a history of science-1-第38章

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had　never　before　existed　anywhere　in　the　world。　The　whole　trend　of　the　time　was　towards　mechanics。　It　was　as　if　the　greatest　thinkers　had　squarely　faced　about　from　the　attitude　of　the　mystical　philosophers　of　the　preceding　century；　and　had　set　themselves　the　task　of　solving　all　the　mechanical　riddles　of　the　universe；　They　no　longer　troubled　themselves　about　problems　of　〃being〃　and　〃becoming〃；　they　gave　but　little　heed　to　metaphysical　subtleties；　they　demanded　that　their　thoughts　should　be　gauged　by　objective　realities。　Hence　there　arose　a　succession　of　great　geometers；　and　their　conceptions　were　applied　to　the　construction　of　new　mechanical　contrivances　on　the　one　hand；　and　to　the　elaboration　of　theories　of　sidereal　mechanics　on　the　other。　The　wonderful　company　of　men　who　performed　the　feats　that　are　about　to　be　recorded　did　not　all　find　their　home　in　Alexandria；　to　be　sure；　but　they　all　came　more　or　less　under　the　Alexandrian　influence。　We　shall　see　that　there　are　two　other　important　centres；　one　out　in　Sicily；　almost　at　the　confines　of　the　Greek　territory　in　the　west；　the　other　in　Asia　Minor；　notably　on　the　island　of　Samosthe　island　which；　it　will　be　recalled；　was　at　an　earlier　day　the　birthplace　of　Pythagoras。　But　whereas　in　the　previous　century　colonists　from　the　confines　of　the　civilized　world　came　to　Athens；　now　all　eyes　turned　towards　Alexandria；　and　so　improved　were　the　facilities　for　communication　that　no　doubt　the　discoveries　of　one　coterie　of　workers　were　known　to　all　the　others　much　more　quickly　than　had　ever　been　possible　before。　We　learn；　for　example；　that　the　studies　of　Aristarchus　of　Samos　were　definitely　known　to　Archimedes　of　Syracuse；　out　in　Sicily。　Indeed；　as　we　shall　see；　it　is　through　a　chance　reference　preserved　in　one　of　the　writings　of　Archimedes　that　one　of　the　most　important　speculations　of　Aristarchus　is　made　known　to　us。　This　illustrates　sufficiently　the　intercommunication　through　which　the　thought　of　the　Alexandrian　epoch　was　brought　into　a　single　channel。　We　no　longer；　as　in　the　day　of　the　earlier　schools　of　Greek　philosophy；　have　isolated　groups　of　thinkers。　The　scientific　drama　is　now　played　out　upon　a　single　stage；　and　if　we　pass；　as　we　shall　in　the　present　chapter；　from　Alexandria　to　Syracuse　and　from　Syracuse　to　Samos；　the　shift　of　scenes　does　no　violence　to　the　dramatic　unities。　Notwithstanding　the　number　of　great　workers　who　were　not　properly　Alexandrians；　none　the　less　the　epoch　is　with　propriety　termed　Alexandrian。　Not　merely　in　the　third　century　B。C。；　but　throughout　the　lapse　of　at　least　four　succeeding　centuries；　the　city　of　Alexander　and　the　Ptolemies　continued　to　hold　its　place　as　the　undisputed　culture…centre　of　the　world。　During　that　period　Rome　rose　to　its　pinnacle　of　glory　and　began　to　decline；　without　ever　challenging　the　intellectual　supremacy　of　the　Egyptian　city。　We　shall　see；　in　a　later　chapter；　that　the　Alexandrian　influences　were　passed　on　to　the　Mohammedan　conquerors；　and　every　one　is　aware　that　when　Alexandria　was　finally　overthrown　its　place　was　taken　by　another　Greek　city；　Byzantium　or　Constantinople。　But　that　transfer　did　not　occur　until　Alexandria　had　enjoyed　a　longer　period　of　supremacy　as　an　intellectual　centre　than　had　perhaps　ever　before　been　granted　to　any　city；　with　the　possible　exception　of　Babylon。

