On certain Tetrahedra, fyc. 117 * Or, if two conies a, )3 intersect in the points a, b, e, d, and through d we draw a transversal meeting a in A, and & in I, and if/> is a fixed point on a and q a fixed point on £, we see at once by anharmonic ratios, taking four positions, that the intersection of the lines kp, Iq moves on a conic through a, b, e, p, q. "