a history of science-2-第14部分

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ving　motion　is　definitely　established。　The　greater　the　sphere　is　in　such　a　case；　so　much　longer　is　the　time　required　for　its　revolution；　the　smaller　the　sphere　the　shorter　the　time。　Saturn；　whose　orbit　surpasses　those　of　all　the　planets　in　size；　traverses　it　in　thirty　years。　Jupiter＇4＇　completes　its　smaller　course　in　twelve　years；　Mars　in　two；　the　moon　performs　its　much　smaller　revolution　within　a　month。　Just　as　clearly　in　the　Medicean　stars；　we　see　that　the　one　nearest　Jupiter　completes　its　revolution　in　a　very　short　timeabout　forty…two　hours；　the　next　in　about　three　and　one…half　days；　the　third　in　seven；　and　the　most　distant　one　in　sixteen　days。　This　rule；　which　is　followed　throughout；　will　still　remain　if　we　ascribe　the　twenty…four…hourly　motion　to　a　rotation　of　the　earth。　If；　however；　the　earth　is　left　motionless；　we　must　go　first　from　the　very　short　rule　of　the　moon　to　ever　greater　onesto　the　two…yearly　rule　of　Mars；　from　that　to　the　twelve…yearly　one　of　Jupiter；　from　here　to　the　thirty…yearly　one　of　Saturn；　and　then　suddenly　to　an　incomparably　greater　sphere；　to　which　also　we　must　ascribe　a　complete　rotation　in　twenty…four　hours。　If；　however；　we　assume　a　motion　of　the　earth；　the　rapidity　of　the　periods　is　very　well　preserved；　from　the　slowest　sphere　of　Saturn　we　come　to　the　wholly　motionless　fixed　stars。　We　also　escape　thereby　a　fourth　difficulty；　which　arises　as　soon　as　we　assume　that　there　is　motion　in　the　sphere　of　the　stars。　I　mean　the　great　unevenness　in　the　movement　of　these　very　stars；　some　of　which　would　have　to　revolve　with　extraordinary　rapidity　in　immense　circles；　while　others　moved　very　slowly　in　small　circles；　since　some　of　them　are　at　a　greater；　others　at　a　less；　distance　from　the　pole。　That　is　likewise　an　inconvenience；　for；　on　the　one　hand；　we　see　all　those　stars；　the　motion　of　which　is　indubitable；　revolve　in　great　circles；　while；　on　the　other　hand；　there　seems　to　be　little　object　in　placing　bodies；　which　are　to　move　in　circles；　at　an　enormous　distance　from　the　centre　and　then　let　them　move　in　very　small　circles。　And　not　only　are　the　size　of　the　different　circles　and　therewith　the　rapidity　of　the　movement　very　different　in　the　different　fixed　stars；　but　the　same　stars　also　change　their　orbits　and　their　rapidity　of　motion。　Therein　consists　the　fifth　inconvenience。　Those　stars；　namely；　which　were　at　the　equator　two　thousand　years　ago；　and　hence　described　great　circles　in　their　revolutions；　must　to…day　move　more　slowly　and　in　smaller　circles；　because　they　are　many　degrees　removed　from　it。　It　will　even　happen；　after　not　so　very　long　a　time；　that　one　of　those　which　have　hitherto　been　continually　in　motion　will　finally　coincide　with　the　pole　and　stand　still；　but　after　a　period　of　repose　will　again　begin　to　move。　The　other　stars　in　the　mean　while；　which　unquestionably　move；　all　have；　as　was　said；　a　great　circle　for　an　orbit　and　keep　this　unchangeably。　〃The　improbability　is　further　increasedthis　may　be　considered　the　sixth　inconvenienceby　the　fact　that　it　is　impossible　to　conceive　what　degree　of　solidity　those　immense　spheres　must　have；　in　the　depths　of　which　so　many　stars　are　fixed　so　enduringly　that　they　are　kept　revolving　evenly　in　spite　of　such　difference　of　motion　without　changing　their　respective　positions。　