[ 43 ° ] 
irregular than my hygrometer is at prefent. Though 
the firft of thefe inftruments was very fimple in it- 
felf, yet barometers hung up in the lame places ufed 
to vary three or four lines from each other. Some 
of the members of the French Academy have been 
themfelves engaged in confidering a barometer that 
always kept 18 lines below the reft, and they have 
formed various hypothefes to account for this differ- 
ence. The variations therefore of the barometer, 
though obfenved only in the fame place, were much 
greater than thofe between my hygrometers. 
64. Nor was the thermometer itlelf, which is 
now brought to fuch a degree of accuracy, much fu- 
perior at firft to our hvgrofcopes, for the purpofe of 
comparative obfervations. The firft philofophers who 
treated of it knew nothing of any fixed point or de- 
termined degree in it; they knew nothing even of 
the effect produced by the difference of liquids. In 
this ftate of uncertainty the Royal Society adopted the 
moft prudent plan that could be thought of; by- 
giving its fandion to a thermometer to ferve as a 
ftandard for the conftrudion of thofe which philo- 
fophers fhould make ufe of. After this fome men 
of genius endeavoured to eftablifh fixed principles for 
the making of this inftrument. Sir Ifaac Newton led 
the way, but the utility of his firft attempts was not 
fufficiently attended to. Fahrenheit and Reaumur 
then laboured with great care to fettle this point, and 
we are much indebted to their inquiries. But Fah- 
renheit’s principles were foon rejected, as being too 
uncertain, though his fcale was preferved; and Mr. 
de Reaumur’s, though in appearance admitted for a 
longer continuance, were in fad; fo indeterminate, 
2 that, 
