a history of science-2-第13部分

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cean　stars。　Turning　attention　to　the　sun　itself；　Galileo　observed　on　the　surface　of　that　luminary　a　spot　or　blemish　which　gradually　changed　its　shape；　suggesting　that　changes　were　taking　place　in　the　substance　of　the　sunchanges　obviously　incompatible　with　the　perfect　condition　demanded　by　the　metaphysical　theorists。　But　however　disquieting　for　the　conservative；　the　sun's　spots　served　a　most　useful　purpose　in　enabling　Galileo　to　demonstrate　that　the　sun　itself　revolves　on　its　axis；　since　a　given　spot　was　seen　to　pass　across　the　disk　and　after　disappearing　to　reappear　in　due　course。　The　period　of　rotation　was　found　to　be　about　twenty…four　days。　It　must　be　added　that　various　observers　disputed　priority　of　discovery　of　the　sun's　spots　with　Galileo。　Unquestionably　a　sun…spot　had　been　seen　by　earlier　observers；　and　by　them　mistaken　for　the　transit　of　an　inferior　planet。　Kepler　himself　had　made　this　mistake。　Before　the　day　of　the　telescope；　he　had　viewed　the　image　of　the　sun　as　thrown　on　a　screen　in　a　camera…obscura；　and　had　observed　a　spot　on　the　disk　which　be　interpreted　as　representing　the　planet　Mercury；　but　which；　as　is　now　known；　must　have　been　a　sun…spot；　since　the　planetary　disk　is　too　small　to　have　been　revealed　by　this　method。　Such　observations　as　these；　however　interesting；　cannot　be　claimed　as　discoveries　of　the　sun…spots。　It　is　probable；　however；　that　several　discoverers　（notably　Johann　Fabricius）　made　the　telescopic　observation　of　the　spots；　and　recognized　them　as　having　to　do　with　the　sun's　surface；　almost　simultaneously　with　Galileo。　One　of　these　claimants　was　a　Jesuit　named　Scheiner；　and　the　jealousy　of　this　man　is　said　to　have　had　a　share　in　bringing　about　that　persecution　to　which　we　must　now　refer。　There　is　no　more　famous　incident　in　the　history　of　science　than　the　heresy　trial　through　which　Galileo　was　led　to　the　nominal　renunciation　of　his　cherished　doctrines。　There　is　scarcely　another　incident　that　has　been　commented　upon　so　variously。　Each　succeeding　generation　has　put　its　own　interpretation　on　it。　The　facts；　however；　have　been　but　little　questioned。　It　appears　that　in　the　year　1616　the　church　became　at　last　aroused　to　the　implications　of　the　heliocentric　doctrine　of　the　universe。　Apparently　it　seemed　clear　to　the　church　authorities　that　the　authors　of　the　Bible　believed　the　world　to　be　immovably　fixed　at　the　centre　of　the　universe。　Such；　indeed；　would　seem　to　be　the　natural　inference　from　various　familiar　phrases　of　the　Hebrew　text；　and　what　we　now　know　of　the　status　of　Oriental　science　in　antiquity　gives　full　warrant　to　this　interpretation。　There　is　no　reason　to　suppose　that　the　conception　of　the　subordinate　place　of　the　world　in　the　solar　system　had　ever　so　much　as　occurred；　even　as　a　vague　speculation；　to　the　authors　of　Genesis。　In　common　with　their　contemporaries；　they　believed　the　earth　to　be　the　all…important　body　in　the　universe；　and　the　sun　a　luminary　placed　in　the　sky　for　the　sole　purpose　of　giving　light　to　the　earth。　There　is　nothing　strange；　nothing　anomalous；　in　this　view；　it　merely　reflects　the　current　notions　of　Oriental　peoples　in　antiquity。　What　is　strange　and　anomalous　is　the　fact　that　the　Oriental　dreamings　thus　expressed　could　have　been　supposed　to　represent　the　acme　of　scientific　knowledge。　