of confequence, refpecting aftronomical knowledge, to inquire into the rate of this variation in bodies of every form. The quantity of variation is denominated by our author the tract of polar evagation; to ascertain which, in given circumftances, is the object of the prefent paper. As it confifts of mathematical reafoning, it cannot be abridged: we must however obferve, that Mr. Landen oppofes, with great force, the arguments of Meffrs. Euler and d'Alembert, whofe conclufions are different from his own. The earth being neither uniformly denfe, nor exactly spheroidal, must have three permanent axes of rotation; and if to these circumftancs be added the effects of other attracting bodies, it must endeavour to revolve about fucceffive momentary axes. But if the earth's rotatory motion be difturbed by no other cause than the centrifugal force, arifing from the vis inertia of its own particles, its tract of polar evagation will nearly form a circle, the diameter of which is very fmall. But in other planets, the tracts of polar evagation may, from a fimilar caufe, be very different.

Art. XVII. Description of a new Marine Animal. By Mr. Everard Home, Surgeon. With anatomical Remarks upon the fame by John Hunter, Efq. F. R.S. This animal, which has never before been described by any writer on natural hiftory, was violently raised from the bottom of the fea by the violent hurricane at Barbadoes in 1780. Its habitation was a brain-ftone, a fpecies of madrepore, with which, however, it was covered by a fhell, immoveably fixed in the ftony cafe, befides two moveable fhells, which protected its fofter parts, not entirely defended by the brain-ftone. We cannot convey an intelligible idea of the animal without the affiftance of the plate; but shall lay before our readers a part of Mr. Hunter's ingenious poftfcript; though the imperfect ftate of the animal, when preferved in fpirits, must render the description less particular than it otherwife would have been:

The animal may be faid to confift of a fleshy covering, a ftomach and inteftinal canal, and the two cones with their tentacula and moveable shell, which laft may be confidered as appendages.

The body of the animal is flattened, and terminates in two edges, which are interfected by rugæ, the fafcicula of tranfverfe muscular fibres which run across the back being continued over them. Upon each of thefe edges is placed a row of fine hairs, which project to some distance from the skin.

The fleshy covering confifts principally of muscular fibres; thofe upon the back are placed tranfverfely, to contract the body laterally; thofe on the belly longitudinally, to fhorten the animal when ftretched out, and to draw it into the fhell.

• The ftomach and inteftine make one ftraight canal; the anterior end of this forms the mouth, which opens into the grooves made

by

by the spiral turns of the tentacula round the ftem of each of the cones; and the intestine at the pofterior end opens externally, forming the anus. From the contracted state of the animal, the intestine is thrown into a number of folds.

On examining the cones and the tentacula, I at first believed that the fpiral form arofe from their being in a contracted state; and that, when the tentacula were erected, the cone untwifted, forming a longer cone with the tentacula arifing from its fides, like the plume from the ftem of a feather; and that this ftem was drawn in or fhortened by means of a mufcle paffing along the centre, which threw the tentacula into a spiral line, fimilar to the penis's of many birds; but how far this is really the cafe, I have not been able to afcertain.

• The internal ftructure of this animal, like most of those which have tentacula, is very fimple; it differs, however, materially from many in having an anus, moit animals of this tribe, as the polypi, having only one opening, by which the food is received, and the excrementitious part of it alfo afterwards thrown out; this we must have fuppofed, from analogy, to take place in the animal which is here defcribed, more particularly fince it is enclosed in a hard fhell, at the bottom of which there appears to be no outlet; but as there is an anus this cannot be the cafe.

It is very fingular, that in the leach, polypi, &c. where no apparent inconvenience can arife from having an anus, there is not one, while in this animal, where it would feem to be attended with many, we find one; but there being no anus in the leach, polypi, &c. may depend upon fome circumitance in the animal economy which we are at prefent not fully acquainted with.

