appeared as clear and as tranfparent as a piece of the finest rock cryftal.' P. 61.

We are not, however, convinced that the circumstances in that experiment will bear him fully through his conclufion. Steam we know will become tranfparent when confined, and clouds enfue on the admiffion of cold air; but the clouds feem to arise from the refraction of light through fluids of different denfities, as the tranfparent fteam and cold air must be, and no conclufion can be drawn, without farther trial, how much the one is cooled and the other heated. When the ice was put in this transparent steam, the melting fhowed that team really communicated its heat; but it formed water, not air; and the water, by continued heat, produced team in a tranfparent vapour, fo that as no fluid differing in denfity from the team was produced, no cloudiness enfued. In other refpe&s, we find no reason to retract the objections we once made to our author's opinions in reviewing the above-mentioned papers. The objections, however, relate chiefly to count Rumford's (then fir Benjamin Thompson's) explanations. With regard to this part of the subject, we are inclined to think, that steam is a conductor of heat; for it communicates its own heat to furrounding bodies, and may therefore communicate additional heat. The count fuppofes, that fteam cannot be chemically changed by additional heat; but, if Sauffure's experiments are faithfully related, the water appears to be decompounded and to become air, either by additional heat or by evaporating from different metals.

The count contends that flame is not a conductor of heat, and that its activity, when impelled by the blow-pipe, arifes from its impinging in fucceffive eddies. He found that whatever kind of air was forced through the blow-pipe, the effects were the fame; but we believe that chemifts in general, who employ vital air with this inftrument, think differently. On the whole, this is not fully proved. Flame is only red hot vapour, and muft, in its different affinities, be the fame as the va pour not ignited; and the queftion is of lefs importance, as the practical conclufion, that the greatest heat is at the apex, not the fide of the flame, is fufficiently established by common experience.

The experiments with boilers of different kinds, we find it difficult to analyfe with advantage. Thofe who would derive benefit from them muft read the whole. In general, dry wood is more œconomical than moift; the bottoms of the boilers must be as thin as is convenient with ftrength; the flame fhould be confined to the bottom of the boiler, and though in general large boilers are more economical than small ones, there is a maximum in the fize above which they become dif ́advantageous.

For the account of different kitchens conftructed by the author, and the particular advantages of many of his contrivances, we refer to the work itself. But we cannot refrain from ranfcribing the following account of a military kitchen, and of a portable boiler. The former is on the plan of closed kitchens for poor houses.

I lately had an opportunity of fitting up a kitchen on these principles, in the conftruction of which there was not a particle of iron ufed, or of any other metal, except for the boiler. On the approach of the French army under general Moreau in August laft, the Bavarian troops being affembled at Munich (under my command) for the defence of the capital, the town was fo full of foldiers, that feveral regiments were obliged to be quartered in public buildings, and encamped on the ramparts, where they had no conveniences for cooking. For the accommodation of a part of them, four large oblong fquare boilers, composed of very thin fheet coppers well tinned, were fitted up in a mass of brick-work in the form of a crofs; each boiler with its feparate fire-place, communicating by double canals, furnished with dampers, with one common chimney, which ftands in the centre of the crofs. The dampers are thin flat tiles; the grates on which the fuel is burned are compofed of common bricks, placed edgewife;and the paffages leading to the fire-place, and to the afh-pit, are clofed by bricks which are made to flide in grooves.

Under the bottom of each boiler, which is quite flat, there are three flues, in the direction of its length; that in the middle, which is as wide as both the others, being occupied by the burning fuck. The opening by which the fuel is introduced is at the end of the boiler farthett from the chimney; and the flame running along the middle fiue to the end of it, divides there, and returning in the two fide flues to the hither end of the boiler, there rifes up into two other flues, in which it paffes along the outfide of the boiler into the chimney. The boilers are furnished with wooden covers divided into two equal parts, united by hinges. In order that the four boilers may be transported with greater facility from place to place, (from one camp to another for inftance) they are not all precisely of the fame fize, but one is so much less than the other, that they may be packed one in the other. The largest of them, which contains the three others, is packed in a wooden cheft, which is made juft large enough to receive it. In the smallest may be packed a circular tent, fufficiently large to cover them all. In the middle of the tent there must be a hole through which the chimney must pass. The four boilers, together with the tent, and all the apparatus and menfils neceffary for a kitchen on this conftruction for a regiment confifting of a thousand men, might easily be transported from place to place on an Irish car drawn by a fingle horse. P. 154.

• There is one more invention for the ufe of armies in the field,

which I wish to recommend, and that is a portable boiler of a ligh and cheap construction, in which victuals may be cooked on a march. There are so many occafions when it would be very defirable to be able to give foldiers, haraffed and fatigued with fevere service, a warm meal, when it is impoffible to stop to light fires and boil the pot, that I cannot help flattering myself that a contrivance, by which the pot actually boiling may be made to keep pace with the troops as they advance, will be an acceptable prefent to every humane officer and wife and prudent general. Many a battle has undoubtedly been loft for the want of a good comfortable meal of warm victuals to recruit the ftrength and raise the spirits of troops fainting with hunger and exceffive fatigue.' P. 157.

Plates are added, with proper explanations. The defcription of the perpetual lime-kiln offers fome valuable improve

ments.

The fubject of the feventh effay was intended to be the conftruction of kitchen fire-places and kitchen utenfils; but, as all the experiments were not finished, the author has filled it with obfervations on the manner in which heat is propagated in fluids; on a remarkable law found to prevail in the condenfation of water with cold, when near the freezing point, with its effects in the economy of nature: to which are added conjectures refpecting the final caufe of the faltness of the fea.'

