474 Mr. Cavendish’s Experiments to determine 
the proper proportion to each other, and on a scale of one to 
thirteen. 
Before I proceed to the account of the experiments, it will be 
proper to say something of the manner of observing. Suppose 
the arm to be at rest, and its position to be observed, let the 
weights be then moved, the arm will not only be drawn aside 
thereby, but it will be made to vibrate, and its vibrations will 
continue a great while; so that, in order to determine how much 
the arm is drawn aside, it is necessary to observe the extreme 
points of the vibrations, and from thence to determine the point 
which it would rest at if its motion was destroyed, or the point 
of rest, as I shall call it. To do this, I observe three successive 
extreme points of a vibration, and take the mean between the first 
and third of these points, as the extreme point of vibration in one 
direction, and then assume the mean between this and the se- 
cond extreme, as the point of rest ; for, as the vibrations are 
continually diminishing, it is evident, that the mean between 
two extreme points will not give the true point of rest. 
It may be thought more exact, to observe many extreme 
points of vibration, so as to find the point of rest by different 
sets of three extremes, and to take the mean result; but it must 
be observed, that notwithstanding the pains taken to prevent 
any disturbing force, the arm will seldom remain perfectly at 
rest for an hour together ; for which reason, it is best to deter- 
mine the point of rest, from observations made as soon after the 
motion of the weights as possible. 
The next thing to be determined is the time of vibration, 
which I find in this manner : I observe the two extreme points 
of a vibration, and also the times at which the arm arrives at 
A 
