a history of science-2-第10章

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however；　that　Da　Vinci　understood　the　principle　of　this　mechanism；　for　he　describes　how　such　a　camera　can　be　made　by　cutting　a　small；　round　hole　through　the　shutter　of　a　darkened　room；　the　reversed　image　of　objects　outside　being　shown　on　the　opposite　wall。　Like　other　philosophers　in　all　ages；　he　had　observed　a　great　number　of　facts　which　he　was　unable　to　explain　correctly。　But　such　accumulations　of　scientific　observations　are　always　interesting；　as　showing　how　many　centuries　of　observation　frequently　precede　correct　explanation。　He　observed　many　facts　about　sounds；　among　others　that　blows　struck　upon　a　bell　produced　sympathetic　sounds　in　a　bell　of　the　same　kind；　and　that　striking　the　string　of　a　lute　produced　vibration　in　corresponding　strings　of　lutes　strung　to　the　same　pitch。　He　knew；　also；　that　sounds　could　be　heard　at　a　distance　at　sea　by　listening　at　one　end　of　a　tube；　the　other　end　of　which　was　placed　in　the　water；　and　that　the　same　expedient　worked　successfully　on　land；　the　end　of　the　tube　being　placed　against　the　ground。　The　knowledge　of　this　great　number　of　unexplained　facts　is　often　interpreted　by　the　admirers　of　Da　Vinci；　as　showing　an　almost　occult　insight　into　science　many　centuries　in　advance　of　his　time。　Such　interpretations；　however；　are　illusive。　The　observation；　for　example；　that　a　tube　placed　against　the　ground　enables　one　to　hear　movements　on　the　earth　at　a　distance；　is　not　in　itself　evidence　of　anything　more　than　acute　scientific　observation；　as　a　similar　method　is　in　use　among　almost　every　race　of　savages；　notably　the　American　Indians。　On　the　other　hand；　one　is　inclined　to　give　credence　to　almost　any　story　of　the　breadth　of　knowledge　of　the　man　who　came　so　near　anticipating　Hutton；　Lyell；　and　Darwin　in　his　interpretation　of　the　geological　records　as　he　found　them　written　on　the　rocks。　It　is　in　this　field　of　geology　that　Leonardo　is　entitled　to　the　greatest　admiration　by　modern　scientists。　He　had　observed　the　deposit　of　fossil　shells　in　various　strata　of　rocks；　even　on　the　tops　of　mountains；　and　he　rejected　once　for　all　the　theory　that　they　had　been　deposited　there　by　the　Deluge。　He　rightly　interpreted　their　presence　as　evidence　that　they　had　once　been　deposited　at　the　bottom　of　the　sea。　This　process　he　assumed　bad　taken　hundreds　and　thousands　of　centuries；　thus　tacitly　rejecting　the　biblical　tradition　as　to　the　date　of　the　creation。　Notwithstanding　the　obvious　interest　that　attaches　to　the　investigations　of　Leonardo；　it　must　be　admitted　that　his　work　in　science　remained　almost　as　infertile　as　that　of　his　great　precursor；　Bacon。　The　really　stimulative　work　of　this　generation　was　done　by　a　man　of　affairs；　who　knew　little　of　theoretical　science　except　in　one　line；　but　who　pursued　that　one　practical　line　until　he　achieved　a　wonderful　result。　This　man　was　Christopher　Columbus。　It　is　not　necessary　here　to　tell　the　trite　story　of　his　accomplishment。　Suffice　it　that　his　practical　demonstration　of　the　rotundity　of　the　earth　is　regarded　by　most　modern　writers　as　marking　an　epoch　in　history。　With　the　year　of　his　voyage　the　epoch　of　the　Middle　Ages　is　usually　regarded　as　coming　to　an　end。　It　must　not　be　supposed　that　any　very　sudden　change　came　over　the　aspect　of　scholarship　of　the　time；　but　the　preliminaries　of　great　things　had　been　achieved；　and　when　Columbus　made　his　famous　voyage　in　1492；　the　man　was　already　alive　who　was　to　bring　forward　the　first　great　vitalizing　thought　in　the　field　of　pure　science　that　the　Western　world　had　originated　for　more　than　a　thousand　years。　This　man　bore　the　name　of　Kopernik；　or　in　its　familiar　Anglicized　form；　Copernicus。　His　life　work　and　that　of　his　disciples　will　claim　our　attention　in　the　succeeding　chapter。

