ART. IX. Decouvertes de M. Marat, fur le Feu, l'Electricité, et la Lumiere, &c. -Discoveries relative to Fire, Electricity, and Light, by M. MARAT *, M. D. Phyfician to the Life-Guards of the Count d'Artois, confirmed by a series of Experiments, which have been repeated and verified by Commiffaries, appointed by the Royal Academy of Sciences, for that Purpose. 8vo. Paris. 1779. T is fingular enough, that though fire is an object perpe Itually before our eyes, and the conftant obfervation of its effects feems to facilitate the means of arriving at the knowledge of its nature, we have hitherto got little farther than the formation of ingenious conjectures and hypothefes on that interesting subject. Thofe who have ftudied it with the most perfevering attention and affiduity, have confidered fire as an emanation from the fun, and heat as the attribute of light; but the refult of curious, new, and well-conducted experiments hath enabled M. MARAT to improve, by important difcoveries, this useful and entertaining branch of natural philofophy, From an attentive confideration of the known phenomena, our Author concluded, that heat and fire are modifications of the motion of a particular fluid; but to know the nature of this fluid, it was neceffary to render it visible at the moment that it escapes with violence from the inflammable matters which it confumes, or difengages itfelf gently from the bodies which it has penetrated. This M. MARAT attempted with fuccefs, but by a method of proceeding entirely new, and by a ufe of the folar microscope, hitherto unknown, and which gives a new and enlarged fphere of operation to this inftrument. It is well known, that the use of the folar microscope has been hitherto confined within narrow bounds. By the ordinary manner of employing it, the object is placed in the focus, and thus only small objects and tranfparent ones can be examined by its affiftance; but by mounting it with its object-glass alone, and placing the object in a proper point of the luminous cone, our Author has adapted it to the examination of objects great and fmall, opaque and tranfparent, whose emanations also it renders vifible. The first thing M. MARAT attempts to prove is, that heat is nothing more than the modification of a particular fluid, and that it is the motion of this fluid, and not merely its prefence, which produces heat and fire. "When we fix, fays he, the folar microscope, mounted with * The author of a Philofophical Effay on Man, &c. published at London in the year 1773, and of which an account was given by us. its object-glafs only, to the window-fhutter of a dark room, and place the flame of a wax-candle in a proper part of the cone, formed by the diverging rays of the fun, and several "feet diftant from the focus, then there is seen to arife on "the linen about the wick an oblong, tranfparent waving cy 66 linder. In this cylinder the image of the flame is easily dif "tinguished: it appears under the form of a ruddy fhuttle, "which contains, within its compafs, a fimilar form lefs co"loured, and in whofe centre there fhines a small point extremely white. This cylinder is terminated by a brilliant "ftripe or border, except at its fummit, which is divided into "feveral whirling, lucid particles or emiffions, each furround"ed by a fmaller ftripe or border. Lighted coal, red-hot iron, "exhibit phenomena analogous to this, and lead us to conclude, "that heat never exifts, but when the igneous fluid is fet in "motion." After analyfing the impreffion that is made on the linen, M. MARAT proves, that the brilliant effluvia obfervable on the linen or paper that is employed in the experiment, are properly portions or undulations of the igneous fluid itself, and not a fort of light vapour, which efcapes from bodies highly heated, and is defigned to communicate warmth; and that the exhalations of an enflamed or candent body are fo far from transmitting the action of the igneous fluid, that they, on the contrary, diminish and weaken it. The properties of the igneous fluid come next into confideration. This fluid is tranfparent and luminous, and its eclat or brilliancy is proportionable to its denfity. Hence this brilliancy is more vivid at the borders of its sphere of activity, more especially in the centre of the flame, where the figure or form of the igneous emiffions (jets) is nearly fpherical. The igneous fluid is moreover a weighty body, endowed with a furprifing mobility, compreffible, and not elastic. We refer our Readers to the Work itself for an accurate and circumftantial account of the experiments, by which our Author undertakes to prove, that the igneous matter (or fire) differs effentially both from luminous matter (light) and the electrical fluid. Thefe are followed by other experiments, which indicate the laws and properties of the motion of the igneous fluid, when its action is excited. From hence M. MARAT proceeds to confider the form of the fphere of activity of this fluid, and the neceffity of air to fupply fire with a compreffible medium, in which it can extend freely the fphere of its activity. The experiments that illuftrate this fact are interefting and curious. Such alfo are his obfervations on the diverfity which may be remarked in the power of bodies to determine the action of the igneous fluid. This diverfity depends on the quantity of phlogifton, which, not being intimately united with with incombuftible principles, may be difengaged from them by the action of the igneous fluid. Deflagration, and the phenomena of refrigeration, next employ the attention of our Author, who alfo enters into curious difcuffions relative to the light which flame diffufes, the different colours of flame, the degrees of purity in the igneous fluid, which this diverfity of colours indicates, and the causes of that figure of an oblong cone which flame always affumnes. The hypothefis of M. MARAT is fupported by 116 experiments ;-nevertheless we fufpend our judgment, and should be glad to fee it fet in a ftill more irrefiftible light. We cannot fay, that either his reafonings, or the account of his experiments, are free from all charge of obfcurity; at least, we have not found them fo.-This however may be our fault, and therefore we shall not farther infift upon this circumftance. Ee that as it may, M. MARAT is certainly a fagacious and acute obferver of nature, and poffeffes all the knowledge and qualities that are requifite to make important difcoveries in natural fcience. ART. X. Nouvelles Lettres d'un Voyageur Anglois.