Sensation and perception were forms in which these external forces acted upon the more nimble and lively existences, more particularly on living creatures. For every body was continually sending forth emanations or images resembling itself sufficiently in form and structure to affect perceptive bodies with an apprehension of that form and structure. These images travelled by a process of successive transmission, similar to that by which wave-motions are propagated in water. They were, in other words, not movements of the _particles_ of the objects, which latter must otherwise in time grow less and fade away, but a modification in the arrangement of the particles immediately next the object, which modification reproduced itself in the next following, and so on right through the medium to the perceptive body.
These images tended by extension in all directions to reach vast dimensions at times, and to influence the minds of men in sleep and on other occasions in strange ways. Hence men imagined gods, and attributed those mighty phenomena of nature--earthquakes, tempests, lightning and thunder, and dire eclipses of sun and moon, to the vaguely visible powers which they imagined they saw. There was indeed a soul or spirit of the universe, as there was a soul or spirit of every individual thing that constituted it. But this was only a finer system of atoms after all. All else is convention or dream; the only realities are Atoms and Emptiness, Matter and Space.
Of absolute verity through the senses we know nothing; our perceptions are only conventional interpretations of we know not what. For to other living creatures these same sensations have other meanings than they have to us, and even the same person is not always affected alike by the same thing; which then is the true of two differing perceptions we cannot say. And therefore either there is no such thing as truth, or, at all events, we know through the senses nothing of it. The only genuine knowledge is that which transcends appearances, and reasons out what is, irrespective of appearances,--in other words, the only genuine knowledge is that of the (atomic) philosopher. And his knowledge is { 81} the result of the happy mixture of his atoms whereby all is in equal balance, neither too hot nor too cold. Such a man seeing in the mind's eye the whole universe a tissue of whirling and interlacing atoms, with no real mystery or terror before or after, will live a life of cheerful fearlessness, undisturbed by terrors of a world to come or of powers unseen. His happiness is not in feastings or in gold, but in a mind at peace. And three human perfections he will seek to attain: to reason rightly, to speak graciously, to do his duty.