being almost impoffible to define and to ascertain an extraordi, nary genius, a healthy conftitution, and a good character. With respect to the internal regulations of this academy, Count R, mentions one circumftance only as deferving of particular no tice; which is, the very fmall expence the pupils occafion for board, lodging, clothing, mafters, fire-wood, light, repairs, and every other article, house-rent only excepted. It is ftated that the whole "amounts to no more than 155 florins, or about fourteen pounds sterling a year for each pupil."

In the other accounts given in this effay, we do not find any thing which feems to deserve our reader's particular notice.

Effay VI. Of the Management of Fire, and the Economy of Fuel. London. 1797.

The great waste of fuel which is generally practifed, and commonly lamented, induced this active obferver to examine the fubject with attention, as there seemed to be much room for very effential improvements in almost all thofe operations in which heat is employed for the purposes of human life. His first object was to calculate and to afcertain how much of the fuel which is generally used, is confumed in vain. And after a variety of accurate experiments and attentive obfervations, he was led to conclude, that not less than feven eighths of the heat generated, or which, with proper management might be generated, from the fuel actually confumed, is carried up into the atmosphere with the smoke, and totally loft."

In the common way of heating culinary veffels in open fireplaces, not only the radiant heat, but that heat likewife which accompanies the flame, the fmoke, and the vapour, is almost entirely loft. Count R. not finding a ready way of ascertaining the quantity of heat which is thus unprofitably diffipated, "endeavoured to find out with how much lefs fuel the fame operation might be performed, by a more advantageous arrangement of the fire, and difpofition of the machinery.”

From feveral experiments, fome of which are particularly defcribed in the Effay, it appears, "that in cooking or boiling over an open fire, nearly five times as much fuel is required, as when the heat is confined in a clofed fire-place, and its operation properly directed."

This, however, is the cafe when the fire in the open fireplace is managed by a skilful and fparing hand. But in common kitchens, where little or no attention is paid to this particular, the Count is of opinion that at least nine tenths of the fuel might be faved. The experiments which Count R. made for the purpose of proving or illuftrating thofe affertions, naturally fuggested a variety of improvements in the conftruction

of

of kitchen fire-places. After a fummary account of thofe improvements, in the first chapter, the author begins to treat in a more methodical manner, (in the fecond chapter) of the generation and other properties of heat, as preparatory to the particular description of œconomical kitchens, and their appendages.

The third chapter treats of the Means of confining Heat, and directing its Operations.

!

In general, the method of confining heat confifts in furrounding the fire, or other fource of heat, with bodies that are bad conductors of heat (which, by the bye, has been long known, and often ufed) it being well known that certain bodies, fuch as the metallic fubftances, are very good conductors; while others, fuch as wood, charcoal, the elaftic fluids, &c. are very imperfect conductors of heat.

"But," fays this author, " among all the various fubftances of which coverings may be formed for confining heat, none can be employed with greater advantage than common atmospheric air. It is what nature employs for that purpofe; and we cannot do better than to imitate her.

"The warmth of the wool and fur of beafts, and of the feathers of birds, is undoubtedly owing to the air in their interftices; which air being ftrongly attracted by thefe fubftances, is confined, and forms a barrier which not only prevents the cold winds from approaching the body of the animal, but which oppofes an almoft infurmountable obftacle to the efcape of the heat of the animal into the atmosphere. And in the fame manner the air in fnow ferves to preferve the heat of the earth in winter. The warmth of all kinds of artificial clothing 'may be fhown to depend on the fame caufe; and were this circumftance more generally known, and more attended to, very important improvements in the management of heat could not fail to result from it." P. • 54.

And further on he shows how this non-conducting property (if we may be allowed to use the expreffion) may be increased.

"Now if heat paffes in a mass of air merely in confequence of the motion it occafions in that air,-if it is tranfported,-not fuffered to pafs,-in that cafe it is clear that whatever can obftruct and impede the internal motion of the air, muft tend to diminish its conducting power and this I have found to be the cafe in fact. I found that a certain quantity of heat, which was able to make its way through a wall, or rather a fheet of confined air, half an inch thick, in 93 minutes, required 213 minutes to make its way through the fame wall, when the internal motion of this air was impeded by mixing with it 56 part of its bulk of eider-down,-of very fine fur, or of fine filk, as fpun by the worm." P. 56.

This chapter concludes with the following remark, which is derived from the above-mentioned experiments;

. That

That not only cold air, but also hot air, and hot steam, and hot mixtures of air and fteam, are non-conductors of heat; confequently that the hot vapour which rifes from burning fuel, and even the flame itfelf, is a non-conductor of heat." P. 64.

The elucidation of this affertion is contained in the following chapter, where it is shown, that flame communicates more or lefs heat, in proportion to the number of its particles, that either by blowing, or otherwife, are made to impinge on the body which is to be heated;

"Hence the boiler muft not only have as large a furface as poffible but it must be of fuch a form as to caufe, the flame which embraces it, to impinge against it with force-to break against it-and to play over its furface in eddies and whirlpools." P. 73.

In the fifth chapter, we have a long account of various experiments, made on boilers and fire-places of different forms and dimenfions; of the relative quantities of heat, produced by certain combuftible bodies, and other particulars of the like nature; but they are not fufceptible of fufficient abridg

ment.

