42 Capt. Kater’s experiments for determining the 
which was- attached to the ball of the pendulum of the clock ; 
and this disk was of such a diameter as when both pendulums 
were at rest, to be just hid from an observer at the opposite 
side of the room, by one of the slips of deal which form the 
extremities of the brass pendulum. 
Though there was little reason to imagine that the vibra- 
tions of the pendulum could communicate any motion to a 
support so firm as that which has been described, it became 
a point of considerable importance to verify this by actual 
experiment. For this purpose I had recourse to a delicate 
and simple instrument invented by Mr. Hardy, clock-maker, 
the sensibility of which is such, that had the slightest motion 
taken place in the support, it must have been instantly de- 
tected. This little instrument is represented in Plate IV. Fig. 4. 
It consists of a steel wire, the lower part of which inserted 
in the piece of brass which serves as its support, is flattened 
so as to form a delicate spring. On the wire, a small weight 
slides, by means of which it may be made to vibrate in the 
same time as the pendulum to which it is to be applied as a 
test. When thus adjusted, it is placed on the material to 
which the pendulum is attached ; and should this not be per- 
fectly firm, its motion will be communicated to the wire, 
which in a little time will accompany the pendulum in its 
vibrations. This ingenious contrivance appeared fully ade- 
quate to the purpose for which it was employed, and afforded 
a satisfactory proof of the stability of the point of suspension. 
A firm triangular wooden stand, as high as the ball of the 
pendulum, was screwed to the floor at the distance of nine 
feet in front of the clock. This served as a support, to which 
was attached a small telescope, magnifying about four times, 
