354 Capt. Kater’s experiments for determining the variation 
“ be chosen for the experiment, it must remain less than three 
“ fourths of the whole correction deduced immediately from 
“ the duplicate proportion of the distances from the earth’s 
“ centre.” 
By this interesting, and I believe new view which Dr. 
Young has taken of the subject, it appears that the correction 
for the elevation above the sea, will vary (according to the 
nature of the eminence and also its density) from one half to 
three fourths of the quantity before deduced from the squares 
of the distances from the earth’s centre, and if the mean den- 
sity of the earth be taken at 5,5, and that of the matter sur- 
rounding the station at 2,5, Dr. Young is of opinion, that the 
quantity deduced from the duplicate ratio of the distances 
should be multiplied by to obtain the correction for a 
table land, and by for that of an eminence of moderate 
declivity. 
By careful levelling, the height of the station at Unst above 
low water, was found to be 28 feet; whence we have 0,12 
for the correction deduced from the squares of the distances 
from the earth’s centre, and as the station at Unst was sur- 
rounded by hills composed of serpentine, I shall take 0,12 x jr 
== 0,06 for the correction to be applied in order to obtain the 
number of vibrations which would be made at the level of 
the sea. 
The last correction to be found, is for the buoyancy of the 
atmosphere. The manner in which this correction is derived, 
has been fully explained in the “ Account of experiments for 
fi< determining the length of the seconds pendulum ” before 
referred to. The specific gravities of the weight and bar of 
the pendulum, were carefully determined. That of the bar 
was found to be 8,628, and of the weight 8,603. The specific 
