262-263. The first of these figures is an end view, and the second a side view, of an arrangement of mechanism for obtaining a series of changes of 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 of the same pitch as the screw, D. The roller, C, would receive a reciprocating motion, the movement in one direction being shorter than that in the other.