If M be used to represent the modulus of the Napierian logarithms we may write
in which the logarithms are of the common kind.
This is La Place’s formula. h in the expression is not the barometric height directly observed at the upper station, but this height reduced to the temperature of the lower station.
The value of
has been determined by trial of the formula upon known altitudes. Ramond in his survey of the Pyrenees determined its value to be 18336.
The unknown term z in the second member is determined by successive approximations.
The first value being
