furnace or chimney, without fetting it on fire, though it turns into flame itself on meeting with the exterior air.

A confiderable heat, kept up among burning combustibles, contributes powerfully to the production of new heat, by occafioning a decompofition of the pure air with the inflammable, inftead of its converfion into fixed air. Experience has taught the Chinese, who often have only ftraw for fuel, to œconomife their fire (its heat being at the fame time confined, and collected on the body to be heated), by continually blowing it; and that the more vivid the flame, the greater is the total heat produced.

The Author is hence led to a particular examination of Argand's lamp, which excellently illuftrates and confirms his principles. Its vivid flame, without fmoke, arifes from the total converfion of the oil into inflammable air, and the fubfequent deftruc tion of that air with the pure air of the ambient atmosphere. When the lamp is in good order, the eye, placed on a level with the circular wick, will diftinguifh, between the wick and the flame, a very fenfible space, perfectly transparent, the inflammable air rifing with fufficient rapidity (the draught being increased by the glais chimney) to maintain this interval for itself alone; but as foon as it meets with the pure air, rifing both on the infide and on the outfide of the wick, the two airs are decompofed together, and form the fine flame that crowns the current of inflammable air. If fuch a decompofition does really take place, water ought to refult from it; and accordingly, an alembic head being placed over one of these lamps, though much of the vapour escaped between it and the flame, half an ounce of pure water was collected in two hours. Part of this water, indeed, was probably no other than what exifted in the oil; but the quantity appears to have been greater than could have arifen wholly from that fource.

The next fection (5th) explains the phenomena of heat relative to liquefaction; and proves, in a clear and fatisfactory manner, that the change of a folid body to a fluid ftate is owing to the chemical union of a quantity of fire with it; and the converfe change, to the feparation of that fire. Water is the grand example of the phenomena of this clafs. When ice is at the melting temperature, whatever heat we apply to it, it does not become hotter; a thermometer, in the middle of the mafs, continues fteady at the thawing point as long as any of the ice remains about it; fo that the fame caufe, which, in other circumftances, would produce an augmentation of heat, produces here only liquefaction. The quantity of heat abforbed by the ice in its change into water (for the difcovery of which the Author gives due honour to Dr. Black), is found to be fuch as would increase the temperature of the water itself about 140 degrees of Fahrenheit's fcale. Converfely, water may be cooled far below REV. April, 1787.

the

the freezing point, down to 14° of Fahrenheit, without freezing: congelation cannot take place till the combined fire is difengaged when any part does congeal, the fire, let loofe from it, warms the water, the thermometer rifes to the freezing point, and continues fteady there till the whole is frozen; after which, as the water in the other cafe, fo the ice in this, obeys the external temperature.

The Author anfwers an objection that may be made to this theory, from a difagreement in the proportions of heat which appear to be loft in fome freezing mixtures; and refutes the hypothefis of Dr. Crawford, who attributes all thefe diminutions and augmentations of heat to a mere variation in the capacity of the fubject-matter, or its becoming capable of containing a greater or lefs quantity. Befide many particular difficulties with which this hypothefis is encumbered, it has the disadvantage of leaving all the grand phenomena unexplained, and accounting only for a fingle circumftance attending them; for if the diminution of heat in liquefaction be owing to the body being capable of containing more heat in a fluid than in a folid ftate, what is the caufe of that increafe of capacity, and of the great transformation itself?

The next fection, which concludes the chapter on fire, confiders the phenomena of heat proceeding from the grofs atinofpheric fluids. As great part of the heat in combustion has been fhewn to arife from a decompofition of these fluids, the Author endeavours here to give fome idea of the quantity of fire contained in them. He defcribes an experiment made by Mr. Watt for afcertaining the quantity of it in watery vapour, by conveying the vapour of boiling water into a known quantity of cold water, with the neceffary precautions to prevent any decompofition of the vapour in its paffage; and he finds it to be fuch, as would communicate to all the water in the vapour (if water could bear fo great a heat) the temperature of 943° of Fahrenheit. Though this appears to be a confiderable fource of heat, it is far inferior to that of the decompofition of inflammable and pure air: when a mixture of thefe airs, confined by mercury, is decomposed by the electric fpark, an expanfive vapour is produced, which, be ing merely aqueous, must contain the quantity of fire effential to that ftate, notwithstanding the diffipation of fire on all fides during the combuftion, which is fo abundant, that part is decompofed, and emits its light.

