a history of science-2-第7章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！


inality；　to　prove　that　his　seeming　inventions　and　discoveries　were　in　reality　adaptations　of　the　Arab　scientists。　It　is　difficult　to　determine　just　how　fully　such　criticisms　are　justified。　It　is　certain；　however；　that　in　this　part　he　describes　the　anatomy　of　the　eye　with　great　accuracy；　and　discusses　mirrors　and　lenses。　The　magnifying　power　of　the　segment　of　a　glass　sphere　had　been　noted　by　Alhazen；　who　had　observed　also　that　the　magnification　was　increased　by　increasing　the　size　of　the　segment　used。　Bacon　took　up　the　discussion　of　the　comparative　advantages　of　segments；　and　in　this　discussion　seems　to　show　that　he　understood　how　to　trace　the　progress　of　the　rays　of　light　through　a　spherical　transparent　body；　and　how　to　determine　the　place　of　the　image。　He　also　described　a　method　of　constructing　a　telescope；　but　it　is　by　no　means　clear　that　he　had　ever　actually　constructed　such　an　instrument。　It　is　also　a　mooted　question　as　to　whether　his　instructions　as　to　the　construction　of　such　an　instrument　would　have　enabled　any　one　to　construct　one。　The　vagaries　of　the　names　of　terms　as　he　uses　them　allow　such　latitude　in　interpretation　that　modern　scientists　are　not　agreed　as　to　the　practicability　of　Bacon's　suggestions。　For　example；　he　constantly　refers　to　force　under　such　names　as　virtus；　species；　imago；　agentis；　and　a　score　of　other　names；　and　this　naturally　gives　rise　to　the　great　differences　in　the　interpretations　of　his　writings；　with　corresponding　differences　in　estimates　of　them。　The　claim　that　Bacon　originated　the　use　of　lenses；　in　the　form　of　spectacles；　cannot　be　proven。　Smith　has　determined　that　as　early　as　the　opening　years　of　the　fourteenth　century　such　lenses　were　in　use；　but　this　proves　nothing　as　regards　Bacon's　connection　with　their　invention。　The　knowledge　of　lenses　seems　to　be　very　ancient；　if　we　may　judge　from　the　convex　lens　of　rock　crystal　found　by　Layard　in　his　excavations　at　Nimrud。　There　is　nothing　to　show；　however；　that　the　ancients　ever　thought　of　using　them　to　correct　defects　of　vision。　Neither；　apparently；　is　it　feasible　to　determine　whether　the　idea　of　such　an　application　originated　with　Bacon。　Another　mechanical　discovery　about　which　there　has　been　a　great　deal　of　discussion　is　Bacon's　supposed　invention　of　gunpowder。　It　appears　that　in　a　certain　passage　of　his　work　he　describes　the　process　of　making　a　substance　that　is；　in　effect；　ordinary　gunpowder；　but　it　is　more　than　doubtful　whether　he　understood　the　properties　of　the　substance　he　describes。　It　is　fairly　well　established；　however；　that　in　Bacon's　time　gunpowder　was　known　to　the　Arabs；　so　that　it　should　not　be　surprising　to　find　references　made　to　it　in　Bacon's　work；　since　there　is　reason　to　believe　that　he　constantly　consulted　Arabian　writings。　The　great　merit　of　Bacon's　work；　however；　depends　on　the　principles　taught　as　regards　experiment　and　the　observation　of　nature；　rather　than　on　any　single　invention。　He　had　the　all…important　idea　of　breaking　with　tradition。　He　championed　unfettered　inquiry　in　every　field　of　thought。　He　had　the　instinct　of　a　scientific　workera　rare　instinct　indeed　in　that　age。　Nor　need　we　doubt　that　to　the　best　of　his　opportunities　he　was　himself　an　original　investigator。

LEONARDO　DA　VINCI　The　relative　infertility　of　Bacon's　thought　is　shown　by　the　fact　that　he　founded　no　school　and　left　no　trace　of　discipleship。　The　entire　century　after　his　death　shows　no　single　European　name　that　need　claim　the　attention　of　the　historian　of　science。　In　the　latter　part　of　the　fifteenth　century；　however；　there　is　evidence　of　a　renaissance　of　science　no　less　than　of　art。　The　German　Muller　became　famous　under　the　latinized　named　of　Regio　Montanus　（1437…1472）；　although　his　actual　scientific　attainments　would　appear　to　have　been　important　only　in　comparison　with　the　utter　ignorance　of　his　contemporaries。　The　most　distinguished　worker　of　the　new　era　was　the　famous　Italian　Leonardo　da　Vincia　man　who　has　been　called　by　Hamerton　the　most　universal　genius　that　ever　lived。　Leonardo's　position　in　the　history　of　art　is　known　to　every　one。　With　that；　of　course；　we　have　no　present　concern；　but　it　is　worth　our　while　to　inquire　at　some　length　as　to　the　famous　painter's　accomplishments　as　a　scientist。　From　a　passage　in　the　works　of　Leonardo；　first　brought　to　light　by　Venturi；＇1＇　it　would　seem　that　the　great　painter　anticipated　Copernicus　in　determining　the　movement　of　the　earth。　He　made　mathematical　calculations　to　prove　this；　and　appears　to　have　reached　the　definite　conclusion　that　the　earth　does　moveor　what　amounts　to　the　same　thing；　that　the　sun　does　not　move。　Muntz　is　authority　for　the　statement　that　in　one　of　his　writings　he　declares；　〃Il　sole　non　si　mouve〃the　sun　does　not　move。＇2＇　Among　his　inventions　is　a　dynamometer　for　determining　the　traction　power　of　machines　and　animals；　and　his　experiments　with　steam　have　led　some　of　his　enthusiastic　partisans　to　claim　for　him　priority　to　Watt　in　the　invention　of　the　steam…engine。　In　these　experiments；　however；　Leonardo　seems　to　have　advanced　little　beyond　Hero　of　Alexandria　and　his　steam　toy。　Hero's　steam…engine　did　nothing　but　rotate　itself　by　virtue　of　escaping　jets　of　steam　forced　from　the　bent　tubes；　while　Leonardo's　〃steam…engine〃　〃drove　a　ball　weighing　one　talent　over　a　distance　of　six　stadia。〃　In　a　manuscript　now　in　the　library　of　the　Institut　de　France；　Da　Vinci　describes　this　engine　minutely。　The　action　of　this　machine　was　due　to　the　sudden　conversion　of　small　quantities　of　water　into　steam　（〃smoke；〃　as　he　called　it）　by　coming　suddenly　in　contact　with　a　heated　surface　in　a　proper　receptacle；　the　rapidly　formed　steam　acting　as　a　propulsive　force　after　the　manner　of　an　explosive。　It　is　really　a　steam…gun；　rather　than　a　steam…engine；　and　it　is　not　unlikely　that　the　study　of　the　action　of　gunpowder　may　have　suggested　it　to　Leonardo。　It　is　believed　that　Leonardo　is　the　true　discoverer　of　the　camera…obscura；　although　the　Neapolitan　philosopher；　Giambattista　Porta；　who　was　not　born　until　some　twenty　years　after　the　death　of　Leonardo；　is　usually　credited　with　first　describing　this　device。　There　is　little　doubt；　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；　r