of phenomena, but he could do this without bringing the two studies into any immediate connexion with each other. Such seems to have been the case with Anaxagoras. He was a professional astronomer and also the author of a modified atomic hypothesis. This, from its greater complexity, seems more likely to have been suggested by the purely quantitative conception of Leucippus than to have preceded it in the order of evolution. Democritus, and probably his teacher also, drew a very sharp distinction between what were afterwards called the primary and secondary qualities of matter. Extension and resistance alone had a real existence in Nature, while the attributes corresponding to our special sensations, such as temperature, taste, and colour, were only subjectively, or, as he expressed it, conventionally true. Anaxagoras affirmed no less strongly than his younger contemporaries that the sum of being can neither be increased nor diminished, that all things arise and perish by combination and division, and that bodies are formed out of indestructible elements; like the Atomists, again, he regarded these elementary substances as infinite in number and inconceivably minute; only he considered them as qualitatively distinct, and as resembling on an infinitesimal scale the highest compounds that they build up. Not only were gold, iron, and the other metals formed of homogeneous particles, but such substances as flesh, bone, and blood were, according to him, equally simple, equally decomposable, into molecules of like nature with themselves. Thus, as Aristotle well observes, he reversed the method of Empedocles, and taught that earth, air, fire, and water were really the most complex of all bodies, since they supplied nourishment to the living tissues, and therefore must contain within themselves the multitudinous variety of units by whose aggregation individualised organic substance is made up.[31] Furthermore, our philosopher held that originally this intermixture had been still more thoroughgoing, all possible qualities being simultaneously present in the smallest particles of matter. The resulting state of chaotic confusion lasted until Nous, or Reason, came and segregated the heterogeneous elements by a process of continuous differentiation leading up to the present arrangement of things. Both Plato and Aristotle have commended Anaxagoras for introducing into speculation the conception of Reason as a cosmic world-ordering power; both have censured him for making so little use of his own great thought, for attributing almost everything to secondary, material, mechanical causes; for not everywhere applying the teleological method; in fact, for not anticipating the Bridgewater Treatises and proving that the world is constructed on a plan of perfect wisdom and goodness. Less fortunate than the Athenians, we cannot purchase the work of Anaxagoras on Nature at an orchestral book-stall for the moderate price