Chap. 3.] NewtorfsandFahrenheiCs'fhermQmeters. in 



proportioned the expansibility of the liquor to the fize 

 of his tube, by diluting it with water, or the contrary; 

 the generality therefore of thermometers made with 

 ipirit of wine are termed Reaumur's thermometers. 



Oil was employed by Sir Ifaac Newton inftead of 

 fpirit of wine, as being capable of a greater degree of 

 expanfion, fince that fluid will bear about four times 

 the heat of boiling water before it boils, and in gene-, 

 ral a very great degree of cold is required to make it 

 freeze. The principal objection to Newton's thermo- 

 meter arifes from the vifcidity of the oil, which occa- 

 fions it to adhere to the fides of the veflel, fo that a 

 confiderable quantity of the fluid being retained by the 

 gkfs, when the thermometer finks, it appears to fink 

 lower at firft than it ought to do, according to the na- 

 tural temperature. 



Thefe thermometers, therefore, were all of them 

 fnperfeded by the famous invention of Olaus Roemur, 

 improved by Fahrenheit, who fubftituted mercury in- 

 ftead of the other fluids. Mercury is found to be a 

 more homogeneous body than any other fluid, and 

 more regular in its expanfions^ befides that it is ca- 

 pable of exhibiting a more copious fcale of both heat 

 and cold. 



Sir Ifaac Newton, obferving that water uniformly 

 froze with a certain degree of cold, and as uniformly 

 boiled when the heat was increafed to a certain degree, 

 took what is called the freezing point for the com- 

 mencement of his fcale, and from that to the boiling 

 point he counted thirty four degrees, and divided his 

 fcale accordingly. It is evident, however, that even 

 in this climate we have many degrees of cold below 

 the freezing point. Reaumur, therefore, though 'he 

 commenced his fcale alfo at the freezing point, yet 

 admits of feveral degrees below it, and proceeds both 

 3 wavs 



