73 - Col. roy’s Experiments for 
By comparing the tables it will be found, that the ob- 
fervations for extreme temperatures belong to the Edin- 
burgh clafs of obfervations (N° 4.) it being thought belt, 
in this cafe, to omit the few hot ones obtained on the in- 
confiderable heights near London : the mean of the 
coldeft, anfwering to the temperature of 2 1°.7 5, make 
the logarithmic excefs and the mean of the hotteft, 
correfponding to the temperature of 69°. 6, give adefedt 
of tw* Now the fum of the two equations being di- 
vided by the difference of temperature 47°.85, we have 
nearly 2.3 for the mean rate of the equation on each 
degree, which is lefs than that refulting from the opera- 
tions of the manometer. Again, from the mean of the 
very beft obfervations, as being made on the greateft 
heights, ivhen the temperature of the air is 52 0 , it ap- 
pears, that the defeat is from — - \ or 2. t for each 
degree nearly, which agrees perfectly well with the ma- 
nometrical expanfion. In this cafe, the ratio of the 
weight of quickfilver to air is as 1 1 3 7 7 to 1 ; greater very 
confiderably than 1 1 232 to 1, affigned to them by Mr. 
de luc, when the temperature is 69°. 3 2, anfwering to 
the zero of his fcale, without any allo wance for the di- 
minution of preffure on his columns, which llioi Id have 
rendered air ftill comparatively lighter. From the Bri- 
tifh obfervations, made on the moft confiderable heights, 
it 
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