a history of science-1-第35章

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mprisoned　in　the　substance　of　the　earth　seems　not　far　afield。　But　a　far　more　remarkable　insight　than　this　would　imply　was　shown　by　Anaxagoras　when　he　asserted　that　a　certain　amount　of　air　is　contained　in　water；　and　that　fishes　breathe　this　air。　The　passage　of　Aristotle　in　which　this　opinion　is　ascribed　to　Anaxagoras　is　of　sufficient　interest　to　be　quoted　at　length：　〃Democritus；　of　Abdera；〃　says　Aristotle；　〃and　some　others；　that　have　spoken　concerning　respiration；　have　determined　nothing　concerning　other　animals；　but　seem　to　have　supposed　that　all　animals　respire。　But　Anaxagoras　and　Diogenes　（Apolloniates）；　who　say　that　all　animals　respire；　have　also　endeavored　to　explain　how　fishes；　and　all　those　animals　that　have　a　hard；　rough　shell；　such　as　oysters；　mussels；　etc。；　respire。　And　Anaxagoras；　indeed；　says　that　fishes；　when　they　emit　water　through　their　gills；　attract　air　from　the　mouth　to　the　vacuum　in　the　viscera　from　the　water　which　surrounds　the　mouth；　as　if　air　was　inherent　in　the　water。〃＇2＇　It　should　be　recalled　that　of　the　three　philosophers　thus　mentioned　as　contending　that　all　animals　respire；　Anaxagoras　was　the　elder；　he；　therefore；　was　presumably　the　originator　of　the　idea。　It　will　be　observed；　too；　that　Anaxagoras　alone　is　held　responsible　for　the　idea　that　fishes　respire　air　through　their　gills；　〃attracting〃　it　from　the　water。　This　certainly　was　one　of　the　shrewdest　physiological　guesses　of　any　age；　if　it　be　regarded　as　a　mere　guess。　With　greater　justice　we　might　refer　to　it　as　a　profound　deduction　from　the　principle　of　the　uniformity　of　nature。　In　making　such　a　deduction；　Anaxagoras　was　far　in　advance　of　his　time　as　illustrated　by　the　fact　that　Aristotle　makes　the　citation　we　have　just　quoted　merely　to　add　that　〃such　things　are　impossible；〃　and　to　refute　these　〃impossible〃　ideas　by　means　of　metaphysical　reasonings　that　seemed　demonstrative　not　merely　to　himself；　but　to　many　generations　of　his　followers。　We　are　told　that　Anaxagoras　alleged　that　all　animals　were　originally　generated　out　of　moisture；　heat；　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