VIII.

IV.--THE OCTAHEDRAL GROUPS.

These groups are at the turns of the spiral in Sir William Crookes'
lemniscates (see p. 28). On the one side is carbon, with below it titanium
and zirconium; on the other silicon, with germanium and tin. The
characteristic form is an octahedron, rounded at the angles and a little
depressed between the faces in consequence of the rounding; in fact, we did
not, at first, recognize it as an octahedron, and we called it the "corded
bale," the nearest likeness that struck us. The members of the group are
all tetrads, and have eight funnels, opening on the eight faces of the
octahedron. The first group is paramagnetic and positive; the corresponding
one is diamagnetic and negative. The two groups are not closely allied in
composition, though both titanium and tin have in common the five
intersecting tetrahedra at their respective centres.

[Illustration: PLATE XV.]

CARBON (Plate III, 5, and XV, 1) gives us the fundamental octahedral form,
which becomes so masked in titanium and zirconium. As before said (p. 30),
the protrusion of the arms in these suggests the old Rosicrucian symbol of
the cross and rose, but they show at their ends the eight carbon funnels
with their characteristic contents, and thus justify their relationship.
The funnels are in pairs, one of each pair showing three "cigars," and
having as its fellow a funnel in which the middle "cigar" is truncated,
thus loosing one atom. Each "cigar" has a leaf-like body at its base, and
in the centre of the octahedron is a globe containing four atoms, each
within its own wall; these lie on the dividing lines of the faces, and each
holds a pair of the funnels together. It seems as though this atom had been