But we must not leave this alluring field of speculation as to the nature of matter without referring to another scientific guess, which soon followed that of Anaxagoras and was destined to gain even wider fame, and which in modern times has been somewhat unjustly held to eclipse the glory of the other achievement. We mean, of course, the atomic theory of Leucippus and Democritus. This theory reduced all matter to primordial elements, called atoms gr atoma because they are by hypothesis incapable of further division. These atoms, making up the entire material universe, are in this theory conceived as qualitatively identical, differing from one another only in size and perhaps in shape. The union of different-sized atoms in endless combinations produces the diverse substances with which our senses make us familiar.

Before we pass to a consideration of this alluring theory, and particularly to a comparison of it with the theory of Anaxagoras, we must catch a glimpse of the personality of the men to whom the theory owes its origin. One of these, Leucippus, presents so uncertain a figure as to be almost mythical. Indeed, it was long questioned whether such a man had actually lived, or whether be were not really an invention of his alleged disciple, Democritus. Latterday scholarship, however, accepts him as a real personage, though knowing scarcely more of him than that he was the author of the famous theory with which his name was associated. It is suggested that he was a wanderer, like most philosophers of his time, and that later in life he came to Abdera, in Thrace, and through this circumstance became the teacher of Democritus. This fable answers as well as another. What we really know is that Democritus himself, through whose writings and teachings the atomic theory gained vogue, was born in Abdera, about the year 460 B.C.—that is to say, just about the time when his great precursor, Anaxagoras, was migrating to Athens. Democritus, like most others of the early Greek thinkers, lives in tradition as a picturesque figure. It is vaguely reported that he travelled for a time, perhaps in the East and in Egypt, and that then he settled down to spend the remainder of his life in Abdera. Whether or not he visited Athens in the course of his wanderings we do not know. At Abdera he was revered as a sage, but his influence upon the practical civilization of the time was not marked. He was pre-eminently a dreamer and a writer. Like his confreres of the epoch, he entered all fields of thought. He wrote voluminously, but, unfortunately, his writings have, for the most part, perished. The fables and traditions of a later day asserted that Democritus had voluntarily put out his own eyes that he might turn his thoughts inward with more concentration. Doubtless this is fiction, yet, as usual with such fictions, it contains a germ of truth; for we may well suppose that the promulgator of the atomic theory was a man whose mind was attracted by the subtleties of thought rather than by the tangibilities of observation. Yet the term "laughing philosopher," which seems to have been universally applied to Democritus, suggests a mind not altogether withdrawn from the world of practicalities.

So much for Democritus the man. Let us return now to his theory of atoms. This theory, it must be confessed, made no very great impression upon his contemporaries. It found an expositor, a little later, in the philosopher Epicurus, and later still the poet Lucretius gave it popular expression. But it seemed scarcely more than the dream of a philosopher or the vagary of a poet until the day when modern science began to penetrate the mysteries of matter. When, finally, the researches of Dalton and his followers had placed the atomic theory on a surer footing as the foundation of modern chemistry, the ideas of the old laughing philosopher of Abdera, which all along had been half derisively remembered, were recalled with a new interest. Now it appeared that these ideas had curiously foreshadowed nineteenth-century knowledge. It appeared that away back in the fifth century B.C. a man had dreamed out a conception of the ultimate nature of matter which had waited all these centuries for corroboration. And now the historians of philosophy became more than anxious to do justice to the memory of Democritus.