Mode of obtaining two reciprocating movements of a rod by one revolution of a shaft, patented in 1836 by B. F. Snyder, has been used for operating the needle of a sewing machine, by J. S. McCurdy, also for driving a gang of saws. The diskj A, on the central rotating shaft has two slots, a, a, crossing each other at a right angle in the center, and the connecting-rod, B, has attached to it two pivoted slides, c, c, one working in each slot.