a history of science-2-第11部分

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hich　includes　the　moon　with　the　earth　for　its　centre；　makes　the　round　of　that　great　circle　between　the　planets；　in　yearly　motion　about　the　sun；　and　revolves　about　the　centre　of　the　universe；　in　which　the　sun　rests　motionless；　and　that　all　which　looks　like　motion　in　the　sun　is　explained　by　the　motion　of　the　earth。　The　extent　of　the　universe；　however；　is　so　great　that；　whereas　the　distance　of　the　earth　from　the　sun　is　considerable　in　comparison　with　the　size　of　the　other　planetary　orbits；　it　disappears　when　compared　with　the　sphere　of　the　fixed　stars。　I　hold　this　to　be　more　easily　comprehensible　than　when　the　mind　is　confused　by　an　almost　endless　number　of　circles；　which　is　necessarily　the　case　with　those　who　keep　the　earth　in　the　middle　of　the　universe。　Although　this　may　appear　incomprehensible　and　contrary　to　the　opinion　of　many；　I　shall；　if　God　wills；　make　it　clearer　than　the　sun；　at　least　to　those　who　are　not　ignorant　of　mathematics。　〃The　order　of　the　spheres　is　as　follows：　The　first　and　lightest　of　all　the　spheres　is　that　of　the　fixed　stars；　which　includes　itself　and　all　others；　and　hence　is　motionless　as　the　place　in　the　universe　to　which　the　motion　and　position　of　all　other　stars　is　referred。　〃Then　follows　the　outermost　planet；　Saturn；　which　completes　its　revolution　around　the　sun　in　thirty　years；　next　comes　Jupiter　with　a　twelve　years'　revolution；　then　Mars；　which　completes　its　course　in　two　years。　The　fourth　one　in　order　is　the　yearly　revolution　which　includes　the　earth　with　the　moon's　orbit　as　an　epicycle。　In　the　fifth　place　is　Venus　with　a　revolution　of　nine　months。　The　sixth　place　is　taken　by　Mercury；　which　completes　its　course　in　eighty　days。　In　the　middle　of　all　stands　the　sun；　and　who　could　wish　to　place　the　lamp　of　this　most　beautiful　temple　in　another　or　better　place。　Thus；　in　fact；　the　sun；　seated　upon　the　royal　throne；　controls　the　family　of　the　stars　which　circle　around　him。　We　find　in　their　order　a　harmonious　connection　which　cannot　be　found　elsewhere。　Here　the　attentive　observer　can　see　why　the　waxing　and　waning　of　Jupiter　seems　greater　than　with　Saturn　and　smaller　than　with　Mars；　and　again　greater　with　Venus　than　with　Mercury。　Also；　why　Saturn；　Jupiter；　and　Mars　are　nearer　to　the　earth　when　they　rise　in　the　evening　than　when　they　disappear　in　the　rays　of　the　sun。　More　prominently；　however；　is　it　seen　in　the　case　of　Mars；　which　when　it　appears　in　the　heavens　at　night；　seems　to　equal　Jupiter　in　size；　but　soon　afterwards　is　found　among　the　stars　of　second　magnitude。　All　of　this　results　from　the　same　causenamely；　from　the　earth's　motion。　The　fact　that　nothing　of　this　is　to　be　seen　in　the　case　of　the　fixed　stars　is　a　proof　of　their　immeasurable　distance；　which　makes　even　the　orbit　of　yearly　motion　or　its　counterpart　invisible　to　us。〃＇1＇

The　fact　that　the　stars　show　no　parallax　had　been　regarded　as　an　important　argument　against　the　motion　of　the　earth；　and　it　was　still　so　considered　by　the　opponents　of　the　system　of　Copernicus。　It　had；　indeed；　been　necessary　for　Aristarchus　to　explain　the　fact　as　due　to　the　extreme　distance　of　the　stars；　a　perfectly　correct　explanation；　but　one　that　implies　distances　that　are　altogether　inconceivable。　It　remained　for　nineteenth…century　astronomers　to　show；　with　the　aid　of　instruments　of　greater　precision；　that　certain　of　the　stars　have　a　parallax。　But　long　before　this　demonstration　had　been　brought　forward；　the　system　of　Copernicus　had　been　accepted　as　a　part　of　common　knowledge。　While　Copernicus　postulated　a　cosmical　scheme　that　was　correct　as　to　its　main　features；　he　did　not　altogether　break　away　from　certain　defects　of　the　Ptolemaic　hypothesis。　Indeed；　he　seems　to　have　retained　as　much　of　this　as　practicable；　in　deference　to　the　prejudice　of　his　time。　Thus　he　records　the　planetary　orbits　as　circular；　and　explains　their　eccentricities　by　resorting　to　the　theory　of　epicycles；　quite　after　the　Ptolemaic　method。　But　now；　of　course；　a　much　more　simple　mechanism　sufficed　to　explain　the　planetary　motions；　since　the　orbits　were　correctly　referred　to　the　central　sun　and　not　to　the　earth。　Needless　to　say；　the　revolutionary　conception　of　Copernicus　did　not　meet　with　immediate　acceptance。　A　number　of　prominent　astronomers；　however；　took　it　up　almost　at　once；　among　these　being　Rhaeticus；　who　wrote　a　commentary　on　the　evolutions；　Erasmus　Reinhold；　the　author　of　the　Prutenic　tables；　Rothmann；　astronomer　to　the　Landgrave　of　Hesse；　and　Maestlin；　the　instructor　of　Kepler。　The　Prutenic　tables；　just　referred　to；　so　called　because　of　their　Prussian　origin；　were　considered　an　improvement　on　the　tables　of　Copernicus；　and　were　highly　esteemed　by　the　astronomers　of　the　time。　