Or　if；　according　to　the　much　more　probable　theory；　the　heavens　are　fluid；　and　every　star　describes　an　orbit　of　its　own；　according　to　what　law　then；　or　for　what　reason；　are　their　orbits　so　arranged　that；　when　looked　at　from　the　earth；　they　appear　to　be　contained　in　one　single　sphere？　To　attain　this　it　seems　to　me　much　easier　and　more　convenient　to　make　them　motionless　instead　of　moving；　just　as　the　paving…stones　on　the　market…place；　for　instance；　remain　in　order　more　easily　than　the　swarms　of　children　running　about　on　them。　〃Finally；　the　seventh　difficulty：　If　we　attribute　the　daily　rotation　to　the　higher　region　of　the　heavens；　we　should　have　to　endow　it　with　force　and　power　sufficient　to　carry　with　it　the　innumerable　host　of　the　fixed　stars　every　one　a　body　of　very　great　compass　and　much　larger　than　the　earthand　all　the　planets；　although　the　latter；　like　the　earth；　move　naturally　in　an　opposite　direction。　In　the　midst　of　all　this　the　little　earth；　single　and　alone；　would　obstinately　and　wilfully　withstand　such　forcea　supposition　which；　it　appears　to　me；　has　much　against　it。　I　could　also　not　explain　why　the　earth；　a　freely　poised　body；　balancing　itself　about　its　centre；　and　surrounded　on　all　sides　by　a　fluid　medium；　should　not　be　affected　by　the　universal　rotation。　Such　difficulties；　however；　do　not　confront　us　if　we　attribute　motion　to　the　earthsuch　a　small；　insignificant　body　in　comparison　with　the　whole　universe；　and　which　for　that　very　reason　cannot　exercise　any　power　over　the　latter。　〃Simplicio。　You　support　your　arguments　throughout；　it　seems　to　me；　on　the　greater　ease　and　simplicity　with　which　the　said　effects　are　produced。　You　mean　that　as　a　cause　the　motion　of　the　earth　alone　is　just　as　satisfactory　as　the　motion　of　all　the　rest　of　the　universe　with　the　exception　of　the　earth；　you　hold　the　actual　event　to　be　much　easier　in　the　former　case　than　in　the　latter。　For　the　ruler　of　the　universe；　however；　whose　might　is　infinite；　it　is　no　less　easy　to　move　the　universe　than　the　earth　or　a　straw　balm。　But　if　his　power　is　infinite；　why　should　not　a　greater；　rather　than　a　very　small；　part　of　it　be　revealed　to　me？　〃Salviati。　If　I　had　said　that　the　universe　does　not　move　on　account　of　the　impotence　of　its　ruler；　I　should　have　been　wrong　and　your　rebuke　would　have　been　in　order。　I　admit　that　it　is　just　as　easy　for　an　infinite　power　to　move　a　hundred　thousand　as　to　move　one。　What　I　said；　however；　does　not　refer　to　him　who　causes　the　motion；　but　to　that　which　is　moved。　In　answer　to　your　remark　that　it　is　more　fitting　for　an　infinite　power　to　reveal　a　large　part　of　itself　rather　than　a　little；　I　answer　that；　in　relation　to　the　infinite；　one　part　is　not　greater　than　another；　if　both　are　finite。　Hence　it　is　unallowable　to　say　that　a　hundred　thousand　is　a　larger　part　of　an　infinite　number　than　two；　although　the　former　is　fifty　thousand　times　greater　than　the　latter。　If；　therefore；　we　consider　the　moving　bodies；　we　must　unquestionably　regard　the　motion　of　the　earth　as　a　much　simpler　process　than　that　of　the　universe；　if；　furthermore；　we　direct　our　attention　to　so　many　other　simplifications　which　may　be　reached　only　by　this　theory；　the　daily　movement　of　the　earth　must　appear　much　more　probable　than　the　motion　of　the　universe　without　the　earth；　for；　according　to　Aristotle's　just　axiom；　'Frustra　fit　per　plura；　quod　potest　fieri　per　p　auciora'　（It　is　vain　to　expend　many　means　where　a　few　are　sufficient）。〃＇2＇

