ButwhiletheContinentwasstrugglingwiththeseillusive"systems，"anddabblinginmystictheoriesthatweretoscarcelyoutlivethemenwhoconceivedthem，thereappearedinEngland——the"landofcommon-sense，"asaGermanscientisthascalledit——"acool，clear，andunprejudicedspirit，"whointhegoldenageofsystemsdeclined"tobelikethemanwhobuildsthechambersoftheupperstoryofhishousebeforehehadlaidsecurelythefoundationwalls。"[1]ThismanwasThomasSydenham1624-1689，who，whilethegreatHarveywasservingthekingassurgeon，wasfightingasacaptainintheparliamentaryarmy。SydenhamtookforhisguidetheteachingsofHippocrates，modifiedtosuittheadvancesthathadbeenmadeinscientificknowledgesincethedaysofthegreatGreek，andestablished，asastandard，observationandexperience。Hecaredlittlefortheoryunlessconfirmedbypractice，buttooktheHippocraticviewthatnaturecureddiseases，assistedbythephysician。Hegaveduecredit，however，totheimportanceofthepartplayedbytheassistant。Ashesawit，medicinecouldbeadvancedinthreeways:1"Byaccuratedescriptionsornaturalhistoriesofdiseases；2byestablishingafixedprincipleormethodoftreatment，foundeduponexperience；3bysearchingforspecificremedies，whichhebelievesmustexistinconsiderablenumbers，thoughheadmitsthattheonlyoneyetdiscoveredisPeruvianbark。"[2]Asithappened，anotherequallyspecificremedy，mercury，whenusedincertaindiseases，wasalreadyknowntohim，butheevidentlydidnotrecognizeitassuch。
　　TheinfluenceonfuturemedicineofSydenham’steachingswasmostpronounced，duemostlytohisteachingofcarefulobservation。Tomostphysicians，however，heisnowrememberedchieflyforhisintroductionoftheuseoflaudanum，stillconsideredoneofthemostvaluableremediesofmodernpharmacopoeias。TheGermangivesthehonorofintroducingthispreparationtoParacelsus，buttheEnglish-speakingworldwillalwaysbelievethatthecreditshouldbegiventoSydenham。
　　IX。PHILOSOPHER-SCIENTISTSANDNEWINSTITUTIONSOFLEARNING
　　WesawthatintheoldGreekdaystherewasnosharplineofdemarcationbetweenthefieldofthephilosopherandthatofthescientist。IntheHellenisticepoch，however，knowledgebecamemorespecialized，andourrecentchaptershaveshownusscientificinvestigatorswhoseeffortswerefarenoughremovedfromtheintangibilitiesofthephilosopher。Itmustnotbeoverlooked，however，thateveninthepresentepochthereweremenwhoseintellectualeffortswereprimarilydirectedtowardsthesubtletiesofphilosophy，yetwhohadalsoapenchantforstrictlyscientificimaginings，ifnotindeedforpracticalscientificexperiments。Atleastthreeofthesemenwereofsufficientimportanceinthehistoryofthedevelopmentofsciencetodemandmorethanpassingnotice。ThesethreearetheEnglishmanFrancisBacon1561-1626，theFrenchmanReneDescartes1596-1650；andtheGermanGottfriedLeibnitz1646-1716。Bacon，astheearliestpath-breaker，showedtheway，theoreticallyatleast，inwhichthesciencesshouldbestudied；
　　Descartes，pursuingthemethodspointedoutbyBacon，carriedthesamelineofabstractreasonintopracticeaswell；whileLeibnitz，comingsomeyearslater，andhavingtheadvantageofthewisdomofhistwogreatpredecessors，wasnaturallyinfluencedbybothinhisviewsofabstractscientificprinciples。
　　Bacon’scareerasastatesmanandhisfaultsandmisfortunesasamandonotconcernushere。OurinterestinhimbeginswithhisentranceintoTrinityCollege，Cambridge，wherehetookupthestudyofallthesciencestaughtthereatthattime。Duringthethreeyearshebecamemoreandmoreconvincedthatsciencewasnotbeingstudiedinaprofitablemanner，untilatlast，attheendofhiscollegecourse，hemadereadytorenouncetheoldAristotelianmethodsofstudyandadvancehistheoryofinductivestudy。ForalthoughhewasagreatadmirerofAristotle’swork，hebecameconvincedthathismethodsofapproachingstudywereentirelywrong。
　　"TheopinionofAristotle，"hesays，inhisDeArgumentumScientiarum，"seemethtomeanegligentopinion，thatofthosethingswhichexistbynaturenothingcanbechangedbycustom；
　　usingforexample，thatifastonebethrowntenthousandtimesupitwillnotlearntoascend；andthatbyoftenseeingorhearingwedonotlearntoseeorhearbetter。Forthoughthisprinciplebetrueinthingswhereinnatureisperemptorythereasonwhereofwecannotnowstandtodiscuss，yetitisotherwiseinthingswhereinnatureadmittethalatitude。Forhemightseethatastraightglovewillcomemoreeasilyonwithuse；andthatawandwillbyusebendotherwisethanitgrew；andthatbyuseofthevoicewespeaklouderandstronger；andthatbyuseofenduringheatorcoldweendureitthebetter，andthelike；whichlattersorthaveanearerresemblanceuntothatsubjectofmannershehandleththanthoseinstanceswhichheallegeth。"[1]
　　Thesewerehisopinions，formedwhileayoungmanincollege，repeatedatintervalsthroughhismatureryears，andreiteratedandemphasizedinhisoldage。Massesoffactsweretobeobtainedbyobservingnatureatfirsthand，andfromsuchaccumulationsoffactsdeductionsweretobemade。Inshort，reasoningwastobefromthespecifictothegeneral，andnotviceversa。