The univalves, whofe bodies are under fimilar circumftances refpecting the shell with this animal, have the inteftine reflected back, and the anus, by that means, brought near to the external opening of the fhell, the more readily to ditcharge the excrement; and although this ftructure, in thefe animals, appears to be folely intended to answer that purpose, yet when we find the fame ftructure in the black fnail, which has no fhell, this reafoning will not wholly apply, and we must refer it to fome other intention in the animal economy.

In this animal we must therefore rest satisfied that the disadvantageous fituation of the anus, with respect to the excrement's being difcharged from the fhell, anfwers fome purpose in the economy of the animal, which more than counterbalances the inconveniences produced by it.

It would appear, from confidering all the circumftances, that the excrement thrown out at the anus muft pafs from the tail along the infide of the tube, between it and the body of the animal, till it comes to the external opening of the fhell, as there is no other evident mode of discharging it."

Art. XVIII. A Description of a new Syftem of Wires in the Focus of a Telescope, for obferving the comparative Right Afcenfions and Declinations of celeftial Objects; together with a Method of inveftigating the fame when obferved by the 6 rhombus,

rhombus, though it happen not to be truly in the equatorial Pofition. By the Rev. Francis Wollaiton, LL. B. F. R. S.Mr. Wollafton had formerly given a plan towards ascertaining the relative fituations of the fixed ftars, by wires croffing each other, and forming a rhombus; but he candidly informs us that, from various caufes, it has not hitherto fucceeded to his expectation. In the prefent paper, he proposes a fquare inscribed in a circle, the radii of which crofs its fides at right angles. This contrivance is more accurately executed by common workmen, and promifes to be of advantage in the inquiry. The author's chief object being to afcertain the right afcenfions and declinations of the stars, by obferving their meridian paffages and meridian altitudes, as well as by their comparative paffage through the field of an equatorial telescope, armed with a fyftem of wires, in a rhomboidal, he has now added another formula for computing the comparative right afcenfions and declinations, when the inftrument is not truly in the plane of the equator.

Art. XIX. An Account of a Stag's Head and Horns, found in Alport, in the Parifh of Youlgreave, in the County of Derby. By the Rev. Robert Barker, D.D. This head and horns were found, with fome other fragments of the horns and bones of animals, in a quarry of the kind of ftone called tuft, which is formed by the depofit left by water paffing through beds of sticks, roots, vegetables, &c. The horns are larger than a pair of great fize, and which is fuppofed to be two or three hundred years old; though, from the appearance of the futures in the fcull, the animal appears to have been a young one. They resemble what is called the throftle-neft horns, in the number of fhort antlers at the upper part; but exceed them in dimenfions.

Art. XX. An Account of the Senfitive Quality of the Tree Overrhoa Carambola. By Robert Bruce, M. D. It appears that in this plant the joint of the petiolus is the irritable part; for unless the impreffion be fo great as to bend the foot-ftalk, no motion enfues. Among the phenomena mentioned by the author we find that the concentrated rays of the fun on the petiolus will produce motion; but a hole may be burnt in the leaf, without any fuch effect. Preflure on the univerfal petiolus will irritate all the leaves; and, what is a fact no less remarkable than useful in explaining the nature of the motion, when the petiolus is preffed by the pincers between any two pair of leaves, those nearest the extremity move fooner than those nearest the body of the plant.

Art. XXI. An Account of fome Experiments on the Lofs of Weight in Bodies on being melted or heated. By George Fordyce, M.D. F.R.S. Dr. Fordyce found that water, in a yeffel hermetically fealed, gained weight by freezing. The

experiment

experiment ascertaining this fact, feems to have been conducted with a degree of accuracy which will not admit of the fuppofition that the refult was fallacious. Of the principle on which it depends, however, it does not pofitively determine, though he is evidently not without an opinion on the fubject.

Art. XXII. Sketches and Defcriptions of three fimple Inftruments for drawing Architecture and Machinery in Perfpective. By Mr. James Peacock. No verbal defcription alone of thefe inftruments could prove fatisfactory to a reader; but they seem to be well adapted to practice.