The fourth and laft chapter, which makes above half of this volume, is on ELECTRICITY. The Author enters into a circumftantial detail of all the leading experiments hitherto publifhed on this obfcure fubject, and adds many new ones of his own; all concurring to establish a very ingenious theory, to which, he acknowledges, the experiments of Mr. Volta first

pointed

pointed the way, and by which all the phenomena are clearly and confiftently explained.

As fire is ranked among vapours on account of the weak union of its deferent fluid with the other matter, the electric fluid belongs à fortiori to the fame class. In fire, the phenomena depending on that weak union are so obfcure, that they could not eafily have been developed, if electricity had not afforded a clue; the corresponding modifications of the electric fluid being marked by diftinct and ftriking phenomena.

The electric fluid agrees with watery vapour, in confifting of a deferent fluid, called the electric deferent, and a gravitating fubftance, called the electric matter;-in being decompofed when brought to a certain degree of denfity;-in its deferent fluid quitting the gravitating matter, to pass to a body that has proportionably lefs, according to certain laws;-in the deferent Auid permeating all bodies, to re-establish the equilibrium refpecting itself, and depofiting the gravitating matter on the body it paffes through, but differently, according to the nature of the bodies in the ingredients, though united, retaining their proper tendencies and affinities (as the fire and water in vapour do), and from this fource moft of the electrical phenomena refult;in the gravitating matter exerting its affinities to different bodies. without choice, as the water in vapour does to hygroscopic bodies; -and laftly, in the laws of equilibrium, that when an equilibrium of the deferent fluid is eftablished between neighbouring bodies, those which have most of the electric matter will have moft of the deferent alfo, the excefs being in a latent state; and that two quantities may be in equilibrio in refpect to expanfive force, though one has lefs of the electric matter than the other, provided it has more of the deferent.

The differences of the electric fluid from watery vapour are: That when the deferent quits the other matter to re-establish an equilibrium, it does not (like fire quitting its watery affociate) remain free, and diffuse itself every way, till the equilibrium is produced, but is determined in its courfe by its tendency to other bodies, and particularly to fome body in the neighbourhood poffeffing less than that which it quitted ;-that the gravitating matter of watery vapour has an affinity, without choice, to hygroscopic fubftances only, but the electric to all fenfible bodies, the groffer atmospheric fluids as well as others; -and that this affinity is not confined to contact, as in watery vapour, but operates at diftances, different according to the nature of the body.

The bodies to which the electric or gravitating matter tends at confiderable diftances, are thofe called conductors: its tendency increases, with its approach, in a very low ratio; and when arrived in contact, it does not adhere, but circulates about them, being carried round by its deferent fluid, analogously to the revolution

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volution of the planets round the fun: the fhorter the curve, in proportion to the velocity, the more it is difpofed to fly off in a tangent; and the outer parts, moft remote from the centre of their tendency, fly off where the turning is fharpeft. To the bodies called non-conductors it tends only at fmall distances, but arrived in contact it adheres; fo that on thefe it may be accumulated more copioufly, and retained longer; and by means of an armature, or conducting medium, to convey it from the whole furface at once, it may be difcharged in a much denser stream.

The general laws of the deferent fluid are: That it tends to all bodies, at greater diftances than the electric matter tends to any; that its tendency, like that of the electric matter, is always from the body which has more, to that which has lefs ;that, cæteris paribus, the body which has most of the electric fluid, has most of the deferent alfo;-that the tendency of the deferent to other bodies diminishes, like that of the electric matter, in proportion to the diftance ;-that it has a particular affinity with the electric matter, but that their union is very weak, infomuch that the electric fluid is in a perpetual state of decompofition and recompofition, even more fo than watery vapours.

