i to Florentine Thermometer. [Book II, 



tity of heat which exifts in bodies, that it foon became 

 an objecb of the utmoil importance, to difcover an ac- 

 curate method for afccrtaining it. The expanfive pro- 

 perty of fire was the property which moft naturally 

 iuggefted itfelf as likely to furnifh an eafy method of 

 accomplifhing this object, fince the evidence of our 

 fenfes affure us that, at leaft in all lower degrees of 

 temperature, the expanfion of bodies bears lome de- 

 gree of proportion to the quantity of the matter of fire 

 which they have imbibed. 



Air, as was intimated in a preceding chapter, was 

 the firft fluid which was employed as a meafure of 

 heat and cold. A fmall tube was prepared, open at 

 the top, into which a quantity of coloured liquor was 

 introduced ; a quantity of air was left in the lower part 

 of the tube, below the liquor, and in proportion as this 

 air expanded or contracted, the heat of the furround- 

 ing medium was fuppofed to be increafed or diini- 

 nilhed. The manifeit inconvenience attending this 

 inftrument was, that as the upper orifice of the tube 

 was necefiarily left open, it was liable to be affected 

 by two caufes, by the natural heat of the medium, and 

 by the weight of the atmofphere preffing upon the li- 

 quor in the upper part of the tube. 



The next fluid that was made ufe of was fpirit of 

 wine, and this, being incloied in a tube which was ex- 

 hauiled of air, afforded an inftrument much more per- 

 fect: than the former. The principal objection to this 

 fpecies of thermometer is, that fpirit of wine is inca- 

 pable of enduring any great degree either of heat or 

 cold, fmce it boils in vacuo at fifty-two degrees. This 

 thermometer is diftinguifhed by the name of the Flo- 

 rentine thermometer, as it was invented by fome of 

 the members of that academy. It was afterwards 

 greatly improved by the celebrated M. Reaumur, who 



proportioned 