Art. XXIII. Experiments on Air. By Henry Cavendish, Efq. F. R. S. and A. S. In a former paper this ingenious philofopher gave it as his opinion that the diminution produced in atmospheric air by phlogistication, was not owing to the generation of fixed air. He thought it seemed most likely that the phlogistication of air by the electric fpark was owing to the burning of fome inflammable matter in the apparatus; and that the fixed air, fuppofed to be produced in that process, was only feparated from that inflammable matter by the burning. Having, at that time, made no experiments on the fubject himfelf, he was obliged to form his opinion upon those already publifhed; but he now finds, that though he was right in fuppofing the phlogiftication of the air does not proceed from phlogifton communicated to it by the electric fpark, and that no part of the air is converted into fixed air; yet that the real caufe of the diminution is very different from what he suspected, and depends upon the converfion of phlogifticated air into nitrous acid. This is an important fact; and if clearly ascertained to proceed from the caufe aligned by Mr, Cavendish, may be applied to valuable purposes in philofophy.

Art. XXIV. An Account of Measurement of a Base on Hounslow Heath. By Major-General William Roy, F. R.S. and A. S. The measurement recited in this paper is founded upon a defign of great national importance, the execution of which would be no lefs conducive to public utility than to the interefts of science. The work relates to a general furvey of the whole kingdom, and appears to have been in agitation for many years; but what immediately led to the operation detailed in the prefent paper, was a Memoir of M. Caffini de Thury, tranfmitted through the French ambassador to one of his majefty's principal fecretaries of ftate. In that memoir M. de Caffini fet forth the great advantages which would accrue to aftronomy by carrying a feries of triangles from the neighbourhood of London to Dover, there to be connected with thofe already executed in France; by which combined operations the relative fituations of the two most famous obfervatories in Europe, Greenwich

Greenwich and Paris, would be more accurately afcertained. His majefty, with his ufual munificence, patronifed the scheme; and the execution of it was committed to Major-General Roy, an officer of diftinguished abilities in works of a mathematical nature, and who feems to have performed it with great judgment and accuracy. Our limits will not admit of giving even a general detail of the methods purfued; but they are recited with great perfpicuity, and will afford much fatisfaction to those readers who have a particular tafte for the fubject.

Art. XXV. Abftract of a Regifter of the Barometer, Thermometer, and Rain, at Lyndon in Rutland, in 1784. By Thomas Barker, Efq. alfo of the Rain at South Lambeth, Surrey; and at Selbourn and Fyfield, Hampshire. Communicated by Thomas White, Efq. F. R.S. The beginning of the year 1784 was remarkable for the severity of the weather. In February the lowest point of the out-door thermometer was 9o. In the prefent register, the obfervations were made only once a day; but, to afford proper information, they always ought to be made twice.

The volume concludes, as usual, with a lift of presents, which, if equally valuable with fome of the papers contained in this part of the volume, would be an important acquifition to the Society.

ART. IX. Ejays, Philofophical, Hiftorical, and Literary. 8vo, 5s. boards. Dilly, London, 1789.

F all the performances that come before us, few appear with fo unpromifing an aspect as effays. The modefty of the title is by fome made the apology for venturing to fend nonfenfe into the world, others having a few loofe notions fluctuating in their brain, are at much pains to find leifure to give them to the world; and a large class of effayifts think it their duty, if they can write to indulge the public with their lucubrations. Thus we have fometimes the commoneft truths, which no one was ever at the trouble of difputing, dreft in agreeable and flowing language, at others the wild fancies of a vifionary, who takes it into his head that he has conceived a new idea; and frequently we have to encounter an uninteresting ill-connected set of obfervations, in the attempting to perufe which, neither hunger nor the impatience of our publisher will fecure us from fleeping.

The author of the work before us is reduceable to neither of thefe claffes. In perufing his effays, we perceive evident traits of a scholar, a philofopher, and a well-read gentleman; of one who has been in the habit of making obfervations, and has been cautious not to commit them to paper, till he had tried them by