CALORIC. 



'VhtTt »re pwlijps fov fubjefts refpeftinj? winch a more 

 remarkablt vcrfmility of general opinion has been evuiced, 

 then wiih rcrard to the cxillence or non-exillcnce ol this 

 pnaciple. Arc the ph) fical cffeas of heat productd by the 

 ooeration of a material 6M fui ge'i^ris, or .s heal men.y an 

 iffcclion of matter, confilUng in internal vibrations and col- 

 lii"u3iis of its particles, or in fome other mode of corpnlcu- 

 hradion of which wc arc ignorant ;— and is there confe- 

 qucntly no fucli thing as caloric ? . , ,,r 



Zcno, it appears conceived that heat was material. We 

 have a curiuiu dillettatioij on this fubjea in Cicero's book, 

 •' Dc N'jluii Deorum," conlilling of a dialogue between 

 an epicunan, a Diatonic, and a lloic, iLfpcding the Supreme 

 Power, which the latter fuppoles to rttide principally in the 

 fun ; and it is remarkable that the autiior has made him 

 fpeak of the materiality and nature of heat very nearly as 

 we do at the prefcnt day. " Thai i.tat is combined with 

 water," he fays, " its liquefadion itfelf fuflicieiitly proves, 

 nor can it either freeze or congeal into fnow or hoar-froft 

 without I'ulfering that heat to efcape." * * * * " Even the 

 air, however cold it may be, is by no means devoid of heat ; 

 indeed it is combined with a great deal of heat ;" and more 

 to this clfctt. 



This indeed appears to have been the mod gen-rr'l notion 

 rcfpefting this part of the fubjeft till about ti-' time of 

 Lord Chancellor Bacon, who in his treatifc " De Forma 

 Calidj" confiders heat as the effed of an inteftine motion 

 or mutual coUifion of the particles of the body heated ; an 

 expanfive undulatory motion in the minute particles of the 

 body, by which they tend witli fome rapidity towards the 

 tircuinference, and at the fame time incline a little up- 

 wards ;" which idea was alfo with fome modification adopt- 

 ed by Defcartes, Newton, Boyle, and the other mechanical 

 philofophers of that and the fucceeding age. The tliemills, 

 however, whofe opinions, at leall, pofTefs that degree of au- 

 thority whicli arifcs from their being moil ufed to the ob- 

 fervation of the effefts of this agent, feem to have ftill re- 

 tained a ftrong notion of the materiality of heat, which, in 

 confcquencc of our improvement in chemical fcicnce, again 

 became general, ad continued fo till the experiments of 

 Count Rumford, which appeared to ihew that it was im- 

 ponderable and capable of being produced ad infinitum, from 

 a finite quantity of matter, again threw fome doubt on this 

 qucllion. 



It is kiiown that when water freezes, a portion of heat is 

 given out by it during the congelation, which is fo confi- 

 dcrable, that if we were to conceive it to be tranfmitted to 

 »nd imbibed by an equal quantity of water at the tempera- 

 ture of 32° of Fahrenheit's thermometer, the latter would 

 be heated no lefs than 140°, or to 172°. If, therefore, 

 heat v.erc a ponderable fubftance, it might be imagined that 

 4 given quantity of water would become lighter when frozen 

 in a velRl hermetically fealed. Count Rumford accordingly 

 made this experiment with great care by the help of a ba- 

 lance of extreme accuracy ; but the refult was, that the ice 

 produced appeared to be of precifcly the fame weight as 

 the water had originally been of at the temperature of 61°, 

 viz. 4214.28 grains ; from which he infers, that all attempts 

 to difcover any effcfl of heat on the apparent weights of 

 bodies will be fruitlcfs. 



