Some of our readers may be glad to have a drawing of the Platonic solids,
since they play so large a part in the building up of elements. The regular
solids are five, and five only; in each:

(1) The lines are equal.
(2) The angles are equal.
(3) The surfaces are equal.

[Illustration]

It will be seen that the tetrahedron is the fundamental form, the
three-sided pyramid on a triangular base, _i.e._, a solid figure formed
from four triangles. Two of these generate the cube and the octahedron;
five of these generate the dodecahedron and the icosahedron.

The rhombic dodecahedron is not regular, for though the lines and surfaces
are equal, the angles are not.

NOTES.

Mr. C. Jinarâjadâsa[1] writes:

The asterisk put before metargon in the list of elements should be omitted,
for metargon had been discovered by Sir William Ramsey and Mr. Travers at
the same time as neon (see _Proceedings of the Royal Society_, vol. lxiii,
p. 411), and therefore before it was observed clairvoyantly. It is not,
however, given in the latest list of elements in the Report of November 13,
1907, of the International Atomic Weights Commission, so it would seem as
though it were not yet fully recognised.