length of the pendulum vibrating seconds. 4 1 
clock is firmly screwed to the wall, in a recess opposite 
to the window. Near to this, on the wall which is at right 
angles to the recess, is fixed another time-piece by Cumming, 
which was the property of the late General Roy, and is con- 
sidered by Mr. Browne to be the best in his possession. 
Respecting this clock, it will be sufficient to remark, that three 
tenths of a second was the greatest variation in its daily rate 
from the 2 2d February, when the observations commenced, 
to the 31st July; and consequently the deviation from its 
mean rate during that period, did not exceed 0,15 of a second 
per day. This clock has been used as the standard of com- 
parison, the time having been taken from the transit instru- 
ment by a chronometer of Arnold’s. With such advantages 
it will be confessed that there can be little chance of error 
arising from the rate of the clock. 
A plank of well seasoned mahogany, two feet wide, and 
three inches thick, was forcibly driven between the walls 
forming the sides of the recess, until it was near the top of 
the clock case.- To this the support of the pendulum before 
described was firmly screwed, and carefully levelled, in such 
a position as to allow the pendulum to vibrate as near as 
possible to the clock case without touching it ; and that when 
at rest, it might appear to an observer in front of the clock, 
to pass over the centre of the dial plate, its extremity reach- 
ing a little below the centre of the ball of the pendulum. 
Beneath, fixed to the clock case, was an arc divided into 
degrees and tenths, to determine the extent of the vibrations. 
Such a portion of the plank was cut away as was necessary 
to admit of the pendulum being placed on its support. A 
circular white disk was pasted on a piece of black paper, 
MDCCCXVIII. G 
