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have had to !)uil(^ upon, he has had the advantage of 

 a new let, which they v.'crc unacquainted wkh. 

 As to the nature of Hre, the great and fundamental 

 difference is, whetl:er it be originally fucli, formed 

 thus by th?grt-'<it Creator himielf, at tlie beginning of 

 thin'^s ? or, whether it be mechanically producible 

 fronT other bodies, by Inducing fonie alteration in 

 the particles of it ? 



Amon^^ the modern writers, Homberg, Boerhaavc, 

 the youncrcv Lemery, and Dr. Gravefande, maintain 

 the former, and the Englifh authors chiefly maintain 



rhc latter. 



Monf. Homberg holds, That the chymical principle 



or element, fulpliur, which is fuppofcd one of the 

 fimple, primary, pre-exiftent ingredients of all natu- 

 ral bodies, is real fire ; and, of confequence, fire is 

 coeval with all bodies. Effai de Souffre Principe, 

 Mem. de I'Academie, anno 1705. 

 Dr. Gravefande proceeds much on the fame princi- 

 ple : according to him, fire enters the compofition of 

 all bodies, is contained in all bodies, and may be fe- 

 parated or procured from all bodies, by rubbing them 

 againft each other, and thus putting their fire in 

 niotion : and he adds, That fire is by no means gene- 

 rated byfuch motion. Elem. Phyf. Tom. II. cap. i. 

 Mr. Lemery the younger, afTerts the abfolute and in- 

 gcnerable nature of fire, and alfo extends it farther ; 

 not contented to confine it, as an element, to bodies, 

 he endeavours to fhew, that it is " Equably diffufed 

 '' through all fpace j is prefenx in all places ; in the 

 " void fpace between bodies, as well as the infenfible 

 " interftices between their parts." Mem. de I'Acad. 



anno 1713. 



This laft fentiment falls in with that of Boerhaave. 

 Of the contrary opinion is tlie Lord Bacon, who, in 

 his treatife de Forma Calidi, deduces from a great 

 number of particulars, that heat in bodies is no other 

 than motion, only a motion fo and fo circumftanti- 

 . ated ; fo that to produce heat in a body, nothing is 

 required but to excite fuch motion in the parts of it. 

 His opinion is feconded by Mr. Boyle, in his treatife 

 of the Mechanical Origin of Heat and Cold -, where 

 he maintains the fame do6trine, with new obferva- 

 tions and experiments, of which two are as follow: 

 He fays, " In the produ6lion of heat there appears 

 " nothing on the part either of the agent or patient 

 " but motion, and its natural effects. When a fmith 

 ** brifldy hammers a fmall piece of iron, the metal 

 .thereby becomes exceedingly hot; yet there is no- 

 " thing to make it fo, except the forcible motion of 



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",thehamm'ei*, imprefilng a vehement and variouQy 



" determined agitation on the fmall parts of the iron > 



;; " which, being a cold body before, becomes by that 



*' fuperinduced commotion of its fmall parts hotj 



V firft, in a more loofe acceptation of the word, with 



^.**. regard tbfome other bodies, compared Avith which 



'^ •* it. was cold before •, thenfenfibly hot, becaufethis 



■-"■^g^tation fenfibly furpafles that of the parts of our 



"fingers. And in this inftance oftentimes the ham-' 



mer and anvil continue cold after the*operat1dn-, 



:Vv;hich fhews,,that the heat acquired by the iron 



" was not communicated by either of thefe . imple- 



;" ments, as heat, but produced in it, by a qiotion 



. " great enough ftrongly to agitate the parts of fo 



: ". foiall a body as the piece of iron, without being 



'V able to have the like cfFed upon fo much greater 



"mafles of metal as the hammer and anvil; though 



V "u the percuffions were often and brifkly renewed, 



." and the hamnier W'cre fmall, this alfo might be 



*| heated ; whence it is not neceflary, that a body it- 



" lelf fhould be hot to give heat. - , , 



It a large nail be driven by a hammer into a 

 plank ot ^yood, it will receive feveral flrokes on its 

 head, ere it grows hot ; but when it is once driven 



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rV J^^^^' a few flrokes fuffice to give it a con- 

 liderable heat; for while at every blow with the 

 hammer the nail enters farther into the wood, the 

 motion produced is chiefly progreffive, and is of the 

 \vhole nail tending one way ; but, when the mo- 

 tion ceafes^ the impulfe given by the ft'roke being 



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'' unable to drive the nail farther on or break it, muft 

 " be fpent in n:iaking a various, vehement, and in- 



*' tefhne commotion of the parts among thcmielvcs, 

 ^' v/herein the nature of hear confuls." 