　　ItwasbyhisteachingsalonethatBaconthuscontributedtothefoundationofmodernscience；and，whilehewasconstantlythinkingandwritingonscientificsubjects，hecontributedlittleinthewayofactualdiscoveries。"Ionlysoundtheclarion，"hesaid，"butIenternotthebattle。"
　　ThecaseofDescartes，however，isdifferent。Hebothsoundedtheclarionandenteredintothefight。HehimselffreelyacknowledgeshisdebttoBaconforhisteachingsofinductivemethodsofstudy，butmoderncriticismplaceshisworkonthesameplaneasthatofthegreatEnglishman。"Ifyoulayholdofanycharacteristicproductofmodernwaysofthinking，"saysHuxley，"eitherintheregionofphilosophyorinthatofscience，youfindthespiritofthatthought，ifnotitsform，hasbeenpresentinthemindofthegreatFrenchman。"[2]
　　Descartes，thesonofanoblefamilyofFrance，waseducatedbyJesuitteachers。LikeBacon，heveryearlyconceivedtheideathatthemethodsofteachingandstudyingsciencewerewrong，butbeponderedthematterwellintomiddlelifebeforeputtingintowritinghisideasofphilosophyandscience。Then，inhisDiscourseTouchingtheMethodofUsingOne’sReasonRightlyandofSeekingScientificTruth，hepointedoutthewayofseekingaftertruth。HiscentralideainthiswastoemphasizetheimportanceofDOUBT，andavoidanceofacceptingastruthanythingthatdoesnotadmitofabsoluteandunqualifiedproof。InreachingtheseconclusionshehadbeforehimthestrikingexamplesofscientificdeductionsbyGalileo，andmorerecentlythediscoveryofthecirculationofthebloodbyHarvey。Thislastcameasarevelationtoscientists，reducingthisseeminglyoccultprocess，asitdid，tothefieldofmechanicalphenomena。
　　Thesamemechanicallawsthatgovernedtheheavenlybodies，asshownbyGalileo，governedtheactionofthehumanheart，and，foraughtanyoneknew，everypartofthebody，andeventheminditself。
　　Havingonceconceivedthisidea，Descartesbeganaseriesofdissectionsandexperimentsupontheloweranimals，tofind，ifpossible，furtherproofofthisgenerallaw。Tohimthehumanbodywassimplyamachine，acomplicatedmechanism，whosefunctionswerecontrolledjustasanyotherpieceofmachinery。
　　Hecomparedthehumanbodytocomplicatedmachineryrunbywater-fallsandcomplicatedpipes。"ThenervesofthemachinewhichIamdescribing，"hesays，"mayverywellbecomparedtothepipesofthesewaterworks；itsmusclesanditstendonstotheothervariousenginesandspringswhichseemtomovethem；itsanimalspiritstothewaterwhichimpelsthem，ofwhichtheheartisthefountain；whilethecavitiesofthebrainarethecentraloffice。Moreover，respirationandothersuchactionsasarenaturalandusualinthebody，andwhichdependonthecourseofthespirits，arelikethemovementsofaclock，oramill，whichmaybekeptupbytheordinaryflowofwater。"[3]
　　InsuchpassagesastheseDescartesanticipatestheideasofphysiologyofthepresenttime。Hebelievedthatthefunctionsareperformedbythevariousorgansofthebodiesofanimalsandmenasamechanism，towhichinmanwasaddedthesoul。Thissoulhelocatedinthepinealgland，adegenerateandpresumablyfunctionlesslittleorganinthebrain。ForyearsDescartes’sideaofthefunctionofthisglandwasheldbymanyphysiologists，anditwasonlytheintroductionofmodernhigh-powermicroscopythatreducedthisalsotoameremechanism，andshowedthatitisapparentlytheremainsofaCyclopeaneyeoncecommontoman’sremoteancestors。
　　Descarteswastheoriginatorofatheoryofthemovementsoftheuniversebyamechanicalprocess——theCartesiantheoryofvortices——whichforseveraldecadesafteritspromulgationreignedsupremeinscience。Itistheingenuityofthistheory，notthetruthofitsassertions，thatstillexcitesadmiration，forithaslongsincebeensupplanted。Itwascertainlythebesthithertoadvanced——thebest"thattheobservationsoftheageadmitted，"accordingtoD’Alembert。
　　Accordingtothistheorytheinfiniteuniverseisfullofmatter，therebeingnosuchthingasavacuum。Matter，asDescartesbelieved，isuniformincharacterthroughouttheentireuniverse，andsincemotioncannottakeplaceinanypartofaspacecompletelyfilled，withoutsimultaneousmovementinallotherparts，thereareconstantmoreorlesscircularmovements，vortices，orwhirlpoolsofparticles，varying，ofcourse，insizeandvelocity。Asaresultofthiscircularmovementtheparticlesofmattertendtobecomeglobularfromcontactwithoneanother。
　　Twospeciesofmatterarethusformed，onelargerandglobular，whichcontinuetheircircularmotionwithaconstanttendencytoflyfromthecentreoftheaxisofrotation，theothercomposedoftheclippingsresultingfromthegrindingprocess。Thesesmaller"filings"fromthemainbodies，becomingsmallerandsmaller，graduallylosetheirvelocityandaccumulateinthecentreofthevortex。Thiscollectionofthesmallermatterinthecentreofthevortexconstitutesthesunorstar，whilethesphericalparticlespropelledinstraightlinesfromthecentretowardsthecircumferenceofthevortexproducethephenomenonoflightradiatingfromthecentralstar。Thusthismatterbecomestheatmosphererevolvingaroundtheaccumulationatthecentre。
