manganese, because of their similarity in internal composition. Manganese
has fourteen spikes, arranged as in the iron group, but radiating from a
central globe. Potassium has nine, rubidium has sixteen, in both cases
radiating from a central globe. Lithium (Plate IV, 2) and fluorine (Plate
IV, 3) are the two types which dominate the group, lithium supplying the
spike which is reproduced in all of them, and fluorine the "nitrogen
balloon" which appears in all save lithium. It will be seen that the
natural affinities are strongly marked. They are all monads and
paramagnetic; lithium, potassium and rubidium are positive, while fluorine
and manganese are negative. We seem thus to have a pair, corresponding with
each other, as in other cases, and the interperiodic group is left
interperiodic and congruous within itself.

[Illustration: PLATE XIX.]

LITHIUM (Plate IV, 2 and Plate XIX, 1) is a striking and beautiful form,
with its upright cone, or spike, its eight radiating petals (_x_) at the
base of the cone, and the plate-like support in the centre of which is a
globe, on which the spike rests. The spike revolves swiftly on its axis,
carrying the petals with it; the plate revolves equally swiftly in the
opposite direction. Within the spike are two globes and a long ovoid; the
spheres within the globe revolve as a cross; within the ovoid are four
spheres containing atoms arranged on tetrahedra, and a central sphere with
an axis of three atoms surrounded by a spinning wheel of six.

LITHIUM: Spike of 63 atoms 63
8 petals of 6 atoms 48
Central globe of 16 atoms 16
----
Total 127