a history of science-1-第19节

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o；　intent　on　studying　the　heavens；　fell　into　a　well；　〃whereupon；〃　says　Hippolytus；　〃a　maid…servant　named　Thratta　laughed　at　him　and　said；　'In　his　search　for　things　in　the　sky　he　does　not　see　what　is　at　his　feet。'　〃　Such　citations　as　these　serve　to　bring　vividly　to　mind　the　fact　that　we　are　entering　a　new　epoch　of　thought。　Hitherto　our　studies　have　been　impersonal。　Among　Egyptians　and　Babylonians　alike　we　have　had　to　deal　with　classes　of　scientific　records；　but　we　have　scarcely　come　across　a　single　name。　Now；　however；　we　shall　begin　to　find　records　of　the　work　of　individual　investigators。　In　general；　from　now　on；　we　shall　be　able　to　trace　each　great　idea；　if　not　to　its　originator；　at　least　to　some　one　man　of　genius　who　was　prominent　in　bringing　it　before　the　world。　The　first　of　these　vitalizers　of　thought；　who　stands　out　at　the　beginnings　of　Greek　history；　is　this　same　Thales；　of　Miletus。　His　is　not　a　very　sharply　defined　personality　as　we　look　back　upon　it；　and　we　can　by　no　means　be　certain　that　all　the　discoveries　which　are　ascribed　to　him　are　specifically　his。　Of　his　individuality　as　a　man　we　know　very　little。　It　is　not　even　quite　certain　as　to　where　he　was　born；　Miletus　is　usually　accepted　as　his　birthplace；　but　one　tradition　makes　him　by　birth　a　Phenician。　It　is　not　at　all　in　question；　however；　that　by　blood　he　was　at　least　in　part　an　Ionian　Greek。　It　will　be　recalled　that　in　the　seventh　century　B。C。；　when　Thales　was　bornand　for　a　long　time　thereafterthe　eastern　shores　of　the　aegean　Sea　were　quite　as　prominently　the　centre　of　Greek　influence　as　was　the　peninsula　of　Greece　itself。　Not　merely　Thales；　but　his　followers　and　disciples；　Anaximander　and　Anaximenes；　were　born　there。　So　also　was　Herodotas；　the　Father　of　History；　not　to　extend　the　list。　There　is　nothing　anomalous；　then；　in　the　fact　that　Thales；　the　father　of　Greek　thought；　was　born　and　passed　his　life　on　soil　that　was　not　geographically　a　part　of　Greece；　but　the　fact　has　an　important　significance　of　another　kind。　Thanks　to　his　environment；　Thales　was　necessarily　brought　more　or　less　in　contact　with　Oriental　ideas。　There　was　close　commercial　contact　between　the　land　of　his　nativity　and　the　great　Babylonian　capital　off　to　the　east；　as　also　with　Egypt。　Doubtless　this　association　was　of　influence　in　shaping　the　development　of　Thales's　mind。　Indeed；　it　was　an　accepted　tradition　throughout　classical　times　that　the　Milesian　philosopher　had　travelled　in　Egypt；　and　had　there　gained　at　least　the　rudiments　of　his　knowledge　of　geometry。　In　the　fullest　sense；　then；　Thales　may　be　regarded　as　representing　a　link　in　the　chain　of　thought　connecting　the　learning　of　the　old　Orient　with　the　nascent　scholarship　of　the　new　Occident。　Occupying　this　position；　it　is　fitting　that　the　personality　of　Thales　should　partake　somewhat　of　mystery；　that　the　scene　may　not　be　shifted　too　suddenly　from　the　vague；　impersonal　East　to　the　individualism　of　Europe。　All　of　this；　however；　must　not　be　taken　as　casting　any　doubt　upon　the　existence　of　Thales　as　a　real　person。　Even　the　dates　of　his　life640　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　period