　　Butthesmallparticlesbeingconstantlywornawayfromtherevolvingsphericalparticlesinthevortex，becomeentangledintheirpassage，andwhentheyreachtheedgeoftheinnerstrataofsolardusttheysettleuponitandformwhatwecallsun-spots。Theseareconstantlydissolvedandreformed，untilsometimestheyformacrustroundthecentralnucleus。
　　Astheexpansiveforceofthestardiminishesinthecourseoftime，itisencroacheduponbyneighboringvortices。Ifthepartoftheencroachingstarbeofalessvelocitythanthestarwhichithassweptup，itwillpresentlyloseitshold，andthesmallerstarpassoutofrange，becomingacomet。Butifthevelocityofthevortexintowhichtheincrustedstarsettlesbeequivalenttothatofthesurroundedvortex，itwillholditasacaptive，stillrevolvingand"wraptinitsownfirmament。"Thustheseveralplanetsofoursolarsystemhavebeencapturedandheldbythesun-vortex，ashavethemoonandothersatellites。
　　Butalthoughthesenewtheoriesatfirstcreatedgreatenthusiasmamongallclassesofphilosophersandscientists，theysooncameunderthebanoftheChurch。WhilenoactualharmcametoDescarteshimself，hiswritingswerecondemnedbytheCatholicandProtestantchurchesalike。Thespiritofphilosophicalinquiryhehadengendered，however，livedon，andislargelyresponsibleformodernphilosophy。
　　InmanywaysthelifeandworksofLeibnitzremindusofBaconratherthanDescartes。Hislifewasspentinfillinghighpoliticalpositions，andhisphilosophicalandscientificwritingswereby-pathsofhisfertilemind。Hewasatheoreticalratherthanapracticalscientist，hiscontributionstosciencebeinginthenatureofphilosophicalreasoningsratherthanpracticaldemonstrations。Hadhebeenabletowithdrawfrompubliclifeanddevotehimselftosciencealone，asDescartesdid，hewouldundoubtedlyhaveprovedhimselfequallygreatasapracticalworker。Butduringthetimeofhisgreatestactivityinphilosophicalfields，betweentheyears1690and1716，hewasallthetimeperformingextraordinaryactivedutiesinentirelyforeignfields。Hisworkmayberegarded，perhaps，asdoingforGermanyinparticularwhatBacon’sdidforEnglandandtherestoftheworldingeneral。
　　Onlyacomparativelysmallpartofhisphilosophicalwritingsconcernushere。Accordingtohistheoryoftheultimateelementsoftheuniverse，theentireuniverseiscomposedofindividualcentres，ormonads。Tothesemonadsheascribednumberlessqualitiesbywhicheveryphaseofnaturemaybeaccounted。Theyweresupposedbyhimtobepercipient，self-actingbeings，notunderarbitrarycontrolofthedeity，andyetGodhimselfwastheoriginalmonadfromwhichalltherestaregenerated。Withthisconceptionasabasis，Leibnitzdeducedhisdoctrineofpre-establishedharmony，wherebythenumerousindependentsubstancescomposingtheworldaremadetoformoneuniverse。Hebelievedthatbyvirtueofaninwardenergymonadsdevelopthemselvesspontaneously，eachbeingindependentofeveryother。
　　Inshort，eachmonadisakindofdeityinitself——amicrocosmrepresentingallthegreatfeaturesofthemacrocosm。
　　Itwouldbeimpossibleclearlytoestimatetheprecisevalueofthestimulativeinfluenceofthesephilosophersuponthescientificthoughtoftheirtime。Therewasoneway，however，inwhichtheirinfluencewasmadeverytangible——namely，intheincentivetheygavetothefoundationofscientificsocieties。
　　SCIENTIFICSOCIETIES
　　Atthepresenttime，whentheelementsoftimeanddistancearepracticallyeliminatedinthepropagationofnews，andwhencheapprintinghasminimizedthedifficultiesofpublishingscientificdiscoveries，itisdifficulttounderstandtheisolatedpositionofthescientificinvestigationoftheagesthatprecededsteamandelectricity。Shutofffromtheworldandcompletelyoutoftouchwithfellow-laborersperhapsonlyafewmilesaway，theinvestigatorswerenaturallyseriouslyhandicapped；andinventionsanddiscoverieswerenotmadewiththesamerapiditythattheywouldundoubtedlyhavebeenhadthesamemenbeenreceivingdaily，weekly，ormonthlycommunicationsfromfellow-laborersallovertheworld，astheydoto-day。Neitherdidtheyhavetheadvantageofpublicorsemi-publiclaboratories，wheretheywerebroughtintocontactwithothermen，fromwhomtogatherfreshtrainsofthoughtandreceivethestimulusoftheirsuccessesorfailures。Inthenaturalcourseofevents，however，neighborswhowereinterestedinsomewhatsimilarpursuits，notofthecharacteroftherivalryoftradeorcommerce，wouldmeetmoreorlessfrequentlyanddiscusstheirprogress。Themutualadvantagesofsuchintercoursewouldbeatonceappreciated；anditwouldbebutashortstepfromthecasualmeetingoftwoneighborlyscientiststotheestablishmentof"societies，"meetingatfixedtimes，andcomposedofmemberslivingwithinreasonabletravellingdistance。Therewould，perhaps，betheweeklyormonthlymeetingsofmeninalimitedarea；andasthenaturaloutgrowthoftheselittlelocalsocieties，withfrequentmeetings，wouldcometheformationoflargersocieties，meetinglessoften，wherememberstravelledaconsiderabledistancetoattend。And，finally，withincreasedfacilitiesforcommunicationandtravel，thegreatinternationalsocietiesofto-daywouldbeproduced——thenaturaloutcomeoftheneighborlymeetingsoftheprimitivemediaevalinvestigators。
