L1

The right frame line touches all the parts on that side, l1 i2 4.

Every line l1 through S1 cuts the surface in two points, viz.

Hence if l1 be a tangent, it lies in that plane τ1 which corresponds to the line S2S1 as a line in the pencil S2.

These planes intersect in p2, so that p2 is a line on the quadric cone generated by the axial pencils l1 and l2.

I have not counted; I am such a bad man of business; but I am sure it is more than L1,400.'