a history of science-1-第22章

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　so　obviously　bright　may　be　in　reality　dark。　The　germ　of　the　conception　of　what　the　philosopher　speaks　of　as　the　noumena；　or　actualities；　back　of　phenomena　or　appearances；　had　perhaps　this　crude　beginning。　Anaxagoras　could　surely　point　to　the　moon　in　support　of　his　seeming　paradox　that　snow；　being　really　composed　of　water；　which　is　dark；　is　in　reality　black　and　not　whitea　contention　to　which　we　shall　refer　more　at　length　in　a　moment。　But　there　is　yet　another　striking　thought　connected　with　this　new　explanation　of　the　phases　of　the　moon。　The　explanation　implies　not　merely　the　reflection　of　light　by　a　dark　body；　but　by　a　dark　body　of　a　particular　form。　Granted　that　reflections　are　in　question；　no　body　but　a　spherical　one　could　give　an　appearance　which　the　moon　presents。　The　moon；　then；　is　not　merely　a　mass　of　earth；　it　is　a　spherical　mass　of　earth。　Here　there　were　no　flaws　in　the　reasoning　of　Anaxagoras。　By　scientific　induction　he　passed　from　observation　to　explanation。　A　new　and　most　important　element　was　added　to　the　science　of　astronomy。　Looking　back　from　the　latter…day　stand…point；　it　would　seem　as　if　the　mind　of　the　philosopher　must　have　taken　one　other　step：　the　mind　that　had　conceived　sun；　moon；　stars；　and　earth　to　be　of　one　substance　might　naturally；　we　should　think；　have　reached　out　to　the　further　induction　that；　since　the　moon　is　a　sphere；　the　other　cosmic　bodies；　including　the　earth；　must　be　spheres　also。　But　generalizer　as　he　was；　Anaxagoras　was　too　rigidly　scientific　a　thinker　to　make　this　assumption。　The　data　at　his　command　did　not；　as　he　analyzed　them；　seem　to　point　to　this　conclusion。　We　have　seen　that　Pythagoras　probably；　and　Parmenides　surely；　out　there　in　Italy　had　conceived　the　idea　of　the　earth's　rotundity；　but　the　Pythagorean　doctrines　were　not　rapidly　taken　up　in　the　mother…　country；　and　Parmenides；　it　must　be　recalled；　was　a　strict　contemporary　of　Anaxagoras　himself。　It　is　no　reproach；　therefore；　to　the　Clazomenaean　philosopher　that　he　should　have　held　to　the　old　idea　that　the　earth　is　flat；　or　at　most　a　convex　diskthe　latter　being　the　Babylonian　conception　which　probably　dominated　that　Milesian　school　to　which　Anaxagoras　harked　back。　Anaxagoras　may　never　have　seen　an　eclipse　of　the　moon；　and　even　if　he　had　he　might　have　reflected　that；　from　certain　directions；　a　disk　may　throw　precisely　the　same　shadow　as　a　sphere。　Moreover；　in　reference　to　the　shadow　cast　by　the　earth；　there　was；　so　Anaxagoras　believed；　an　observation　open　to　him　nightly　which；　we　may　well　suppose；　was　not　without　influence　in　suggesting　to　his　mind　the　probable　shape　of　the　earth。　The　Milky　Way；　which　doubtless　had　puzzled　astronomers　from　the　beginnings　of　history　and　which　was　to　continue　to　puzzle　them　for　many　centuries　after　the　day　of　Anaxagoras；　was　explained　by　the　Clazomenaean　philosopher　on　a　theory　obviously　suggested　by　the　theory　of　the　moon's　phases。　Since　the　earth…　like　moon　shines　by　reflected　light　at　night；　and　since　the　stars　seem　obviously　brighter　on　dark　nights；　Anaxagoras　was　but　following　up　a　perfectly　logical　induction　when　he　propounded　the　theory　that　the　stars　in　the　Milky　Way　seem　more　numerous　and　brighter　than　those　of　any　other　part　of　the　heavens；　merely　because　the　Milky　Way　marks　the　shadow　of　the　earth。　Of　course　the　inference　was　wrong；　so　far　as　the　shadow　of　the　earth　is　concerned；　yet　it　contained　a　part　truth；　the　force　of　which　was　never　fully　recognized　until　the　time　of　Galileo。　This　consists　in　the　assertion　that　the　brightness　of　the　Milky　Way　is　merely　due　to　the　glow　of　many　stars。　The　shadow…　theory　of　Anaxagoras　would　naturally　cease　to　have　validity　so　soon　as　the　sphericity　of　the　earth　was　proved；　and　with　it；　seemingly；　fell　for　the　time　the　companion　theory　that　the　Milky　Way　is　made　up　of　a　multitude　of　stars。　It　has　been　said　by　a　modern　critic＇1＇　that　the　shadow…theory　was　childish　in　that　it　failed　to　note　that　the　Milky　Way　does　not　follow　the　course　of　the　ecliptic。　But　this　criticism　only　holds　good　so　long　as　we　reflect　on　the　true　character　of　the　earth　as　a　symmetrical　body　poised　in　space。　It　is　quite　possible　to　conceive　a　body　occupying　the　position　of　the　earth　with　reference　to　the　sun　which　would　cast　a　shadow　having　such　a　tenuous　form　as　the　Milky　Way　presents。　Such　a　body　obviously　would　not　be　a　globe；　but　a　long…drawn…out；　attenuated　figure。　There　is；　to　be　sure；　no　direct　evidence　preserved　to　show　that　Anaxagoras　conceived　the　world　to　present　such　a　figure　as　this；　but　what　we　know　of　that　philosopher's　close…reasoning；　logical　mind　gives　some　warrant　to　the　assumptiongratuitous　though　in　a　sense　it　be　that　the　author　of　the　theory　of　the　moon's　phases　had　not　failed　to　ask　himself　what　must　be　the　form　of　that　terrestrial　body　which　could　cast　the　tenuous　shadow　of　the　Milky　Way。　Moreover；　we　must　recall　that　the　habitable　earth；　as　known　to　the　Greeks　of　that　day；　was　a　relatively　narrow　band　of　territory；　stretching　far　to　the　east　and　to　the　west。

