for adjujling 'thermometers. 839 
fuch thermometers, yet the heat of the atmofphere never 
differs fo much from the mean heat, as to make that cor- 
redtion of much confequence a> . But, on the other hand, 
this method of making and ufing thermometers is much 
lefs exadt than the former, and therefore is unfit for nice 
experiments ; and, befides, a corredtion would be as ne- 
cefiary with this kind of thermometer in trying the heat 
of air, artificially heated, or in finding the heat of large 
quantities of hot liquors, in which it would be difficult 
to prevent the quickfilver in the tube from being heated 
(k) The degrees on all thermometers are intended to anfvver to equal por- 
tions of the folid contents of the tube; and, confequently, if the quickfilver in 
the tube is kept conflantly of the fame heat as that in the ball, the degrees will 
anfwer to equal increments of bulk of the whole quantity of quickfilver in the 
thermometer, that is of a given weight of quickfilver. But if only the quick- 
filver in the ball is heated, and that in the tube is kept always of the fame heat, 
the degrees will anfwer to equal increments of a given bulk of quickfilver; fo 
that the fcale of the thermometers will be really different in thefe two methods 
of proceeding, and in high degrees the difference will be very confiderable ; for 
example, let two thermometers be made, and in the firfi: of them let care be 
taken, both in adjufting the fixed points and in trying the heat of liquors, that 
the quickfilver in the tube fhall be of the fame heat as that in the ball; and in 
adjufling the fixed points of the fecond, and in trying the heat of liquors with 
it, let care be taken that the quickfilver in the tube fhall remain always of the 
fame invariable heat, and let the freezing and boiling points be marked 32 and 
212 on both of them : then will the degree of 620 on the firfi: anfwer to that of 
600 on the fecond; that of 406 to 400; that of 302 to 300; and that of 
1 19.7 to 120; that is, a liquor which appears to be of 620° of heat by the firfi 
will appear to be of 600 by the fecond, &c. It appears from hence, that it would 
be improper to employ the latter method of adjufling and ufing thermometers 
for ordinary purpofes, and the former for nice experiments. 
3 b y 
