a history of science-1-第31章

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；　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　i