　　InItaly，ataboutthetimeofGalileo，severalsmallsocietieswereformed。OneofthemostimportantofthesewastheLynceanSociety，foundedabouttheyear1611，Galileohimselfbeingamember。ThissocietywassucceededbytheAccademiadelCimento，atFlorence，in1657，whichforatimeflourished，withsuchafamousscientistasTorricelliasoneofitsmembers。
　　InEnglandanimpetusseemstohavebeengivenbySirFrancisBacon’swritingsincriticismandcensureofthesysternofteachingincolleges。ItissupposedthathissuggestionsastowhatshouldbetheaimsofascientificsocietyledeventuallytotheestablishmentoftheRoyalSociety。Hepointedouthowlittlehadreallybeenaccomplishedbytheexistinginstitutionsoflearninginadvancingscience，andassertedthatlittlegoodcouldevercomefromthemwhiletheirmethodsofteachingremainedunchanged。Hecontendedthatthesystemwhichmadethelecturesandexercisesofsuchanaturethatnodeviationfromtheestablishedroutinecouldbethoughtofwaspernicious。Butheshowedthatifanyteacherhadthetemeritytoturnfromthetraditionalpaths，thedaringpioneerwaslikelytofindinsurmountableobstaclesplacedinthewayofhisadvancement。
　　Thestudieswere"imprisoned"withinthelimitsofacertainsetofauthors，andoriginalityinthoughtorteachingwastobeneithercontemplatednortolerated。
　　ThewordsofBacon，giveninstrongandunsparingtermsofcensureandcondemnation，butneverthelesswithperfectjustification，soonborefruit。Asearlyastheyear1645asmallcompanyofscientistshadbeeninthehabitofmeetingatsomeplaceinLondontodiscussphilosophicalandscientificsubjectsformentaladvancement。In1648，owingtothepoliticaldisturbancesofthetime，someofthemembersofthesemeetingsremovedtoOxford，amongthemBoyle，Wallis，andWren，wherethemeetingswerecontinued，aswerealsothemeetingsofthoseleftinLondon。In1662，however，whenthepoliticalsituationbadbecomemoresettled，thesetwobodiesofmenwereunitedunderacharterfromCharlesII。，andBacon’sideaswerepracticallyexpressedinthatlearnedbody，theRoyalSocietyofLondon。AnditmatterslittlethatinsomerespectsBacon’sviewswerenotfollowedinthepracticalworkingsofthesociety，orthatthedivisionoflaborintheearlystageswassomewhatdifferentthanatpresent。Theaimofthesocietyhasalwaysbeenonefortheadvancementoflearning；andifBaconhimselfcouldlookoveritsrecords，hewouldsurelyhavelittlefaulttofindwiththeaidithasgivenincarryingouthisideasforthepromulgationofusefulknowledge。
　　TenyearsafterthecharterwasgrantedtotheRoyalSocietyofLondon，LordBacon’swordstookpracticaleffectinGermany，withtheresultthattheAcademiaNaturaeCuriosorumwasfounded，undertheleadershipofProfessorJ。C。Sturm。Theearlylaborsofthissocietyweredevotedtoarepetitionofthemostnotableexperimentsofthetime，andtheworkoftheembryosocietywaspublishedintwovolumes，in1672and1685respectively，whichwerepracticallytext-booksofthephysicsoftheperiod。Itwasnotuntil1700thatFrederickI。foundedtheRoyalAcademyofSciencesatBerlin，aftertheelaborateplanofLeibnitz，whowashimselfthefirstpresident。
　　PerhapsthenearestrealizationofBacon’sideal，however，isintheRoyalAcademyofSciencesatParis，whichwasfoundedin1666
　　undertheadministrationofColbert，duringthereignofLouisXIV。Thisinstitutionnotonlyrecognizedindependentmembers，buthadbesidestwentypensionnaireswhoreceivedsalariesfromthegovernment。Inthiswayaselectbodyofscientistswereenabledtopursuetheirinvestigationswithoutbeingobligedto"givethoughttothemorrow"fortheirsustenance。Inreturntheyweretofurnishthemeetingswithscientificmemoirs，andonceayeargiveanaccountoftheworktheywereengagedupon。Thusacertainnumberofthebrightestmindswereencouragedtodevotetheirentiretimetoscientificresearch，"deliveredalikefromthetemptationsofwealthortheembarrassmentsofpoverty。"ThatsuchaplanworkswellisamplyattestedbytheresultsemanatingfromtheFrenchacademy。Pensionnairesinvariousbranchesofscience，however，eitherpaidbythestateorbylearnedsocieties，arenolongerconfinedtoFrance。
