402 Mr. Greatorex’s observations on the heights 
From the near agreement of the measured and barome- 
trical heights on the summit of Skiddaw, I had formed san- 
guine hopes that the barometer would prove a most exact 
determinator of altitudes, and almost supersede the necessity 
of having recourse to any other mode; but the subsequent 
observations lead me to fear that the state of the atmosphere 
has an effect which we cannot yet account for, and to which 
we cannot apply a correction. When the operation was dis- 
continued on the evening of the 5th, the air was dry and 
clear ; but on the morning of the 6th, the top of the mountain 
was clouded about 300 yards down, which might be the 
reason of the two observations differing by more than four 
yards. 
But the object of this paper is not to surmise, or submit 
any hypothesis ; but faithfully to state the result of opera- 
tions carried on with all the exactness I was capable of. If 
what I have done be deemed worthy of any attention by the 
learned and distinguished Society of which you. Sir, are a 
member, I shall be most highly gratified, and amply com- 
pensated for the toil attending operations on high mountains. 
THOMAS GREATOREX. 
P. S. Dr. Maskelyne’s rules for determining the height 
of mountains by the barometer, are these : 
ist. Take the difference of the tabular logarithms of the 
observed barometrical heights at the two stations, considering 
the four first figures (exclusive of the index) as whole num- 
bers, and the remaining figures to the right as decimals, 
gdly. Observe the difference of Fahrenheit’s thermometer 
