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jects, and the excellence of his ftile, have diftinguifhed him as one of the firft rank of this kind of writers: and, perhaps, the greatest merit of our author himself, as far as it relates to the prefent work, confifts rather in his turn of expreffion, and verfification, than in any inftance of his penetration or invention.

Hiftoire de l'Academie Royale des Sciences et Belles Lettres. 4to. Berlin.

The Hiftory of the Royal Academy of Sciences and Belles-Lettres.

In our Review for April laft, page 371, we made first mention of this volume, and particularized the feveral articles of Experimental Philofophy that it contained. We fhall now do the fame by thofe ranked in the clafs of Mathematics, confifting only of four. The firft is an enquiry into the nature, and caufe of the Variation of the Needle; by Mr. Euler,

The ftrange irregularity which has been obferved in this Variation, hath occafioned frequent attempts to difcover fome theory whereby it might be always known and accounted for. Hitherto, however, thefe attempts have been attended with little fuccefs; the difficulty of reducing fuch a variety of obfervations, apparently incompatible and inconfiftent, having been as yet infurmountable. The celebrated author of this article fets out with controverting the well-known theory of Dr. Halley; which he cenfures as inconclufive and unphilofophical. But we do not know that the Doctor himself, or any body elfe, ever laid any great ftrefs on his hypothefis. It was undoubtedly ingenious; and, tho' it might not appear very fatisfactory, yet we do not fee what great advantages. can be gained, or advances made, by formally combating profeffed conjecture,

The Doctor, indeed, to account for these very furprizing and inconfiftent phoenomena, fuppofed the exiftence of four magnetical Poles: viz. two moveable, and two fixed. His reafon for which fuppofition was, that if the earth was conceived to have but two magnetical Poles, the Needle should be found in any Meridian to vary conftantly, in every place under that fame line, the fame way; either toward Eaft or Weft: whereas, under the Meridian, paffing over Hudfon's Bay, and the coafts of Brazil, it had been obferved, that the Declination was weftward in the former place, and eastward in the latter, and that to a very confiderable degree of both.

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Mr. Euler does not judge this obfervation a fufficient reafon for thinking the Variation of the Needle inexplicable, on the fuppofition of there being two magnetic Poles only. He obferves, that if we fuppofe the two Poles to be placed diametrically oppofite to each other, it could not, indeed, happen that in any two places, under one and the fame Meridian, the declination fhould be found, in the one to be East, and in the other Weft. But, fays he, if thefe Poles are not diametrically oppofite, but pofited obliquely, with refpect to the earth's diameter, fuch a Variation may happen. This he proves geometrically; and thence takes occafion, as abovementioned, to cenfure Halley's hypothefis of four Poles, as exceptionable; and afferts it to be abfurd, to have recourse to fuch a fuppofition before it be proved, that the Variation cannot be accounted for on the principle of there being but two. After having thus endeavoured to obviate the objections that might be made to his theory, as a needlefs innovation, he lays down his general problem; viz. How are we to account for, and determine, the Declination of the Needle, at any time, and on every part of the globe, on the suppofition of there being two magnetical Poles only. We cannot enter minutely into his argument, without trefpaffing too much on our plan; and to make an abstract, fhort enough for our purpose, would be difficult, without doing the author injuftice.

The fecond article, written by the fame hand, relates to the ftrength of Columns. It confifts chiefly of Calculations, tending to explain a rule for determining the ftrength of any pillar, or the greatest weight it can bear without giving way; fuppofing the preffure to be vertical, and fuch column to be equally ftrong throughout its whole length.

Article the third is entitied, General Rules for the ConAtruction of Telescopes and Microfcopes, of whatever number of Glaffes. By the Same. This paper contains a very plain and intelligible account of the principles on which the difpofition and form of the glaffes, in all inftruments of this kind are founded; and the manner in which the whole inftrument must be conftructed, fo as to be poffeffed of the feveral properties effential to its perfection. These Mr. Euler particularizes thus. First, the object should be magnified to the given degree. It fhould be rendered fufficiently luminous, diftinct, and clear. The field fhould be made as large as poffible: and, laftly, the eye fhould be never incommoded with those prifmatic colours, that arife from the different refrangibility of the rays of light,

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The fourth, and laft article, is written alfo by Mr. Euler, and relates to the conftruction of Perfpectives with three glaffes, reprefenting the object inverted. In this Memoir, our Geometrician applies the principles laid down in the preceding article, and demonftrates, that with due care, these kind of telescopes might be brought to a much greater degree of perfection, than it appears our best artists have, as yet, attained to.

Bigarrures Philofophiques.

Or, Philofophical Rhapsodies. 2 vols. 12mo. Amfterdam; for Merkus, 1759.

The fightly author of Amilec✶ hath here published as whimfical a medley, of truth and error, argument and fable, fense and nonfenfe, as perhaps ever afforded entertainment to the public. My principal intention, fays he, is hereby to expofe the feveral philofophical fyftems in vogue, and point out the degree of confidence worthy to be placed in each.

We conceive, however, if this were his chief defign, he has failed in effecting it: unless he intended that degree of confidence fhould be very little, indeed. For, tho' he fometimes, ingenioufly enough, rallies the Hypothefifts, he feldom mends the matter, by giving proofs of greater fagacity in himself.

