a history of science-2-第39节

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vity　of　any　number　of　interdependent　bodies　cannot　rise　higher　than　the　point　from　which　it　falls；　he　reached　correct　conclusions　as　to　the　general　principle　of　the　conservation　of　vis　viva；　although　he　did　not　actually　prove　his　conclusions。　This　was　the　first　attempt　to　deal　with　the　dynamics　of　a　system。　In　this　work；　also；　was　the　true　determination　of　the　relation　between　the　length　of　a　pendulum　and　the　time　of　its　oscillation。　In　1681　he　returned　to　Holland；　influenced；　it　is　believed；　by　the　attitude　that　was　being　taken　in　France　against　his　religion。　Here　he　continued　his　investigations；　built　his　immense　telescopes；　and；　among　other　things；　discovered　〃polarization；〃　which　is　recorded　in　Traite　de　la　Lumiere；　published　at　Leyden　in　1690。　Five　years　later　he　died；　bequeathing　his　manuscripts　to　the　University　of　Leyden。　It　is　interesting　to　note　that　he　never　accepted　Newton's　theory　of　gravitation　as　a　universal　property　of　matter。

XI。　NEWTON　AND　THE　COMPOSITION　OF　LIGHT　Galileo；　that　giant　in　physical　science　of　the　early　seventeenth　century；　died　in　1642。　On　Christmas　day　of　the　same　year　there　was　born　in　England　another　intellectual　giant　who　was　destined　to　carry　forward　the　work　of　Copernicus；　Kepler；　and　Galileo　to　a　marvellous　consummation　through　the　discovery　of　the　great　unifying　law　in　accordance　with　which　the　planetary　motions　are　performed。　We　refer；　of　course；　to　the　greatest　of　English　physical　scientists；　Isaac　Newton；　the　Shakespeare　of　the　scientific　world。　Born　thus　before　the　middle　of　the　seventeenth　century；　Newton　lived　beyond　the　first　quarter　of　the　eighteenth　（1727）。　For　the　last　forty　years　of　that　period　his　was　the　dominating　scientific　personality　of　the　world。　With　full　propriety　that　time　has　been　spoken　of　as　the　〃Age　of　Newton。〃　Yet　the　man　who　was　to　achieve　such　distinction　gave　no　early　premonition　of　future　greatness。　He　was　a　sickly　child　from　birth；　and　a　boy　of　little　seeming　promise。　He　was　an　indifferent　student；　yet；　on　the　other　hand；　he　cared　little　for　the　common　amusements　of　boyhood。　He　early　exhibited；　however；　a　taste　for　mechanical　contrivances；　and　spent　much　time　in　devising　windmills；　water…clocks；　sun…dials；　and　kites。　While　other　boys　were　interested　only　in　having　kites　that　would　fly；　Newtonat　least　so　the　stories　of　a　later　time　would　have　us　understandcared　more　for　the　investigation　of　the　seeming　principles　involved；　or　for　testing　the　best　methods　of　attaching　the　strings；　or　the　best　materials　to　be　used　in　construction。　Meanwhile　the　future　philosopher　was　acquiring　a　taste　for　reading　and　study；　delving　into　old　volumes　whenever　he　found　an　opportunity。　These　habits　convinced　his　relatives　that　it　was　useless　to　attempt　to　make　a　farmer　of　the　youth；　as　had　been　their　intention。　He　was　therefore　sent　back　to　school；　and　in　the　summer　of　1661　he　matriculated　at　Trinity　College；　Cambridge。　Even　at　college　Newton　seems　to　have　shown　no　unusual　mental　capacity；　and　in　1664；　when　examined　for　a　scholarship　by　Dr。　Barrow；　that　gentleman　is　said　to　have　formed　a　poor　opinion　of　the　applicant。　It　is　said　that　the　knowledge　of　the　estimate　placed　upon　his　abilities　by　his　instructor　piqued　Newton；　and　led　him　to　take　up　in　earnest　the　mathematical　studies　in　which　he　afterwards　attained　such　distinction。　The　study　of　Euclid　and　Descartes's　〃Geometry〃　roused　in　him　a　latent　interest　in　mathematics；　and　from　that　time　forward　his　investigations　were　carried　on　with　enthusiasm。　In　1667　he　was　elected　Fellow　of　Trinity　College；　taking　the　degree　of　M。A。　the　following　spring。　It　will　thus　appear　that　Newton's　boyhood　and　early　manhood　were　passed　during　that　troublous　time　in　British　political　annals　which　saw　the　overthrow　of　Charles　I。；　the　autocracy　of　Cromwell；　and　the　eventual　restoration　of　the　Stuarts。　His　maturer　years　witnessed　the　overthrow　of　the　last　Stuart　and　the　reign　of　the　Dutchman；　William　of　Orange。　In　his　old　age　he　saw　the　first　of　the　Hanoverians　mount　the　throne　of　England。　Within　a　decade　of　his　death　such　scientific　path…finders　as　Cavendish；　Black；　and　Priestley　were　bornmen　who　lived　on　to　the　close　of　the　eighteenth　century。　In　a　full　sense；　then；　the　age　of　Newton　bridges　the　gap　from　that　early　time　of　scientific　awakening　under　Kepler　and　Galileo　to　the　time　which　we　of　the　twentieth　century　think　of　as　essentially　modern。

