after Mr. Mitchell's method. Mr. Arderon did not find magneticBrass to attract Iron; but does not pretend to determine the cause. Different pieces were found to receive Magnetism in different degrees; and fome not at all; without any evident reafon for the peculiarity. The author propofes two ends to be obtained by profecuting thefe experiments: firft, to fhew the impropriety of making Compafs-boxes of Brafs; which may occafion fatal effects and, fecondly, that if Brafs Needles could be made to act as strong as Iron ones, they would be preferable, becaufe lefs liable to ruft. ACCOUNT of FOREIGN BOOKS. Fabularum fopiarum Libri quinque. Auctore Francifco Jofepha Defbillons, é Soc. Jefu. Ejufdem Fabularum Libri quinque alteri nunc primum editi. That is, Fables written after the manner of fop. In ten Books. Printed at Paris, for Barbou, 1759 12mo. TH HE first five books of the Fables before us, were printed at Glafcow, in the year 1754; and a fecond edition of them at Paris in 1756. The ingenious author has now acknowleged the work, and obliged the public with a more correct and improved copy; having added five new books to the former publication. The whole contains about 350 Fables; the greater part of which are tranflated, or paraphrafed, from the writings of the moft eminent Fabulifts, ancient and modern. La Fontaine, in particular, appears to be our author's favourite; he having imitated him, in a great variety of well-chofen Fables. The famous tale of Perrette, the Milk-maid, fo well told by that excellent Fabulift, is thus concisely imitated by our author, in the twelfth Fable of his fixth book. Summo repofitum capite lactis cymbium R 4 Numerum Numerum diminuet, ut porco non fint pares Our author does not appear, however, to be altogether a mere Imitator; his work containing a confiderable number of apt and well-turned Fables, of his own particular invention and application. For the entertainment of those claffical readers, who are not too much prejudiced against the Latin of the moderns, we fhall quote one of thefe, as a further fpecimen of this writer's abilities. Book the eighth, Fable the fourteenth. DE CORVO ET LEPORE. PER odora rura dum thymum pafcit Lepus ; Miferamque pecudem nifi, ait, admoneam citò, Delapfus ergò poftquam confedit folo, Leporem quietuin hortatur monitor anxius, Fugiat, fuoque fe recipiat latibulo, Ac venatorum vitet adventum, et necem. Nam venatores alio curfum verterant. At Corvus, ut humo tollere fe tentat pedes Retineri fentit impeditos caffibus, In quos latentes induit fe improvidus, Saluti alterius providere dum cupit. Rebus alienis qui ftudent vigilantiùs, Quàm fit opus, hi fæpè nihil in propriis vident. Thus tranflated, for the fake of our English readers. The CROW and the HARE. THE flow'ry meads were in their prime, Sawufs fecurely fcaft below; «Alas, "Alas, poor Hare! ere yet too late, The Hare, alarm'd, with speed withdrew, Who meddle thus with others' cares, The feveral books, into which our author has divided his work, are introduced each by a Prologue, in the manner of Phædrus; in imitation of whom, alfo, he gives us, in one of them, the following description of himself, as to his dif pofition and manner of life. Vivo mihi propè uni cognitus: It may be fufpected, that a man who confeffedly draws his knowlege of mankind folely from books, must be very unequal to the task of a Fabulift. To invent Fables, indeed, with any great degree of fuccefs, at this time of day, may require a more intimate acquaintance with the vices and foibles of mankind, than our author feems to be poffeffed of; but it should be remembered, that elegance and fimplicity of expreffion contribute much to form the character of the Fabulift. Fontaine invented little; and yet his choice of fub jects, jects, and the excellence of his ftile, have diftinguished him as one of the firft rank of this kind of writers: and, perhaps, the greateft 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 firft 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, these 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 hypothesis. 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 thefe very furprizing and inconfiftent phoenomena, fuppofed the existence 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 fhould 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 Hudson'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. Mr. Mr. Euler does not judge this obfervation a sufficient reason 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 these Poles are not diametrically oppofite, but pofited obliquely, with respect 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 recourfe 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 fuppofition 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, short enough for our purpose, would be difficult, without doing the author injustice. The second article, written by the fame hand, relates to the strength of Columns. It confifts chiefly of Calculations, tending to explain a rule for determining the strength 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 entitled, General Rules for the Conftruction of Telescopes and Microscopes, 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 should be made as large as poffible: and, laftly, the eye should be never incommoded with those prifmatic colours, that arife from the different refrangibility of the rays of light, The |