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ART. IX. Decouvertes de M. Marat, sur le Feu, l'Ele&ricité, et la Lumiere, &c,
-Discoveries relative to Fire, Electricity, and Light, by M. MARAT", M. D. Physician to the Life-Guards of the Count d'Artois, confirmed by a series of Experiments, which have been repeated and verified by Commissaries, appointed by the Royal Academy of Sciences, for that Purpose. 8vo. Paris. 1779. T is fingular enough, that though fire is an object perpe
effects seems 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 hypotheses on that interesting subject. Those who have studied it with the most persevering attention and assiduity, have considered fire as an emanation from the fun, and heat as the attribute of light; but the result of curious, new, and well-conducted experiments hath enabled M. MARAT to improve, by important discoveries, this useful and entertaining branch of natural philorophy,
From an attentive consideration of the known phenomena, our Author concluded, that heat and fire are modifications of the motion of a particular Auid; but to know the nature of this Auid, it was necessary to render it visible at the moment that it escapes with violence from the infiammable matters which it confumes, or disengages itself gently from the bodies which it has penetrated. This M. MARAT attempted with success, but by a method of proceeding entirely new, and by a use of the solar microscope, hitherto unknown, and which gives a new and enlarged sphere of operation to this instrument. It is well known, that the use of the solar 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 transparent 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 small, opaque and transparent, whose emanations also it renders visible.
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 presence, which produces heat and fire.
“ When we fix, says he, the solar microscope, mounted with
* The author of a Philosophical Ejay on Man, &c. published at London in the year 1773, and of which an account was given by us.
* its object-glass only, to the window-shutter of a dark room, ço and place the flame of a wax-candle in a proper part of the $ cone, formed by the diverging rays of the sun, and several “ feet distant from the focus,-then there is seen to arise on " the linen about the wick an oblong, transparent waving cy“ Jinder. In this cylinder the image of the fame is easily dir“ tinguished : it appears under the form of a ruddy shuttle, “ which contains, within its compass, a fimilar form less co“ loured, and in whose centre there shines a small point ex“ tremely white. This cylinder is terminated by a brilliant “ ftripe or border, except at its summit, which is divided into “ several whirling, lucid particles or emissions, each surround" ed by a smaller stripe 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 Auid is set in “ motion.” After analysing the impression that is made on the linen, M. Marat proves, that the brilliant effluvia observable on the linen or paper that is employed in the experiment, are properly portions or undulations of the igneous fuid itself, and not a sort of light vapour, which escapes from bodies highly heated, and is designed to communicate warmth; and that the exhalations of an enflamed or candent body are so far from transmitting the action of the igneous fluid, that they, on the contrary, diminish and weaken it.
The properties of the igneous Auid come next into consideration. This Auid is transparent and luminous, and its eclat or brilliancy is proportionable to its density. Hence this brilliancy is more vivid at the borders of its sphere of activity, more especially in the centre of the Aame, where the figure or form of the igneous emissions (jets) is nearly spherical. The igneous Auid is moreover a weighty body, endowed with a surprising mobility, compressible, and not elastic.
We refer our Readers to the Work itself for an accurate and circumstantial account of the experiments, by which our Author undertakes to prove, that the igneous matter (or fire) differs essentially both from luminous matter (light) and the electrical fluid. These 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 consider the form of the sphere of activity of this Auid, and the neceflity of air to supply fire with a compresible medium, in which it can extend freely the sphere of its activity. The experiments that illustrate this fact are interesting and curious. Such also are his observations on the diversity which may be remarked in the power of bodies to determine the action of the igneous Auid. This diversity depends on the quantity of phlogiston, which, not being intimately united
with incombustible principles, may be disengaged from them by the action of the igneous fluid.
Deflagration, and the phenomena of refrigeration, next em. ploy the attention of our Author, who also enters into curious discusions relative to the light which fame diffuses, the different colours of Aame, the degrees of purity in the igneous fluid, which this diversity of colours indicates, and the causes of that figure of an oblong cone which fame always aflumnes.
The hypothefis of M. MARAT is supported by 116 experiments ;--nevertheless we suspend our judgment, and Mould be glad to see it set in a ftill more irresistible light. We cannot fay, that either his reasonings, or the account of his experiments, are free from all charge of obscurity; at least, we have not found them fo.—This however may be our fault, and therefore we shall not further infiit upon this circumstance. Ee that as it may, M. MARAT is certainly a fagacious and acute observer of nature, and pofleffes all the knowledge and qualities that are requisite to make important discoveries in natural Science,
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.
prospect of approaching fame. It is as follows, Incenditque animum famæ venientis amore.
