[Fig. 155]. A combination movement, in which the weight W moves with a reciprocating movement, the down-stroke being shorter than the up-stroke. B is a revolving disc, carrying a drum which winds around itself the cord D. An arm C is jointed to the disc and to the upper arm A, so that when the disc 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, tie it to the 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 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 disc 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.
Figs. 153, 154, 155. Hooks—Sprocket—Combination movement
Figs. [156, 157]. The first of these figures is an end view, and the second is a side view of an arrangement or mechanism for obtaining a series of changes in velocity and direction. D is a screw on which is placed eccentrically the cone B, and C is a friction roller, which is pressed against the cone by a spring or weight. Continuous rotary motion, at a uniform velocity of the screw D carrying the eccentric cone, gives a series of changes of velocity and direction to the roller C. It will be understood that during every revolution of the cone the roller would press against a different part of the cone, and that it would describe thereon a spiral motion, the movement in one direction being shorter than that in the other.
Figs. 156, 157. Change of speed
[Fig. 158]. An engine governor. The rise and fall of the balls K are guided by the parabolic curved arms B, on which the anti-friction wheels L run. The rods F, connecting the wheel L with the sleeve, move it up and down the spindle C D.
[Fig. 159]. Toe and lifter for working poppet-valves in steam engines. The curved toe on the rock-shaft operates on the lifter attached to the lifting rod to raise the valve.