Note 167, [p. 108]. A tetrahedron is a solid contained by four triangular surfaces, as fig. 40: of this solid there are many varieties.
Fig. 40.
Note 168, [p. 108]. There are many varieties of the octahedron. In that mentioned in the text, the base a a a a, fig. 38, is a square, but the base may be a rhomb; this solid may also be elongated in the direction of its axis A X, or it may be depressed.
Note 169, pp. [109], [192], [273]. A rhombohedron is a solid contained by six plane surfaces, as in fig. 63, the opposite planes being equal and similar rhombs parallel to one another; but all the planes are not necessarily equal or similar, nor are its angles right angles. In carbonate of lime the angle C A B is 105°·55, and the angle B or C is 75°·05.
Note 170, [p. 109]. Sublimation. Bodies raised into vapour which is again condensed into a solid state.
Note 171, [p. 112]. Platinum. The heaviest of metals; its colour is between that of silver and lead.
Note 172, [p. 113]. The surface of a column of water, or spirit of wine, in a capillary tube, is hollow; and that of a column of quicksilver is convex, or rounded, as in fig. 41.
Note 173, [p. 113]. Inverse ratio, &c. The elevation of the liquid is greater in proportion as the internal diameter of the tube is less.
Note 174, [p. 114]. In fig. 41 the line c d shows the direction of the resulting force in the two cases.