a history of science-1-第16章

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640　to　546　B。C。may　be　accepted　as　at　least　approximately　trustworthy；　and　the　specific　discoveries　ascribed　to　him　illustrate　equally　well　the　stage　of　development　of　Greek　thought；　whether　Thales　himself　or　one　of　his　immediate　disciples　were　the　discoverer。　We　have　already　mentioned　the　feat　which　was　said　to　have　given　Thales　his　great　reputation。　That　Thales　was　universally　credited　with　having　predicted　the　famous　eclipse　is　beyond　question。　That　he　actually　did　predict　it　in　any　precise　sense　of　the　word　is　open　to　doubt。　At　all　events；　his　prediction　was　not　based　upon　any　such　precise　knowledge　as　that　of　the　modern　astronomer。　There　is；　indeed；　only　one　way　in　which　he　could　have　foretold　the　eclipse；　and　that　is　through　knowledge　of　the　regular　succession　of　preceding　eclipses。　But　that　knowledge　implies　access　on　the　part　of　some　one　to　long　series　of　records　of　practical　observations　of　the　heavens。　Such　records；　as　we　have　seen；　existed　in　Egypt　and　even　more　notably　in　Babylonia。　That　these　records　were　the　source　of　the　information　which　established　the　reputation　of　Thales　is　an　unavoidable　inference。　In　other　words；　the　magical　prevision　of　the　father　of　Greek　thought　was　but　a　reflex　of　Oriental　wisdom。　Nevertheless；　it　sufficed　to　establish　Thales　as　the　father　of　Greek　astronomy。　In　point　of　fact；　his　actual　astronomical　attainments　would　appear　to　have　been　meagre　enough。　There　is　nothing　to　show　that　he　gained　an　inkling　of　the　true　character　of　the　solar　system。　He　did　not　even　recognize　the　sphericity　of　the　earth；　but　held；　still　following　the　Oriental　authorities；　that　the　world　is　a　flat　disk。　Even　his　famous　cosmogonic　guess；　according　to　which　water　is　the　essence　of　all　things　and　the　primordial　element　out　of　which　the　earth　was　developed；　is　but　an　elaboration　of　the　Babylonian　conception。　When　we　turn　to　the　other　field　of　thought　with　which　the　name　of　Thales　is　associatednamely；　geometrywe　again　find　evidence　of　the　Oriental　influence。　The　science　of　geometry；　Herodotus　assures　us；　was　invented　in　Egypt。　It　was　there　an　eminently　practical　science；　being　applied；　as　the　name　literally　suggests；　to　the　measurement　of　the　earth's　surface。　Herodotus　tells　us　that　the　Egyptians　were　obliged　to　cultivate　the　science　because　the　periodical　inundations　washed　away　the　boundary…lines　between　their　farms。　The　primitive　geometer；　then；　was　a　surveyor。　The　Egyptian　records；　as　now　revealed　to　us；　show　that　the　science　had　not　been　carried　far　in　the　land　of　its　birth。　The　Egyptian　geometer　was　able　to　measure　irregular　pieces　of　land　only　approximately。　He　never　fully　grasped　the　idea　of　the　perpendicular　as　the　true　index　of　measurement　for　the　triangle；　but　based　his　calculations　upon　measurements　of　the　actual　side　of　that　figure。　Nevertheless；　he　had　learned　to　square　the　circle　with　a　close　approximation　to　the　truth；　and；　in　general；　his　measurement　sufficed　for　all　his　practical　needs。　Just　how　much　of　the　geometrical　knowledge　which　added　to　the　fame　of　Thales　was　borrowed　directly　from　the　Egyptians；　and　how　much　he　actually　created　we　cannot　be　sure。　Nor　is　the　question　raised　in　disparagement　of　his　genius。　Receptivity　is　the　first　prerequisite　to　progressive　thinking；　and　that　Thales　reached　out　after　and　imbibed　portions　of　Oriental　wisdom　argues　in　itself　for　the　creative　character　of　his　genius。　Whether　borrower　of　originator；　however；　Thales　is　credited　with　the　expression　of　the　following　geometrical　truths：　1。　That　the　circle　is　bisected　by　its　diameter。　2。　That　the　angles　at　the　base　of　an　isosceles　triangle　are　equal。　3。　That　when　two　straight　lines　cut　each　other　the　vertical　opposite　angles　are　equal。　4。　