； and earth particles。 Just what opinion he held concerning man's development we are not informed。 Yet there is one of his phrases which suggestswithout； perhaps； quite provingthat he was an evolutionist。 This phrase asserts； with insight that is fairly startling； that man is the most intelligent of animals because he has hands。 The man who could make that assertion must； it would seem； have had in mind the idea of the development of intelligence through the use of hands an idea the full force of which was not evident to subsequent generations of thinkers until the time of Darwin。
Physical Speculations Anaxagoras is cited by Aristotle as believing that 〃plants are animals and feel pleasure and pain； inferring this because they shed their leaves and let them grow again。〃 The idea is fanciful； yet it suggests again a truly philosophical conception of the unity of nature。 The man who could conceive that idea was but little hampered by traditional conceptions。 He was exercising a rare combination of the rigidly scientific spirit with the poetical imagination。 He who possesses these gifts is sure not to stop in his questionings of nature until he has found some thinkable explanation of the character of matter itself。 Anaxagoras found such an explanation； and； as good luck would have it； that explanation has been preserved。 Let us examine his reasoning in some detail。 We have already referred to the claim alleged to have been made by Anaxagoras that snow is not really white； but black。 The philosopher explained his paradox； we are told； by asserting that snow is really water； and that water is dark； when viewed under proper conditionsas at the bottom of a well。 That idea contains the germ of the Clazomenaean philosopher's conception of the nature of matter。 Indeed； it is not unlikely that this theory of matter grew out of his observation of the changing forms of water。 He seems clearly to have grasped the idea that snow on the one hand； and vapor on the other； are of the same intimate substance as the water from which they are derived and into which they may be again transformed。 The fact that steam and snow can be changed back into water； and by simple manipulation cannot be changed into any other substance； finds； as we now believe； its true explanation in the fact that the molecular structure； as we phrase itthat is to say； the ultimate particle of which water is composed； is not changed； and this is precisely the explanation which Anaxagoras gave of the same phenomena。 For him the unit particle of water constituted an elementary body； uncreated； unchangeable； indestructible。 This particle； in association with like particles； constitutes the substance which we call water。 The same particle in association with particles unlike itself； might produce totally different substancesas； for example； when water is taken up by the roots of a plant and becomes； seemingly； a part of the substance of the plant。 But whatever the changed association； so Anaxagoras reasoned； the ultimate particle of water remains a particle of water still。 And what was true of water was true also； so he conceived； of every other substance。 Gold； silver； iron； earth； and the various vegetables and animal tissuesin short； each and every one of all the different substances with which experience makes us familiar； is made up of unit particles which maintain their integrity in whatever combination they may be associated。 This implies； obviously； a multitude of primordial particles； each one having an individuality of its own； each one； like the particle of water already cited； uncreated； unchangeable； and indestructible。 Fortunately； we have the philosopher's own words to guide us as to his speculations here。 The fragments of his writings that have come down to us （chiefly through the quotations of Simplicius） deal almost exclusively with these ultimate conceptions of his imagination。 In ascribing to him； then； this conception of diverse； uncreated； primordial elements； which can never be changed； but can only be mixed together to form substances of the material world； we are not reading back post…Daltonian knowledge into the system of Anaxagoras。 Here are his words： 〃The Greeks do not rightly use the terms 'coming into being' and 'perishing。' For nothing comes into being； nor； yet； does anything perish； but there is mixture and separation of things that are。 So they would do right in calling 'coming into being' 'mixture' and 'perishing' 'separation。' For how could hair come from what is not hair？ Or flesh from what is not flesh？〃 Elsewhere he tells us that （at one stage of the world's development） 〃the dense； the moist； the cold； the dark； collected there where now is earth； the rare； the warm； the dry； the bright； departed towards the further part of the aether。 The earth is condensed out of these things that are separated； for water is separated from the clouds； and earth from the water； and from the earth stones are condensed by the cold； and these are separated farther from the water。〃 Here again the influence of heat and cold in determining physical qualities is kept pre…eminently in mind。 