them, instead of being bent in its middle, and its two extremities turned upwards, is quite ftraight in the middle; and its two extremities, to which its two balls are attached, are turned perpendicularly upwards, fo as to form each a right angle with the middle part of the tube, which remains in a horizontal pofition.' At one of the elbows of this tube' (continues our author) there is inferted a fhort tube of nearly the fame diameter, by means of which a very small quantity of spirit of wine, tinged of a red colour, is introduced into the inftrument; and after this is done, the end of this fhort tube (which is only about an inch long) is fealed hermetically; and all communication is cut off between the air in the balls of the inftrument and in its tube, and the external air of the atmosphere.' He then goes on to explain the application of this inftrument, by paffing a portion of the liquid into the horizontal tube, and allowing it to remain at the middle joint, in which position it muft continue, while the temperature of the air in the balls, and confequently their elafticity, is equal. But if bodies radiating unequal degrees of heat be expofed to the balls, or if one ball be expofed to a hot body, and the other defended from it, then the liquor will recede from the ball exposed to the greatest elevation of temperature; and if a cold body be applied to one ball, the other being defended from its influence, the liquor will move towards this ball, fo expofed. All this he illuftrates by a figure, and by various explanations. We have defcribed it fufficiently, to prove that the thermofcope is exactly Mr Leflie's elegant inftrument, denominated by him, not a hygrometer, as Count Rumford is pleafed to fay, but a differential thermometer. According to the Count's own ftatement, he borrows the whole idea from that gentleman; yet, with an ardour for discoveries not quite fcientific, he talks of it as his own contrivance, and, with his accustomed love of nomenclature, he gives it a new appellation. The changes which he makes upon the structure, are utterly unconnected with the theory of the inftrument; but it must be remarked that they impede the performance of the experiment. The figure of the tube is both incommodious, and lefs adapted to the eafy paffage of the fluids; while the mode of introducing the liquid by a feparate tube is extremely clumfy, and in every way worfe contrived than Mr Leflie's method. The ufe and operation, as well as the whole that is worth any thing in the Count's thermofcope, is precifely Mr Leflie's, to which he thinks fit to fay, he has invented one like.' Indeed, Mr Leflie had publifhed a defcription of his beautiful contrivance in feveral parts of Nicolfon's Journal for the year 1800; and every chemilt was acquainted both with that general form of the inftrument, and with its application to the purposes of a photometer, long before the year 1803, when Count Rumford's Cca experiments firmation (which it certainly did not), he has taken very great pains, in the elaborate performance now before us, to fupply a variety of new proofs. This inquiry deferves our serious attention in many points of view: The exact coincidence of the only valuable and original matter which it contains, with the late curious and unexpected experiments of Mr Leslie, throws a fufpicion upon one or other of thefe authors which the public have a right to fee removed. The merits of Count Rumford, too, have been fo much a theme of converfation, and have had fuch an active influence in the fashionable world of fcience, that it is proper his pretenfions fhould at length be fifted. But, above all, a paper filled with theoretical matter, abounding in pulfes, vibrations, internal motions, and ethereal fluids, deferves to be expofed; the more, because these chimeras are mingled with a portion of induction, and have received the ill-deferved honour of a place in the Philofophical Tranfactions. We fhall, therefore, enter pretty fully into the fubject of this inquiry, and are not without hopes that both Count Rumford and the public may be benefited by the difcuffion. We fhall confider this paper under its two obvious divifionsthe original experiments which it contains, and the theories in which these are involved. I. It is by no means our intention to argue against the originality of Count Rumford, or of Mr Leflie, from the circumftance of their coincidence in fome minute particulars. Each of these writers begins with ftating the neceffity of previously defcribing his apparatus; and not only do the chief parts of the machinery tally, but we find them both hitting, at the outfet, on the fame important experiment, and then defcribing the effects of this