DIRIGENT

, a term expressing the line of motion, along which a describent line, or surface, is carried in the genesis of any plane or solid figure.

Thus, if the line AB move parallel to itself, and along the line AD, so that the point A always keeps in the line AD, and the point B in the line BC; a parallelogram ABCD will be formed; of which the line AB is the describent, and the line AD the dirigent. So also, if the surface ABEG be supposed carried along the line AD, in a position always parallel to itself at its first situation, the solid AF will be formed; where the surface AE is the describent, and the line AD is the dirigent.