in the length of. the pendulum vibrating seconds. 355 
gravity therefore of the whole pendulum may be taken at 
8,610, 
The mean height of the barometer during the experiments 
at Unst, was 29,98 inches, and that of the thermometer 57, 0 8. 
The weight of water is to that of air at 29,27 inches of the 
barometer, and 53 0 of the thermometer, as 836 to 1, and the 
expansion of air for each degree of the thermometer is 
of its bulk. From these data we find that the specific gravity 
of the pendulum was to that of air, at the time of the experi- 
ments, as 7099 to 1. The square of the number of vibrations 
must therefore be increased part, or 6,07 be added to 
the number of vibrations in 24 hours, to obtain the number 
of vibrations which would be made during the same period in 
vacuo. 
These corrections being added to the mean number of 
vibrations before given, we have 86096,90 for the number of 
vibrations made by the pendulum in a mean solar day, in vacuo 
at the level of the sea. 
The very unfavourable weather which I experienced at 
Unst, prevented my obtaining so many observations for the 
rate of the clock, as I could have wished ; but though the 
greatest difference between the seven resulting numbers of 
vibrations amounts to so much as 0,49, I think it probable, 
after a careful examination, that the final result must be 
within one tenth of a vibration of the truth. 
On the 23d July, 1 was so fortunate as to obtain one series 
of meridional observations of the sun, with the repeating 
circle, for the latitude of the station, which will be given 
hereafter, and on the 29th I embarked on board the Cherokee, 
and took leave of my kind host Mr. Edmondstone, to whose 
most friendly hospitality the eloquent pen of M. Biot has 