occurrence in opening a wide field of new research, and the eagerness with which they entered this field. Such particulars, we are fenfible, may conftitute merely an accidental coincidence; and had the fimilarity of the two inquiries gone no farther, we certainly fhould not have made the remark. But if we were to ftate the opinion with which a review of the whole work has impreffed us, we fhould fay that Count Rumford had borrowed Mr Leflie's leading difcovery, without completely understanding its nature and extent; that he had purfued it imperfectly, and fo mixed it up with error and fanciful theory, as to disfigure it, and almoft prevent one from recognizing the property. The fame inference will probably occur to fuch of our readers as attend to the following details; and we hope to make it still more obvious in our review of Mr Leslie's work. The apparatus at first employed by Count Rumford, confifted of feveral very delicate and accurate mercurial thermometers, with long cylindrical bulbs, inferted in cylinders of steel ors brafs, to the whole extent of the bulb. Thefe cylinders were filled with hot water, and coated on the outfide with various thin fubftances. The cooling of the water was observed by the finking of the mercury, and noted down at different times, The ends of the cylinders were fometimes defended by various bad conductors of heat, as eider-down, varnish, &c.; and first, it was afcertained by various trials, that the defcent of the thermometer through any given fmall number of degrees, was performed in equal times, at all heights and all temperatures of the atmosphere, provided the heights were equally above the temperature of the atmosphere. The interval he generally chose, was that between the fiftieth and the fortieth of Fahrenheit above the temperature of the atmosphere. Although he generally was able to note the defcent at small intervals, yet, for the fake of continuity, our author obferves that he endeavoured to inveftigate the law of the cooling of hot bodies in a cold fluid medium,' and found reafon to conclude that a logarithmic will have its ordinates proportional to the degrees of the thermometer, the abfciffa being taken proportional to the times.' He had, indeed, good reafon to draw this conclufion; for Sir Ifaac Newton and Brook Taylor, luckily for Count Rumford, long ago inveftigated this very law, and recorded the refult in the earlier numbers of the Philofophical Tranfactions, where our author probably found it, and thus may be faid to have discovered it. This, however, was the general rationale of the experiments first performed: we proceed to the refults of the trials themfelves. One of the cylinders, prepared and filled as above, being coated with thin Irifh linen, and the other expofed to the. air, bright and polifhed, without any coating, the times of cooling were repeatedly noted. The covered veffel: cooled from 94° to 84° in 364 minutes the uncovered in 55 minutes. Both having at laft cooled nearly to the heat of the atmosphere, they were removed into a warmer room, and the covered inftrument received heat confiderably faster than the naked one. In cate the linen might produce this effect by preventing the adhesion of the air to the veffel, the experiment was repeated with coats ings of glue and of fpirit varnish, with the fame refults; only, that beyond a certain number of coatings the paffage of heat was not accelerated. For the coating of varnish, black and white fize paint were fubftituted, and then the tarnish of a candlefame, with the fame effect. Our author computes, by an eafy calculation, the quantity of heat which paffes through the des of the inftrument, that is, through the parts compared together VOL. IV. NO. 8." and and, reducing the whole of the refults to one standard, it ap pears that the velocity with which the heat paffed through the polifhed furface, is to the velocity with which it paffed through the fame furface covered with four coats of spirit varnish, as 4,566 to 10,000, (for this is evidently the proportion, though our author reverfes it by miftake in p. 101.); and that the velocity of its paffage through the plain metal is to the velocity of its paflage through the metal tarnifhed with fmoke, as 5,654 to 10,000. The coating of fmoke which produces fo great a difference cannot poffibly be more than of an inch in thicknefs. Now, we are forcibly ftruck, we acknowledge, with the exact coincidence between all thefe curious experiments, and thofe of Mr Leflie, as detailed in the fixteenth chapter of his Inquiry into the Nature and Propagation of Heat. The fame series of obfervations upon the cooling of hot water through plain and coated veffels--the fame fort of calculations, though