a history of science-1-第27章

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　be　the　cause　of　this　by　having　a　spherical　form。　And　again；　from　the　appearance　of　the　stars　it　is　clear；　not　only　that　the　earth　is　round；　but　that　its　size　is　not　very　large；　for　when　we　make　a　small　removal　to　the　south　or　the　north；　the　circle　of　the　horizon　becomes　palpably　different；　so　that　the　stars　overhead　undergo　a　great　change；　and　are　not　the　same　to　those　that　travel　in　the　north　and　to　the　south。　For　some　stars　are　seen　in　Egypt　or　at　Cyprus；　but　are　not　seen　in　the　countries　to　the　north　of　these；　and　the　stars　that　in　the　north　are　visible　while　they　make　a　complete　circuit；　there　undergo　a　setting。　So　that　from　this　it　is　manifest；　not　only　that　the　form　of　the　earth　is　round；　but　also　that　it　is　a　part　of　a　not　very　large　sphere；　for　otherwise　the　difference　would　not　be　so　obvious　to　persons　making　so　small　a　change　of　place。　Wherefore　we　may　judge　that　those　persons　who　connect　the　region　in　the　neighborhood　of　the　pillars　of　Hercules　with　that　towards　India；　and　who　assert　that　in　this　way　the　sea　is　one；　do　not　assert　things　very　improbable。　They　confirm　this　conjecture　moreover　by　the　elephants；　which　are　said　to　be　of　the　same　species　towards　each　extreme；　as　if　this　circumstance　was　a　consequence　of　the　conjunction　of　the　extremes。　The　mathematicians　who　try　to　calculate　the　measure　of　the　circumference；　make　it　amount　to　four　hundred　thousand　stadia；　whence　we　collect　that　the　earth　is　not　only　spherical；　but　is　not　large　compared　with　the　magnitude　of　the　other　stars。〃　But　in　giving　full　meed　of　praise　to　Aristotle　for　the　promulgation　of　this　doctrine　of　the　sphericity　of　the　earth；　it　must　unfortunately　be　added　that　the　conservative　philosopher　paused　without　taking　one　other　important　step。　He　could　not　accept；　but；　on　the　contrary；　he　expressly　repudiated；　the　doctrine　of　the　earth's　motion。　We　have　seen　that　this　idea　also　was　a　part　of　the　Pythagorean　doctrine；　and　we　shall　have　occasion　to　dwell　more　at　length　on　this　point　in　a　succeeding　chapter。　It　has　even　been　contended　by　some　critics　that　it　was　the　adverse　conviction　of　the　Peripatetic　philosopher　which；　more　than　any　other　single　influence；　tended　to　retard　the　progress　of　the　true　doctrine　regarding　the　mechanism　of　the　heavens。　Aristotle　accepted　the　sphericity　of　the　earth；　and　that　doctrine　became　a　commonplace　of　scientific　knowledge；　and　so　continued　throughout　classical　antiquity。　But　Aristotle　rejected　the　doctrine　of　the　earth's　motion；　and　that　doctrine；　though　promulgated　actively　by　a　few　contemporaries　and　immediate　successors　of　the　Stagirite；　was　then　doomed　to　sink　out　of　view　for　more　than　a　thousand　years。　If　it　be　a　correct　assumption　that　the　influence　of　Aristotle　was；　in　a　large　measure；　responsible　for　this　result；　then　we　shall　perhaps　not　be　far　astray　in　assuming　that　the　great　founder　of　the　Peripatetic　school　was；　on　the　whole；　more　instrumental　in　retarding　the　progress　of　astronomical　science　that　any　other　one　man　that　ever　lived。　The　field　of　science　in　which　Aristotle　was　pre…eminently　a　pathfinder　is　zoology。　His　writings　on　natural　history　have　largely　been　preserved；　and　they　constitute　by　far　the　most　important　contribution　to　the　subject　that　has　come　down　to　us　from　antiquity。　They　show　us　that　Aristotle　had　gained　possession　of　the　widest　range　of　facts　regarding　the　animal　kingdom；　and；　what　is　far　more　important；　had　attempted　to　classify　these　facts。　