The　commentary　of　Rhaeticus　gives　us　the　interesting　information　that　it　was　the　observation　of　the　orbit　of　Mars　and　of　the　very　great　difference　between　his　apparent　diameters　at　different　times　which　first　led　Copernicus　to　conceive　the　heliocentric　idea。　Of　Reinhold　it　is　recorded　that　he　considered　the　orbit　of　Mercury　elliptical；　and　that　he　advocated　a　theory　of　the　moon；　according　to　which　her　epicycle　revolved　on　an　elliptical　orbit；　thus　in　a　measure　anticipating　one　of　the　great　discoveries　of　Kepler　to　which　we　shall　refer　presently。　The　Landgrave　of　Hesse　was　a　practical　astronomer；　who　produced　a　catalogue　of　fixed　stars　which　has　been　compared　with　that　of　Tycho　Brahe。　He　was　assisted　by　Rothmann　and　by　Justus　Byrgius。　Maestlin；　the　preceptor　of　Kepler；　is　reputed　to　have　been　the　first　modern　observer　to　give　a　correct　explanation　of　the　light　seen　on　portions　of　the　moon　not　directly　illumined　by　the　sun。　He　explained　this　as　not　due　to　any　proper　light　of　the　moon　itself；　but　as　light　reflected　from　the　earth。　Certain　of　the　Greek　philosophers；　however；　are　said　to　have　given　the　same　explanation；　and　it　is　alleged　also　that　Leonardo　da　Vinci　anticipated　Maestlin　in　this　regard。＇2＇　While；　various　astronomers　of　some　eminence　thus　gave　support　to　the　Copernican　system；　almost　from　the　beginning；　it　unfortunately　chanced　that　by　far　the　most　famous　of　the　immediate　successors　of　Copernicus　declined　to　accept　the　theory　of　the　earth's　motion。　This　was　Tycho　Brahe；　one　of　the　greatest　observing　astronomers　of　any　age。　Tycho　Brahe　was　a　Dane；　born　at　Knudstrup　in　the　year　1546。　He　died　in　1601　at　Prague；　in　Bohemia。　During　a　considerable　portion　of　his　life　he　found　a　patron　in　Frederick；　King　of　Denmark；　who　assisted　him　to　build　a　splendid　observatory　on　the　Island　of　Huene。　On　the　death　of　his　patron　Tycho　moved　to　Germany；　where；　as　good　luck　would　have　it；　he　came　in　contact　with　the　youthful　Kepler；　and　thus；　no　doubt；　was　instrumental　in　stimulating　the　ambitions　of　one　who　in　later　years　was　to　be　known　as　a　far　greater　theorist　than　himself。　As　has　been　said；　Tycho　rejected　the　Copernican　theory　of　the　earth's　motion。　It　should　be　added；　however；　that　he　accepted　that　part　of　the　Copernican　theory　which　makes　the　sun　the　centre　of　all　the　planetary　motions；　the　earth　being　excepted。　He　thus　developed　a　system　of　his　own；　which　was　in　some　sort　a　compromise　between　the　Ptolemaic　and　the　Copernican　systems。　As　Tycho　conceived　it；　the　sun　revolves　about　the　earth；　carrying　with　it　the　planets…Mercury；　Venus；　Mars；　Jupiter；　and　Saturn；　which　planets　have　the　sun　and　not　the　earth　as　the　centre　of　their　orbits。　This　cosmical　scheme；　it　should　be　added；　may　be　made　to　explain　the　observed　motions　of　the　heavenly　bodies；　but　it　involves　a　much　more　complex　mechanism　than　is　postulated　by　the　Copernican　theory。　Various　explanations　have　been　offered　of　the　conservatism　which　held　the　great　Danish　astronomer　back　from　full　acceptance　of　the　relatively　simple　and；　as　we　now　know；　correct　Copernican　doctrine。　From　our　latter…day　point　of　view；　it　seems　so　much　more　natural　to　accept　than　to　reject　the　Copernican　system；　that　we　find　it　difficult　to　put　ourselves　in　the　place　of　a　sixteenth…century　observer。　Yet　if　we　recall　that　the　traditional　view；　having　warrant　of　acceptance　by　nearly　all　thinkers　of　every　age；　recorded　the　earth　as　a　fixed；　immovable　body；　we　shall　see　that　our　surprise　should　be　excited　rather　by　the　thinker　who　can　break　away　from　this　view　than　by　the　one　who　still　tends　to　cling　to　it。　Moreover；　it　is　useless　to　attempt　to　disguise　the　fact　that　something　more　than　a　mere　vague　tradition　was　supposed　to　support　the　idea　of　the　earth's　overshadowing　importance　in　the　cosmical　scheme。　The　sixteenth…century　mind　was　overmastered　by　the　tenets　of　ecclesiasticism；　and　it　was　a　dangerous　heresy　to　doubt　that　the　Hebrew　writings；　upon　which　ecclesiasticism　based　its　claim；　contained　the　last　word　regarding　matters　of　science。　But　the　writers　of　the　Hebrew　text　had　been　under　the　influence　of　that　Babylonian　conception　of　the　universe　which　accepted　the　earth　as　unqualifiedly　centralwhich；　indeed；　had　never　so　much　as　conceived　a　contradictory　hypothesis；　and　so　the　Western　world；　which　had　come　to　accept　these　writings　as　actually　supernatural　in　origin；　lay　under　the　spell　of　Oriental　ideas　of　a　pre…scientific　era。　In　our　own　day；　no　one　speaking　with　authority　thinks　of　these　Hebrew　writings　as　having　any　scientific　weight　whatever。　Their　interest　in　this　regard　is　purely　antiquarian；　hence　from　our　changed