78 M. Biot m the Length of the Secmids Pendulum. 
The time was determined by 49 series of altitudes of the sun^ 
taken with a repeating circle of Fortin, both in the morning and 
evening, and calculated so as to avoid the influence of the con- 
stant errors to which this instrument might be liable. They 
were observed with an excellent chronometer of Breguet’s, 
which, however, served only as a reckoner ; for its indications 
were transported by comparisons, either before or after each 
series, and often at both these epochs, to an excellent clock of 
the same artist, which served for the measures of the pendulum, 
and which had gone with the greatest uniformity for nearly two 
months. These results were also confirmed by observing the 
passages of stars with a fixed telescope. 
The latitude is certain only within some seconds, because it 
was calculated only from three or four series of observations of 
the sun and stars, made to the south of the zenith. This was 
more than sufficient for the pendulum ; but the exact calculation 
of the latitude ought to be made from the whole serieses of ob- 
servations on the sun and stars, which amount to 55. 
A correction of this result must still be made on account of 
the radius of curvature of the knife’s edge employed for sus- 
pending the pendulum. This correction will no doubt be ex- 
tremely small ; for, upon observing the edge in a microscope^ 
with an excellent micrometer traced upon glass by M. Le Bail- 
lif, I found its width to be less than ^lo^h of a millimetre,, 
which gives less than ^l^th of a millimetre for the radius of 
the edge supposed to be spherical. The correction, however,, 
depending upon this cause will be given directly both by the 
observations which I have made at Unst with pendulums of dif- 
ferent lengths, but with the same knife edge, and by those 
which I made at Edinburgh with pendulums of equal lengths, 
but with different knife edges. 
It is easy to see that the preceding length of the pendulum, 
combined with that of Formentera, Paris, or Dunkirk, and with 
these last ones taken together, gives a degree of oblateness in 
perfect accordance with that which has been deduced from the 
Lunar Theory, or from the comparison of degrees measured at 
very great distances. But, in order to deduce this element in a 
definitive manner, we must wait till all the other observations 
have been calculated. It is very probable that these results will 