The other deduGion, of the poffibility of producing an 

 inexhauftible fupply of heat from a given quantity of mat- 

 ter, was made from the following experiment. The Count 

 eaufed a cylinder of brafs to be turned yi inches in diameter, 

 and 9.8 inches long, which was bored like a cannon with a 

 calibre 3.7 inches in diameter, and 7.2 deep, fo that the 

 bottom was a. 6 inches m Uiickncfs. The hoUow cylindtr 



6 



contained 385 J cubic inches of brafs, and weighed 113.T3 

 lbs. avoirdupoife. By means of the engine ufed for boring 

 cannon in the arfenal of Munich, a blunt borer or fl.it-piece 

 of hardened fteel, 4 inches long, 0.63 inch thick and .5f 

 inches wide, was kept with one of its extremities, whofe 

 area was about 2^ fquare inches, prtffed againft the bottom 

 of this hollow cylinder on the infide with a force of about 

 loooo lbs. avoirdupoife, whilft the latter was turned about 

 its axis with a velocity of 32 revolutions in a minute. The 

 cylinder was in one experiment covered on the ontfide with 

 a coating of thick flannel to prevent the accefs of heat from 

 the atmofphere ; in another the borer was made to work 

 through a collar of leathers fo as to prevent the accefs of 

 air alio to the inttrior of the bore ; in a third, the whole 

 cylinder was immerfed in water, the borer ftiU working 

 through a collar of leathers fo as to prevent its accefs to the 

 interior of the bore ; in a fourth, the collar of leathers was 

 removed, and the water had accefs to the bottom of the in- 

 terior of the cylinder where the friction took place. The 

 refult was, that in all thefe cafes heat was generated by the 

 fridion in fufKcient quantity to caufe about 264 lbs. of ice- 

 cold water to boil in two hours and a half, or at about the 

 fame rate as that at which it would have been producLd 

 by '; large wax candles ; the capacity of the brafs for heat, 

 or .ts power of producing it by friftion,did not appear to be 

 diminiihcd, and it feemed as if this generation of heat would 

 have gone on for ever if the friilion had been continued ; 

 the fource was inexhauftible. Now, as any thing which an 

 inlulated body or fyllem of bodies can continue to fupply 

 without limitation cannot pofTibly be a material fubllance, 

 the Count's inference is, that heat is not of this defcription^ 

 but that it mull be an cfTcil ariling from fome fpecies of 

 corpufcular adtion amongll the conllituent particles of the 

 body. 



We will confLfs, however, that we conceive neither of 

 thefe experiments nor any other with which we are at pre- 

 fect acquauited to be conclulive in favour of the immateri- 

 ality of caloric. Omitting the queftion, whether gravitation 

 is effential to matter, we may obferve that there may be an 

 indefinite feries of material fubllances, each a million of times 

 rarer than the preceding, of which, though the weight of 

 the heavieft be imperceptible by our nicefl balances, the 

 lightell may Hill be ponderable. Any inftruments which 

 we at prefent poflefs would fcarcely enable us to deteft the 

 weight of a fluid which was only a thoufand times lighter 

 than atmofpheric air. 



The other experiment affords an argument againft the ma- 

 teriality of this principle, to which it is perhaps fomewHat 

 more difficult to give a dillinftand decifive anfwer ; and yet, 

 notwithllanding the precautions which were taken, it is by no 

 means demonftrative, that the heat which was evolved was 

 not derived ab cxtero, for there is no abfurdity in fuppofing, 

 that a body may be receiving caloric in one ftate or at one 

 part of it, and giving it out in another. We have an in- 

 llance of the fimultaneous attraftion and emifGon of a fubtle 

 fluid, the materiality of which is admitted by every one, in 

 the cafe of an excited eleilric, which at the fame time re- 

 ceives the fluid from the rubber, and communicates it to 

 the conductor. In Count Rumford's experiment we mull 

 recoUetl, that the whole apparatus was immerfed in a great 

 bath of caloric, the atmofphere. 



With regard to this part of our fubjeft, we ought alfo 

 not to omit, that in another experiment of the fame author, 

 heat luas found to be communicated through aTorrkelUan vacuunu 

 Now it is manifeft, that in fuch a vacuum there could be no- 

 thing to communicate or propagate motion. Heat therefore 

 muft be material : the conelufion is almoil phyitcally certain. 



Without 



