734 -Co/, roy’s Experiments for 
air for each degree of the thermometer ; the quotient 
will give the number of degrees, in the firft cafe, to be 
added to, and in the laft fubtradted from, the tempera- 
ture of the air in the observation ; the fum or difference 
anfwers to the zero of the fcale, or that temperature 
when the logarithmic refult gives the real height in 
Englilh fathoms and 1000th parts. 
According to this mode of computation, we have, 
from the aggregate of the feveral clafles of Britilh ob- 
servations, the place of the zero as follows : 
Zero, 
By the i ft clafs of obfervations in and near London, 
between the temperatures of — — 
2d, near Taybridge, — — 
3d, near Lanark, — — 
4th, near Edinburgh, — — 
5th, near Linhoufe, — — 
6 th, near Carnarvon, — — 
25.5 and 71.2 at 32.2 
46.1 — 62.9 - 31,1 
44. — 62. - 32.8 
x 7« — 7°*7 “ 3 l 3 
26.1 — 46.5 - 29.9 
49.1 — 62.3 - 32 9 
Mean place of the zero at 
3'-7 
The number 3i°.7 differing fo very little from 3 2°, 
we may hereafter confider that remarkable point of fah- 
renheit’s thermometer, as the zero of the fcale depend- 
ing on the temperature of the air; and hence is deduced 
the fecond part, of the rule for meafuring heights with 
the barometer. When the mean temperature of the co- 
lumn of air to be meafured is at 3 1° of Fahrenheit, the 
difference 
