The twenty-seven lines upon the cubic surface ... by Archibald Henderson.

CONFIGURATIONS OF THE LINES UPON THE CUBIC SURFACE 95
and having twenty-one distinct lines lying wholly upon the surface.
The four points 01, 02, 03, 04 such that the plane of any one of them
with respect to one triheder is identical with its polar plane with
respect to the other triheder, are the conical points of the four cubic
surfaces. Through each one of these points pass six lines, conditioned
by the scheme (A) above, which lie not only upon a quadric cone but
also upon the cubic surface through the nine lines above mentioned
and for which that point is the only conical point.