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The Theory of Jupiter and Saturn. By M. DE LA PLACE.'''

By observations, it appears that the motions of Jupiter and Saturn have undergone confiderable variations, which could not be reconciled with the laws of gravity as delivered by NEWTON, The comparison of modern, with the ancient, observations, indicates an acceleration in the motion of Jupiter and a retardation in that of Saturn; while the observations of the moderns, com • pared with each other, offer a contrary result; for M. LAMBERT has remarked that, since the time of Hevelius to the present, Jupiter's motion has been retarded, while that of Saturn has been very sensibly accelerated ; and M. DE LA LANDE, from observations on Saturn's oppofitions, hath also concluded the mean motion of this planet to have increased within a century.. Hítherto, the causes of these variations have not been explained on the principles of universal attraction : M. DE DA Place, therefore, undertakes this laborious talk; and he shews tbat, so far from being an exception to the general laws of gravity, this apparent irregularity is a necessary consequence of these laws; and that it confirms the truth of the admirable principles of the Newtonian theory.

The memoir is divided into three sections; in the firft, M. DE LA PLACE gives an analytical theory of the periodical and secular inequalities of the motions of Jupiter and Saturn, arising from their mutual action on each other. He has been particularly anxious to give to his results the most fimple forms; by: which means he has rendered them extremely convenient, and easily applicable to the usual modes of calculation. What principally distinguishes this from the preceding theories, is the confideration of those inequalities which depend on the squares and higher powers of the excentricities and inclinations of their orbits; former astronomers, regarding only the first powers of these quantities in their investigations, have consequently left their results, wbich are at best only approximations, much more imperfect than those of M. DE LA PLACE, who has included the 2d, 3d, and 4th powers.

Having in the first section determined the several inequalities, M. DE LA Place proceeds in the second to establish the theory of Saturn's orbit and motion. In order to apply the theorems. which he had deduced in the former section, to either of the planets, it is absolutely necessary to know the value of the conAtant quantities which make part of the algebraical expreffions already delivered; these are the mean distance from the sun, the mean longitude at a given epoch, the excentricity, the pofition of the aphelion and nodes, and the inclination of the orbit. The author remarks, that observations give only the true motions of the planets, and that, to determine the preceding elements, it is necessary to have a previous knowlege of the perturbations

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to which the planets are liable: the determination, therefore, of the inequalities, and of the elements of the planets, depend mutually on each other, and the only method of obtaining a knowlege of each is by a succession of continual approximations, M. DE LA PLACE, therefore, uses the elements that former aftronomers have eftablished, to approximate nearly the changes wbich the planetary motions undergo; and the elements, re&tified by the considerations of these changes, being again substituted in the algebraical expressions, give the inequalities with great precision. The epoch wbich M. DE LA PLACE has affumed, is the middle of the present century, viz. the beginning of the year 1750: and the corrected elements of Saturn at that time, are, Mean longitude of the planet,

70 21° 20' 44" Mean longitude of the aphelion,

9 Mean longitude of the ascending node, 3 21 31 17 Inclination of the orbit,

2 30 20 Excentricity,

0.056336 Mean diftance from the fun,

9.540073 Mean fidereal motion in 365 days, 12° 12' 46".6

Having thus established the elements, M. DE LA PLACE proceeds with rules for calculating Saturn's place at any given time. Rather than form new tables, he has adapted a correction for those of Halley, and shews how it is to be applied ; and in order to evince its truth, he has added a long list of observed places of Saturn, and compared them with the calculated places ; the difference does not, in any case, amount to 2 seconds in longitude.

The agreement of ancient observations with M. DE LA Place's theory, serves as a proof that the comets have no senfible influence on our planetary fyftem. The irregularities of Saturn's motion have been shewn to proceed from the action of Jupiter alone, and consequently that of the comets must necefsarily be extremely little. May we not hence conclude that the comets are bodies whose specific gravities are much less than those of our planets, and confequently that the motions of the comets will be much more affected by our planetary system, than the motions of the planets are by the comets?

The great length of thefe investigations has obliged M. DE LA Place to reserve the third fection of this memoir, which will contain the theory of Jupiter, for the subsequent volume of the Hiftory of the Academy. Experiments on the Smoking Oil of Vitriol from Saxony, and the

volatile Concrete Salt obtained from it by Distillation. By M. DE FOURCROY. This smoking oil of vitriol has been particularly mentioned by former chemists, especially by Meyer and BERNHARD ;

many

biany of its properties, however, are not fufficiently described, nor the phenomena attending it properly explained.

This acid, which, from its confiftence, might be deemed. extremely concrete, is only 5 gros * heavier than an ounce of water of the same bulk; in contact with the air it continually emits a thick white vapour of a sulphureous linell, but in other respects, perfe&ly resembles common oil of vitriol. Being put into a retort, to which a receiver was fixed, with the flightest degree of heat, a large quantity of thick white vapour passed over, and a confiderable quantity escaped from the juncture of the vessels, smelling like the vapours of burnt fulphur: in a little time, and while the vapours were also paffing, a few drops of liquor came from the mouth of the retort, which arriving at the bottom of the receiver, formed themselves into a brown gelatinous mass; the vapours which were condensed on the superior and lateral parts of the receiver, formed white crystals, re. sembling in shape and texture the fal sedativus. The liquor which continued to come over, collected itself at the bottom of the receiver, and dissolved the gelatinous matter before mentioned. The vapour diyided itself into two portions, the lighter, following the curve of the superior part of the receiver, was there condensed into a crystalline mass; and the heavier, falling on the liquor, was disfulved in it. These appearances continued about two hours, when, scarcely any vapours coming over, the receiver was changed, and the distillation continued with an increased fire. After seven hours, the liquor in the retort became perfectly white, a dark coloured liquor having passed into the receiver. Ten hours were consumed before the distillation came ad ficcitatem ; in the receiver were then found 7{ ounces of ambercoloured oil of vitriol, whose specific gravity was twice that of water; and the residuum was about 6 grains of a white faline porous substance which had all the properties of calcined alum. The first receiver, as soon as it was opened, was immediately, filled with a thick white smoke, and it was with difficulty that the faline concretions formed in it, could be extracted. One ounce and 3 gros only could be collected; the quantity lost was estimated ar 5 gros.

