On the use of the barometric thermometer for the determina­tion of relative heights

Abstract

The objects of this communication, as stated by the author, are, first, to show the theoretical foundation of the very simple law pointed out by Professor Forbes, according to which the difference of the boiling temperature of water at two stations is connected with their difference of level ; and next, to test the accuracy of this law by a comparison of results deduced from his own observations on the boiling-point of water at different stations among the Alps of Savoy, Piedmont and Switzerland, with the heights of the same stations as determined by other observers and by different means ; and thus to arrive at a just conclusion with respect to the value of the barometric thermometer as an instrument for determining differences of level. Combining DeLuc’s formula reduced to English units, b = 99 log 10 β - 60.804, .899 where b is the variable boiling-point on Fahrenheit’s scale and β the corresponding barometric pressure, with the formula of Laplace for the determination of the difference in level of two stations from barometric observations, he obtains the formula H = 547.99 ( b - b' ) { 1 + ( t - 32°) .00222 } , where b and b' are the boiling-points on Fahrenheit’s scale at-the two stations, t the mean temperature of the air at the stations, and H their difference of level in English feet.