The fixth, or laft chapter, contains the defcriptions of various kitchens and fire places for different ufes, which have been conftructed under Count Rumford's direction. Yet, after all, the reader is left to his own judgment and discretion, for the choice of a fire-place proper for any particular purpose. His choice, indeed, may be directed by the defcriptions of this laft, and by the experiments of the preceding chapter; but this, we prefume, is not eafily determined by a great majority of readers; and, in fact, the Count himfelf, fenfible of the difficulty, fays in the beginning of the laft chapter," thofe who may not have leifure to enter into thefe fcientific investigations, and who, notwithstanding, may wish to imitate these inventions, will find all the information they want in my next Effay.' But in the next, or feventh Effay, he apologizes for being obliged, on account of unfinished experiments, &c. to defer the business of kitchen fire-places to a future time.

This Effay is accompanied with fix copper-plates, exhibiting fome of the principal improvements, and of the conftructions that are mentioned in the courfe of the work.

Effay VII. Of the Manner in which Heat is propagated in Fluids. Of a remarkable Law which has been found to obtain in the Condenfation of Water with Cold, when it is near the Temperature at which it Freezes; and of the wonderful Effects which are produced by the Operation of that Law, in the Economy of Nature. Together with Conjectures refpecting the final Caufe of the Saltnels of the Sea. London, 1797.

The

The author's principal object in this Essay, is to establish a new and interefting theory, relative to the propagation of heat through fluids. His experiments, and his reafonings, though not entirely new, nor, in our opinion, ultimately conclufive, are, however, highly deferving of the attention of philofophers, efpecially on account of their extenfive application.

Count Rumford's new proposition is," that although the particles of any fluid, individually, can receive heat from other bodies, or communicate it to them; yet, among these particles themselves, all interchange and communication of heat is abfolutely impoffible." They, therefore, are perfect non-con. ductors of heat.

The principal facts upon which he establishes this propofition, are, that whenever a fluid is undergoing a change of temperature, a proportionate motion takes place among its particles, and that whatever impedes this internal motion or circulation, does, at the fame time, retard or obftruct the change of temperature in that fluid. Thus, if a thermometer be placed in the middle of a veffel full of water, and the veffel be fet in boiling water, or in ice, the mercury in the thermometer will be affected by the heat or cold much quicker, when the water of the veffel is pure, than when it is mixed with ftarch, or eider-down, or, in fhort, with any thing that obftructs the internal motion of its parts.

In order to render the above-mentioned internal motion of a fluid vifible, Count R. mixed, in an alkaline folution, a coarse powder of yellow amber, the particles of which, on account of their being nearly of the fame specific gravity as the alkaline folution, will remain fufpended in the fluid, without showing any tendency either towards the bottom or towards the furface. With this mixture he filled a glafs veffel, nearly of the fhape of a common thermometer, whofe bulb was 2 inches in diameter, and whofe cylindrical tube was 12 inches long, and of an inch in diameter.

"The firft experiment," fays he, "I made with this inftrument was to plunge it into a tall glass jar, nearly filled with water almost boiling hot. The refult was just what I expected. Two currents, in oppofite directions, began at the fame instant to move with great celecity in the liquid in the cylindrical tube, the afcending current occupying the fides of the tube, while that which moved downwards, occupied its axis.

As the faline liquor grew warm, the velocity of these currents gradually diminished; and at length, when the liquor had acquired the temperature of the furrounding water in the jar, these motions ceafed entirely.

"On taking the glass body out of the hot water, the internal motions of the liquor recommenced; but the currents had changed their directions, that which occupied the axis of the tube being now the afcending current,

"When

"When the cylindrical tube, inftead of being held in a vertical pofition, was inclined a little, the afcending current occupied that fide of it which happened to be uppermoft, while the under fide of it was occupied by the current which moved (with equal velocity) downwards.

"When the contents of the glafs body had acquired the temperature of the air of the room, these motions ceased, but they immediately recommenced on expofing the inftrument to any change of temperature.

66

In all cafes where the inftrument received heat, the current in the axis of its cylindrical tube, when it was placed in a vertical pofition (and that which occupied its upper fide when it was inclined) moved downwards. When it parted with heat, its motion was in an oppofite directions, that is to fay, upwards.

"A change of temperature, amounting only to a few degrees of Fahrenheit's fcale, was fufficient to fet the contents of the inftrument in motion; and the motion was more or lefs rapid, as the velocity was greater or lefs with which it acquired or parted with heat, and the motion was most rapid in those parts of the inftrument where the communication was not rapid.

"A partial motion might, at any time, be produced in any part of the inftrument, by applying to that part of it any body either hotter or colder than the inftrument. If the body fo applied were hotter than the inftrument, the motion of the faline liquor in it, in that part of it immediately in contact with the hot body, was upwards,-if colder, downwards; and whenever a hot or cold body produced a current upwards or downwards, this current immediately produced another in fome other part of the liquid which flowed in an oppofite direction.

"On inclining the cylindrical tube of the inftrument to an angle of about 45° with the plane of the horizon, and holding the middle of it over the flame of a candle, at the distance of three or four inches above the point of the flame; the motion of the fluid in the upper part of the tube became exceffively rapid, while that in the lower end of it, where it was united to the globe, as well as that in the globe itfelf, remained almoft perfectly at reft.

"I even found that I could make the fluid in the upper part of the tube actually boil, without that in the lower part of it appearing to the hand to be fenfibly warmed. But when the flame was directed against the lower part of the tube, all the upper parts of it in contact with the liquid, and especially that fide of it which was uppermoft as it lay in an inclined pofition, where the afcending current was most rapid, where it impinged against the glass, were very foon heated very hot.

"The motions in oppofite directions, in the liquid in the tube, were exceedingly rapid on this fudden application of a ftrong heat, and afforded a very entertaining fight." P. 237.

In corroboration of the above-mentioned doctrine, the author proceeds to relate feveral experiments, which prove, that

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