a history of science-1-第28章

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ly；　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；　even　when　agreeing　perfectly　on　the　subject　of　anatomy　itself。　Their　contribution　to　the　knowledge　of　the　scientific　treatment　of　diseases　holds　no　such　place；　therefore；　as　their　anatomical　investigations。　Half　a　century　after　the　time　of　Herophilus　there　appeared　a　Greek　physician；　Heraclides；　whose　reputation　in　the　use　of　drugs　far　surpasses　that　of　the　anatomists　of　the　Alexandrian　school。　His　reputation　has　been　handed　down　through　the　centuries　as　that　of　a　physician；　rather　than　a　surgeon；　although　in　his　own　time　he　was　considered　one　of　the　great　surgeons　of　the　period。　Heraclides　belonged　to　the　〃Empiric〃　school；　which　rejected　anatomy　as　useless；　depending　entirely　on　the　use　of　drugs。　He　is　thought　to　have　been　the　first　physician　to　point　out　the　value　of　opium　in　certain　painful　diseases。　His　prescription　of　this　drug　for　certain　cases　of　〃sleeplessness；　spasm；　cholera；　and　colic；〃　shows　that　his　use　of　it　was　not　unlike　that　of　the　modern　physician　in　certain　cases；　and　his　treatment　of　fevers；　by　keeping　the　patient's　head　cool　and　facilitating　the　secretions　of　the　body；　is　still　recognized　as　〃good　practice。〃　He　advocated　a　free　use　of　liquids　in　quenching　the　fever　patient's　thirsta　recognized　therapeutic　measure　to…day；　but　one　that　was　widely　condemned　a　century　ago。

ARCHIMEDES　OF　SYRACUSE　AND　THE　FOUNDATION　OF　MECHANICS　We　do　not　know　just　when　Euclid　died；　but　as　he　was　at　the　height　of　his　fame　in　the　time　of　Ptolemy　I。；　whose　reign　ended　in　the　year　285　B。C。；　it　is　hardly　probable　that　he　was　still　living　when　a　young　man　named　Archimedes　came　to　Alexandria　to　study。　Archimedes　was　born　in　the　Greek　colony　of　Syracuse；　on　the　island　of　Sicily；　in　the　year　287　B。C。　When　he　visited　Alexandria　he　probably　found　Apollonius　of　Perga；　the　pupil　of　Euclid；　at　the　head　of　the　mathematical　school　there。　Just　how　long　Archimedes　remained　at　Alexandria　is　not　known。　When　he　had　satisfied　his　curiosity　or　completed　his　studies；　he　returned　to　Syracuse　and　spent　his　life　there；　chiefly　under　the　patronage　of　King　Hiero；　who　seems　fully　to　have　appreciated　his　abilities。　Archimedes　was　primarily　a　mathematician。　Left　to　his　own　devices；　he　would　probably　have　devoted　his　entire　time　to　the　study　of　geometrical　problems。　But　King　Hiero　had　discovered　that　his　protege　had　wonderful　mechanical　ingenuity；　and　he　made　good　use　of　this　discovery。　Under　stress　of　the　king's　urgings；　the　philosopher　was　led　to　invent　a　great　variety　of　mechanical　contrivances；　some　of　them　most　curious　ones。　Antiquity　credited　him　with　the　invention　of　more　than　forty　machines；　and　it　is　these；　rather　than　his　purely　mathematical　discoveries；　that　gave　his　name　popular　vogue　both　among　his　contemporaries　and　with　posterity。　Every　one　has　heard　of　the　screw　of　Archimedes；　through　which　the　paradoxical　effect　was　produced　of　making　water　seem　to　flow　up　hill。　The　best　idea　of　this　curious　mechanism　is　obtained　if　one　will　take　in　hand　an　ordinary　corkscrew；　and　imagine　this　instrument　to　be　changed　into　a　hollow　tube；　retaining　precisely　the　same　shape　but　increased　to　some　feet　in　length　and　to　a　proportionate　diameter。　If　one　will　hold　the　corkscrew　in　a　slanting　direction　and　turn　it　slowly　to　the　right；　supposing　that　the　point　dips　up　a　portion　of　water　each　time　it　revolves；　one　can　in　imagination　follow　the　flow　of　that　portion　of　water　from　spiral　to　spiral；　the　water　always　running　downward；　of　course；　yet　paradoxically　being　lifted　higher　and　higher　towards　the　base　of　the　corkscrew；　until　finally　it　pours　out　（in　the　actual　Archimedes'　tube）　at　the　top。　There　is　another　form　of　the　screw　in　which　a　revolving　spiral　blade　operates　within　a　cylinder；　but　the　principle　is　precisely　the　same。　With　either　form　water　may　be　lifted；　by　the　mere　turning　of　the　screw；　to　any　desired　height。　The　ingenious　mechanism　excited　the　wonder　of　the　contemporaries　of　Archimedes；　as　well　it　might。　More　efficient　devices　have　superseded　it　in　modern　times；　but　it　still　excites　the　admiration　of　all　who　examine　it；　and　its　effects　seem　as　parad