Natural Philosophy. ----'Astronomy, S83 
servations with so much exactness, Dr Brinkley concludes that 
the period of its revolution must be considerable. 
This comet is remarkable on account of its small perihelion 
distance. In its great inclination, and its small perihelion disr 
tance, it agrees with the comet of 1593. 
On the ^d April, Captain Hall observed that the tail of the 
comet seemed to be split, or to have a dark streak between its 
sides. On its first appearance it was of a dull-white colour. 
3. Length of the Pendulum at Madras. — A series of very accu- 
rate observations has been made at Madras by John Golding- 
ham, Esq. F. R. S., for determining the length of the pendulum 
in latitude 13° 4^ 9".l. The pendulum employed was one on 
Captain Kater’s principle, and made under the direction of that 
able astronomer. 
By the first series of observations, made at Madras, the 
length of the seconds’ pendulum was 39.026323087, the num- 
ber of vibrations in 24 hours being 86172,375. By the second 
series its length was 39.026280417, the number of vibrations 
in 24 hours being 86172,328. 
The mean of both these results is 39.026302 inches, which, 
according to Sir George Shuckburgh’s scale, is the true length 
of the seconds’ pendulum at Madras, in latitude 13° 4' 9 ' N., 
at the level of the sea in vacuo, and at a temperature of 70° of 
Fahrenheit. 
Captain Kater found that the same pendulum made 86293,14 
vibrations in a mean solar day, in latitude 51° 31' 8". 4, the tem- 
perature being 70°, and the height above the level of the sea 
83 feet. 
By comparing the mean length at Madras with 39,142213 
inches, the length in Lat. 51° 31' 8''.4 N., the diminution of gra- 
vity from the Pole to the Equator will be 10052897, and the 
ellipticity of the earth nearly. See doQ Phil. Trans. 1822, 
Part I. p. 167. &c. 
Derangement of the great Mural Circle at Greenwich. — Mr 
Pond has lately discovered that a derangement has taken place 
in the mural circle at the Royal Observatory. Although the 
telescope may be applied to every part of the mural circle, yet, 
•^hen fixed for observations, the principle of the instrument re- 
