artificial origin.  It consists in a tacit agreement among mankind to abstain from injuring one another.  The security that every man has in his person and property, is the great consideration urging to abstinence from injuring others.  But is it not possible to commit injustice with safety?  The answer was, ’Injustice is not an evil in itself, but becomes so from the fear that haunts the injurer of not being able to escape the appointed avengers of such acts.’

The Physics of Epicurus were borrowed in the main from the atomic theory of Democritus, but were modified by him in a manner subservient and contributory to his ethical scheme.  To that scheme it was essential that those celestial, atmospheric, or terrestrial phenomena that the public around him ascribed to the agency and purposes of the gods, should be understood as being produced by physical causes.  An eclipse, an earthquake, a storm, a shipwreck, unusual rain or drought, a good or a bad harvest—­and not merely these, but many other occurrences far smaller and more unimportant, as we may see by the eighteenth chapter of the Characters of Theophrastus—­were then regarded as visitations of the gods, requiring to be interpreted by recognized prophets, and to be appeased by ceremonial expiations.  When once a man became convinced that all these phenomena proceeded from physical agencies, a host of terrors and anxieties would disappear from the mind; and this Epicurus asserted to be the beneficent effect and real recommendation of physical philosophy.  He took little or no thought for scientific curiosity as a motive per se, which both Democritus and Aristotle put so much in the foreground.

Epicurus adopted the atomistic scheme of Democritus, but with some important variations.  He conceived that the atoms all moved with equal velocity in the downward direction of gravity.  But it occurred to him that upon this hypothesis there could never occur any collisions or combinations of the atoms—­nothing but continued and unchangeable parallel lines.  Accordingly, he modified it by saying that the line of descent was not exactly rectilinear, but that each atom deflected a little from the straight line, and each in its own direction and degree; so that it became possible to assume collisions, resiliences, adhesions, combinations, among them, as it had been possible under the variety of original movements ascribed to them by Democritus.  The opponents of Epicurus derided this auxiliary hypothesis; they affirmed that he invented the individual deflection of each atom, without assigning any cause, and only because he was perplexed by the mystery of man’s free-will.  But Epicurus was not more open to attack on this ground than other physical philosophers.  Most of them (except perhaps the most consistent of the Stoic fatalists) believed that some among the phenomena of the universe occurred in regular and predictable sequence, while others were essentially irregular and unpredictable;