378 
MR. S. A. HILL ON THE WINDS OF NORTHERN INDIA. 
The pressures represented are not, however, mean pressures, but those prevailing in the 
middle of the day, between 10 a.m. and 4 p.m. They have been computed from the 
observations made at 40 stations (including nearly all those above 1500 feet) by 
assuming the temperatui'e to decrease at the rates represented on Plate 21, and applying 
a Table computed by Major Allan Cunningham, Pt.E., on the basis of Professor 
Rankine’s modification of Laplace’s formula. 
Plate 21 shows the probable rate of decrease of temperature, on ascending, in the 
day time, through the atmosphere over a plain ; the form of the curves, which are 
slightly different for clear and cloudy skies, being deduced from Mr. Glaisher’s 
observations made during balloon ascents. The straight line shows the theoretical 
rate of temperature decrement in a mass of air carried upwards without gain or loss 
of heat. 
