Some properties of the line of striction of a ruled surface

Abstract

1. It is known that (i) the line of striction of a ruled surface is the locus of points at which the geodesic curvatures of the orthogonal trajectories of the generators vanish, (ii) if at each point of a curve C on a surface, a tangent to the surface is drawn, and these tangents generate a ruled surface of which C is the line of striction, then, if each tangent is turned through a constant angle α about its point of contact in the tangent plane, the new set of tangents also form a ruled surface with C as a line of striction.