 That fire is the real caufe of all the changes in na- 

 ture, wall appear from the following conficreration. 

 All bodies are either Iblid or fluid ■, the folid of them- 

 felves are either commonly fuppofed to be inactive or 

 motionleis ; the ikiid both move and are m^oved. 

 And all folids are found to be fo much the more firm 

 and contrafted, as they have the lefs fire in them. 

 This is evident in iron, which, when heated, expands 

 itfelf into a much greater fpace than when it was cold ; 

 fo that any folid and hard body, by being freed from 

 all fire, would fink into a much Icfs bulk, and its 



parts would cohere more nearly, and with greater 

 force than before. 



As to fluids, they all harden, {o as to be vifible to 

 the eye upon the abfcnce of fire ; as water, by the 

 cold of a fcverc winter, wnll form itfelf into a folid 

 globe, and yet even then contains a great deal of fire, 

 as appears evidently upon applying a thermometer to 

 it, which is capable of falling twenty divifions lower 

 before it arrive at the point of the mofl intenle cold : 

 and hence it is, that the fpirit of v/ine is kept from 

 freezing in the thermometer, which v/ould undergo 

 the common fate of other things, were there not 

 abundantly more fire in it. 



The air itfelf expands by a greater quantity of fire, 

 and condenfes by a lefs ; but it ftill contains a large 

 quantity of- fire, where it is moft of all contradled ; 

 this is evident from the ftriking of a flint againfl: a 

 fteel, which is followed by fparks of fire, 

 Likewife if this fire could be taken from the air, it • 

 would become folid and perfeftly at refl:, and, by con- 

 fequence, uncapable of change. 



Fire (fays Dr. Gravefande, in Element. Phyf) na- 

 turally unites itfelf with bodies ; and hence it is," 

 that a body brought near to the fire grows hot, 

 *' in which cafe it alfo expands or fwells ; which ex* 

 " panfion is not only obferved in very folid bodies, 

 ^* but in thofe whofe parts do not cohere ; in whicff' ' 

 ** cafe they likewife acquire a great degree of elaf- 

 " ticity, as is obferved in air and vapours." 

 Fire being thus acknowledged the inftrumental caufe 

 of all motion, it remains that itfelf be moved ; nay, 

 to move, muft be more natural and immediate to fire, 

 than to any other body ; and hence fome have ventured 

 to make motion eiTential to fire :^ but as this is incon- 



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fiftent with the notion of matter, which is defined to 

 be inert: and paflive,' and as fire is capable of being 

 proved material, we diight rather to agree, that the 

 motion of fire itfelf is derived frdfft f6nie higher and 

 metaphyfical caufe. A property of perpetual mo- 

 bility may indeed be fuperadded to the other proper- 

 ties of fire, but it has no natural neceflary connexion 

 with them; nor can it be maintained with them 

 otherwife than by fome extrinfic efficacy of afupeTior 



-caule. ;■ - *■' ■ '' - ^'-'^ ■ ^^--^v-*:-. 



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However, that it is by motion that fire produces its 

 ■ effefts, is evident ; and hence the adion of fire can- 

 not make any alteration in the elementary fubftance 

 , ;of bodies ; for it is neceflfary, that what ads upon an 

 " objeft, be without that objeft, i. e. the fire muft not 

 ^^penetrate the elementary parts, but only enter the pores 

 and interftices of bodies ; fo that it does nof feem ca- 

 : pable of making thofe tranfmutations, which Sir Ifaac 

 Newton afcribes to it. ' ''^ ' '"'^ /^ V. - 

 In effe£t, as to all our puVpofes, it may perhaps be 

 faid, that fire is always in motion.. For inftance, 

 take fix feveral forts of thermometers, and two vef- 

 ^ fels of water with fal armoniac mixed therein, and ap- 

 ply the thermometers to itVand the confequence will 

 be, that the air being condenfed in them, the fpirit 

 will defccnd in all of them : remove the veffels of 

 ■ water, and the air growing warmer, and rarefying, 

 the fpirit will afcend again ; fo that the aftive force 

 in air, which produces fo many effects, does really aU 

 arife from the fire contained in it. , - .; ^"rf : 



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