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Art. XIII.— -0?z the Length of the Seconds Pendulum^ observed 
at Unst^ the most northern of the Shetland Isles. Ey M. Biot, 
F. R. S. Loud, and Edin. Member of the Royal Institute 
of France, &c. he. &c. Communicated by the Author. 
In the notice which I published last year of the operations un- 
dertaken in England and France for the determination of the 
Figure of the Earth, I announced that the length of the pen- 
dulum at the Shetland Isles, agreed with the oblateness dedu- 
ced from the lunar theory, and from a comparison of degrees ob- 
served in very distant latitudes. This agreement was deduced 
from a single series of the decimal pendulum, which I had acci- 
dentally chosen out of those I had made, and which I had cal- 
culated before my departure from Unst. I am now able to give 
more certainty to this result. I had taken at Unst three sys- 
tems of measures of the pendulum. In the first I employed a 
platina ball, different from that which v/e used in Spain and in 
France, and the metal of w hich was given me for this purpose 
by MM. Cuocq and Couturier of Paris. The length of the 
pendulum, which was sexagesimal, was measured with a rule of 
iron, tiie length of wdiich M. Arago and I had measured in 
Paris, by comparing it wdth the metre of the archives. In the 
second system of observations I employed the same rule, but a 
platina ball which was used in the experiments of Bor da, and 
which we had also used in France and Spain; and in the third 
system, I employed the same ball, but I rendered the pendu- 
lum decimal, and measured its length with the same rule which 
w^e had used at Bourdeaux, Clermont, Figeac, and Dunkirk, in 
order that the results might be immediately comparable wdth 
those which we had obtained on the arc of France and Spain. 
The second system of observations, has been completely calcu- 
lated, partly by myself, and partly by M. Blanc, a young man 
as much distinguished by tlie precision as by the extent of his 
knowledge. The following ai-e the results : 
Latitude of the place of observation, - 60*^ 45' 35" north. 
Length of the seconds pendulum, reduced ) Metre, 
to a vacuum, and to the level of the sea, i 
* This result, when reduced to English inches, by using the length of the metre, 
as determined by Captain Kater, namely, 39,S707'9, gives 39,1719 inches as the 
length of the pendulum at Uust.— Ea. 