VIRG. From what quarter the trumpet-bearing goddess is to make her approaches to our Author-whether or not she has already set out-or how far she may have advanced in her journey, we know not;-neither can we guess what route she will take. If the comes through his Advice to a young Italian Poet *, this
may help her on a little in her way, and give her some 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 several steps backward, and even think of sending Patience in her place. The New Letters, now before us, will not, we fear, induce her to arrive, and hover, with her Spread wings, over our Author's head : and yet Mr. Sherlock does not seem disposed to put up with scanty marks of her benevolence : for the last words of his short Preface are Glory or Death. As to Glory, we could not, in conscience, 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 these twenty Letters, ibid. p. 462.
and as to Death (if he means oblivion by that term), it will in all likelihood come of itself.
There are indeed several good things in these Letters ; but they are very unequal in quantity to the inaccurate relations, injudicious reflections, illiberal censures and invectives, and trite observations that disfigure the work. Mr. SHERLOCK sets out in his short, but emphatic Preface, with an uncommon air of confidence and self-importance. We shall translate the Preface, to thew that this accufation is not groundless. '« Readers in general have so little knowledge and quickness " of discernment, that it may be almost looked upon as an “ instance of folly to appear in print. - There are, nevertheless, “ exceptions to this general rule; and I hope, Reader, that
you are of the number. If you are not,-! confess honestly, " that you would give me more pleasure, by throwing my book “ into the fire, than by reading it: If you are-I ask no quare “ ter:- GLORY or DEATH."
Of the Forty-four Letters that compose this work, the first fifteen relate to Italy. The first and second describe the natural beauties of that delightful country, in animated prose, that sometimes runs mad, in which we often find an uncommon felicity both of thought and expression, mixed with absurd epithets, and tinsel phrases. Thus, after having mentioned the pictures in Italy, he tells us, that Italy itself is the most beautiful picture in the 'world, -that Nature cast it (l'a jetté) in a happy moment, and that this great mafler, to prevent the fatiety ariling from a continual accumulation of beauties, has shaded the composition with barren mountains, and extensive dismai marthes. He also calls the burning volcanos, and tbe rocky mountains, terrible graces, which is surely an epithet that the three amiable sisters must reject without hesitation, as nothing that excites or resembles terror can belong to their domain. In short, all this is a motley business. The second Letter is above censure ; for it confits of two Latin pages from the fecond book of Virgil's Georgics-of two French pages, which contain the Abbé Delisle's translation of that passage-of an English page from Addison's letter from Italy-of a quotation from Pliny, and of a passage of Voltaire's Henriade.
There is nothing either new, instructive, or ingenious in what he says of the Roman artists in the third Letter, which is superficial, fighty, and frothy,characters that predominate too much in the whole of this publication. The fourth points out the remarkable difference, or rather opposition, that there is between the reserved, insidious, and crafty character of the Romans (which is still much the same as we have it described by Sallust), and the character of the Neapolitans, which is frank and open in the midst of their libertinism and profiigacy. Mr,
SHERLOCK observes 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 same fimplicity which charactised them in the time of Tacitus, which we know to be more or less false.
The fifth and fixth Letters contain nothing remarkable. In the seventh Mr. SHERLOCK tells us, that the Italian women pleased him, not only because they fing sweetly, but because they reason well; and nothing, says he, pleases me so much as a woman who reasons. Now to Thew, 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 conversation : “Madam (faid I, to one of them), how comes it that the “ ladies of this country admit the suits of so 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 sought for $ to nourish it, and thus we take to ourselves a husband. But o the heart of this husband is soon exhausted: and then we take
to ourselves a lover : The lover leaves us in the lurch ;“ then we feel a dreadful void, which it is necessary to fill; “ therefore we take another lover, and then another, and then « a fourth (for they all desert us). So you see, conti“ nued the, that if we are not constant, 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 subject, is, that the logic of the Italian ladies may be either said or sung ;-—" for (as our Author goes on to observe) “ four verses of Metaftafio will form “ a sufficient proof for an Italian lady on any subject whatever,
as they enter into the soul by a very sensible 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, so happily ex. “ prelled in these three little verses: