844 
Proceedings of the Royal Society 
these observations, the hourly variation of atmospheric temperature, 
pressure, and wind velocity have been calculated, and the results, 
illustrated by diagrams, were submitted to the meeting. From the 
double set of observations, it is seen that the rate of decrease of 
temperature with height is 1° for every 270 feet of ascent. This 
result has a peculiar value attached to it, seeing that both at the 
Observatory and at the sea-level station, the arrangements carried 
out are such as to minimise the effects of solar and terrestrial 
radiation. 
The corrections to sea-level for the barometric observations at the 
Observatory, 4406 feet high, have been emphatically determined 
from the double set of observations, for each tenth inch of the 
pressure at sea-level from 28 ’500 inches to 30-600 inches, and for 
every 2 o, 0 of the outside temperature from 18°*0 to 60° '0. The 
results are closely accordant with the figures for a sea-level pressure 
of 30-000 inches published by General Hagan of the U.S. Signal 
Office, and in use by the American observers. For each 2 o, 0 from 
18°*0 to 60°*0, the sea-level corrections for Ben Nevis are 0'020 
inch greater than the figures of the Signal Office. 
The sea-level corrections for the Observatory have been worked 
out from the formula given by Laplace in his Mechanique Celeste 
in the form employed by the Meteorological Council. At an outside 
temperature of 45°, the correction derived from the formula is the 
same as the correction calculated directly from the observations. 
At lower temperatures, the correction from the formula steadily 
increases, and at a temperature of 20°, and sea-level pressure of 
30-000 inches, it is 0'040 inch larger than the empirically deter- 
mined correction. At temperatures higher than 45°, the empirically 
determined correction is the larger one. The general result is, 
while by the formula, the correction for each increase of 2° of the 
temperature is 0‘018 inch less, by the observations directly it is 
only 0’015 inch less, or the difference in the correction for a 
difference of 2° of the outside temperature is a sixth part greater 
than observations shows it to be. 
