C 2 99 .] 
GENERAL PRECEPTS, for the CALCULATION of HEIGHTS by 
thefe TABLES-. 
FROM the common tables of logarithms, name- 
ly, thofe which exhibit the Briggian logarithms to 
eight places, write out the logarithms of the num- 
bers, which exprefs the obferved heights of the quick- 
filver, in the portable barometers, at the two Nations. 
2. Subtract the lefier logarithm from the greater. 
3. Divide the remainder by 1000. The quotient 
is a certain number of fathom. 
4. Take the difference of the temperatures of the 
quickfilver, as indicated by the thermometers in the 
cafes of your portable barometers, and look for the 
correction correfponding thereto, in the third column 
of table hi. and add that correction to the num- 
ber lafl found, if the barometer at the higher ftation 
hath been the warmer of the two; otherwife fubtraCt 
it. Call the fum in the firft cafe, the remainder in 
the latter, the approximate height . 
5. Add together the temperatures exprefled at the 
two ffations by the thermometers in the open air, 
under their proper figns. Take half the aggregate, 
and call it the temperature of the air. 
6. In the principal table of the equation for the 
temperature of the air (table iv.), look a- top for the 
decade of degrees next lefs than the temperature of 
the air, found by the laft rule; and from the column 
underneath it (by repeated entries if need be) collect 
the corrections for the units, decades, and centuries of 
Qq 2 fathom 