certainly much better inftituted the fame obfervation of an uniform increase of cooling or heating, by coats of ifinglafs and lampblack, form the prominent features of both inductions. Mr Leflie's experiments, however, are more various and masterly; his mathematical illustrations and proofs are much more skilful; and, though we are not prepared, in this place, to examine the truth of his remote theoretical deductions, we are fatisfied with the accuracy of his intermediate refults, which far exceed thofe of Count Rumford in their number and generality. The next part of the inquiry now before us, is, however, ftill more ftriking, from its coincidence with Mr Leflie, to whom the author has not been able to conceal his obligations, although he has certainly abstained from acknowledging them. He commences his next courfe of experiments with stating, that he found it neceffary. to contrive an inftrument for measuring, or rather for discovering thofe very fmall changes of temperature in bodies, which are occafioned by the radiations of other neighbouring bodies which happen to be at a higher or at a lower temperature. p. 1o. This, too, is the precife object of Mr Lelie's differential thernometer; and, how far the fame end has been attained by fimilar means in the two cafes, let the following moft fingular paffage determine. This inftrument (fays Count Rumford) which I fhall take the li berty to call a thermofcope, is very fimple in its conftruction. Like the bygrometer of Mr Leflie (as he has chofen to call his inftrument) it is compofed of two glafs balls, attached to the two ends of a bent glas tube; but the balls, inftead of being near together, are placed at a confiderable distance from each other; and the tube which connects them, them, inftead of being bent in its middle, and its two extremities turned upwards, is quite ftraight in the middle; and its two extremities, to which its two balls are attached, are turned perpendicularly upwards, fo as to form each a right angle with the middle part of the tube, which remains in a horizontal pofition.' At one of the elbows of this tube' (continues our author) there is inferted a short tube of nearly the fame diameter, by means of which a very small quantity of fpirit of wine, tinged of a red colour, is introduced into the inftrument; and after this is done, the end of this fhort tube (which is only about an inch long) is fealed hermetically; and all communication is cut off between the air in the balls of the inftrument and in its tube, and the external air of the atmosphere.' He then goes on to explain the application of this inftrument, by paffing a portion of the liquid into the horizontal tube, and allowing it to remain at the middle joint, in which pofition it muft continue, while the temperature of the air in the balls, and confequently their elafticity, is equal. But if bodies radiating unequal degrees of heat be expofed to the balls, or if one ball be expofed to a hot body, and the other defended from it, then the liquor will recede from the ball exposed to the greatest elevation of temperature; and if a cold body be applied to one ball, the other being defended from its influence, the liquor will move towards this ball, fo expofed. All this he illuftrates by a figure, and by various explanations. We have defcribed it fufficiently, to prove that the thermofcope is exactly Mr Leflie's elegant inftrument, denominated by him, not a hygrometer, as Count Rumford is pleafed to fay, but a differential thermometer. According to the Count's own ftatement, he borrows the whole idea from that gentleman; yet, with an ardour for discoveries not quite fcientific, he talks of it as his own contrivance, and, with his accuftomed love of nomenclature, he gives it a new appellation. The changes which he makes upon the structure, are utterly unconnected with the theory of the inftrument; but it must be remarked that they impede the performance of the experiment. The figure of the tube is both incommodious, and lefs adapted to the eafy paffage of the fluids; while the mode of introducing the liquid by a feparate tube is extremely clumfy, and in every way worfe contrived than Mr Leflie's method. The ufe and operation, as well as the whole that is worth any thing in the Count's thermofcope, is precifely Mr Leflie's, to which he thinks fit to fay, he has invented one like.' Indeed, Mr Leflie had publifhed a defcription of his beautiful contrivance in feveral parts of Nicolfon's Journal for the year 1800; and every chemift was acquainted both with that general form of the inftrument, and with its application to the purposes of a photometer, long before the year 1803, when Count Rumford's Cca experiments |