The 12 almond-like projections, above and below, are
severally contained in shadowy funnels, impossible to reproduce in the
drawing; the central globe contains three globes, and the connecting
portion has swollen out into an egg, with a very complicated central
arrangement. The dumb-bell appears also in chlorine, bromine and iodine,
but there is no trace of it in hydrogen, the head of the group. We have not
met it elsewhere. It may be remarked that, in Sir William Crookes' scheme,
in which they are all classed as monads, these two groups are the nearest
to the neutral line, on the ingoing and outgoing series, and are
respectively positive and negative.
II and IIa. _The Tetrahedron._--The characteristics of this form are four
funnels, containing ovoid bodies, opening on the face of a tetrahedron. The
funnels generally, but not always, radiate from a central globe. We give
beryllium (glucinum) as the simplest example (2 on Plate III), and to this
group belong calcium and strontium. The tetrahedron is the form of chromium
and molybdenum, but not that of the head of their group, oxygen, which is,
like hydrogen, _sui generis_. These two groups are marked in orthodox
chemistry as respectively positive and negative, and are closely allied.
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