That　the　angle　in　a　semicircle　is　a　right　angle。　5。　That　one　side　and　one　acute　angle　of　a　right…angle　triangle　determine　the　other　sides　of　the　triangle。　It　was　by　the　application　of　the　last　of　these　principles　that　Thales　is　said　to　have　performed　the　really　notable　feat　of　measuring　the　distance　of　a　ship　from　the　shore；　his　method　being　precisely　the　same　in　principle　as　that　by　which　the　guns　are　sighted　on　a　modern　man…of…war。　Another　practical　demonstration　which　Thales　was　credited　with　making；　and　to　which　also　his　geometrical　studies　led　him；　was　the　measurement　of　any　tall　object；　such　as　a　pyramid　or　building　or　tree；　by　means　of　its　shadow。　The　method；　though　simple　enough；　was　ingenious。　It　consisted　merely　in　observing　the　moment　of　the　day　when　a　perpendicular　stick　casts　a　shadow　equal　to　its　own　length。　Obviously　the　tree　or　monument　would　also　cast　a　shadow　equal　to　its　own　height　at　the　same　moment。　It　remains　then　but　to　measure　the　length　of　this　shadow　to　determine　the　height　of　the　object。　Such　feats　as　this　evidence　the　practicality　of　the　genius　of　Thales。　They　suggest　that　Greek　science；　guided　by　imagination；　was　starting　on　the　high…road　of　observation。　We　are　told　that　Thales　conceived　for　the　first　time　the　geometry　of　lines；　and　that　this；　indeed；　constituted　his　real　advance　upon　the　Egyptians。　We　are　told　also　that　he　conceived　the　eclipse　of　the　sun　as　a　purely　natural　phenomenon；　and　that　herein　lay　his　advance　upon　the　Chaldean　point　of　view。　But　if　this　be　true　Thales　was　greatly　in　advance　of　his　time；　for　it　will　be　recalled　that　fully　two　hundred　years　later　the　Greeks　under　Nicias　before　Syracuse　were　so　disconcerted　by　the　appearance　of　an　eclipse；　which　was　interpreted　as　a　direct　omen　and　warning；　that　Nicias　threw　away　the　last　opportunity　to　rescue　his　army。　Thucydides；　it　is　true；　in　recording　this　fact　speaks　disparagingly　of　the　superstitious　bent　of　the　mind　of　Nicias；　but　Thucydides　also　was　a　man　far　in　advance　of　his　time。　All　that　we　know　of　the　psychology　of　Thales　is　summed　up　in　the　famous　maxim；　〃Know　thyself；〃　a　maxim　which；　taken　in　connection　with　the　proven　receptivity　of　the　philosopher's　mind；　suggests　to　us　a　marvellously　rounded　personality。　The　disciples　or　successors　of　Thales；　Anaximander　and　Anaximenes；　were　credited　with　advancing　knowledge　through　the　invention　or　introduction　of　the　sundial。　We　may　be　sure；　however；　that　the　gnomon；　which　is　the　rudimentary　sundial；　had　been　known　and　used　from　remote　periods　in　the　Orient；　and　the　most　that　is　probable　is　that　Anaximander　may　have　elaborated　some　special　design；　possibly　the　bowl…　shaped　sundial；　through　which　the　shadow　of　the　gnomon　would　indicate　the　time。　The　same　philosopher　is　said　to　have　made　the　first　sketch　of　a　geographical　map；　but　this　again　is　a　statement　which　modern　researches　have　shown　to　be　fallacious；　since　a　Babylonian　attempt　at　depicting　the　geography　of　the　world　is　still　preserved　to　us　on　a　clay　tablet。　Anaximander　may；　however；　have　been　the　first　Greek　to　make　an　attempt　of　this　kind。　Here　again　the　influence　of　Babylonian　science　upon　the　germinating　Western　thought　is　suggested。　It　is　said　that　Anaximander　departed　from　Thales's　conception　of　the　earth；　and；　it　may　be　added；　from　the　Babylonian　conception　also；　in　that　he　conceived　it　as　a　cylinder；　or　rather　as　a　truncated　cone；　the　upper　end　of　which　is　the　habitable　portion。　This　conception　is　perhaps　the　first　of　these　guesses　through　which　the　Greek　mind　attempted　to　explain　the　apparent　fixity　of　the　earth。　To　ask　what　supports　the　earth　in　space　is　most　natural；　but　the　answer　given　by　Anaximander；　like　that　more　familiar　Greek　solution　which　transformed　the　cone；　or　cylinder；　into　the　giant　Atlas；　is　but　another　illustration　of　that　substitution　of　unwarranted　inference　for　scientific　induction　which　we　have　already　so　often　pointed　out　as　characteristic　of　the　primitive　stages　of　thought。　