Foci, how found when two Pairs of corresponding Points are given Condition that six Points or Lines should form a system in Involution System of Conics through four Points cut any Transversal in Involution System of Conics touching four Lines, when cut a Transversal in Involution Proof by Involution of Feuerbach's Theorem concerning the Circle through middle Points of Sides of Triangle
The six Vertices of two self-conjugate Triangles lie on same Conic (see also p. 341) 322 Chord of a Conic passes through a fixed Point, if the Angle it subtends at a
Locus of free Vertex of a Polygon all whose sides touch one Conic, and all whose Vertices but one move on another Condition that Lines joining to opposite vertices, Points where Conic meets Triangle of reference should form two sets of three meeting in a Point