, a philosopher of considerable eminence in the fifth century B. C. the first propagator of the system of atoms, is said by Diogenes Laertius, who has written his life, to have been a native of Elea. He was a disciple of Zeno the Eleatic philosopher. Dissatisfied with the attempts of former philosophers to account for the nature and origin of the universe metaphysically, Leucippus, and his follower Democritus, determined to restore the alliance between reason and the senses, which metaphysical subtleties had dissolved, by introducing the doctrine of indivisible atoms, possessing within themselves a principle of motion; and although several other philosophers, before their time, had considered matter as divisible into indefinitely small particles, Leucippus and Democritus were the first who taught, that these particles were originally destitute of all qualities except figure and motion, and therefore may justly be reckoned the authors of the atomic system of philosophy. They looked upon the qualities, which preceding philosophers had ascribed to matter, as the mere creatures of abstraction; and they determined to admit nothing into their system, which they could not establish upon the sure testimony of the senses. They were also of opinion, that both the Eleatic philosophers, and those of other sects, had unnecessarily encumbered their respective systems, by assigning some external or internal cause of motion, of a nature not to be discovered by the senses. They therefore resolved to reject all metaphysical principles, and, in their explanation of the phenomena of nature, to proceed upon no other ground than the sensible and mechanical properties of bodies. By the help of the internal principle of motion, which they attributed to the indivisible particles of matter, they made a feeble and fanciful effort to account for the production of all natural bodies from physical causes, without the intervention of Deity. But, whether they meant entirely to discard the notion of a divine nature from the universe, is uncertain. This first idea of the atomic system was improved by Democritus, and afterwards carried to all the perfection which a system so fundamentally defective would admit of, by Epicurus. The following summary of the doctrine of Leucippus will exhibit the infant state of the atomic philosophy, and at the same time sufficiently expose its absurdity.

The universe, which is infinite, is in part a. plenum, and in part a vacuum. The plenum contains innumerable | corpuscles or atoms, of various figures, which falling into the vacuum, struck against each other; and hence arose a variety of curvilinear motions, which continued till, at length, atoms of similar forms met together, and bodies were produced. The primary atoms being specifically of equal weight, and not being able, on account of their multitude, to move in circles, the smaller rose to the exterior parts of the vacuum, whilst the larger, entangling themselves, formed a spherical shell, which revolved about its centre, and which included within itself all kinds of bodies. This central mass was gradually increased by a perpetual accession of particles from the surrounding shell, till at last the earth was formed. In the mean time, the spherical shell was continually supplied with new bodies, which, in its revolution, is gathered up from without. Of the particles thus collected in the spherical shell, some in their combination formed humid masses, which, by their circular motion, gradually became dry, and were at length ignited, and became stars. The sun was formed in the same manner, in the exterior surface of the shell; and the moon, in its interior surface. In this manner the world was formed; and by an inversion of the process, it will at length be dissolved. 1

1 DM*. Laertius. Stanley’s Hist. —Brucker Gen. Dict.