uivalent of that universal energy of motion which science recognizes as operating between the particles of matter； and which the theologist personifies as Deity。 It is Pantheistic deity as Anaxagoras conceives it； his may be called the first scientific conception of a non… anthropomorphic god。 In elaborating this conception Anaxagoras proved himself one of the most remarkable scientific dreamers of antiquity。 To have substituted for the Greek Pantheon of anthropomorphic deities the conception of a non…anthropomorphic immaterial and ethereal entity； of all things in the world 〃the most rarefied and the purest；〃 is to have performed a feat which； considering the age and the environment in which it was accomplished； staggers the imagination。 As a strictly scientific accomplishment the great thinker's conception of primordial elements contained a germ of the truth which was to lie dormant for 2200 years； but which then； as modified and vitalized by the genius of Dalton； was to dominate the new chemical science of the nineteenth century。 If there are intimations that the primordial element of Anaxagoras and of Dalton may turn out in the near future to be itself a compound； there will still remain the yet finer particles of the nous of Anaxagoras to baffle the most subtle analysis of which to…day's science gives us any pre…vision。 All in all； then； the work of Anaxagoras must stand as that of perhaps the most far…seeing scientific imagination of pre…Socratic antiquity。
LEUCIPPUS AND DEMOCRITUS 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 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。 It is possible that this effort at poetical restitution has carried the enthusiast too far。 There is； indeed； a curious suggestiveness in the theory of Democritus； there is philosophical allurement in his reduction of all matter to a single element； it contains； it may be； not merely a germ of the science of the nineteenth…century chemistry； but perhaps the germs also of the yet undeveloped chemistry of the twentieth century。 Yet we dare suggest that in their enthusiasm for the atomic theory of Democritus the historians of our generation have done something less than justice to that philosopher's precursor； Anaxagoras。 And one suspects that the mere accident of a name has been instrumental in producing this result。 Democritus called his primordial element an atom； Anaxagoras； too； conceived a primordial element； but he called it merely a seed or thing； he failed to christen it distinctively。 Modern science adopted the word atom and gave it universal vogue。 It owed a debt of gratitude to Democritus for supplying it the word； but it somewhat overpaid the debt in too closely linking the new meaning of the word with its old original one。 For； let it be clearly understood； the Daltonian atom is not precisely comparable with the atom of Democritus。 The atom； as Democritus conceived it； was monistic； all atoms； according to this hypothesis； are of the same substance； one atom differs from another merely in size and shape； but not at all in quality。 But the Daltonian hypothesis conceived； and nearly all the experimental efforts of the nineteenth century seemed to prove； that there are numerous classes of atoms； each differing in its very essence from the others。 As the case stands to…day the chemist deals with seventy…odd substances； which he calls elements。 Each one of these substances is； as he conceives it； made up of elementary atoms having a unique personality； each differing in quality from all the others。 As far as experiment has thus far safely carried us； the atom of gold is a primordial element which remains an atom of gold and nothing else； no matter with what other atoms it is associated。 So； too； of the atom of silver； or zinc； or sodiumin short； of each and every one of the seventy…odd elements。 There are； indeed； as we shall see； experiments that suggest the dissolution of the atomthat suggest； in short； that the Daltonian atom is misnamed； being a structure that may； under certain conditions； be broken asunder。 But these experiments have； as yet； the warrant rather of philosophy than of pure science； and to…day we demand that the philosophy of science shall be the handmaid of experiment。 When experiment shall have demonstrated that the Daltonian atom is a compound； and that in truth there is but a single true atom； which； combining with its fellows perhaps in varying numbers and in different special relations； produces the Daltonian atoms； then the philosophical theory of monism will have the experimental warrant which to…day it lacks； then we shall be a step nearer to the atom of Democritus in one direction； a step farther away in the other。 We shall be nearer； in that the conception of Democritus was； in a sense； monistic； farther away； in that all the atoms of Democritus； large and small alike； were considered as permanently fixed in size。 Democritus postulated all his atoms as of the same substance； differing not at all in quality； yet he was obliged to conceive that the varying size of the atoms gave to them varying functions which amounted to qualitative differences。 He might claim for his largest atom the same quality of substance as for his smallest； but so long as he conceived that the large atoms； when adjusted together to form a tangible substance； formed a substance different in quality from the substance which the small atoms would make up when similarly grouped； this concession amounts to the predication of difference of quality between the atoms themselves。 The entire question reduces itself virtually to a quibble over the word quality； So long as one atom conceived to be primordial and indivisible is conceded to be of such a nature as necessarily to produce a different impression on our senses； when grouped with its fellows； from the impression produced by other atoms when similarly grouped； such primordial atoms do differ among themselves in precisely the same way for all practical purposes as do the primordial elements of Anaxagoras。 The monistic conception towards which tw