The five Platonic solids. Historical engraving from Davisson's Philosophia Pyrotechnia (Paris, 1642) of the five Platonic solids, to illustrate early ideas on chemical elements. A Platonic solid is a polyhedron all of whose faces are coinciding regular polygons and where the same number of faces meet at every point. They are, clockwise from upper left, a hexahedron (cube), tetrahedron, dodecahedron, icosahedron and octahedron. Early ideas on chemical elements saw them as qualities (hotness, dryness, fieriness, oiliness, earthi- ness) rather than as real substances. They were also mystically linked with the five planets then known, and with the five Platonic solids.