143. Circular motion into alternate rectilinear motion. Motion is transmitted through pulley at the left upon the worm-shaft. Worm slides upon shaft, but is made to turn with it by means of a groove cut in shaft, and a key in hub of worm. Worm is carried by a small traversing-frame, which slides upon a horizontal bar of the fixed frame, and the traversing-frame also carries the toothed wheel into which the worm gears. One end of a connecting-rod is attached to fixed frame at the right and the other end to a wrist secured in toothed wheel. On turning worm-shaft, rotary motion is transmitted by worm to wheel, which, as it revolves, is forced by connecting-rod to make an alternating traverse motion.