A mechanism may be defined as a combination of plates, bars, or flexible members jointed together, so that, while the parts may move relatively to each other, the relative positions of all the different parts are determinate for each given possible relative position of any two parts.

It follows immediately that the simultaneous relative displacements, velocities, and accelerations of velocity of all parts are also strictly determinate.

This determination, by accurate graphic means, forms the subject of this paper. In it those mechanisms alone are considered that are composed of rigid members, the motions of whose parts are all continually parallel to one plane, the constancy of the plane being defined relatively to one of the members of the mechanism itself.