Yet　such　a　hold　had　these　writings　taken　upon　the　Western　world　that　not　even　a　Galileo　dared　contradict　them　openly；　and　when　the　church　fathers　gravely　declared　the　heliocentric　theory　necessarily　false；　because　contradictory　to　Scripture；　there　were　probably　few　people　in　Christendom　whose　mental　attitude　would　permit　them　justly　to　appreciate　the　humor　of　such　a　pronouncement。　And；　indeed；　if　here　and　there　a　man　might　have　risen　to　such　an　appreciation；　there　were　abundant　reasons　for　the　repression　of　the　impulse；　for　there　was　nothing　humorous　about　the　response　with　which　the　authorities　of　the　time　were　wont　to　meet　the　expression　of　iconoclastic　opinions。　The　burning　at　the　stake　of　Giordano　Bruno；　in　the　year　1600；　was；　for　example；　an　object…lesson　well　calculated　to　restrain　the　enthusiasm　of　other　similarly　minded　teachers。　Doubtless　it　was　such　considerations　that　explained　the　relative　silence　of　the　champions　of　the　Copernican　theory；　accounting　for　the　otherwise　inexplicable　fact　that　about　eighty　years　elapsed　after　the　death　of　Copernicus　himself　before　a　single　text…book　expounded　his　theory。　The　text…book　which　then　appeared；　under　date　of　1622；　was　written　by　the　famous　Kepler；　who　perhaps　was　shielded　in　a　measure　from　the　papal　consequences　of　such　hardihood　by　the　fact　of　residence　in　a　Protestant　country。　Not　that　the　Protestants　of　the　time　favored　the　heliocentric　doctrinewe　have　already　quoted　Luther　in　an　adverse　sensebut　of　course　it　was　characteristic　of　the　Reformation　temper　to　oppose　any　papal　pronouncement；　hence　the　ultramontane　declaration　of　1616　may　indirectly　have　aided　the　doctrine　which　it　attacked；　by　making　that　doctrine　less　obnoxious　to　Lutheran　eyes。　Be　that　as　it　may；　the　work　of　Kepler　brought　its　author　into　no　direct　conflict　with　the　authorities。　But　the　result　was　quite　different　when；　in　1632；　Galileo　at　last　broke　silence　and　gave　the　world；　under　cover　of　the　form　of　dialogue；　an　elaborate　exposition　of　the　Copernican　theory。　Galileo；　it　must　be　explained；　had　previously　been　warned　to　keep　silent　on　the　subject；　hence　his　publication　doubly　offended　the　authorities。　To　be　sure；　he　could　reply　that　his　dialogue　introduced　a　champion　of　the　Ptolemaic　system　to　dispute　with　the　upholder　of　the　opposite　view；　and　that；　both　views　being　presented　with　full　array　of　argument；　the　reader　was　left　to　reach　a　verdict　for　himself；　the　author　having　nowhere　pointedly　expressed　an　opinion。　But　such　an　argument；　of　course；　was　specious；　for　no　one　who　read　the　dialogue　could　be　in　doubt　as　to　the　opinion　of　the　author。　Moreover；　it　was　hinted　that　Simplicio；　the　character　who　upheld　the　Ptolemaic　doctrine　and　who　was　everywhere　worsted　in　the　argument；　was　intended　to　represent　the　pope　himselfa　suggestion　which　probably　did　no　good　to　Galileo's　cause。　The　character　of　Galileo's　artistic　presentation　may　best　be　judged　from　an　example；　illustrating　the　vigorous　assault　of　Salviati；　the　champion　of　the　new　theory；　and　the　feeble　retorts　of　his　conservative　antagonist：　〃Salviati。　Let　us　then　begin　our　discussion　with　the　consideration　that；　whatever　motion　may　be　attributed　to　the　earth；　yet　we；　as　dwellers　upon　it；　and　hence　as　participators　in　its　motion；　cannot　possibly　perceive　anything　of　it；　presupposing　that　we　are　to　consider　only　earthly　things。　On　the　other　hand；　it　is　just　as　necessary　that　this　same　motion　belong　apparently　to　all　other　bodies　and　visible　objects；　which；　being　separated　from　the　earth；　do　not　take　part　in　its　motion。　