THE　COMPOSITION　OF　WHITE　LIGHT　In　December；　1672；　Newton　was　elected　a　Fellow　of　the　Royal　Society；　and　at　this　meeting　a　paper　describing　his　invention　of　the　refracting　telescope　was　read。　A　few　days　later　he　wrote　to　the　secretary；　making　some　inquiries　as　to　the　weekly　meetings　of　the　society；　and　intimating　that　he　had　an　account　of　an　interesting　discovery　that　he　wished　to　lay　before　the　society。　When　this　communication　was　made　public；　it　proved　to　be　an　explanation　of　the　discovery　of　the　composition　of　white　light。　We　have　seen　that　the　question　as　to　the　nature　of　color　had　commanded　the　attention　of　such　investigators　as　Huygens；　but　that　no　very　satisfactory　solution　of　the　question　had　been　attained。　Newton　proved　by　demonstrative　experiments　that　white　light　is　composed　of　the　blending　of　the　rays　of　diverse　colors；　and　that　the　color　that　we　ascribe　to　any　object　is　merely　due　to　the　fact　that　the　object　in　question　reflects　rays　of　that　color；　absorbing　the　rest。　That　white　light　is　really　made　up　of　many　colors　blended　would　seem　incredible　had　not　the　experiments　by　which　this　composition　is　demonstrated　become　familiar　to　every　one。　The　experiments　were　absolutely　novel　when　Newton　brought　them　forward；　and　his　demonstration　of　the　composition　of　light　was　one　of　the　most　striking　expositions　ever　brought　to　the　attention　of　the　Royal　Society。　It　is　hardly　necessary　to　add　that；　notwithstanding　the　conclusive　character　of　Newton's　work；　his　explanations　did　not　for　a　long　time　meet　with　general　acceptance。　Newton　was　led　to　his　discovery　by　some　experiments　made　with　an　ordinary　glass　prism　applied　to　a　hole　in　the　shutter　of　a　darkened　room；　the　refracted　rays　of　the　sunlight　being　received　upon　the　opposite　wall　and　forming　there　the　familiar　spectrum。　〃It　was　a　very　pleasing　diversion；〃　he　wrote；　〃to　view　the　vivid　and　intense　colors　produced　thereby；　and　after　a　time；　applying　myself　to　consider　them　very　circumspectly；　I　became　surprised　to　see　them　in　varying　form；　which；　according　to　the　received　laws　of　refraction；　I　expected　should　have　been　circular。　They　were　terminated　at　the　sides　with　straight　lines；　but　at　the　ends　the　decay　of　light　was　so　gradual　that　it　was　difficult　to　determine　justly　what　was　their　figure；　yet　they　seemed　semicircular。　〃Comparing　the　length　of　this　colored　spectrum　with　its　breadth；　I　found　it　almost　five　times　greater；　a　disproportion　so　extravagant　that　it　excited　me　to　a　more　than　ordinary　curiosity　of　examining　from　whence　it　might　proceed。　I　could　scarce　think　that　the　various　thicknesses　of　the　glass；　or　the　termination　with　shadow　or　darkness；　could　have　any　influence　on　light　to　produce　such　an　effect；　yet　I　thought　it　not　amiss；　first；　to　examine　those　circumstances；　and　so　tried　what　would　happen　by　transmitting　light　through　parts　of　the　glass　of　divers　thickness；　or　through　holes　in　the　window　of　divers　bigness；　or　by　setting　the　prism　without　so　that　the　light　might　pass　through　it　and　be　refracted　before　it　was　transmitted　through　the　hole；　but　I　found　none　of　those　circumstances　material。　The　fashion　of　the　colors　was　in　all　these　cases　the　same。　〃Then　I　suspected　whether　by　any　unevenness　of　the　glass　or　other　contingent　irregularity　these　colors　might　be　thus　dilated。　And　to　try　this　I　took　another　prism　like　the　former；　and　so　placed　it　that　the　light；　passing　through　them　both；　might　be　refracted　contrary　ways；　and　so　by　the　latter　returned　into　that　course　from　which　the　former　diverted　it。　For；　by　this　means；　I　thought；　the　regular　effects　of　the　first　prism　would　be　destroyed　by　the　second　prism；　but　the　irregular　ones　more　augmented　by　the　multiplicity　of　refractions。　The　event　was　that　the　light；　which　by　the　first　prism　was　diffused　into　an　oblong　form；　was　by　the　second　reduced　into　an　orbicular　one　with　as　much　regularity　as　when　it　did　not　all　pass　through　them。　So　that；　whatever　was　the　cause　of　that　length；　'twas　not　any　contingent　irregularity。　〃I　then　proceeded　to　examine　more　critically　what　might　be　effected　by　the　difference　of　the　incidence　of　rays　coming　from　divers　parts　of　the　sun；　and　to　that　end　measured　the　several　lines　and　angles　belonging　to　the　image。　Its　distance　from　the　hole　or　prism　was　22　feet；　its　utmost　length　13　1/4　inches；　its　breadth　2　5/8；　the　diameter　of　the　hole　1/4　of　an　inch；　the　angle　which　the　rays；　tending　towards　the　middle　of　the　image；　made　with　those　lines；　in　which　they　would　have　proceeded　without　refraction；　was　44　degrees　56'；　and　the　vertical　angle　of　the　prism；　63　degrees　12'。　Also　the　refractions　on　both　sides　of　the　prismthat　is；　of　the　incident　and　emergent　rayswere；　as　near　as　I　could　make　them；　equal；　and　consequently　about　54　degrees　4'；　and　the　rays　fell　perpendicularly　upon　the　wall。　Now；　subducting　the　diameter　of　the　hole　from　the　length　and　breadth　of　the　image；　there　remains　13