11. We cannot (M. Necker goes on to remark) consider the Integrant Molecules as individuals. These are useful abstractions, but abstractions only, which we must not deal with as real objects. Haüy himself warns us[57] that his doctrine of increments is a purely abstract conception, and that nature, in fact, follows a different process. Accordingly, Weiss and Mohs express laws identical with those of Haüy, without even [149] speaking of molecules; and Wollaston and Davy have deemed it probable that the molecules are not polyhedrons, but spheres or spheroids. Such mere creations of the mind can never be treated as individuals. If the maxim of natural history,—that the Species is a collection of Individuals—be applied so as to make those individuals mere abstractions; or if, instead of Individuals, we take such an abstraction as Substance or Matter, the course of natural history is altogether violated. And yet this errour has hitherto generally prevailed; and mineralogists have classified, not things, but abstract ideas[58].
[57] Ib. p. 61.
[58] Règne Mineral, p. 67.
12. But it may be said[59], will not the small solids obtained by Cleavage better answer the idea of individuals? To this it is replied, that these small solids have no independent existence. They are only the result of a mode of division. They are never found separate and independent. The secondary forms which they compose are determined by various circumstances (the nature of the solution, &c.); and the cleavage which produces these small solids is only one result among many, from the crystalline forces[60].
[59] Ib. p. 69.
[60] Ib. p. 71.
Thus neither Integrant Molecules, nor Solids obtained by Cleavage, can be such mineralogical Individuals as the spirit of natural history requires. Hence it appears that we must take the real Crystals for Individuals[61].
[61] Ib. p. 73.
13. We must, however, reject crystals (generally large ones) which are obviously formed of several smaller ones of a similar form (as occurs so often in quartz and calc spar). We must also distinguish cases in which a large regular form is composed of smaller but different regular forms (as octahedrons of fluor spar made up of cubes). Here the small component forms are the individuals. Also we must notice the cases[62] in which we have a natural crystal, similar to the primary form. Here the face will show whether [150] the body is a result obtained by cleavage or a natural individual.
[62] Ib. p. 75.