　　AmongtheotherearlyscientificsocietieswastheImperialAcademyofSciencesatSt。Petersburg，projectedbyPetertheGreat，andestablishedbyhiswidow，CatharineI。，in1725；andalsotheRoyalSwedishAcademy，incorporatedin1781，andcountingamongitsearlymemberssuchmenasthecelebratedLinnaeus。Butafterthefirstimpulsehadresultedinafewlearnedsocieties，theirmanifestadvantagewassoevidentthatadditionalnumbersincreasedrapidly，untilatpresentalmosteverybranchofeveryscienceisrepresentedbymoreorlessimportantbodies；andtheseare，individuallyandcollectively，addingtoknowledgeandstimulatinginterestinthemanyfieldsofscience，thusvindicatingLordBacon’sasseverationsthatknowledgecouldbesatisfactorilypromulgatedinthismanner。
　　X。THESUCCESSORSOFGALILEOINPHYSICALSCIENCE
　　Wehavenowtowitnessthediversifiedeffortsofacompanyofmenwho，workingforthemostpartindependently，greatlyaddedtothedataofthephysicalsciences——suchmenasBoyle，Huygens，VonGericke，andHooke。Itwillbefoundthatthestudiesofthesemencoveredthewholefieldofphysicalsciencesasthenunderstood——thefieldofso-callednaturalphilosophy。WeshallbesttreatthesesuccessorsofGalileoandprecursorsofNewtonsomewhatbiographically，pointingoutthecorrespondencesanddifferencesbetweentheirvariousaccomplishmentsasweproceed。
　　Itwillbenotedinduecoursethattheworkofsomeofthemwasanticipatoryofgreatachievementsofalatercentury。
　　ROBERTBOYLE1627-1691
　　SomeofRobertBoyle’sviewsastothepossiblestructureofatmosphericairwillbeconsideredalittlefartheroninthischapter，butforthemomentwewilltakeuptheconsiderationofsomeofhisexperimentsuponthataswellasothergases。Boylewasalwaysmuchinterestedinalchemy，andcarriedonextensiveexperimentsinattemptingtoaccomplishthetransmutationofmetals；buthedidnotconfinehimselftotheseexperiments，devotinghimselftoresearchesinallthefieldsofnaturalphilosophy。HewasassociatedatOxfordwithacompanyofscientists，includingWallisandWren，whoheldmeetingsandmadeexperimentstogether，thesegatheringsbeingthebeginning，asmentionedamomentago，ofwhatfinallybecametheRoyalSociety。
　　ItwasduringthisresidenceatOxfordthatmanyofhisvaluableresearchesuponairweremade，andduringthistimebeinventedhisair-pump，nowexhibitedintheRoyalSocietyroomsatBurlingtonHouse。[1]
　　Hisexperimentstoprovetheatmosphericpressurearemostinterestingandconclusive。"Havingthreesmall，roundglassbubbles，blownattheflameofalamp，aboutthesizeofhazel-nuts，"hesays，"eachofthemwithashort，slenderstem，bymeanswhereoftheyweresoexactlypoisedinwaterthataverysmallchangeofweightwouldmakethemeitheremergeorsink；atatimewhentheatmospherewasofconvenientweight，Iputthemintoawide-mouthedglassofcommonwater，andleavingtheminaquietplace，wheretheywerefrequentlyinmyeye，Iobservedthatsometimestheywouldbeatthetopofthewater，andremainthereforseveraldays，orperhapsweeks，together，andsometimesfalltothebottom，andafterhavingcontinuedthereforsometimeriseagain。Andsometimestheywouldriseorfallastheairwashotorcold。"[2]
　　ItwasinthecourseoftheseexperimentsthattheobservationsmadebyBoyleledtotheinventionofhis"staticalbarometer，"
　　themercurialbarometerhavingbeeninvented，aswehaveseen，byTorricelli，in1643。Indescribingthisinventionhesays:
　　"Makingchoiceofalarge，thin，andlightglassbubble，blownattheflameofalamp，Icounterpoiseditwithametallicweight，inapairofscalesthatweresuspendedinaframe，thatwouldturnwiththethirtiethpartofagrain。Boththeframeandthebalancewerethenplacednearagoodbarometer，whenceImightlearnthepresentweightoftheatmosphere；when，thoughthescaleswereunabletoshowallthevariationsthatappearedinthemercurialbarometer，yettheygavenoticeofthosethatalteredtheheightofthemercuryhalfaquarterofaninch。"[3]
　　Afairlysensitivebarometer，afterall。Thisstaticalbarometersuggestedseveralusefulapplicationstothefertileimaginationofitsinventor，amongothersthemeasuringofmountain-peaks，aswiththemercurialbarometer，therareficationoftheairatthetopgivingadefiniteratiotothemorecondensedairinthevalley。
　　Anotherofhisexperimentswasmadetodiscovertheatmosphericpressuretothesquareinch。Afterconsiderabledifficultyhedeterminedthattherelativeweightofacubicinchofwaterandmercurywasaboutonetofourteen，andcomputingfromotherknownweightshedeterminedthat"whenacolumnofquicksilverthirtyincheshighissustainedinthebarometer，asitfrequentlyhappens，acolumnofairthatpressesuponaninchsquarenearthesurfaceoftheearthmustweighaboutfifteenavoirdupoispounds。"[4]Asthepressureofairatthesea-levelisnowestimatedat14。7304poundstothesquareinch，itwillbeseenthatBoyle’scalculationwasnotfarwrong。
