This is to be read, following the lines of the "figures of eight": H, He,
Li, Gl, B, C, N, and so on, each successive element being heavier than the
one preceding it in order. The disks which fall immediately below each
other form a class; thus: H, Cl, Br, I; these resemble each other in
various ways, and, as we shall presently see, the same forms and groupings
re-appear.

Another chart--taken from Erdmann's _Lehrbuch_--arranges the elements on a
curved line, which curiously resembles the curves within the shell of a
nautilus. The radiating lines show the classes, the whole diameter building
up a family; it will be observed that there is an empty radius between
hydrogen and helium, and we have placed occultum there; on the opposite
radius, iron, rubidium and osmium are seen.

[Illustration]

The external forms may be classified as follows; the internal details will
be dealt with later :--

[Illustration: PLATE III.]

1. _The Dumb-bell._--The characteristics of this are a higher and lower
group, each showing 12 projecting funnels, grouped round a central body,
and a connecting rod. It appears in sodium, copper, silver, and gold,[17]
and gold is given (1 on Plate III) as the most extremely modified example
of this form. 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,