We have used, with our author, the term conductor of heat, without accurately defining his meaning. It is neceffary now to be more clear and definite. When heat, as in metals, is communicated from one particle to another, while these particles are at reft, the body is properly called a conductor of heat; but, when there appears to be no for a very flight) communication of heat between these particles, while at reft, the body is faid to be a non, or a bad, conductor of heat. Probably a perfect non-conductor is not known, but many bodies are very imperfect conductors. Air is certainly fo, and water perhaps does not greatly excel air in that refpect. Those who have been accustomed to mix warm and cold water, particularly in tempering baths, must be convinced of this fact; for it requires long time and frequent agitation before the temparature of the bath is uniform. If water and air then were at reft they would conduct heat very flowly, but they are never in a state of perfect tranquillity, and the motion of the particles on each other, which conflitutes their fluidity, enables them to conduct heat fo well as they do. The particles by these motions communicate their heat to the furrounding veffel, which in turn heats the contiguous particles of fluid. The first fuggeftion of this method of communicating heat was, from obferving the motion of the particles of fpirit

of wine in a thermometer, rendered confpicuous by accidental impurities; and a fimilar inteftine motion may be obferved in boiling fluids. The writer accounts for any pulpy fubstance, or, in reality, any gluten added to water, rendering the fluid a worfe conductor of heat, by preventing this inteftine motion. We formerly explained the effect, from the difficulty with which a particle of water communicates its heat to a particle of the down or pulp, while the contiguous drop receives the heat with equal difficulty, fo that heat is tranfinitted through fuch fubftances with a flownefs proportioned to the number of particles interpofed, in other words to the finenefs of the down or pulp. Probably both caufes may have their influence; but whatever may be the reafon, the difficulty of communicating heat may be the final caufe, as our author alleges, of the vifcolity of the fluids of plants. They retain in this way the heat communicated by the ground more tenacioufly, and, for this reafon probably, the vifcidity of the fap is increafed in winter. We well know, that geraniums and many fucculent plants of warin climates, may expofed to the common colds of our winters with impunity, by a gradual fubtraction of their ufual fupply of water.

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Our author brought his doctrine of the communication of heat in water, by the commotion of its particles, to the test of experience, by mixing powdered amber in water. Amber he chofe as it refembles water fo nearly in fpecific gravity, while the excels of gravity in the amber was compenfated by increafing that of the water, which for this purpose had fome falt diffolved in it. His method was unneceffarily operafe, for the fame effect might have been produced by a more minute divifion of any heavier body.

It is nevertheless a very pleafing and inftructive experiment, relembling that in common ufe, by which it is proved that no heat is felt at the bottom of a tea-kettle while boiling, though it is perfectly and painfully fenfible when the boiling ceafes. Yet the latter part of the phænomena is not peculiar to water, for we found the fame want of communication of heat in boiling mercury, in the torricellian tube. To make the vacuum more complete, the mercury was boiled in portions from the bottom to the top, before it was inferted into the bafin; and, though fome defence was required for the hands while the under portion boiled, and the tube was held by the top, the upper portions, when boiling, communicated no heat below. Perhaps the fame law takes place in all fluids; at least the inquiry is not unimportant, and our author hints at it in P. 241.

The count's next object was an inquiry into the communication of heat from water to ice. This inveftigation prefents

fome very curions and unexpected refults. By pouring boiling water on ice, lefs than part of the heat loft by the water was communicated to the ice; and the ice melted eighty times more flowly at the bottom than at the top of the water. This might be fuppofed in fome measure from the former experiments, fince the heat afcends, and the ice might have remained unaffected under the flip of wood which confined it to the bottom, though not in contact except at the edge of the cake, by abforbing heat fafter than the frozen fluid. We know that ice receives heat very flowly. When the ice was covered by a tin plate with a circular hole, it was diffolved only at the part where the cover was perforated. This was a fingular event; but it is ingenioufly explained from fir Charles Blagden's experiments. He found that all fluids were gradually condenfed by cold, in proportion to its intentity, except water, which is condenfed only till it has reached its 40th degree, when it begins to expand as we know, from the feparation of air. When the hot water then reaches the ice, it is foon copled to the 40th degree, and then becomes lighter than the water above, though of a higher temperature. The confequence is, that the hotter water defcends; but the cover pre,vents it from touching the ice, except at the point where the perforation is, and by defcending through it the excavation is formed, which, when over filled, forms a channel over the furface of the cake down the edges. This might have also been the caufe of the ice remaining unchanged under the wood.

Thefe principles lead to an extraordinary fact, viz. that water of 40° will melt as much ice, when ftanding on its furface, as boiling water; and our author has confirmed it by ingenious and operofe experiments. We have preferred giving the foregoing detail in our own language that we might add the conclufion, and the table which refults from it, more at length.. The general deduction is, that whatever may be the heat of the water which is poured on ice, no water above 40° can remain in contact while any ice is left; for the moment the water acquires a lower temperature it afcends, fince the rarefaction produced by the emultion of air is greater than that occafioned by the heat of water under 112°, as it must be when brought from the fire. Our author has, however, confirmed it by experiment, and he finds that 190 grains of ice may be melted by water of 41° in about 10'. These experiments feem very clearly to thow that water is a non-conductor of heat.

Other mifcellaneous experiments were added, and circumftances occurred in thofe above mentioned which contributed to establish our author's principal pofition. The impulfe of the water when poured on the ice mult add to the heat, as we commonly find in heated air; but it feemed to add to the effect, by increating the motion of the particles on cach other. When