GENESIS, in Geometry, denotes the formation of a line, plane, or solid, by the motion or flux of a point, line, or surface. See FLUXIONS.
The genesis or formation, e. gr. of a globe or sphere, is conceived by supposing a semicircle to revolve upon a right line, drawn from one extreme thereof to the other, called its axis, or axis of circumvolution: the motion or revolution of that semicircle is the genesis of the sphere, &c.
In the genesis of figures, &c. the line or surface that moves is called the describent; and the line round which, or according to which, the revolution or motion is made, the dirigent.