Upon rotation of tube 1, rigidly mounted on shaft A and partly filled with mercury, the centre of gravity of the mercury moves away from axis x-x in proportion to the angular velocity of shaft A. This increases the moment of inertia of the shaft-tube system. Thus, by varying its own moment of inertia, the system equalizes the angular velocity of the shaft which is subject to periodic disturbing fluctuations.
$3780$SHP,FD$