The　correct　method　to　discover　whether　one　can　ascribe　motion　to　the　earth；　and　what　kind　of　motion；　is；　therefore；　to　investigate　and　observe　whether　in　bodies　outside　the　earth　a　perceptible　motion　may　be　discovered　which　belongs　to　all　alike。　Because　a　movement　which　is　perceptible　only　in　the　moon；　for　instance；　and　has　nothing　to　do　with　Venus　or　Jupiter　or　other　stars；　cannot　possibly　be　peculiar　to　the　earth；　nor　can　its　seat　be　anywhere　else　than　in　the　moon。　Now　there　is　one　such　universal　movement　which　controls　all　othersnamely；　that　which　the　sun；　moon；　the　other　planets；　the　fixed　starsin　short；　the　whole　universe；　with　the　single　exception　of　the　earthappears　to　execute　from　east　to　west　in　the　space　of　twenty…four　hours。　This　now；　as　it　appears　at　the　first　glance　anyway；　might　just　as　well　be　a　motion　of　the　earth　alone　as　of　all　the　rest　of　the　universe　with　the　exception　of　the　earth；　for　the　same　phenomena　would　result　from　either　hypothesis。　Beginning　with　the　most　general；　I　will　enumerate　the　reasons　which　seem　to　speak　in　favor　of　the　earth's　motion。　When　we　merely　consider　the　immensity　of　the　starry　sphere　in　comparison　with　the　smallness　of　the　terrestrial　ball；　which　is　contained　many　million　times　in　the　former；　and　then　think　of　the　rapidity　of　the　motion　which　completes　a　whole　rotation　in　one　day　and　night；　I　cannot　persuade　myself　how　any　one　can　hold　it　to　be　more　reasonable　and　credible　that　it　is　the　heavenly　sphere　which　rotates；　while　the　earth　stands　still。　〃Simplicio。　I　do　not　well　understand　how　that　powerful　motion　may　be　said　to　as　good　as　not　exist　for　the　sun；　the　moon；　the　other　planets；　and　the　innumerable　host　of　fixed　stars。　Do　you　call　that　nothing　when　the　sun　goes　from　one　meridian　to　another；　rises　up　over　this　horizon　and　sinks　behind　that　one；　brings　now　day；　and　now　night；　when　the　moon　goes　through　similar　changes；　and　the　other　planets　and　fixed　stars　in　the　same　way？　〃Salviati。　All　the　changes　you　mention　are　such　only　in　respect　to　the　earth。　To　convince　yourself　of　it；　only　imagine　the　earth　out　of　existence。　There　would　then　be　no　rising　and　setting　of　the　sun　or　of　the　moon；　no　horizon；　no　meridian；　no　day；　no　nightin　short；　the　said　motion　causes　no　change　of　any　sort　in　the　relation　of　the　sun　to　the　moon　or　to　any　of　the　other　heavenly　bodies；　be　they　planets　or　fixed　stars。　All　changes　are　rather　in　respect　to　the　earth；　they　may　all　be　reduced　to　the　simple　fact　that　the　sun　is　first　visible　in　China；　then　in　Persia；　afterwards　in　Egypt；　Greece；　France；　Spain；　America；　etc。；　and　that　the　same　thing　happens　with　the　moon　and　the　other　heavenly　bodies。　Exactly　the　same　thing　happens　and　in　exactly　the　same　way　if；　instead　of　disturbing　so　large　a　part　of　the　universe；　you　let　the　earth　revolve　about　itself。　The　difficulty　is；　however；　doubled；　inasmuch　as　a　second　very　important　problem　presents　itself。　If；　namely；　that　powerful　motion　is　ascribed　to　the　heavens；　it　is　absolutely　necessary　to　regard　it　as　opposed　to　the　individual　motion　of　all　the　planets；　every　one　of　which　indubitably　has　its　own　very　leisurely　and　moderate　movement　from　west　to　east。　If；　on　the　other　hand；　you　let　the　earth　move　about　itself；　this　opposition　of　motion　disappears。　〃The　improbability　is　tripled　by　the　complete　overthrow　of　that　order　which　rules　all　the　heavenly　bodies　in　which　the　revolving　motion　is　definitely　established。　The　greater　the　sphere　is　in　such　a　case；　so　much　longer　is　t