　　Fromhisnumerousexperimentsupontheair，Boylewasledtobelievethatthereweremany"latentqualities"duetosubstancescontainedinitthatsciencehadasyetbeenunabletofathom，believingthatthereis"notamoreheterogeneousbodyintheworld。"Hebelievedthatcontagiousdiseaseswerecarriedbytheair，andsuggestedthateruptionsoftheearth，suchasthosemadebyearthquakes，mightsendup"venomousexhalations"thatproduceddiseases。Hesuggestedalsothattheairmightplayanimportantpartinsomeprocessesofcalcination，which，asweshallsee，wasprovedtobetruebyLavoisierlateintheeighteenthcentury。Boyle’snotionsoftheexactchemicalactioninthesephenomenawereofcoursevagueandindefinite，buthehadobservedthatsomepartwasplayedbytheair，andhewasrightinsupposingthattheair"mayhaveagreatshareinvaryingthesaltsobtainablefromcalcinedvitriol。"[5]
　　Althoughhewashimselfsuchapainstakingobserveroffacts，hehadthefaultofhisageofplacingtoomuchfaithinhear-sayevidenceofuntrainedobservers。Thus，fromthenumerousstoriesheheardconcerningthegrowthofmetalsinpreviouslyexhaustedmines，hebelievedthattheairwasresponsibleforproducingthisgrowth——inwhichheundoubtedlybelieved。Thestoryofatin-minerthat，inhisowntime，afteralapseofonlytwenty-fiveyears，aheap，ofearthpreviouslyexhaustedofitsorebecameagainevenmorerichlyimpregnatedthanbeforebylyingexposedtotheair，seemstohavebeenbelievedbythephilosopher。
　　AsBoylewasanalchemist，andundoubtedlybelievedinthealchemictheorythatmetalshave"spirits"andvariousotherqualitiesthatdonotexist，itisnotsurprisingthathewascredulousinthematterofbeliefsconcerningpeculiarphenomenaexhibitedbythem。Furthermore，heundoubtedlyfellintotheerrorcommonto"specialists，"orpersonsworkingforlongperiodsoftimeononesubject——theerrorofover-enthusiasminhissubject。Hehaddiscoveredsomanyremarkablequalitiesintheairthatitisnotsurprisingtofindthatheattributedtoitmanymorethathecouldnotdemonstrate。
　　Boyle’sworkuponcolors，althoughprobablyoflessimportancethanhisexperimentsanddeductionsuponair，showthathewasinthevanasfarasthescienceofhisdaywasconcerned。Ashepointsout，theschoolsofhistimegenerallytaughtthat"colorisapenetratingquality，reachingtotheinnermostpartofthesubstance，"and，asanexampleofthis，sealing-waxwascited，whichcouldbebrokenintominutebits，eachparticleretainingthesamecolorasitsfellowsortheoriginalmass。Torefutethistheory，andtoshowinstancestothecontrary，Boyle，amongotherthings，showsthatvariouscolors——blue，red，yellow——maybeproducedupontemperedsteel，andyetthemetalwithin"ahair’s-breadthofitssurface"havenoneofthesecolors。
　　Therefore，hewasledtobelievethatcolor，inopaquebodiesatleast，issuperficial。
　　"Butbeforewedescendtoamoreparticularconsiderationofoursubject，"hesays，"’tispropertoobservethatcolorsmayberegardedeitherasaqualityresidinginbodiestomodifylightafteraparticularmanner，orelseaslightitselfsomodifiedastostrikeupontheorgansofsight，andcausethesensationwecallcolor；andthatthislatteristhemoreproperacceptationofthewordcolorwillappearhereafter。Andindeeditisthelightitself，whichafteracertainmanner，eithermixedwithshadesorother-wise，strikesoureyesandimmediatelyproducesthatmotionintheorganwhichgivesusthecolorofanobject。"[6]
　　Inexaminingsmoothandroughsurfacestodeterminethecauseoftheircolor，hemadeuseofthemicroscope，andpointedouttheveryobviousexampleofthedifferenceincolorofaroughandapolishedpieceofthesameblockofstone。Heusedsomestrikingillustrationsoftheeffectoflightandthepositionoftheeyeuponcolors。"Thusthecolorofplushorvelvetwillappearvariousifyoustrokepartofitonewayandpartanother，thepostureoftheparticularthreadsinregardtothelight，ortheeye，beingtherebyvaried。And’tisobservablethatinafieldofripecorn，blownuponbythewind，therewillappearwavesofacolordifferentfromthatoftherestofthecorn，becausethewind，bydepressingsomeoftheearsmorethanothers，causesonetoreflectmorelightfromthelateralandstrawypartsthananother。"[7]Hisworkuponcolor，however，asuponlight，wasentirelyovershadowedbytheworkofhisgreatfellow-countrymanNewton。
　　Boyle’sworkonelectricitywasacontinuationofGilbert’s，towhichheaddedseveralnewfacts。HeaddedseveralsubstancestoGilbert’slistof"electrics，"experimentedonsmoothandroughsurfacesinexcitingofelectricity，andmadetheimportantdiscoverythatamberretaineditsattractivevirtueafterthefrictionthatexciteditbadceased。"Fortheattritionhavingcausedanintestinemotioninitsparts，"hesays，"theheattherebyexcitedoughtnottoceaseassoonasevertherubbingisover，buttocontinuecapableofemittingeffluviaforsometimeafterwards，longerorshorteraccordingtothegoodnessoftheelectricandthedegreeofthecommotionmade；allwhich，joinedtogether，maysometimesmaketheeffectconsiderable；andbythismeans，onawarmday，I，withacertainbodynotbiggerthanapea，butveryvigorouslyattractive，movedasteelneedle，freelypoised，aboutthreeminutesafterIhadleftoffrubbingit。"[8]
　　MARIOTTEANDVONGUERICKE
