A new departure is made at line 920, and it is shown that the atoms must be infinite in number, and space infinite in extent;--the contrary supposition being both inconceivable and incompatible with the origin, preservation, and renewal of all existing things. It is shown also that the existing order of things has not come into being through design, but by infinite experiments through infinite time. The doctrine that all things tend to a centre is denied, and the book concludes with the imaginative presentation of the thought that, if matter were not infinite, the whole visible fabric of the world would perish in a moment, 'and leave not a rack behind.' The second book opens with an impressive passage, in which the security and charm of the contemplative life is contrasted with the restless anxieties and alarms of the life of worldly ambition. The argument then proceeds to explain the process by which these atoms, primordial, indestructible, and infinite in number, combine together in infinite space, so as to carry on the birth, growth, and decay of all things. While the sum of things always remains the same, there is constant change in all phenomena. This is explicable only on the supposition of the original elements being in eternal motion. The atoms are borne through space, either by their own weight, or by contact with one another, with a rapidity of motion far beyond that of any visible bodies. All motion is naturally in a downward direction and in parallel lines, but to account for the contact of the atoms with one another it must be supposed that in their movements they make a slight declension from the straight line at uncertain intervals. This liability to declension is the sole thing to break the chain of necessity--'quod fati foedera rumpat.' It is through this liability in the primal elements that volition in living beings becomes possible. As the sum of matter in the universe is constant, so the motions of the atoms always have been and always will be the same[381]. All things are in ceaseless motion, although they may present to our senses the appearance of perfect rest. It is necessary further to assume the existence of other properties in the atoms, in order to account for the variety in Nature, and the individuality of existing things. They have original differences in form; some are smooth, others round, others rough, others hooked, &c. These varieties in form are not infinite, but limited in number. As the diversity in the world depends on the diversity of these forms, the order and regularity of Nature imply that there is a limit to these varieties. But while they are limited, the individuals of each kind are infinite, otherwise the primordial atoms would be finite in number, and there could be no cohesion among atoms of the same kind, in the vast and chaotic sea of matter-- Unde ubi qua vi et quo pacto congressa coibunt Materiae tanto in pelago turbaque aliena?[382]