The　work　was　widely　circulated；　and　it　was　received　with　an　interest　which　bespeaks　a　wide…spread　undercurrent　of　belief　in　the　Copernican　doctrine。　Naturally　enough；　it　attracted　immediate　attention　from　the　church　authorities。　Galileo　was　summoned　to　appear　at　Rome　to　defend　his　conduct。　The　philosopher；　who　was　now　in　his　seventieth　year；　pleaded　age　and　infirmity。　He　had　no　desire　for　personal　experience　of　the　tribunal　of　the　Inquisition；　but　the　mandate　was　repeated；　and　Galileo　went　to　Rome。　There；　as　every　one　knows；　he　disavowed　any　intention　to　oppose　the　teachings　of　Scripture；　and　formally　renounced　the　heretical　doctrine　of　the　earth's　motion。　According　to　a　tale　which　so　long　passed　current　that　every　historian　must　still　repeat　it　though　no　one　now　believes　it　authentic；　Galileo　qualified　his　renunciation　by　muttering　to　himself；　〃E　pur　si　muove〃　（It　does　move；　none　the　less）；　as　he　rose　to　his　feet　and　retired　from　the　presence　of　his　persecutors。　The　tale　is　one　of　those　fictions　which　the　dramatic　sense　of　humanity　is　wont　to　impose　upon　history；　but；　like　most　such　fictions；　it　expresses　the　spirit　if　not　the　letter　of　truth；　for　just　as　no　one　believes　that　Galileo's　lips　uttered　the　phrase；　so　no　one　doubts　that　the　rebellious　words　were　in　his　mind。　After　his　formal　renunciation；　Galileo　was　allowed　to　depart；　but　with　the　injunction　that　he　abstain　in　future　from　heretical　teaching。　The　remaining　ten　years　of　his　life　were　devoted　chiefly　to　mechanics；　where　his　experiments　fortunately　opposed　the　Aristotelian　rather　than　the　Hebrew　teachings。　Galileo's　death　occurred　in　1642；　a　hundred　years　after　the　death　of　Copernicus。　Kepler　had　died　thirteen　years　before；　and　there　remained　no　astronomer　in　the　field　who　is　conspicuous　in　the　history　of　science　as　a　champion　of　the　Copernican　doctrine。　But　in　truth　it　might　be　said　that　the　theory　no　longer　needed　a　champion。　The　researches　of　Kepler　and　Galileo　had　produced　a　mass　of　evidence　for　the　Copernican　theory　which　amounted　to　demonstration。　A　generation　or　two　might　be　required　for　this　evidence　to　make　itself　everywhere　known　among　men　of　science；　and　of　course　the　ecclesiastical　authorities　must　be　expected　to　stand　by　their　guns　for　a　somewhat　longer　period。　In　point　of　fact；　the　ecclesiastical　ban　was　not　technically　removed　by　the　striking　of　the　Copernican　books　from　the　list　of　the　Index　Expurgatorius　until　the　year　1822；　almost　two　hundred　years　after　the　date　of　Galileo's　dialogue。　But　this；　of　course；　is　in　no　sense　a　guide　to　the　state　of　general　opinion　regarding　the　theory。　We　shall　gain　a　true　gauge　as　to　this　if　we　assume　that　the　greater　number　of　important　thinkers　had　accepted　the　heliocentric　doctrine　before　the　middle　of　the　seventeenth　century；　and　that　before　the　close　of　that　century　the　old　Ptolemaic　idea　had　been　quite　abandoned。　A　wonderful　revolution　in　man's　estimate　of　the　universe　had　thus　been　effected　within　about　two　centuries　after　the　birth　of　Copernicus。

V。　GALILEO　AND　THE　NEW　PHYSICS　After　Galileo　had　felt　the　strong　hand　of　the　Inquisition；　in　1632；　he　was　careful　to　confine　his　researches；　or　at　least　his　publications；　to　topics　that　seemed　free　from　theological　implications。　In　doing　so　he　reverted　to　the　field　of　his　earliest　studies　namely；　the　field　of　mechanics；　and　the　Dialoghi　delle　Nuove　Scienze；　which　he　finished　in　1636；　and　which　was　printed　two　years　later；　attained　a　celebrity　no　less　than　that　of　the　heretical　dialogue　that　had　preceded　it。　The　later　work　was　free　from　all　apparent　heresies；　yet　perhap