(97.) Attractions may be primarily distributed into two classes; one consisting of those which exist between the molecules or constituent parts of bodies, and the other between bodies themselves. The former are sometimes called, for distinction, _molecular_ or _atomic_ attractions. Without the agency of molecular forces, the whole face of nature would be deprived of variety and beauty; the universe would be a confused heap of material atoms dispersed through space, without form, shape, coherence, or motion. Bodies would neither have the forms of solid, liquid, or air; heat and light would no longer produce their wonted effects; organised beings could not exist; life itself, as connected with body, would be extinct. Atoms of matter, whether distant or in juxtaposition, would have no tendency to change their places, and all would be eternal stillness and rest. If, then, we are asked for a proof of the existence of molecular forces, we may point to the earth and to the heavens; we may name every object which can be seen or felt. The whole material world is one great result of the influence of these powerful agents. (98.) It has been proved (11. _et seq._) that the constituent particles of bodies are of inconceivable minuteness, and that they are not in immediate contact (23), but separated from each other by interstitial spaces, which, like the atoms themselves, although too small to be directly observed, yet are incontestably proved to exist, by observable phenomena, from which their existence demonstratively follows. The resistance which every body opposes to compression, proves that a repulsive influence prevails between the particles, and that this repulsion is the cause which keeps the atoms separate, and maintains the interstitial spaces just mentioned. Although this repulsion is found to exist between the molecules of all substances whatever, yet it has different degrees of energy in different bodies. This is proved by the fact, that some substances admit of easy compression, while in others, the exertion of considerable force is necessary to produce the smallest diminution in bulk. The space around each atom of a body, through which this repulsive influence extends, is generally limited, and immediately beyond it, a force of the opposite kind is manifested, viz. attraction. Thus, in solid bodies, the particles resist separation as well as compression, and the application of force is as necessary to break the body, or divide it into separate parts, as to force its particles into closer aggregation. It is by virtue of this attraction that solid bodies maintain their figure, and that their parts are not separated and scattered like those of fluids, merely by their own weight. This force is called the _attraction of cohesion_.