d the uppermost cross-piece is attached to the axis of suspension.
It is easy, therefore, to see that the expansion of the steel bars tends to lengthen the pendulum, while that of the brass ones tends to shorten it; and, consequently, if the two expansions exactly counteract each other, the length of the pendulum will remain unchanged.
The relative lengths of the brass and steel bars are determined by the expansions of the two metals, which are found by experiments to be generally nearly as 100 to 61.
A compensation pendulum (f) has been contrived, in which, by means of a compound bar of metal, a certain portion of the weight of the bob is lifted when heat extends the pendulum-rod.
The bent bar is a compound of brass and steel, brazed together brass downward.
As brass expands more than steel with a given increment of heat, it carries the weights up with it, raising the center of gravity of the aggregate weight to compensate for the extension of the rod.
The conical pendulum