In　so　doing　he　became　the　founder　of　systematic　zoology。　Aristotle's　classification　of　the　animal　kingdom　was　known　and　studied　throughout　the　Middle　Ages；　and；　in　fact；　remained　in　vogue　until　superseded　by　that　of　Cuvier　in　the　nineteenth　century。　It　is　not　to　be　supposed　that　all　the　terms　of　Aristotle's　classification　originated　with　him。　Some　of　the　divisions　are　too　patent　to　have　escaped　the　observation　of　his　predecessors。　Thus；　for　example；　the　distinction　between　birds　and　fishes　as　separate　classes　of　animals　is　so　obvious　that　it　must　appeal　to　a　child　or　to　a　savage。　But　the　efforts　of　Aristotle　extended；　as　we　shall　see；　to　less　patent　generalizations。　At　the　very　outset；　his　grand　division　of　the　animal　kingdom　into　blood…bearing　and　bloodless　animals　implies　a　very　broad　and　philosophical　conception　of　the　entire　animal　kingdom。　The　modern　physiologist　does　not　accept　the　classification；　inasmuch　as　it　is　now　known　that　colorless　fluids　perform　the　functions　of　blood　for　all　the　lower　organisms。　But　the　fact　remains　that　Aristotle's　grand　divisions　correspond　to　the　grand　divisions　of　the　Lamarckian　systemvertebrates　and　invertebrates　which　every　one　now　accepts。　Aristotle；　as　we　have　said；　based　his　classification　upon　observation　of　the　blood；　Lamarck　was　guided　by　a　study　of　the　skeleton。　The　fact　that　such　diverse　points　of　view　could　direct　the　observer　towards　the　same　result　gives；　inferentially；　a　suggestive　lesson　in　what　the　modern　physiologist　calls　the　homologies　of　parts　of　the　organism。　Aristotle　divides　his　so…called　blood…bearing　animals　into　five　classes：　（1）　Four…footed　animals　that　bring　forth　their　young　alive；　（2）　birds；　（3）　egg…laying　four…　footed　animals　（including　what　modern　naturalists　call　reptiles　and　amphibians）；　（4）　whales　and　their　allies；　（5）　fishes。　This　classification；　as　will　be　observed；　is　not　so　very　far　afield　from　the　modern　divisions　into　mammals；　birds；　reptiles；　amphibians；　and　fishes。　That　Aristotle　should　have　recognized　the　fundamental　distinction　between　fishes　and　the　fish…　like　whales；　dolphins；　and　porpoises　proves　the　far　from　superficial　character　of　his　studies。　Aristotle　knew　that　these　animals　breathe　by　means　of　lungs　and　that　they　produce　living　young。　He　recognized；　therefore；　their　affinity　with　his　first　class　of　animals；　even　if　he　did　not；　like　the　modern　naturalist；　consider　these　affinities　close　enough　to　justify　bringing　the　two　types　together　into　a　single　class。　The　bloodless　animals　were　also　divided　by　Aristotle　into　five　classesnamely：　（1）　Cephalopoda　（the　octopus；　cuttle…fish；　etc。）；　（2）　weak…shelled　animals　（crabs；　etc。）；　（3）　insects　and　their　allies　（including　various　forms；　such　as　spiders　and　centipedes；　which　the　modern　classifier　prefers　to　place　by　themselves）；　（4）　hard…shelled　animals　（clams；　oysters；　snails；　etc。）；　（5）　a　conglomerate　group　of　marine　forms；　including　star…fish；　sea…urchins；　and　various　anomalous　forms　that　were　regarded　as　linking　the　animal　to　the　vegetable　worlds。　This　classification　of　the　lower　forms　of　animal　life　continued　in　vogue　until　Cuvier　substituted　for　it　his　famous　grouping　into　articulates；　mollusks；　and　radiates；　which　grouping　in　turn　was　in　part　superseded　later　in　the　nineteenth　century。　What　Aristotle　did　for　the　animal　kingdom　his　pupil；　Theophrastus；　did　in　some　measure　for　the　vegetable　kingdom。　