Movement 261

261. A combination movement, in which the weight, W, moves vertically with a reciprocating movement; the down-stroke being shorter than the up-stroke. B is a revolving disk, carrying a drum which winds round itself the cord, D. An arm, C, is jointed to the disk and to the upper arm, A, so that when the disk revolves the arm, A, moves up and down, vibrating on the point, G. This arm carries with it the pulley, E. Suppose we detach the cord from the drum and tie it to a fixed point, and then move the arm, A, up and down, the weight, W, will move the same distance, and in addition the movement given to it by the cord, that is to say, the movement will be doubled. Now let us attach the cord to the drum and revolve the disk, B, and the weight will move vertically with the reciprocating motion, in which the down-stroke will be shorter than the up-stroke, because the drum is continually taking up the cord.