27 lines on cubic surface

cubic.jpg 27 lines on cubic surface


This surface is called the Clebsch diagonal surface and the defining equation is given by homogeneous coordinates as

X03 +X13 +X23 +X33 +X43 = 0

X0 +X1 +X2 +X3 +X4 = 0

There are 27 lines on the surface. Among them there is pair of 6 lines which do not intersect each other. They are indicated as

1, 2, 3, 4, 5, 6 ; 1', 2', 3', 4', 5', 6'

on the model. Moreover, there are 15 lines indicated as

ij, i<j, i,j=1, ..., 6.

They intersect with the lines i, j, i', j'.

The configuration of these 27 lines was studied by Schläfli.

Schläfli's double six

High resolution picture of the Clebsch diagonal surface made in alminium (by Yamada Seiki Co. Ltd.)