684 Col. roy’s Experiments for 
of Fahrenheit. In the formulae adapting his rule to 
Englifh meafures (Phil. Tranf. vol. LXVII. N° xx. and 
xxx.) hath been fhewn, that the eafieft and fimpleft me- 
thod is, to make the difference of temperature of the two 
barometers the argument for the equation ; and that it is 
fufficient to reduce either column to what would have 
been its height in the temperature of the other. But 
whatever may heretofore have been the method of ufing 
the equation for the heat of the quickfilver, while it was 
con fide red as arithmetical ; now that it hath been fhewn, 
from the preceding experiments, to be progrelfive, there 
feems at leaft to be propriety in applying to each baro- 
meter the equation anfwering to its particular tempera- 
ture. And though, for this purpofe, any fixed tempera- 
ture might have been affumed at pleafure, as that to 
which both barometers were to be reduced; yet, the 
( 
freezing point being fundamental in all thermometers, 
and that being likewife the zero of the fcale for the equa- 
tion depending on the heat of the air, as will be fhewn 
hereafter, it hath been preferred to any other. 
From the experiments it appears, that a column of 
quickfilver of the temperature of 32 0 , fuftained, by the 
weight of the atmofphere, to the height of 30 inches in 
the barometer, when gradually affected by different de- 
grees of heat, fuffers a progreffive expanfion ; and that, 
having 