It is not difficult, even for men of the loweft capacity, to perplex the faireft reafoner, by doubts and objections; and much lefs fo for a man of wit and words, to represent the foundeft argument in a light ludicrous enough to make it feem ridiculous. But it fhould be remembered, that it is much eafier to laugh at the best system, than to form one of the worft.

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As a work of entertainment, nevertheless, our author's Rhapsodies have their merit: and had he pretended to nothin more than amusement, or, in his own words,— égayer de temps en temps ces hommes phlegmatiques, qui voudroient toujours penfer; et faire penfer de temps en temps ces efprits frivoles, qui voudroient toujours s' egayer.' Publifhed with this view only, his book might, perhaps, have entirely answered his intentions, while his readers, refpecting him as another Saiouph, un philofophe enjoué au posible, had honoured him with the diftinguishing appellation of the joyous Philofopher.

Anile, ou la graine des Hommes; attributed to Mr. de la Roche, of Cuen.

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But to give our readers a more particular idea of the work. It is divided into two parts; the first containing the Visions of Ibraim, an Arabian Philofopher, and an Effay on the Nature of the Soul. The second confifts of A Voyage to Limbo; and a continuation of the foregoing eflay.

Ibraim, our philosophical Arab had studied under Saiouph a facetious profeffor, who played the drole in his academy, and folved problems with the fame face and gefture, as if he had been making puns, or cracking jefts: for, indeed, he was fully convinced that none of the sciences were of confequence enough to be treated feriously. The following is one of his extempore lectures, delivered publicly in the schools, in defence of the influence of the moon.

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It was formerly the custom, my dear pupils, to take things on truft, and to believe without feeing; whence the world were apt sometimes to fall into errors. It is now, on the contrary, the fashion to believe nothing but what we do fee; and by that means, there are a thousand interesting truths we give no credit to at all. It is generally believed, for inftance, that the moon has the power to raise the waters of the fea; because we see the effect of it, in the tides: and yet no body thinks the fame planet hath the like effect on the fmall quantity of fluid which circulates in the or'ganized bodies of plants or animals: and that for no other • reafon but because they cannot fee it. Thus the influence of the moon, fo univerfally acknowleged of yore, is now entirely difcredited. But, wherefore? Hath that planet the power to disturb the immenfe body of water in the ocean, and not that of affecting the small stream of vegetable fap, or the invifible current of the animal spirits? < For my part, I do not fee why that planet fhould not have a fimilar influence over all bodies. I think I have obferved • the difpofition of all terreftrial objects to vary, according to the fituation of the planets. For example, toward the Vernal Equinox, you fee all the fprings of Nature come into play. The multiplication of the animal fpecies goes on, to a miracle. Vegetation performs wonders too: and every object around us is alive and merry. Then is the time to fow, to plant, to make verses, to folve problems in metaphyfics, to form fyftems, &c.-I can affure you, I know a very honeft, good fort of a man, who hath always more or lefs wit, according to the changes of the moon. Some years ago, he took it into his head to write a tragedy; and as he never wrote a line but at seasons indicated to him by ← a judicious aftrologer, of his acquaintance, he made a to• lerable

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• lerable piece of work of it. Unhappily, indeed, the first night of its reprefentation, the Sun entered Pifces: An univerfal dulinefs prevailed: the actors had neither fpirit to perform, nor the spectators to applaud: in fhort, the piece C was damned. The catastrophe, indeed, was fomewhat bloody, and, as it must be confefled, the actor topped his part in the murder, that incident contributed no little to the ill fuccefs of the play. The afpect of the Planets was, at that juncture, by no means favourable to the effufion of fo much Chriftian blood: but had the fun been in Aries, I would have laid a wager that this very circumftance would have fet pit, box, and galleries in an uproar: the whole houfe would have thundered with applaufe. In fact, authors always write well or ill, according to the planetary afpect; and their readers judge of their writings, according to the changes of the moon. Even in this lecture I am now giving, you have a proof of the truth of this doctrine. The moon is in her last quarter, had I deferred my difcourfe but a few days, I fhould have faid a thoufand good things which I must now omit: being, indeed, incapable of devifing them till after the new moon. But, whether her influence be effected by any emanations, iffuing from that planet, and reaching the earth, I know not. Whether the tenuity of its light be equal to what is afferted, I cannot tell. • Whether it attracts or repels, I am quite ignorant. I only know, that it acts: for if it be the caufe of the tides, fome how or other it muft certainly and indisputably act.'

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Under fo knowing a tutor, it is no wonder Ibraim, our vifionary, fhould profit in philofophical knowlege. The first inftance he gives of it is, a Differtation on Sleep. There is little difference, fays he, in effect, between a man in a profound fleep, and a plant. He can only be faid to vegetate; the mind, which fhould diftinguifh him from other creatures, being in a torpid ftate, bordering on inactivity: the animal fpirits circulate no longer in his brain; and nothing more is required to reduce the greateft genius to a level with a fimple vegetable. It is to the animal fluid alone, we owe the characteristics of human being. When that is properly in motion, we wake, act, think, and reafon: but this motion once ceafing, we fall faft afleep, and act, think, and reafon no longer. By vigilance, or watchfulness, indeed, is generally understood Activity, or motion of body and yet, fo it is, that thofe bufy fellows, who are perpetually gadding about, here, there, and every where, are commonly more found afleep than any body elfe. With thefe, the animal fpirits perform

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