C 2 59 3 
theBriggian curve, B =s= — ^ B is the length of the 
fubtangent of the atmoijpherical curve, in ioooths 
of an Englifh fathom. And putting L for the 
difference of the tabular logarithms of the obferved 
heights of the barometer, at two flations, cor- 
rected by the equation for the temperature of the 
quickfilver, and n for the mean difference of the 
temperatures of the air, in degrees of bird’s Fah- 
renheit, above or below 39,74, the difference of 
the elevation of the two ftations, is expreffed in 
1 cooths of an Englifh fathom by L dr 
I 
n X 8 
3591 
L. 
Upon thefe principles I have made a table, by 
ti x 8 
which the equation L may be computed for any 
temperature not above 4- 8o, nor below o of bird’s 
Fahrenheit, and for any height lefs than 10000 
fathom. 
It hath already been remarked, that the tempe- 
rature of the quickfilver, in the portable barometer, 
may happen to be very different from that of the, 
air, at the place and time of oblervation. For this 
reafon, M. de luc advifes, that every portable 
barometer fhould be furnifhed with two thermome- 
ters; one fixed to the frame of the barometer, to 
indicate the temperature of the quickfilver ; another, 
to be expoled, at the time of obfervation, to the 
open air. The ufe of the annexed tables might be 
anfwered by a particular divifion of the fcales of 
thefe thermometers. The thermometers which ac- 
company the two barometers, made for the fociety, 
by Mr. edward nairne, under my directions, 
L 1 2 are 
