CALORIC. 



Witliont further iiifidliiT, liowevcr, tliat we can conclu- 

 fivtly (lemonlti-ate the cxilknce ol caloric, it at leall appears 

 upon tlie whole, that, in the prcfciit itate of our knowledge, 

 we ought rather to confuier it as a material fubllanee, be. 

 caiifc of the two theories, that whieh fiippofes it to be fo is 

 infinitely the mod intelligible, the molt agreeable to the ana- 

 logy of nature, and the leaft exceptionable ; and we fliall 

 accordingly regard it as an elallic fluid fui generis, capable 

 of pervading with various degrees of facility, all tile folid 

 bodies with which we are acquauued, and of being imbibed 

 and retained by them in different proportions according to 

 their refptftive degrees of fpeciiic atlradion or capacity 

 for it. See Capacity. 



It will eafily be conceived that from the eladicity and 

 power of pervading other fuhilances, wliicli we have attri- 

 buted to this fluid, it mull necelTarily follow, that whenever 

 a bcdy is by any means charged with a larger quantity of it 

 than is proportional to its niafs and capacity, wlien com- 

 pared with th'jfe of other bodies in its vicinity, the fnrplus 

 will be communicated to thofe other bodies, until the denlit v 

 of the fluid in every body in the fyllem becomes equal ; in 

 like manner as a quantity of air thrown into one of a num- 

 ber of vefTels com iiunicating with each other will pafs from it 

 to the others, uritil it becomes diftributedamongll the whole 

 of them in proportion to their refpeftive capacities, or till it 

 becomes of equal denfity in all of them. This (late of den- 

 fity or comprtflion of the caloric, contained in a body, cou- 

 ilitutes what is called its temperature ; fee this article. 



The celerity and facility with which this fluid pervades 

 different fubflancesare however extremely various, as maybe 

 (hewn by the following experiment. Take a fmall cyhndri- 

 cal earthen or wooden veffel, between three and four inches 

 ill diameter, and infert into it, through holes drilled in its 

 bottom for that purpofe, feveral wires, about an eighth of an 

 inch in diameter, and lix or feven inches long, of equal fize in 

 every refpedl, but of different metals, as i;oId, filver, copper, 

 iron, brafs, and zinc ; and alfo two fmall rods, one of glafs 

 and the other of wood, of equal dimenfions with the wires, 

 fo that they may each of them project about half an inch 

 on the infide of the veffel, the reft of them being on the out- 

 fide, and forming a kind of (land for it. Dip a portion of 

 the inferior extremities of thefe wires and rods into melted 

 wax, fo that they may become equally coated with it. When 

 the wax has cooled, fill the vcflel with a heated fluid, as 

 boiling water or melted lead, and obferve the intervals be- 

 tween the time of filling it and the melting of the wax, 

 which intervals will indicate the relative condufting power 

 of the fubftances. Dr. Ingenhoufz tried this experiment, 

 though in a fomewhat different manner, with wires ot filver, 

 copper, gold, tin, iron. Heel, and lead, whole condutling 

 powers he conceived to be in the order in which we have 

 enumerated them, though he found fome differences in the 

 rtfults, except with regard to the filver and lead, of which 

 the former always appeared to be the bell, and the latter 

 the woril conduftor. In the experiment which we have de- 

 fcribed it will be found, that the condufting powers of glafs 

 and wood are almoll infinitely fmaller than thofe of any of 

 the metals which are the bell condnftors known. Fluids of 

 every kind are almoll peifeft non-conduftors ; and light 

 fpongy fubftances, or fuch as contain fluid?; in their inter- 

 iijces, conduft heat with great flownefs and difficulty. 



