We here meet the tetrahedron for the first time, with each angle occupied by a six-atomed group, the atoms arranged as on the end triangles of a prism. This form recurs very often, and was noted, last month, as seen in copper (Plate VI, 3); it revolves with extreme rapidity around its longitudinal axis, and looks like a pencil sharpened at both ends, or a cigar tapering at both ends; we habitually spoke of it as "the cigar." It appears to be strongly coherent, for, as will be seen below, its six atoms remain attached to each other as meta-compounds and even when divided into two triplets as hyper-compounds, they revolve round each other. Above the tetrahedron is a balloon-shaped figure, apparently drawn into shape by the attraction of the tetrahedron. The body below the tetrahedron looks like a coil of rope, and contains fifteen atoms; they are arranged on a slanting disk in a flat ring, and the force goes in at the top of one atom, and out of the bottom of it into the top of the next, and so on, making a closed circuit. The two little spheres, each containing a triplet, are like fill-up paragraphs to a compositor--they seem to be kept standing and popped in where wanted. The sphere marked _x_ is a proto-compound, the balloon when set free. As was noted under gold (p. 41), sixteen occultum bodies, re-arranged, make up the connecting rod in gold:-- OCCULTUM: Tetrahedron 24 Balloon 9 Triplets 6 Rope-circle 15 ---- Total 54 ---- Atomic weight Not known Number weight 54/18 3 DISSOCIATION OF ATOMS. Before proceeding to the study of other chemical atoms, as to their general internal arrangements, it is desirable to follow out, in those already shown, the way in which these atoms break up into simpler forms, yielding successively what we have called proto-, meta-, and hyper-compounds. It is naturally easier to follow these in the simpler atoms than in the more complex, and if the earlier dissociations are shown, the latter can be more readily and more intelligibly described.