12 Lieutenant Foster’s account of 
circumstances of weather, the results of which, differ only 
one-tenth of a vibration in 24 hours from those in June. The 
total number of factors for the first series being 275,5, and 
for the second 66 , a mean in that ratio has finally been taken. 
The experiment marked III. was made at the Royal Obser- 
vatory at Greenwich in November, 1825, after the return of 
the Expedition. 
The number of vibrations in 24 hours, deduced from this 
experiment, differing more than was likely to arise from 
errors in observation, being 0,24 of a vibration in excess of 
the number obtained before leaving England in 1824, I 
thought it right to repeat the experiment, especially as the 
rate of the clock appeared to be somewhat unsteady. The 
results of this repetition, made with the rate of the clock 
more uniform, being precisely the same, I have not considered 
it necessary to give them in detail. 
The difference alluded to in the number of vibrations of 
the pendulum in 24 hours, being on that side which would 
arise from the effects of wear of the knife edge of the pen- 
dulum, and which seemed probable, from the fine metallic 
line distinguishable on the agate planes after its removal, I 
feel disposed to adopt this explanation ; and assuming an 
equable wear, I have taken the mean of the first and last 
series, as the actual number of vibrations made at Greenwich, 
to compare with those at Port Bowen, which being interme- 
diate, of course required no correction on that account. 
The results of this comparison are given in a subsequent 
page preceding the third set of experiments. It will therefore 
be sufficient to state here, that the ellipticity of the earth de- 
duced from these experiments, appears to be 