This difference in the condufting powers of various fub- 

 ftances is the fource of many praftical convcniencies and in- 

 conveniencies. The cellular texture of organized fubftances 

 enables them x.6 withftand the cfTefts of change of tempera- 

 ture in the atmofphere, by refifting the pan"age of this fluid, 

 and the wooden handle of a tea-pot, and the cloth made ule 



of lor handling hot iron?, arc familiar cT.amples of the ccar.o. ' 

 mical application of this property. An iron door to a fur- 

 naee will bend hot before the furnace itftlf, if of any earthy 

 compofition, is heated in any confiderable degree. Large 

 iron b.-ir8 or cylinders are made to paf« from the lire for the 

 purpofe of communicating heat to tliofc ovens which arc 

 conHrufted at the fide of kitchen-ranges, and a poker put 

 into a low fire improves it by promoting a fimilar coTimuni- 

 cation amongft the dilTerent portions of the fuel through 

 which it pafles. 



We will, in the next place, confider very fhortly the 

 cfTefts anlliig from the condcnfation or rarefaflion of this 

 fluid in bodies. I'.y the former their tempci-ature is elevated, 

 or they are heated ; by the latter it ii< deprcffed, or they 

 become cooled. 



In our inveltigation of the moft univerfal operations of 

 nature we generally find that the more immediate inflru- 

 ments employed fur the produclion of the cffefts which wc 

 perceive are two counterafting powers, by whofe co-opera- 

 tion and mutual counterpolfe the ncccfl'ary equilibrium is 

 preferved, and the purjiofcs of their creation cll'cfted with 

 greater regularity than would probably refult from the em- 

 ployment of a fingle agent. Thus, gravity is, as we know, 

 counterafted by inertia, that tendency whieh all bodies have 

 to continue in a ftatc of reftilinear motion, when once tliey 

 are thrown into it by the impulfe of force. The cffefts of 

 cohefion, a no lefs univerfal principle than gravity, are in 

 like manner reftrained and modified by the agency of caloric ; 

 and, as without inertia all the celellial bodies would be 

 drawn together into fome one part of extendcc'! fpace, fo, 

 without heat all the matter iu the univerfe would become a 

 congealed and concrete mafs ; and fluidity, organization, ve- 

 getation, and life could have no exiftcncc. SohJs become 

 firft expanded, and then liquified by its influerce, and liquid) 

 affume the aeriform ftate. It is cfl'entiai to the idea of a 

 folid body, that it fliould in a certain degree refill both com- 

 preffion and dilatation, that is, that its particles fliould repel 

 each other when brought nearer together, and attraft each 

 other when farther feparated within cctain limits, and it is 

 incontrovertible, that they can only remain in a quiefcent 

 ftate by the equilibrium of thefe oppofitc forces. The lat- 

 ter of thefe cunftitutcs cohefion, and the exiftence of the 

 former is, perhaps, attributable to the fubllanee of whieh we 

 are now fpeaking. Be this as it may, it i} at leall a faft, 

 that the repulfive energies of thefe corpufcles are increafcd, 

 and the fphete of aftion enlarged by its mfluence, for the 

 body becomes expanded ; that is, this equilibrium no longer 

 takes place, unltfs its moleculas are removed farther from 

 each other than when it was at a lower temperature. Elevate 

 its temperature ftill farther, and the body fules; that is, the 

 attraftive power of its particles becomes annihilated or 

 wholly counterafted, and they are only kept together like 

 a quantity of fliot by the aftiun of gravity, operating inde- 

 pendently on each. Incrcafe Uill the aftion of heat on the 

 body, an<l the fphere of rcpulfion of its particles, or the dif- 

 tance, to which this power operates, again becomes much 

 farther extended, perhaps infinitely fo ; it is now fuflTieitnt 

 to overpower the aftion of gravity, and the body becomes 

 refolved into an elaftic fluid. Wc know of no fubftancc 

 which is capable of refilling the power of this univcrfp.l fol- 

 vent. Gold itfclf may be expanded into vapour by the 

 aftion of heat, and as thefe cflTefts are always producible by 

 the fame caufe, fo is it, at leaft, probable, that the converfc 

 of thi,; is alio true ; that v.henever a fubftancc is formed in 

 a ftate of fluidity it i- attiihiuable foUly to this caufe, and 

 that the abflraftion of the caloric, by which it is holdcn in 

 folution, would again redtice it to a folid. Mercury is, wc 

 5 K 2 know, 