Such are the general laws which Mr. De Luc, with great fagacity, has developed and applied to the folution of the feveral phenomena. We shall give, for an example, the hitherto inexplicable phenomenon of the Leyden jar, or (which is the fame thing in a fimpler form) the magic picture, that an accumulation of electricity on one fide produces a deficiency on the other.

The electric fluid being analogous to watery vapour, let us fuppofe a plate of glafs, of the fame temperature with the neighbouring bodies, to be bedewed with decompofed vapour on both fides, and to receive on one of its fides, A, a ftream of vapour warmer than the plate itfelf. Thefe vapours, on touching the plate, will be in part decompofed; their water will be depofited on the fide A, and the fire, now liberated, paffing through the glafs, will unite with the water on the other fide, B, and promote evaporation from that fide. This greater evaporation from the fide B confumes the fire that came from A; and the fide A, by this lofs of its heat, becomes able to condenfe more vapour. Thus the water continues diminishing on the one furface, and increafing on the other, till the whole plate has acquired the temperature of the vapours: the condensation muft then ceafe, and the inequality of diftribution is at its maximum ; in which state, as the fide B is a little more diftant than A from the fource of heat, its vapours will have fomewhat lefs expansive force than those which fall upon A. The Author thews, that the cafe is precifely the fame with the electric fluid; and describes an apparatus, by which all the phenomena of the electric jar or plate, even the difcharge, may be imitated with watery vapour,

except only in thofe particulars which depend upon the extreme rapidity, or other characteristic and incommunicable properties of the electric fluid or its deferent.

The chapter concludes with fome conjectures on the component parts of the electric fluid, as they difcover themselves in its decompofition. When the quantity furrounding the largest conductor paffes off at once in a small thread, its denfity and velocity must be amazingly increased, and the deferent fluid itself appears to be decompoled, the light, which is the general principle of all the deferents, being difengaged. Some curious hints are added refpecting magnetiím, and the probable exiftence of fome other fluids as yet unknown. But we must take leave, for the prefent, of this pleafing, as well as inftructive, writer; and hope to meet him again foon, in the fecond volume.

Chi

ART. VI. The Fair Syrian, a Novel. By the Author of Mount Henneth *, and Barham Downs f. 12mo. 2 Vols. 6s. fewed. Walter. 1787.

Tis unquestionably the bufinefs both of the dramatic writer and the novelift, "to hold as 'twere the mirror up to nature; to fhew virtue her own feature, vice her own image, and the very age and body of the time his form and preffure." The man of genius, therefore, who writes with the view of affording amusement to his readers, will, when felecting materials for his work, make choice of fuch particular incidents and scenes in life as may be fomewhat familiar to the people in general, but which are ftill of fuch a nature as to admit of amplification, and which will allow him to exercife his inventive faculty in a certain and limited degree; that is, in fuch a degree as that he do not 'o'erstep the modesty of nature,' or in all events, that probability do not receive from it any great or violent fhock.

Our three great novel-writers are Richardfon, Fielding, and Smollet; and thefe,-to illuftrate one art or profeffion by another, we would compare with Reynolds, Le Brun, and Hogarth. The firft for truth and beauty of colouring, the fecond for a lively difplay of the paffions, and the third for caricatura. We almost despair of feeing them equalled. It is, however, no little fatisfaction to us to find, amid the multitude of unfinished things,' which are continually iffuing from the prefs under the denomination of novels, or romances; and which we should really be at a lofs to characterize, were it not that the writers of them have kindly, and in imitation of the fhowman, fet down in the title-pages of their respective performances- this is a novel-it is no little fatisfaction to us, we fay, to meet with Ib. vol. lxxi. p. 223.

* See Rev. vol. lxvi. p. 129.

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a writer