IV。　THE　NEW　COSMOLOGYCOPERNICUS　TO　KEPLER　AND　GALILEO　We　have　seen　that　the　Ptolemaic　astronomy；　which　was　the　accepted　doctrine　throughout　the　Middle　Ages；　taught　that　the　earth　is　round。　Doubtless　there　was　a　popular　opinion　current　which　regarded　the　earth　as　flat；　but　it　must　be　understood　that　this　opinion　had　no　champions　among　men　of　science　during　the　Middle　Ages。　When；　in　the　year　1492；　Columbus　sailed　out　to　the　west　on　his　memorable　voyage；　his　expectation　of　reaching　India　had　full　scientific　warrant；　however　much　it　may　have　been　scouted　by　certain　ecclesiastics　and　by　the　average　man　of　the　period。　Nevertheless；　we　may　well　suppose　that　the　successful　voyage　of　Columbus；　and　the　still　more　demonstrative　one　made　about　thirty　years　later　by　Magellan；　gave　the　theory　of　the　earth's　rotundity　a　certainty　it　could　never　previously　have　had。　Alexandrian　geographers　had　measured　the　size　of　the　earth；　and　had　not　hesitated　to　assert　that　by　sailing　westward　one　might　reach　India。　But　there　is　a　wide　gap　between　theory　and　practice；　and　it　required　the　voyages　of　Columbus　and　his　successors　to　bridge　that　gap。　After　the　companions　of　Magellan　completed　the　circumnavigation　of　the　globe；　the　general　shape　of　our　earth　would；　obviously；　never　again　be　called　in　question。　But　demonstration　of　the　sphericity　of　the　earth　had；　of　course；　no　direct　bearing　upon　the　question　of　the　earth's　position　in　the　universe。　Therefore　the　voyage　of　Magellan　served　to　fortify；　rather　than　to　dispute；　the　Ptolemaic　theory。　According　to　that　theory；　as　we　have　seen；　the　earth　was　supposed　to　lie　immovable　at　the　centre　of　the　universe；　the　various　heavenly　bodies；　including　the　sun；　revolving　about　it　in　eccentric　circles。　We　have　seen　that　several　of　the　ancient　Greeks；　notably　Aristarchus；　disputed　this　conception；　declaring　for　the　central　position　of　the　sun　in　the　universe；　and　the　motion　of　the　earth　and　other　planets　about　that　body。　But　this　revolutionary　theory　seemed　so　opposed　to　the　ordinary　observation　that；　having　been　discountenanced　by　Hipparchus　and　Ptolemy；　it　did　not　find　a　single　important　champion　for　more　than　a　thousand　years　after　the　time　of　the　last　great　Alexandrian　astronomer。　The　first　man；　seemingly；　to　hark　back　to　the　Aristarchian　conception　in　the　new　scientific　era　that　was　now　dawning　was　the　noted　cardinal；　Nikolaus　of　Cusa；　who　lived　in　the　first　half　of　the　fifteenth　century；　and　was　distinguished　as　a　philosophical　writer　and　mathematician。　His　De　Docta　Ignorantia　expressly　propounds　the　doctrine　of　the　earth's　motion。　No　one；　however；　paid　the　slightest　attention　to　his　suggestion；　which；　therefore；　merely　serves　to　furnish　us　with　another　interesting　illustration　of　the　futility　of　propounding　even　a　correct　hypothesis　before　the　time　is　ripe　to　receive　itparticularly　if　the　hypothesis　is　not　fully　fortified　by　reasoning　based　on　experiment　or　observation。　The　man　who　was　destined　to　put　forward　the　theory　of　the　earth's　motion　in　a　way　to　command　attention　was　born　in　1473；　at　the　village　of　Thorn；　in　eastern　Prussia。　His　name　was　Nicholas　Copernicus。　There　is　no　more　famous　name　in　the　entire　annals　of　science　than　this；　yet　posterity　has　never　been　able　fully　to　establish　the　lineage　of　the　famous　expositor　of　the　true　doctrine　of　the　solar　system。　The　city　of　Thorn　lies　in　a　province　of　that　border　territory　which　was　then　under　control　of　Poland；　but　which　subsequently　became　a　part　of　Prussia。　It　is　claimed　that　the　aspects　of　the　city　were　essentially　German；　and　it　is　admitted　that　the　mother　of　Copernicus　belonged　to　that　race。　The　nationality　of　the　father　is　more　in　doubt；　but　it　is　urged　that　Copernicus　used　German　as　his　mother…tongue。　His　great　work　was；　of　course；　written　in　Latin；　according　to　the　custom　of　the　time；　but　it　is　said　that；　when　not　employing　that　language；　he　always　wrote　in　German。　The　disputed　nationality　of　Copernicus　strongly　suggests　that　he　came　of　a　mixed　racial　lineage；　and　we　are　reminded　again　of　the　influences　of　those　ethnical　minglings　to　which　we　have　previously　more　than　once　referred。　The　acknowledged　centres　of　civilization　towards　the　close　of　the　fifteenth　century　were　Italy　and　Spain。　Therefore；　the　birthplace　of　Copernicus　lay　almost　at　the　confines　of　civilization；　reminding　us　of　that　earlier　period　when　Greece　was　the　centre　of　culture；　but　when　the　great　Greek　thinkers　were　born　in　Asia　Minor　and　in　Italy。　As　a　young　man；　Copernicus　made　his　way　to　Vienna　to　study　medicine；　and　subsequently　he　jou