47 s Mr. Cavendish's Experiments to determine 
nish the time of vibration; and, consequently, the error in the 
result would be much less, when the force required to draw the 
arm aside was deduced from experiments made at the time* 
than when it was taken from previous experiments. 
Account oj the Experiments. 
In my first experiments, the wire by which the arm was sus- 
pended was gqi inches long, and was of copper silvered, one 
foot of which weighed 2 T %- grains : its stiffness was such, as to 
make the arm perform a vibration in about 15 minutes. I imme- 
diately found, indeed, that it was not stiff enough, as the at- 
traction of the weights drew the balls so much aside, as to make 
them touch the sides of the case ; I, however, chose to make 
some experiments with it, before I changed it. 
In this trial, the rods by which the leaden weights were sus- 
pended were of iron ; for, as I had taken care that there should 
be nothing magnetical in the arm, it seemed of no signification 
whether the rods were magnetical or not ; but, for greater se- 
curity, I took off the leaden weights, and tried what effect the 
rods would have by themselves. Now I find, by computation, 
that the attraction of gravity of these rods on the balls, is to 
that of the weights, nearly as 17 to 2500 ; so that, as the attrac- 
tion of the weights appeared, by the foregoing trial, to be suffi- 
cient to draw the arm aside by about 3 5 divisions, the attraction 
of the rods alone should draw it aside about t *q of a division ; 
and, therefore, the motion of the rods from one near position to 
the other, should move it about jr of a division. 
The result of the experiment was, that for the first 15 
minutes after the rods were removed from one near position 
to the other, very little motion was produced in the arm, and 
