Quadrics of Revolution through a Given Conic

From the view-point ot Projective Geometry, the quadrics considered in this paper are those which pass through one conic and have double contact with another.

When a quadric becomes singular tangentially, it stands for a definite plane and a definite conic in that plane. Hence two conies in space determine two other covariant conies, all the four being the singular members of the same tangential pencil.