a history of science-1-第57章

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ic　thinkersmen　who　have　put　their　mark　upon　the　progress　of　civilization；　but　we　shall　see；　as　we　look　forward　for　a　corresponding　period；　that　the　ensuing　thirty　generations　produced　scarcely　a　single　scientific　thinker　of　the　first　rank。　Eight　hundred　years　of　intellectual　activity　thirty　generations　of　greatness；　then　eight　hundred　years　of　stasisthirty　generations　of　mediocrity；　such　seems　to　be　the　record　as　viewed　in　perspective。　Doubtless　it　seemed　far　different　to　the　contemporary　observer；　it　is　only　in　reasonable　perspective　that　any　scene　can　be　viewed　fairly。　But　for　us；　looking　back　without　prejudice　across　the　stage　of　years；　it　seems　indisputable　that　a　great　epoch　came　to　a　close　at　about　the　time　when　the　barbarian　nations　of　Europe　began　to　sweep　down　into　Greece　and　Italy。　We　are　forced　to　feel　that　we　have　reached　the　limits　of　progress　of　what　historians　are　pleased　to　call　the　ancient　world。　For　about　eight　hundred　years　Greek　thought　has　been　dominant；　but　in　the　ensuing　period　it　is　to　play　a　quite　subordinate　part；　except　in　so　far　as　it　influences　the　thought　of　an　alien　race。　As　we　leave　this　classical　epoch；　then；　we　may　well　recapitulate　in　brief　its　triumphs。　A　few　words　will　suffice　to　summarize　a　story　the　details　of　which　have　made　up　our　recent　chapters。　In　the　field　of　cosmology；　Greek　genius　has　demonstrated　that　the　earth　is　spheroidal；　that　the　moon　is　earthlike　in　structure　and　much　smaller　than　our　globe；　and　that　the　sun　is　vastly　larger　and　many　times　more　distant　than　the　moon。　The　actual　size　of　the　earth　and　the　angle　of　its　axis　with　the　ecliptic　have　been　measured　with　approximate　accuracy。　It　has　been　shown　that　the　sun　and　moon　present　inequalities　of　motion　which　may　be　theoretically　explained　by　supposing　that　the　earth　is　not　situated　precisely　at　the　centre　of　their　orbits。　A　system　of　eccentrics　and　epicycles　has　been　elaborated　which　serves　to　explain　the　apparent　motions　of　the　heavenly　bodies　in　a　manner　that　may　be　called　scientific　even　though　it　is　based；　as　we　now　know；　upon　a　false　hypothesis。　The　true　hypothesis；　which　places　the　sun　at　the　centre　of　the　planetary　system　and　postulates　the　orbital　and　axial　motions　of　our　earth　in　explanation　of　the　motions　of　the　heavenly　bodies；　has　been　put　forward　and　ardently　championed；　but；　unfortunately；　is　not　accepted　by　the　dominant　thinkers　at　the　close　of　our　epoch。　In　this　regard；　therefore；　a　vast　revolutionary　work　remains　for　the　thinkers　of　a　later　period。　Moreover；　such　observations　as　the　precession　of　the　equinoxes　and　the　moon's　evection　are　as　yet　unexplained；　and　measurements　of　the　earth's　size；　and　of　the　sun's　size　and　distance；　are　so　crude　and　imperfect　as　to　be　in　one　case　only　an　approximation；　and　in　the　other　an　absurdly　inadequate　suggestion。　But　with　all　these　defects；　the　total　achievement　of　the　Greek　astronomers　is　stupendous。　To　have　clearly　grasped　the　idea　that　the　earth　is　round　is　in　itself　an　achievement　that　marks　off　the　classical　from　the　Oriental　period　as　by　a　great　gulf。　In　the　physical　sciences　we　have　seen　at　least　the　beginnings　of　great　things。　Dynamics　and　hydrostatics　may　now；　for　the　first　time；　claim　a　place　among　the　sciences。　Geometry　has　been　perfected　and　trigonometry　has　made　a　sure　beginning。　The　conception　that　there　are　four　elementary　substances；　earth；　water；　air；　and　fire；　may　not　appear　a　secure　foundation　for　chemistry；　yet　it　marks　at　least　an　attempt　in　the　right　direction。　Similarly；　the　conception　that　all　matter　is　made　up　of　indivisible　particles　and　that　these　have　adjusted　themselves　and　are　perhaps　held　in　place　by　a　whirling　motion；　while　it　is　scarcely　more　than　a　scientific　dream；　is；　after　all；　a　dream　of　marvellous　insight。　In　the　field　of　biological　science　progress　has　not　been　so　marked；　yet　the　elaborate　garnering　of　facts　regarding　anatomy；　physiology；　and　the　zoological　sciences　is　at　least　a　valuable　preparation　for　the　generalizations　of　a　later　time。　