　　WorkingcontemporaneouslywithBoyle，andamanwhosenameisusuallyassociatedwithhisasthepropounderofthelawofdensityofgases，wasEdmeMariottedied1684，anativeofBurgundy。Mariottedemonstratedthatbutfortheresistanceoftheatmosphere，allbodies，whetherlightorheavy，denseorthin，wouldfallwithequalrapidity，andheprovedthisbythewell-known"guinea-and-feather"experiment。Havingexhaustedtheairfromalongglasstubeinwhichaguineapieceandafeatherhadbeenplaced，heshowedthatinthevacuumthusformedtheyfellwithequalrapidityasoftenasthetubewasreversed。FromhisvariousexperimentsastothepressureoftheatmospherehededucedthelawthatthedensityandelasticityoftheatmospherearepreciselyproportionaltothecompressingforcethelawofBoyleandMariotte。Healsoascertainedthatairexistedinastateofmechanicalmixturewithliquids，"existingbetweentheirparticlesinastateofcondensation。"Hemademanyotherexperiments，especiallyonthecollisionofbodies，buthismostimportantworkwasupontheatmosphere。
　　ButmeanwhileanothercontemporaryofBoyleandMariottewasinterestinghimselfinthestudyoftheatmosphere，andhadmadeawonderfulinventionandamoststrikingdemonstration。ThiswasOttovonGuericke1602-1686，BurgomasterofMagdeburg，andcouncillortohis"mostsereneandpotentHighness"theelectorofthatplace。Whennotengrossedwiththedutiesofpublicoffice，hedevotedhistimetothestudyofthesciences，particularlypneumaticsandelectricity，boththenintheirinfancy。ThediscoveriesofGalileo，Pascal，andTorricelliincitedhimtosolvetheproblemofthecreationofavacuum——adesideratumsincebeforethedaysofAristotle。Hisfirstexperimentswerewithawoodenpumpandabarrelofwater，buthesoonfoundthatwithsuchporousmaterialaswoodavacuumcouldnotbecreatedormaintained。Hethereforemadeuseofaglobeofcopper，withpumpandstop-cock；andwiththishewasabletopumpoutairalmostaseasilyaswater。Thus，in1650，theair-pumpwasinvented。Continuinghisexperimentsuponvacuumsandatmosphericpressurewithhisnewlydiscoveredpump，hemadesomestartlingdiscoveriesastotheenormouspressureexertedbytheair。
　　Itwasnothisintention，however，todemonstratehisnewlyacquiredknowledgebywordsortheoriesalone，norbymerelaboratoryexperiments；buthechoseinsteadanopenfield，towhichwereinvitedEmperorFerdinandIII。，andalltheprincesoftheDietatRatisbon。Whentheywereassembledheproducedtwohollowbrasshemispheresabouttwofeetindiameter，andplacingtheirexactlyfittingsurfacestogether，proceededtopumpouttheairfromtheirhollowinterior，thuscausingthemtosticktogetherfirmlyinamostremarkableway，apparentlywithoutanythingholdingthem。Thisofitselfwasstrangeenough；butnowtheworthyburgomasterproducedteamsofhorses，andharnessingthemtoeithersideofthehemispheres，attemptedtopulltheadheringbrassesapart。Five，ten，fifteenteams——thirtyhorses，inall——wereattached；butpullandtugastheywouldtheycouldnotseparatethefirmlyclaspedhemispheres。Theenormouspressureoftheatmospherehadbeenmoststrikinglydemonstrated。
　　Butitisonethingtodemonstrate，anothertoconvince；andmanyofthegoodpeopleofMagdeburgshooktheirheadsoverthis"devil’scontrivance，"andpredictedthatHeavenwouldpunishtheHerrBurgomaster，asindeedithadoncebystrikinghishousewithlightningandinjuringsomeofhisinfernalcontrivances。
　　Theypredictedhisfuturepunishment，buttheydidnotmolesthim，fortohisfellow-citizens，whotalkedandlaughed，drankandsmokedwithhim，andknewhimforthehonestcitizenthathewas，hedidnotseembewitchedatall。Andsohelivedandworkedandaddedotherfactstoscience，andhisbrasshemisphereswerenotdestroyedbyfanaticalInquisitors，butarestillpreservedintheroyallibraryatBerlin。
　　Inhisexperimentswithhisair-pumphediscoveredmanythingsregardingtheactionofgases，amongothers，thatanimalscannotliveinavacuum。Heinventedtheanemoscopeandtheair-balance，andbeingthusenabledtoweighttheairandnotethechangesthatprecededstormsandcalms，hewasablestillfurthertodumfoundhiswonderingfellow-Magde-burgersbymoreorlessaccuratepredictionsabouttheweather。
　　VonGuerickedidnotacceptGilbert’stheorythattheearthwasagreatmagnet，butinhisexperimentsalonglinessimilartothosepursuedbyGilbert，henotonlyinventedthefirstelectricalmachine，butdiscoveredelectricalattractionandrepulsion。Theelectricalmachinewhichheinventedconsistedofasphereofsulphurmountedonanironaxistoimitatetherotationoftheearth，andwhich，whenrubbed，manifestedelectricalreactions。
　　Whenthisglobewasrevolvedandstrokedwiththedryhanditwasfoundthatitattachedtoit"allsortsoflittlefragments，likeleavesofgold，silver，paper，etc。""Thusthisglobe，"hesays，"whenbroughtratherneardropsofwatercausesthemtoswellandpuffup。Itlikewiseattractsair，smoke，etc。"[9]BeforethetimeofGuericke’sdemonstrations，Cabaeushadnotedthatchaffleapedbackfroman"electric，"buthedidnotinterpretthephenomenonaselectricalrepulsion。VonGuericke，however，recognizeditassuch，andreferstoitaswhathecalls"expulsivevirtue。""Evenexpulsivevirtueisseeninthisglobe，"hesays，"foritnotonlyattracts，butalsoREPELSagainfromitselflittlebodiesofthissort，nordoesitreceivethemuntiltheyhavetouchedsomethingelse。"Itwillbeobservedfromthisthathewasveryclosetodiscoveringthedischargeoftheelectrificationofattractedbodiesbycontactwithsomeotherobject，afterwhichtheyarereattractedbytheelectric。