The dense； the moist； the cold； the dark are contrasted with the rare； the warm； the dry； and bright； and the formation of stones is spoken of as a specific condensation due to the influence of cold。 Here； then； we have nearly all the elements of the Daltonian theory of atoms on the one hand； and the nebular hypothesis of Laplace on the other。 But this is not quite all。 In addition to such diverse elementary particles as those of gold； water； and the rest； Anaxagoras conceived a species of particles differing from all the others； not merely as they differ from one another； but constituting a class by themselves； particles infinitely smaller than the others； particles that are described as infinite； self…powerful； mixed with nothing； but existing alone。 That is to say （interpreting the theory in the only way that seems plausible）； these most minute particles do not mix with the other primordial particles to form material substances in the same way in which these mixed with one another。 But； on the other hand； these 〃infinite； self…powerful； and unmixed〃 particles commingle everywhere and in every substance whatever with the mixed particles that go to make up the substances。 There is a distinction here； it will be observed； which at once suggests the modern distinction between physical processes and chemical processes； or； putting it otherwise； between molecular processes and atomic processes； but the reader must be guarded against supposing that Anaxagoras had any such thought as this in mind。 His ultimate mixable particles can be compared only with the Daltonian atom； not with the molecule of the modern physicist； and his 〃infinite； self… powerful； and unmixable〃 particles are not comparable with anything but the ether of the modern physicist； with which hypothetical substance they have many points of resemblance。 But the 〃infinite； self… powerful； and unmixed〃 particles constituting thus an ether…like plenum which permeates all material structures； have also； in the mind of Anaxagoras； a function which carries them perhaps a stage beyond the province of the modern ether。 For these 〃infinite； self powerful； and unmixed〃 particles are imbued with； and； indeed； themselves constitute； what Anaxagoras terms nous； a word which the modern translator has usually paraphrased as 〃mind。〃 Neither that word nor any other available one probably conveys an accurate idea of what Anaxagoras meant to imply by the word nous。 For him the word meant not merely 〃mind〃 in the sense of receptive and comprehending intelligence； but directive and creative intelligence as well。 Again let Anaxagoras speak for himself： 〃Other things include a portion of everything； but nous is infinite； and self…powerful； and mixed with nothing； but it exists alone； itself by itself。 For if it were not by itself； but were mixed with anything else； it would include parts of all things； if it were mixed with anything； for a portion of everything exists in every thing； as has been said by me before； and things mingled with it would prevent it from having power over anything in the same way that it does now that it is alone by itself。 For it is the most rarefied of all things and the purest； and it has all knowledge in regard to everything and the greatest power； over all that has life； both greater and less； nous rules。 And nous ruled the rotation of the whole； so that it set it in rotation in the beginning。 First it began the rotation from a small beginning； then more and more was included in the motion； and yet more will be included。 Both the mixed and the separated and distinct； all things nous recognized。 And whatever things were to be； and whatever things were； as many as are now； and whatever things shall be； all these nous arranged in order； and it arranged that rotation； according to which now rotate stars and sun and moon and air and aether； now that they are separated。 Rotation itself caused the separation； and the dense is separated from the rare； the warm from the cold； the bright from the dark； the dry from the moist。 And when nous began to set things in motion； there was separation from everything that was in motion； all this was made distinct。 The rotation of the things that were moved and made distinct caused them to be yet more distinct。〃＇3＇ Nous； then； as Anaxagoras conceives it； is 〃the most rarefied of all things； and the purest； and it has knowledge in regard to everything and the greatest power； over all that has life； both greater and less； it rules。〃 But these are postulants of omnipresence and omniscience。 In other words； nous is nothing less than the omnipotent artificer of the material universe。 It lacks nothing of the power of deity； save only that we are not assured that it created the primordial particles。 The creation of these particles was a conception that for Anaxagoras； as for the modern Spencer； lay beyond the range of imagination。 Nous is the artificer； working with 〃uncreated〃 particles。 Back of nous and the particles lies； for an Anaxagoras as for a Spencer； the Unknowable。 But nous itself is the equivalent of that universal energy of motion which science recognizes as operating between the partic