2 Captain Kater/s account of the 
plates, on which the pendulum had rested during the expe- 
riments, had suffered penetration by the knife edges. The 
length of the seconds pendulum however, deduced from 
these first experiments, did not differ more than two ten- 
thousandths of an inch from the final determination. 
It may also be seen, that in repairing the knife edges after 
the first set of experiments had been concluded, one of them 
was broken ; and when replaced by another, the distance 
between the knife edges was increased about one hundredth 
of an inch ; so that two results, differing by so small a quan- 
tity from each other, may be considered as having been 
obtained by two different instruments. 
The Philosophical Transactions for 1819 contain an account 
of experiments for determining the variation in length of the 
seconds pendulum at the principal stations of the Trigonome- 
trical Survey of Great Britain, For this purpose I constructed 
an invariable pendulum, the number of vibrations made by 
which being observed in London, and also at the principal 
stations of the Trigonometrical Survey, the length of the 
seconds pendulum, at such stations, could readily be deduced 
from the previously known length of the pendulum vibrating 
seconds in London. 
In this manner, the length of the pendulum vibrating 
seconds at Unst was found to be 39,17146 inches, and at 
Leith Fort 39,15554 inches. 
The “ Recueil d’ Observations Geodesiques,” &c. which may 
be considered as a fourth volume of the “ Base du Systeme 
metrique ” affords me an opportunity of comparing these 
last results with those of M. Biot, whose very valuable 
labours for determining the length of the pendulum vibrating 