EUCLID　（ABOUT　300　B。C。）　Our　present　concern　is　with　that　first　wonderful　development　of　scientific　activity　which　began　under　the　first　Ptolemy；　and　which　presents；　in　the　course　of　the　first　century　of　Alexandrian　influence；　the　most　remarkable　coterie　of　scientific　workers　and　thinkers　that　antiquity　produced。　The　earliest　group　of　these　new　leaders　in　science　had　at　its　head　a　man　whose　name　has　been　a　household　word　ever　since。　This　was　Euclid；　the　father　of　systematic　geometry。　Tradition　has　preserved　to　us　but　little　of　the　personality　of　this　remarkable　teacher；　but；　on　the　other　hand；　his　most　important　work　has　come　down　to　us　in　its　entirety。　The　Elements　of　Geometry；　with　which　the　name　of　Euclid　is　associated　in　the　mind　of　every　school…boy；　presented　the　chief　propositions　of　its　subject　in　so　simple　and　logical　a　form　that　the　work　remained　a　textbook　everywhere　for　more　than　two　thousand　years。　Indeed　it　is　only　now　beginning　to　be　superseded。　It　is　not　twenty　years　since　English　mathematicians　could　deplore　the　fact　that；　despite　certain　rather　obvious　defects　of　the　work　of　Euclid；　no　better　textbook　than　this　was　available。　Euclid's　work；　of　course；　gives　expression　to　much　knowledge　that　did　not　originate　with　him。　We　have　already　seen　that　several　important　propositions　of　geometry　had　been　developed　by　Thales；　and　one　by　Pythagoras；　and　that　the　rudiments　of　the　subject　were　at　least　as　old　as　Egyptian　civilization。　Precisely　how　much　Euclid　added　through　his　own　investigations　cannot　be　ascertained。　It　seems　probable　that　he　was　a　diffuser　of　knowledge　rather　than　an　originator；　but　as　a　great　teacher　his　fame　is　secure。　He　is　credited　with　an　epigram　which　in　itself　might　insure　him　perpetuity　of　fame：　〃There　is　no　royal　road　to　geometry；〃　was　his　answer　to　Ptolemy　when　that　ruler　had　questioned　whether　the　Elements　might　not　be　simplified。　Doubtless　this；　like　most　similar　good　sayings；　is　apocryphal；　but　whoever　invented　it　has　made　the　world　his　debtor。

HEROPHILUS　AND　ERASISTRATUS　The　catholicity　of　Ptolemy's　tastes　led　him；　naturally　enough；　to　cultivate　the　biological　no　less　than　the　physical　sciences。　In　particular　his　influence　permitted　an　epochal　advance　in　the　field　of　medicine。　Two　anatomists　became　famous　through　the　investigations　they　were　permitted　to　make　under　the　patronage　of　the　enlightened　ruler。　These　earliest　of　really　scientific　investigators　of　the　mechanism　of　the　human　body　were　named　Herophilus　and　Erasistratus。　These　two　anatomists　gained　their　knowledge　by　the　dissection　of　human　bodies　（theirs　are　the　first　records　that　we　have　of　such　practices）；　and　King　Ptolemy　himself　is　said　to　have　been　present　at　some　of　these　dissections。　They　were　the　first　to　discover　that　the　nerve…　trunks　have　their　origin　in　the　brain　and　spinal　cord；　and　they　are　credited　also　with　the　discovery　that　these　nerve…trunks　are　of　two　different　kindsone　to　convey　motor；　and　the　other　sensory　impulses。　They　discovered；　described；　and　named　the　coverings　of　the　brain。　The　name　of　Herophilus　is　still　applied　by　anatomists；　in　honor　of　the　discoverer；　to　one　of　the　sinuses　or　large　canals　that　convey　the　venous　blood　from　the　head。　Herophilus　also　noticed　and　described　four　cavities　or　ventricles　in　the　brain；　and　reached　the　conclusion　that　one　of　these　ventricles　was　the　seat　of　the　soula　belief　shared　until　comparatively　recent　times　by　many　physiologists。　He　made　also　a　careful　and　fairly　accurate　study　of　the　anatomy　of　the　eye；　a　greatly　improved　the　old　operation　for　cataract。　With　the　increased　knowledge　of　anatomy　came　also　corresponding　advances　in　surgery；　and　many　experimental　operations　are　said　to　have　been　performed　upon　condemned　criminals　who　were　handed　over　to　the　surgeons　by　the　Ptolemies。　While　many　modern　writers　have　attempted　to　discredit　these　assertions；　it　is　not　improbable　that　such　operations　were　performed。　In　an　age　when　human　life　was　held　so　cheap；　and　among　a　people　accustomed　to　torturing　condemned　prisoners　for　comparatively　slight　offences；　it　is　not　unlikely　that　the　surgeons　were　allowed　to　inflict　perhaps　less　painful　tortures　in　the　cause　of　science。　Furthermore；　we　know　that　condemned　criminals　were　sometimes　handed　over　to　the　medical　profession　to　be　〃operated　upon　and　killed　in　whatever　way　they　thought　best〃　even　as　late　as　the　sixteenth　century。　Tertullian＇1＇　probably　exaggerates；　however；　when　he　puts　the　number　of　such　victims　in　Alexandria　at　six　hundred。　Had　Herophilus　and　Erasistratus　been　as　happy　in　their　deductions　as　to　the　functions　of　the　organs　as　they　were　in　their　knowledge　of　anatomy；　the　science　of　medicine　would　have　been　placed　upon　a　very　high　plane　even　in　their　time。　Unfortunately；　however；　they　not　only　drew　erroneous　inferences　as　to　the　functions　of　the　organs；　but　also　disagreed　radically　as　to　what　functions　certain　organs　performed；　and　how　diseases　should　be　treated；　e