416 
MR. BAILY ON THE CORRECTION OF 
pendulum, including- the wooden tail pieces (which would probably weigh 500 
or 600 grains), is stated to be only 66904 grains. 
No. 25, 26 are the two knife edges A and B of a convertible pendulum, 
formed of a plain brass bar, 2 inches wide, fths of an inch thick, and 62*2 
inches long. The form and construction of this pendulum will be best 
seen from the annexed sketch, which is taken from the description given 
of the two following ones in the Philosophical Magazine for August 
1828, page 137- At 5 inches from one end of the bar is placed one 
of the knife edges (A), fastened to knee pieces in the usual manner ; 
and at 39*4 inches therefrom is placed the other knife edge (B). 
The adjustment to synchronism is coarsely effected by filing away 
from the requisite end : and ultimately to great exactness by means 
of a small screw inserted at the end B, reduced to a weight proper 
for such purpose. Its specific gravity, as obtained from a piece of brass, 
said to be from the same casting, I found to be 8*034 : its weight is 121406 
A 
grains. 
No. 27, 28 are the two knife edges A and B of a copper bar, similar to the 
last, except that it is \ an inch thick, and 62*5 inches long. Its specific gra- 
vity, as obtained in the manner described in the preceding pendulum, I found 
to be 8*629 : its weight is 155750 grains. 
No. 29, 30 are the two knife edges A and B of an iron bar, similar to the 
copper one, except that it is 62*1 inches long. Its specific gravity, as ob- 
tained in the manner described above, I found to be 7‘686 : its weight is 
140547 grains. 
These two last-mentioned pendulums have been already described 
by me in the Philosophical Magazine as above stated. They belong 
to the Royal Astronomical Society, and are the same that were taken 
out by Captain Foster in his late scientific voyage. 
No. 31, 32, 33, 34 are the four knife edges A, B, C, D, of a brass 
bar similar to the three last-mentioned ones, except that it is fths of 
an inch thick, and 62 inches long. The position of the knife edges 
will be best understood from the annexed diagram, which is taken 
from the Philosophical Magazine for February 1829, page 97, where 
this pendulum is more fully described. It may be sufficient here to 
- - A 
-- B 
D 
