meafuring Heights with the Barometer. 747 
the S.outh-fea, where the defcent of quickfilver at the 
upper ftation was exactly an inch in the mean heat of 
the day, anfwering to 84°^. On the former fuppofition 
of the weight of quickfilver to air, the height would be 
13 1 00 inches or 109 1.7 feet. 
Hence 8 + |-i6 9 ^9-76i| = 8 6 
^28.930 84|-l69=28.76l j 
the logarithmic refult, which is defective 201.1, or 
nearly parts. Now this equation being divided by 
2.45 the mean expanfion of air, we have nearly 92 0 
for the difference between 84°^-, the temperature of the 
obfervation, and the zero of the fcale, which reduces it 
to ~7°| of Fahrenheit. If it fhould be thought that I 
have fuppofed the air to be too light at the level of the 
fea under the equator, let it be taken to quickfilver only, 
at a mean between 13 100 and 12672, which feems to 
have been the ratio of their weights at Genoa, when Mr. 
de lug’s temperature was 79% and we fhall have 
12881 inches, or 1073.4 feet of air, for the counter- 
poife to the inch of quickfilver in the barometer : hence 
1073.4-890.6=^— ^=8 3°.7, will denote the number 
of degrees that the zero of the fcale would, in that cafe, be 
below the temperature of the air, which brings it to within 
lefs than a degree of the cypher of Fahrenheit. But in 
middle latitudes the zero of the fcale is at 32 0 , anc ^ ^ ie 
a equation 
