PROCEEDINGS OF SECTION E. I83 
Half the distance between both determinations is equal to the 
distance of the respective centres of gravity from the centre of 
the instrument. The calculations of these distances according 
to the second method employed agreed well with the experimen- 
tal results, both giving 3.65 in. as the distance of the centre of 
gravity from the centre. 
MountTING OF THE PENDULUM. 
On the central line of the whole apparatus, passing through 
the telescope and the little hole at the lower extremity of the 
clock pendulum, is erected a cedar pillar, 9 in. square and 5 ft. 
2 in. long; the lower end of the same is embedded in a brick 
wall forming part of the foundation of the house; its upper ex- 
tremity is fixed to a heavy piece of wood, well seasoned, and of 
the following dimensions: 3 ft. 4 in. long, 2 ft. broad, and 5 in. 
thick. This piece of wood is cemented into the walls on both 
sides, and as the distance between the two walls is only 2 ft. 8 
in., there remains a piece on both sides of 4 in., which is put 
into the wall. Care was taken that this plank was in a horizon- 
tal position, while the pillar supporting it is fixed perpendicu- 
larly. The apparatus, on which the pendulum is to swing, iden- 
tical with the one described by Captain Kater (Phil. Trans. 
1818), is firmly screwed to this plank, so that when the pendu- 
lum is suspended it is 1$ in. from the pillar and exactly in the 
middle of it. This brings the lower end of the reversion pen- 
dulum, when resting on the agate-planes, in a level with the 
telescope and the little hole in the clock pendulum, and 7 ft. 
114 in. distant from the latter. A glass case encloses the whole, 
the door in front is made to open in two parts, the lower one 
only being open during the observation ; the rest of the case is 
closed, and protects the pendulum against currents of air and 
sudden changes in temperature. <A scale with a white stripe 
upon black ground 0.02 in. broad is fixed to the pillar. 
OvSERVING THE COINCIDENCES. 
The mode applied in effecting this is very much the same as 
that of Bessel, described in his Unter suchungen (pas. "Tt 
and 12), the only differences being such as are consequent upon 
the difference in construction of the two different pendulums ; 
So, for instance, is the cylinder of Bessel replaced by the follow- 
ing construction; the ends of the reversion pendulum are re- 
duced in breadth so much, that they are of equal size as the 
cylinder above referred to. 
The arrangement for observing the coincidences through the 
telescope was in so tar different from any other as the observa- 
tion of the are of oscillation at the time of each coincidence 
could not be observed by the same telescope, but had to be read 