In a second diftillation, with an apparatus proper for obtaining the elastic Auid, there was the same saline concretion in the receiver, and the quantity of permanently elastic fluid produced from 2 pounds of the smoking oil, measured 6 French pines to The academician is rather deficient in his description of this fluid : he only says, it appears to contain a little vital air, be

* A gros is į a grain lighter than our apothecaries drachm, or 597 grains Troy.

7 A French pint is 58.3 Englith cubic inches, that is, a's, or nearly 1, of an inch greater than our wine quart.

cause II

cause a candle burat in it rather better than in the atmospheric air.'

The concrete falt is the next object of M. de FOUR CROY'S attention. From numerous experiments, he concludes that it owes its concrete ftate to fulphureous gas, fixed and diffolved in a concentrated vitriolic acid,

Water being mixed with the smoking oil of vitriol, and more especially with the concrete salt, disengages a confiderable quantity of sulphureous gas, with effervescence ; after which difengagement, tbe oil loles its property of smoking, or of yielding the concrete falt: hence he concludes the gas to be the cause of the particular phenomena which this acid presents. Two Memoirs on the Tendons, and their Mucous Capsula. By

the same. In our Review for December last, p. 497, we gave a Chort history of these capsule, under the name of Bursa Mucose, and we thould not now have resumed the subject, had it not been for the sake of informing our anatomical readers, in addition to what we before said, that a diftinct treatise on this subject was published at Leipfic in 1753, by Professor JANCKE. M. de FOURCROY gives an analyfis of this work, and thews the imperfections under which it labours. The chief motive, which seems to have induced him to apply himself to the confideration of the mucous capsule, was the light notice that has bitherto been taken of them by the generality of anatomifts.

In the first memoir, M. DE FOURCROY explains the general structure of the capsula, describes their internal structure; and, by considering their origin, thews the essential differences between them and other membraneous productions, efpecially the cellular membrane and muscular fheaths; and toward the end of the memoir he points out their uses.

The second memoir contains a specific description of all the mucous catfulæ, which M. de FOURcROY has discovered, in bis diflections, about the shoulder and the elbow. The description of the remaining capsule will be given in a subsequent me. moir. On the Structure of different metallic Crystals. By the Abbé

HAÜY. In this curious memoir, the Abbé considers the geometrical properties of the crystals which he describes. There are more seasons for investigations of this kind than may generally be imagined: the most obvious one is, that crystals are seldom found detached, or whole; and if, from the fize of the angle, the inclination of the sides, or some other circumstance (which may be determined by viewing only a part of the cryfta), we can form a juft idea of the whole, this part of natural hiftory will be confiderably benefited.

The particular cryftals which the Abbé here considers are, the cubical ferruginous pyrites ; ferruginous pyrites with 12 pentagonal fides; the same with 20 triangular fides ; cubic iron ore; iron ore with rhomboidal fides ; iron ore with 24 fides, of which 6 are pentagons and 18 are triangles.

Independently of the utility which may be derived, from this memoir, to the science of mineralogy, the speculative geometrician will find much amusement in the investigations of the properties of these folids.

We are, at all times, happy in having it in our power to perform the literary promises which we make to the Pablic; and are as much disappointed, as (we would modestly trust) they are, when we are not able completely to fulfil them. With respect to FOREIGN LITERATURE, various unavoidable inci. dents occur to make the latter case but too frequent. With mucb satisfaction, therefore, we have thus completed our account of the last volume of the Parisian Memoirs; thereby presenting to our readers many curious and useful particulars, with which, we hope, they will all be entertained, and some, perhaps, instructed.

A

ART. II. Lettres Américaines, &c. i. e. Letters concerning America, by Count

J. R. CARLI, Privy Counsellor to his Imperial Majesty; with Observations and Additions by the Translator. 8vo. 2 Volumes. Boston printed ; and sold in Paris. 1788.

Veil of mystery is thrown over this publication, which,

like a fine lady's gauze handkerchief, scems calculated to tempt, rather than repress, curiosity. It is said to be printed at Boston; though the type and the paper are evidently French. It appears to have been translated from the Italian; but this we are left to guels; and the translator, who has not only added a preface and notes, but also confiderably enlarged the text, conceals his name, though he frequently refers the reader to his Notes on Don Ulloa's Memoirs, and to a Latin edition of Silius Italicus, which he says he has published.

We do not see any thing in the work, that can render this appearance of caution at all necessary; except, that the Count diffents from the opinion of the church of Rome with respect to chronology, and assigns to the deluge a much earlier period than. is generally allowed: there are indeed a few misrepresentations of paffages of Scripture history, while the author professes the greatest regard for the sacred writings; we are therefore inclined to consider them as rather the effea of ignorance, than of any design to depreciate revelation. But most of these errors ale corrected by the annotations of the French translator, who seems to be better

acquainted

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