All the works of Democritus, which were numerous, are lost. He was the first to teach that the milky way was occasioned by a confused light from a multitude of stars. He may be considered as the parent of experimental philosophy; in the prosecution of which he was so ardent, that he declared he would prefer the discovery of one of the causes of the works of nature, to the diadem of Persia. He is said to have made artificial emeralds by chemical means, and to have tinged them with various colors; he likewise found the art of dissolving stones and softening ivory. He was the author of the atomic theory; he viewed all matter, in which he included mind, as reducible to atoms; he considered the universe to consist only of matter and empty space. The mind he regarded as round atoms of fire. He argued that nothing could arise out of nothing; and also that nothing could utterly perish and become nothing. Hence he inferred the eternity of the universe, and dispensed with the existence of a Creator. He explained the difference in substances by a difference in their component atoms; and all material phenomena, by different motions, backward or forward, taking place of necessity. He did not seem to perceive that under this word, _necessity_, he concealed a deity. He explained sensation by supposing sensible images to issue from bodies. In moral philosophy, he only taught that a cheerful state of mind was the greatest attainable good. The theories of Democritus appear absurd enough in our time; but philosophy was then in its infancy. His struggles after light and truth display the darkness of the age, and the ingenuity of the philosopher. They may also teach us by what a process of mental toil, for centuries piled upon centuries, the knowledge we possess has been attained. The school he established, was supplanted, about a century after, by that of Epicurus. [Illustration] [Footnote 12: Heraclitus flourished about 500 years B. C. He was a native of Ephesus; and being of a melancholy disposition, he spent his time in mourning and weeping over the frailties of human nature, and the miseries of human life. He employed himself for a time, in writing different treatises, in which he maintained that all things are governed by a fatal necessity. His opinions, in some things, were adopted by the Stoics. He became at last a man-hater, and retired to the mountains, so as to be entirely separated from his fellow-men. Here he fed on grass, which brought on a dropsical complaint: to get cured of this, he returned to the town. He established his residence on a dunghill, hoping that the warmth might dissipate his disease; but this proved ineffectual, and he died in his sixtieth year.] [Illustration] PERICLES.