-More Letters of an English Traveller. By M. SHERLOCK. 8vo. London and Paris. 1780. HE motto at the head of this new publication of Mr. SHERLOCK fhews, that his fpirits are raifed under the profpect of approaching fame. It is as follows, Incenditque animum fame venientis amore. VIRG. From what quarter the trumpet-bearing goddess is to make her approaches to our Author-whether or not he has already fet out or how far fhe may have advanced in her journey, we know not; neither can we guess what route fhe will take. If fhe comes through his Advice to a young Italian Poet*, this may help her on a little in her way, and give her fome propenfity to put the trumpet to her mouth in our Author's favour;-but the first Twenty Letters of an English Traveller + will probably make her take feveral fteps backward, and even think of fending Patience in her place. The New Letters, now before us, will not, we fear, induce her to arrive, and hover, with her fpread wings, over our Author's head and yet Mr. Sherlock does not feem difpofed to put up with fcanty marks of her benevolence for the laft words of his fhort Preface are Glory or Death. As to GLORY, we could not, in confcience, give it to him for this new publication, if we had it in our giving; • See an account of this work in our Review, vol. Ixi. p. 460. + See our Review of thefe twenty Letters, ibid. p. 462. and and as to Death (if he means oblivion by that term), it will in all likelihood come of itfelf. There are indeed feveral good things in thefe Letters; but they are very unequal in quantity to the inaccurate relations, injudicious reflections, illiberal cenfures and invectives, and trite obfervations that disfigure the work. Mr. SHERLOCK fets out in his fhort, but emphatic Preface, with an uncommon air of confidence and felf-importance. We fhall tranflate the Preface, to fhew that this accufation is not groundless. 1 Readers in general have fo little knowledge and quicknefs "of difcernment, that it may be almoft looked upon as an "inftance of folly to appear in print. There are, nevertheless, "exceptions to this general rule; and I hope, Reader, that 66 you are of the number. If you are not,-I confefs honeftly, "that you would give me more pleasure, by throwing my book "into the fire, than by reading it: If you are-I ask no quar"ter:- GLORY or DEATH." Of the Forty-four Letters that compofe this Work, the firft fifteen relate to Italy. The firft and second describe the natural beauties of that delightful country, in animated profe, that fometimes runs mad, in which we often find an uncommon felicity both of thought and expreffion, mixed with abfurd epithets, and tinfel phrafes. Thus, after having mentioned the pictures in Italy, he tells us, that Italy itfelf is the moft beautiful picture in the 'world,-that Nature caft it (l'a jetté) in a happy moment, and that this great mafler, to prevent the fatiety arifing from a continual accumulation of beauties, has fhaded the compofition with barren mountains, and extenfive difmal marthes. He also calls the burning volcanos, and the rocky mountains, terrible graces, which is furely an epithet that the three amiable fifters must reject without hefitation, as nothing that excites or resembles terror can belong to their domain. In fhort, all this is a motley bufinefs. The fecond Letter is above cenfure; for it confifts of two Latin pages from the fecond book of Virgil's Georgics-of two French pages, which contain the Abbé Delifle's tranflation of that paffage-of an English page from Addifon's letter from Italy-of a quotation from Pliny, and of a paffage of Voltaire's Henriade. There is nothing either new, inftructive, or ingenious in what he says of the Roman artifts in the third Letter, which is fuperficial, flighty, and frothy,-characters that predominate too much in the whole of this publication. The fourth points out the remarkable difference, or rather oppofition, that there is between the referved, infidious, and crafty character of the Romans (which is ftill much the fame as we have it defcribed by Salluft), and the character of the Neapolitans, which is frank and open in the midst of their libertinifm and profligacy. Mr. SHERLOCK SHERLOCK obferves in this Letter, that few of the European nations retain their original character, and that French manners and modes have been almost universally adopted in them all. He adds, that the capital cities in Germany are entirely French in their manner of living, which may be more or less true, and that the little towns in that empire retain the fame fimpli city which charactifed them in the time of Tacitus, which we know to be more or less falfe. The fifth and fixth Letters contain nothing remarkable. In the seventh Mr. SHERLOCK tells us, that the Italian women pleafed him, not only because they fing fweetly, but because they reafon well; and nothing, fays he, pleafes me fo much as a woman who reafons. Now to fhew, that he does not extol, without foundation, the reasoning powers of the Italian ladies, he gives us a specimen of their logic in the following converfation: "Madam (faid I, to one of them), how comes it that the "ladies of this country admit the fuits of fo many lovers? "What would you have us do? (replied fhe.) Nature has "given us a heart-now the heart fades and decays, when it is ❝not nourished:-therefore another heart must be fought for ❝ to nourish it; and thus we take to ourfelves a husband. But "the heart of this husband is foon exhausted: and then we take 66 to ourselves a lover: The lover leaves us in the lurch;"then we feel a dreadful void, which it is neceffary to fill; "therefore we take another lover, and then another, and then "a fourth (for they all defert us). So you fee, conti"nued fhe, that if we are not conftant, it is not our fault, "but that of the men, not one of whom knows what fidelity "is."(Rare logic, indeed, Mr. SHERLOCK!) And what is peculiarly agreeable on this fubject, is, that the logic of the Italian ladies may be either faid or fung;-" for (as our Author goes on to obferve)" four verfes of Metaftafio will form a fufficient proof for an Italian lady on any subject whatever, "as they enter into the foul by a very fenfible and feeling part-I mean the ear: join, therefore, the charm of poetry "with the profound logic, of which I have already quoted an "example, and then judge whether these poor women are to "be blamed, who follow inviolably the maxim, fo happily ex"preffed in these three little verfes: Molti averne, Un goderne, 2. e. To have many (lovers), To enjoy one, The |