■ fneafuring Heights "doitb the Barometer. 735 
difference of the common logarithms of the equated 
heights of quickfilver in the inferior and fuperior baro- 
meters, expreffed in 1 o o oth parts of an inch, gives the real 
height in fathoms and 1 oooth parts, the three figures 
towards the right-hand being decimals, and the reft in- 
tegers; which, being multiplied by fix, gives the refult 
in feet. 
Let us next confider, in a general way, how far this 
will correfpond, or otherwife, with Mr. de luc’s obfer- 
vations in extreme temperatures. 
I have already had occafion to remark, that when the 
temperature of the air was at 69°. 3 2, as indicated by 
thermometers expofed to the Sun’s rays, Mr. de luc 
found that the differences of the common logarithms of 
the heights of the barometers at the two ftations, gave the 
altitude between them, in French toifes and 1 oooth 
parts : in which cafe the fpecific gravity of quickfilver to 
air was as 1123a to 1. When his formula is adapted to 
Englifh meafures, the zero of the fcaie necefiarily de- 
fcends to 39.74, where the Englifh fathom bears the 
fame proportion to the modulus of the common loga- 
rithms, as, in the former cafe, the French toife did to char 
modulus, the equation for the intermediate tempers a - 
being now applied with the contrary fign. As it i r 
been fhewn, that the Britifh obfervat ions differ in their 
Vol. LXVII. 5 B 
circum 