Theophrastus；　however；　was　much　less　a　classifier　than　his　master；　and　his　work　on　botany；　called　The　Natural　History　of　Development；　pays　comparatively　slight　attention　to　theoretical　questions。　It　deals　largely　with　such　practicalities　as　the　making　of　charcoal；　of　pitch；　and　of　resin；　and　the　effects　of　various　plants　on　the　animal　organism　when　taken　as　foods　or　as　medicines。　In　this　regard　the　work　of　Theophrastus；　is　more　nearly　akin　to　the　natural　history　of　the　famous　Roman　compiler；　Pliny。　It　remained；　however；　throughout　antiquity　as　the　most　important　work　on　its　subject；　and　it　entitles　Theophrastus　to　be　called　the　〃father　of　botany。〃　Theophrastus　deals　also　with　the　mineral　kingdom　after　much　the　same　fashion；　and　here　again　his　work　is　the　most　notable　that　was　produced　in　antiquity。

IX。　GREEK　SCIENCE　OF　THE　ALEXANDRIAN　OR　HELLENISTIC　PERIOD　We　are　entering　now　upon　the　most　important　scientific　epoch　of　antiquity。　When　Aristotle　and　Theophrastus　passed　from　the　scene；　Athens　ceased　to　be　in　any　sense　the　scientific　centre　of　the　world。　That　city　still　retained　its　reminiscent　glory；　and　cannot　be　ignored　in　the　history　of　culture；　but　no　great　scientific　leader　was　ever　again　to　be　born　or　to　take　up　his　permanent　abode　within　the　confines　of　Greece　proper。　With　almost　cataclysmic　suddenness；　a　new　intellectual　centre　appeared　on　the　south　shore　of　the　Mediterranean。　This　was　the　city　of　Alexandria；　a　city　which　Alexander　the　Great　had　founded　during　his　brief　visit　to　Egypt；　and　which　became　the　capital　of　Ptolemy　Soter　when　he　chose　Egypt　as　his　portion　of　the　dismembered　empire　of　the　great　Macedonian。　Ptolemy　had　been　with　his　master　in　the　East；　and　was　with　him　in　Babylonia　when　he　died。　He　had　therefore　come　personally　in　contact　with　Babylonian　civilization；　and　we　cannot　doubt　that　this　had　a　most　important　influence　upon　his　life；　and　through　him　upon　the　new　civilization　of　the　West。　In　point　of　culture；　Alexandria　must　be　regarded　as　the　successor　of　Babylon；　scarcely　less　directly　than　of　Greece。　Following　the　Babylonian　model；　Ptolemy　erected　a　great　museum　and　began　collecting　a　library。　Before　his　death　it　was　said　that　he　had　collected　no　fewer　than　two　hundred　thousand　manuscripts。　He　had　gathered　also　a　company　of　great　teachers　and　founded　a　school　of　science　which；　as　has　just　been　said；　made　Alexandria　the　culture…centre　of　the　world。　Athens　in　the　day　of　her　prime　had　known　nothing　quite　like　this。　Such　private　citizens　as　Aristotle　are　known　to　have　had　libraries；　but　there　were　no　great　public　collections　of　books　in　Athens；　or　in　any　other　part　of　the　Greek　domain；　until　Ptolemy　founded　his　famous　library。　As　is　well　known；　such　libraries　had　existed　in　Babylonia　for　thousands　of　years。　The　character　which　the　Ptolemaic　epoch　took　on　was　no　doubt　due　to　Babylonian　influence；　but　quite　as　much　to　the　personal　experience　of　Ptolemy　himself　as　an　explorer　in　the　Far　East。　The　marvellous　conquering　journey　of　Alexander　had　enormously　widened　the　horizon　of　the　Greek　geographer；　and　stimulated　the　imagination　of　all　ranks　of　the　people；　It　was　but　natural；　then；　that　geography　and　its　parent　science　astronomy　should　occupy　the　attention　of　the　best　minds　in　this　succeeding　epoch。　In　point　of　fact；　such　a　company　of　star…gazers　and　earth…measurers　came　upon　the　scene　in　this　third　century　B。C。　as　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　t