Anaxagoras　as　Meteorologist　The　man　who　had　studied　the　meteorite　of　aegospotami；　and　been　put　by　it　on　the　track　of　such　remarkable　inductions；　was；　naturally；　not　oblivious　to　the　other　phenomena　of　the　atmosphere。　Indeed；　such　a　mind　as　that　of　Anaxagoras　was　sure　to　investigate　all　manner　of　natural　phenomena；　and　almost　equally　sure　to　throw　new　light　on　any　subject　that　it　investigated。　Hence　it　is　not　surprising　to　find　Anaxagoras　credited　with　explaining　the　winds　as　due　to　the　rarefactions　of　the　atmosphere　produced　by　the　sun。　This　explanation　gives　Anaxagoras　full　right　to　be　called　〃the　father　of　meteorology；〃　a　title　which；　it　may　be；　no　one　has　thought　of　applying　to　him；　chiefly　because　the　science　of　meteorology　did　not　make　its　real　beginnings　until　some　twenty…four　hundred　years　after　the　death　of　its　first　great　votary。　Not　content　with　explaining　the　winds；　this　prototype　of　Franklin　turned　his　attention　even　to　the　tipper　atmosphere。　〃Thunder；〃　he　is　reputed　to　have　said；　〃was　produced　by　the　collision　of　the　clouds；　and　lightning　by　the　rubbing　together　of　the　clouds。〃　We　dare　not　go　so　far　as　to　suggest　that　this　implies　an　association　in　the　mind　of　Anaxagoras　between　the　friction　of　the　clouds　and　the　observed　electrical　effects　generated　by　the　friction　of　such　a　substance　as　amber。　To　make　such　a　suggestion　doubtless　would　be　to　fall　victim　to　the　old　familiar　propensity　to　read　into　Homer　things　that　Homer　never　knew。　Yet　the　significant　fact　remains　that　Anaxagoras　ascribed　to　thunder　and　to　lightning　their　true　position　as　strictly　natural　phenomena。　For　him　it　was　no　god　that　menaced　humanity　with　thundering　voice　and　the　flash　of　his　divine　fires　from　the　clouds。　Little　wonder　that　the　thinker　whose　science　carried　him　to　such　scepticism　as　this　should　have　felt　the　wrath　of　the　superstitious　Athenians。

Biological　Speculations　Passing　from　the　phenomena　of　the　air　to　those　of　the　earth　itself；　we　learn　that　Anaxagoras　explained　an　earthquake　as　being　produced　by　the　returning　of　air　into　the　earth。　We　cannot　be　sure　as　to　the　exact　meaning　here；　though　the　idea　that　gases　are　imprisoned　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　b