If　with　a　map　before　us　we　glance　at　the　portion　of　the　globe　which　was　known　to　the　workers　of　the　period　now　in　question；　bearing　in　mind　at　the　same　time　what　we　have　learned　as　to　the　seat　of　labors　of　the　various　great　scientific　thinkers　from　Thales　to　Galen；　we　cannot　fail　to　be　struck　with　a　rather　startling　fact；　intimations　of　which　have　been　given　from　time　to　timethe　fact；　namely；　that　most　of　the　great　Greek　thinkers　did　not　live　in　Greece　itself。　As　our　eye　falls　upon　Asia　Minor　and　its　outlying　islands；　we　reflect　that　here　were　born　such　men　as　Thales；　Anaximander；　Anaximenes；　Heraclitus；　Pythagoras；　Anaxagoras；　Socrates；　Aristarchus；　Hipparchus；　Eudoxus；　Philolaus；　and　Galen。　From　the　northern　shores　of　the　aegean　came　Lucippus；　Democritus；　and　Aristotle。　Italy；　off　to　the　west；　is　the　home　of　Pythagoras　and　Xenophanes　in　their　later　years；　and　of　Parmenides　and　Empedocles；　Zeno；　and　Archimedes。　Northern　Africa　can　claim；　by　birth　or　by　adoption；　such　names　as　Euclid；　Apollonius　of　Perga；　Herophilus；　Erasistratus；　Aristippus；　Eratosthenes；　Ctesibius；　Hero；　Strabo；　and　Ptolemy。　This　is　but　running　over　the　list　of　great　men　whose　discoveries　have　claimed　our　attention。　Were　we　to　extend　the　list　to　include　a　host　of　workers　of　the　second　rank；　we　should　but　emphasize　the　same　fact。　All　along　we　are　speaking　of　Greeks；　or；　as　they　call　themselves；　Hellenes；　and　we　mean　by　these　words　the　people　whose　home　was　a　small　jagged　peninsula　jutting　into　the　Mediterranean　at　the　southeastern　extremity　of　Europe。　We　think　of　this　peninsula　as　the　home　of　Greek　culture；　yet　of　all　the　great　thinkers　we　have　just　named；　not　one　was　born　on　this　peninsula；　and　perhaps　not　one　in　five　ever　set　foot　upon　it。　In　point　of　fact；　one　Greek　thinker　of　the　very　first　rank；　and　one　only；　was　born　in　Greece　proper；　that　one；　however；　was　Plato；　perhaps　the　greatest　of　them　all。　With　this　one　brilliant　exception　（and　even　he　was　born　of　parents　who　came　from　the　provinces）；　all　the　great　thinkers　of　Greece　had　their　origin　at　the　circumference　rather　than　the　centre　of　the　empire。　And　if　we　reflect　that　this　circumference　of　the　Greek　world　was　in　the　nature　of　the　case　the　widely　circling　region　in　which　the　Greek　came　in　contact　with　other　nations；　we　shall　see　at　once　that　there　could　be　no　more　striking　illustration　in　all　history　than　that　furnished　us　here　of　the　value　of　racial　mingling　as　a　stimulus　to　intellectual　progress。　But　there　is　one　other　feature　of　the　matter　that　must　not　be　overlooked。　Racial　mingling　gives　vitality；　but　to　produce　the　best　effect　the　mingling　must　be　that　of　races　all　of　which　are　at　a　relatively　high　plane　of　civilization。　In　Asia　Minor　the　Greek　mingled　with　the　Semite；　who　had　the　heritage　of　centuries　of　culture；　and　in　Italy　with　the　Umbrians；　Oscans；　and　Etruscans；　who；　little　as　we　know　of　their　antecedents；　have　left　us　monuments　to　testify　to　their　high　development。　The　chief　reason　why　the　racial　mingling　of　a　later　day　did　not　avail　at　once　to　give　new　life　to　Roman　thought　was　that　the　races　which　swept　down　from　the　north　were　barbarians。　It　was　no　more　possible　that　they　should　spring　to　the　heights　of　classical　culture　than　it　would；　for　example；　be　possible　in　two　or　three　generations　to　produce　a　racer　from　a　stock　of　draught　horses。　Evolution　does　not　proceed　by　such　vaults　as　this　would　imply。　Celt；　Goth；　Hun；　and　Slav　must　undergo　progressive　development　for　many　generations　before　the　population　of　northern　Europe　can　catch　step　with　the　classical　Greek　and　prepare　to　march　forward。　That；　perhaps；　is　one　reason　why　we　come　to　a　period　of　stasis　or　retrogression　when　the　time　of　classical　activity　is　over。　But；　at　best；　it　is　only　one　reason　of　several。　The　influence　of　the　barbarian　nations　will　claim　further　attention　as　we　proceed。　But　now；　for　the　moment；　we　must　turn　our　eyes　in　the　other　direction　and　give　attention　to　certain　phases　of　Greek　and　of　Oriental　thought　which　were　destined　to　play　a　most　important　part　in　the　development　of　the　Western　minda　more　important　part；　indeed；　in　the　early　mediaeval　period　than　that　played　by　those　important　inductions　of　science　which　have　chiefly　claimed　our　attention　in　recent　chapters。　The　subject　in　qu