9^ Captain HalPs and Mr Henry Foster’s Experiments 
don, in 1820, made 86285,98 vibrations in the same interval, 
it follows, that the length of the seconds pendulum at Galapa- 
gos, is 39,01717 of Sir G. Shuckburgh’s scale, the length of the 
seconds pendulum in London being assumed at 39,13929. 
By comparing this result with those obtained by Captain 
Kater at the different stations of the Trigonometrical Survey, 
(as already given in diis Journal, Vol II. p. 321 and 322), 
Captain Hall finds that the 
Mean diminution of gravity frc«n the Pole to the Equator, is .0051412 
The mean Ellipticity, .... 
The Mean Ellipticity, as deduced from Captain Sabine’s) 1 , 
observations at Melville Island, is • . / 292.14 
Length of equatorial pendulum, . . . 39.017196. 
San Bias, where the second set of observations was made, is 
a sea-port town of Mexico, in West Longitude 105° 15', and 
North Latitude 21° 30' 24". The station was 115 feet above 
the level of the sea, and on the summit of a rock of compact 
whinstone. The number of vibrations made by the pendulum, 
in a mean solar day, was 86125,03, in vacuo, at the level of the 
sea, and at 68° of Fahrenheit. As the same pendulum, when 
brought back to London, in 1823, made 86236,95 vibrations, it 
follows, that the length of the seconds pendulum at San Bias, 
is 39,03776 inches. By comparing this with Captain Kater’s 
results. Captain Hall finds that the 
Mean diminution of grayity from the Pole to the Equator, is .0054611 
Mean Ellipticity, 
Length of equatorial pendulum, 
1 
313,55 
39.00904 
From a second set of experiments made by Mr Henry Foster, 
the numbers were. 
Diminution of gravity. 
Length of seconds pendulum, 
Mean ellipticity, 
.0054095 
39.03881 
1 
308. 5(> 
These observations, however, were made under cu’cumstances 
less favourable than those of Captain Hall. 
Rio de Janeiro, where the third set of observations was made, 
is situated on the coast of Brazil. The station was on granite, 
72 feet above the sea, and in West Longitude 43°, and South 
Latitude 22° 55' 22". The pendulum performed 86131,70 vi- 
brations in a mean solar day, in vacuo, at the level of the sea,, 
and at 60° of Fahrenheit, Hence Captain Hall finds that 
