in order to af certain the height of Mountains. 583 
\vhen the difference of the heights of the quickfilver 
in the two barometers happens not to exceed -f or even 
3^of an inch (and this will frequently be the cafe in level- 
ling flat countries, or meafuring fmall heights) in fuch 
circumftances the moft convenient way of reducing the 
obfervations will .be by means of the column of differences 
only; thofe numbers exprefling the length of a column 
of the atmofphere which correfponds to -f of an inch of 
quickfilver, at any afligned height of the barometer. 
EXAM P L E IV. 
Suppofe the following obfervations had been made at 
the top and bottom of any eminence ; viz. at the top, 
barometer 29.985 inches,, attached thermometer 70'f. 
detached thermometer 76°; and below, barometer at 
30.08 2, attached thermometer 71 rt , and the detached • 
one 68° ; what was the height of the eminence ? 
Obfer- 