Anaximander　held　at　least　one　theory　which；　as　vouched　for　by　various　copyists　and　commentators；　entitles　him　to　be　considered　perhaps　the　first　teacher　of　the　idea　of　organic　evolution。　According　to　this　idea；　man　developed　from　a　fishlike　ancestor；　〃growing　up　as　sharks　do　until　able　to　help　himself　and　then　coming　forth　on　dry　land。〃＇1＇　The　thought　here　expressed　finds　its　germ；　perhaps；　in　the　Babylonian　conception　that　everything　came　forth　from　a　chaos　of　waters。　Yet　the　fact　that　the　thought　of　Anaximander　has　come　down　to　posterity　through　such　various　channels　suggests　that　the　Greek　thinker　had　got　far　enough　away　from　the　Oriental　conception　to　make　his　view　seem　to　his　contemporaries　a　novel　and　individual　one。　Indeed；　nothing　we　know　of　the　Oriental　line　of　thought　conveys　any　suggestion　of　the　idea　of　transformation　of　species；　whereas　that　idea　is　distinctly　formulated　in　the　traditional　views　of　Anaximander。

VI。　THE　EARLY　GREEK　PHILOSOPHERS　IN　ITALY　Diogenes　Laertius　tells　a　story　about　a　youth　who；　clad　in　a　purple　toga；　entered　the　arena　at　the　Olympian　games　and　asked　to　compete　with　the　other　youths　in　boxing。　He　was　derisively　denied　admission；　presumably　because　he　was　beyond　the　legitimate　age　for　juvenile　contestants。　Nothing　daunted；　the　youth　entered　the　lists　of　men；　and　turned　the　laugh　on　his　critics　by　coming　off　victor。　The　youth　who　performed　this　feat　was　named　Pythagoras。　He　was　the　same　man；　if　we　may　credit　the　story；　who　afterwards　migrated　to　Italy　and　became　the　founder　of　the　famous　Crotonian　School　of　Philosophy；　the　man　who　developed　the　religion　of　the　Orphic　mysteries；　who　conceived　the　idea　of　the　music　of　the　spheres；　who　promulgated　the　doctrine　of　metempsychosis；　who　first；　perhaps；　of　all　men　clearly　conceived　the　notion　that　this　world　on　which　we　live　is　a　ball　which　moves　in　space　and　which　may　be　habitable　on　every　side。　A　strange　development　that　for　a　stripling　pugilist。　But　we　must　not　forget　that　in　the　Greek　world　athletics　held　a　peculiar　place。　The　chief　winner　of　Olympian　games　gave　his　name　to　an　epoch　（the　ensuing　Olympiad　of　four　years）；　and　was　honored　almost　before　all　others　in　the　land。　A　sound　mind　in　a　sound　body　was　the　motto　of　the　day。　To　excel　in　feats　of　strength　and　dexterity　was　an　accomplishment　that　even　a　philosopher　need　not　scorn。　It　will　be　recalled　that　aeschylus　distinguished　himself　at　the　battle　of　Marathon；　that　Thucydides；　the　greatest　of　Greek　historians；　was　a　general　in　the　Peloponnesian　War；　that　Xenophon；　the　pupil　and　biographer　of　Socrates；　was　chiefly　famed　for　having　led　the　Ten　Thousand　in　the　memorable　campaign　of　Cyrus　the　Younger；　that　Plato　himself　was　credited　with　having　shown　great　aptitude　in　early　life　as　a　wrestler。　If；　then；　Pythagoras　the　philosopher　was　really　the　Pythagoras　who　won　the　boxing　contest；　we　may　suppose　that　in　looking　back　upon　this　athletic　feat　from　the　heights　of　his　priesthoodfor　he　came　to　be　almost　deifiedhe　regarded　it　not　as　an　indiscretion　of　his　youth；　but　as　one　of　the　greatest　achievements　of　his　life。　Not　unlikely　he　recalled　with　pride　that　he　was　credited　with　being　no　less　an　innovator　in　athletics　than　in　philosophy。　At　all　events；　tradition　credits　him　with　the　invention　of　〃scientific〃　boxing。　Was　it　he；　perhaps；　who　taught　the　Greeks　to　strike　a　rising　and　swinging　blow　from　the　hip；　as　depicted　in　the　famous　metopes　of　the　Parthenon？　If　so；　the　innovation　of　Pythagoras　was　as　little　heeded　in　this　regard　in　a　subsequent　age　as　was　his　theory　of　the　motion　of　the　earth；　for　to　strike　a　swinging　blow　from　the　hip；　rather　than　from　the　shoulder；　is　a　trick　wh