, which hence arifes, is curious;-How is fo large a proportion of pot-afh produced, independently of vegetation? This falt, though it is commonly procured from the vegetable kingdom, must be occafionally produced independently of vegetable life; and from its occurrence in fome of the granites, it may be fometimes of mineral origin. We fee no reason to hesitate, in fuppofing that the natron may be changed to pot-ash, as it feems to be, on other occafions, changed to magnefia. As this falt, however, contains a large proportion of calcareous earth, it may be a queftion, whether the pot-afh is not de-`' rived from lime: in fupport of this opinion, we may add, that M. Pelletier found the proportion of nitre and calcareous earth, from this mineral, nearly the fame. The abbé Fortis⚫ defcribes the mine and its different firata. His defcription fhows its intimate connexion with the fea; and it is remarkable that this mineral, lixiviated with a muriatic water, produced fcarcely any thing but common falt. The court of Naples has been hitherto blind to this treafure; and we cannot fay when its eyes will be opened.

We obferve a full abstract of two curious memoirs on the acid of cork, read to the National Inftitute by Bouillon de la Grange Itis procured, as ufual, by the nitric acid, and is in a folid form, not cryftallifable; when it is obtained by precipitation, the appearance is that of a powder; by evaporation, that of thin irregular pellicles. Its tafte is flightly bitter, and

acid; when diffolved in water, pungent, exciting cough." It attracts moisture from the air, especially if not quite. pure, and grows brown, when expofed to folar light. The elective attractions of this acid to the following fubftances are in the fubjoined order; barytes, pot-ath, foda, lime, ammonia, magnefia, and alum. It differs from the gallic acid, in its yellow precipitation; from the malic, in its folid form; from the acid of tartar, in not burning or fioking on hot coals. The oxalic acid has a stronger elective attraction for lime; and the acid of cork gives a green hue to a folution of the nitrate of copper, without occafioning any precipitate. This acid, therefore, differs, as well as its refin, from other known vegetable acids; but probably differs from them only in its proportion of oxygene, and the change of its hydro-carbonated radical.

M. Klaproth inforins us, that the emerald of Peru contains more than two-thirds of filiceous earth, and nearly one-third of alumine. In this he differs from Bergman, who found the largest proportion to be alumine, with fome lime; but there is reafon to think that the ftone examined by him, though fimilar in colour, was not the true Peruvian emerald.

The almanac of chemifts and apothecaries, published annually by M. Goetling, fupplies the next article. Its fubjects are mifcellaneous, and are treated concifely. We will felect fome paffages from it.

Profeffor Wurzer's durable coating for glafs veffels is compofed of coarfely powdered porcelain, the fine powder being previously separated. To this is added fome pure clay, moistened with a faturated folution of common falt; and the whole is worked up into a pafle, of a proper confiftence, to be applied in the ufual manner.'

The powder of lapis hæmatites is blackened in its colour. and brought nearer to a state of metal, by the action of light,'

M. Humbolt employs the oxygenated gas in a lamp; and a defcription of the inftrument is added.

It ferves to light the fhafts of mines, and other places, where the ufual lights will not burn, for want of pure air.'

An abstract is given of M. Pronft's memoir on Pruffian blue. Its object is to fhow, that iron, like other metals, is fufceptible of two conftant proportions of oxygene, refem bling, in this refpect, tin, mercury, lead, &c. In the concluGion of the article, the author promifes to give an account of the oxyd which refults from carbone, joined with a fmaller

proportion of oxygene than is néceffary to form carbonic aeid..

An abitract of M. Defcotil's memoir on ceylanite, follows. This ftone is carefully defcribed and analyfed. It contains 0.68 of alumine, with about 0.12 of magnesia, 0.2 of flint, and 0.7 of oxyd of iron, The experiments show, that a compofition of this kind, though principally confifting of a foft earth, can attain, by its intimate combination, perhaps cryftallifation, confiderable hardness; and that, in this ftate of combination, thefe earths do not contribute to promote the fufion of each other, or of the whole.

Bartholdi's experiments on a calculus, found in the rectum of a horfe, are curious. It contained 0.18 of magnesia; and he fuppofes that this earth may have been furnished by the bran, which was probably its food, as it was a miller's horfe. But the magncfia, which the bran contains, may come alfo, he thinks, from the millitones. The French burs, however, we know to be granites partly decompofed; and the magnetia contained in them is only found in the mica, which is in fmall proportion, and is with difficulty decompounded.

M. Bouillon de la Grange confirms the difcovery of Kofe, garten, that camphor contains a real acid; which, as ufual, may be extricated by the nitric acid. The characters of this acid are too long for infertion. It differs from other vegetable acids, by its cryftallifation; by its imperfect folubility when cold; in burning without leaving any refiduum; in not precipitating lime-water; and in forming particular neutrals, which exhibit, by the blowpipe, a blue flame. Camphor itfelf is a volatile oil, rendered concrete by carbone; and, by the addition of alumine, or even common clay, two products may be obtained-carbone and a volatile oil, not acid. Mixed with water, alkalies, and the oxygenated muriatic acid, this oil becomes of a milky whitenefs; and the concrete falt is regenerated.

The papers which follow are very important. Fourcroy and Vauquelin have been long engaged in the analysis of vegetable fubitances. Two memoirs on this fubject are here inferted; one explaining the action of fulphuric acid on dry vegetable fubftances, the other exhibiting the process of makjug æther.

A black powder is precipitated, by putting a piece of ftraw, for inftance, in the fulphuric acid; the acid is weakened, without any decompofition, and no feparation of gas takes place. M. Foureroy endeavours to fhow, that the acid de compofes the ftraw, by attracting fome of the water in its campofition; and thus deftroys the mutual attraction of its component parts. A portion of the carbone is precipitated,