88 Invention of the Thermometer. [Book II. 



though the fire is certainly not generated by fuch mo- 

 tion *. 



One of thefe philofophers (M. Lemery) indeed car- 

 ried his fyftem much further, and made a very near 

 approach to the received doctrines of the prefent day. 

 He afiferted, that fire is not only contained in thofe 

 bodies which are inflammable, but even in water itfelf. 

 Jce he affirmed to be the natural ftate of water ; and 

 he added, that the fluidity of that fubftance is a real 

 fufion, like that of metals expofed to the fire, only dif- 

 fering as to the quantity of heat neceflary to preferve 

 it in fufion f. 



About the commencement of the laft century in- 

 flrnments were firft contrived for meafuring the heat 

 of bodies by the degree of expanfion; and this inven- 

 tion ieemed to give fome colour to the hypolhefis of 

 the German philofophers, fince it is not very clear 

 how a mere increafe. of motion can increafe the ex- 

 tent of bodies. It was long obferved, that all bodies 

 are expanded by an increafe of heatj and it was evi- 

 dent that fluid matters were affected more than folids. 

 The firft fubftance therefore that was employed, was 

 the very expansible and elaftic fluid air; a quantity of 

 this fluid was inclofed within a fmall tube, with a fmall 

 drop of oil, or fome coloured liquor, at the top, which 

 ferved to fhew the expanfion which the inclofed air 

 underwent from the increafe of temperature. As this 

 thermometer, however, was open at the top, it was 

 alfo found to be affected by the prcffure of the ex- 

 ternal air ; tubes hermetically -fealed were therefore 

 prefently fubftituted, and the coloured liquors them- 

 Jelves were found to be fufficiently expanfible to mark 



* The reafons in fupport of each of thcfe theories will be con- 

 litlercd in the following chapter. 

 f MQIH. de 1'Acad. Roy. 1709, 



the 



