A contrivance for regulating the driving power of a machine. In the steam-engine the power of the connecting rod to turn the crank varies with their relative position. When the rod is at right angles to the crank its turning effect is greatest, and when they are in the same straight line this power is nil. There is thus introduced a cause of unevenness in the motion through the whole length of the stroke. To obviate this difficulty the fly-wheel is fixed on the axis. This is a large wheel with a heavy rim, which, when once started, requires little work to keep it in motion ; but, since it possesses much energy in consequence of its motion, it acts to make uniform the motion of the rod and crank.