　　Heperformedamostinterestingexperimentwithhissulphurglobeandafeather，andindoingsocamenearanticipatingBenjaminFranklininhisdiscoveryoftheeffectsofpointedconductorsindrawingoffthedischarge。Havingrevolvedandstrokedhisglobeuntilitrepelledabitofdown，heremovedtheglobefromitsrackandadvancingittowardsthenowrepellentdown，droveitbeforehimabouttheroom。Inthischaseheobservedthatthedownpreferredtoalightagainst"thepointsofanyobjectwhatsoever。"Henoticedthatshouldthedownchancetobedrivenwithinafewinchesofalightedcandle，itsattitudetowardstheglobesuddenlychanged，andinsteadofrunningawayfromit，itnow"flewtoitforprotection"——thechargeonthedownhavingbeendissipatedbythehotair。Healsonotedthatifonefaceofafeatherhadbeenfirstattractedandthenrepelledbythesulphurball，thatthesurfacesoaffectedwasalwaysturnedtowardstheglobe；sothatifthepositionsofthetwowerereversed，thesidesofthefeatherreversedalso。
　　Stillanotherimportantdiscovery，thatofelectricalconduction，wasmadebyVonGuericke。Untilhisdiscoverynoonehadobservedthetransferenceofelectricityfromonebodytoanother，althoughGilberthadsometimebeforenotedthatarodrenderedmagneticatoneendbecamesoattheother。VonGuericke’sexperimentsweremadeuponalinenthreadwithhissulphurglobe，which，hesays，"havingbeenpreviouslyexcitedbyrubbing，canexerciselikewiseitsvirtuethroughalinenthreadanellormorelong，andthereattractsomething。"Butthisdiscovery，andhisequallyimportantonethatthesulphurballbecomesluminouswhenrubbed，werepracticallyforgottenuntilagainbroughttonoticebythediscoveriesofFrancisHauksbeeandStephenGrayearlyintheeighteenthcentury。FromthiswemaygatherthatVonGuerickehimselfdidnotrealizetheimportofhisdiscoveries，forotherwisehewouldcertainlyhavecarriedhisinvestigationsstillfurther。Butasitwasheturnedhisattentiontootherfieldsofresearch。
　　ROBERTHOOKE
　　Aslender，crooked，shrivelled-limbed，cantankerouslittleman，withdishevelledhairandhaggardcountenance，bad-temperedandirritable，penuriousanddishonest，atleastinhisclaimsforpriorityindiscoveries——thisisthepictureusuallydrawn，alikebyfriendsandenemies，ofRobertHooke1635-1703，amanwithanalmostunparalleledgeniusforscientificdiscoveriesinalmostallbranchesofscience。Historygivesfewexamplessostrikingofamanwhosereallygreatachievementsinsciencewouldalonehavemadehisnameimmortal，andyetwhohadthepusillanimousspiritofacharlatan——analmostinsanemania，asitseems——forclaimingthecreditofdiscoveriesmadebyothers。
　　Thisattitudeofmindcanhardlybeexplainedexceptasamania:
　　itiscertainlymorecharitablesotoregardit。Forhisowndiscoveriesandinventionsweresonumerousthatafewmoreorlesswouldhardlyhaveaddedtohisfame，ashisreputationasaphilosopherwaswellestablished。Admirationforhisabilityandhisphilosophicalknowledgemustalwaysbemarredbytherecollectionofhisarrogantclaimstothediscoveriesofotherphilosophers。
　　ItseemsprettydefinitelydeterminedthatHookeshouldbecreditedwiththeinventionofthebalance-springforregulatingwatches；butforalongtimeaheatedcontroversywaswagedbetweenHookeandHuygensastowhowastherealinventor。ItappearsthatHookeconceivedtheideaofthebalance-spring，whiletoHuygensbelongsthecreditofhavingadaptedtheCOILED
　　springinaworkingmodel。HethusmadepracticalHooke’sconception，whichiswithoutvalueexceptasappliedbythecoiledspring；but，nevertheless，theinventor，aswellastheperfector，shouldreceivecredit。Inthiscontroversy，unlikemanyothers，theblamecannotbelaidatHooke’sdoor。
　　HookewasthefirstcuratoroftheRoyalSociety，andwhenanythingwastobeinvestigated，usuallyinventedthemechanicaldevicesfordoingso。Astronomicalapparatus，instrumentsformeasuringspecificweights，clocksandchronometers，methodsofmeasuringthevelocityoffallingbodies，freezingandboilingpoints，strengthofgunpowder，magneticinstruments——inshort，allkindsofingeniousmechanicaldevicesinallbranchesofscienceandmechanics。Itwashewhomadethefamousair-pumpofRobertBoyle，basedonBoyle’splans。Incidentally，Hookeclaimedtobetheinventorofthefirstair-pumphimself，althoughthisclaimisnowentirelydiscredited。
　　Withinaperiodoftwoyearshedevisednolessthanthirtydifferentmethodsofflying，allofwhich，ofcourse，cametonothing，butgotoshowthefertileimaginationoftheman，andhistirelessenergy。Heexperimentedwithelectricityandmadesomenovelsuggestionsuponthedifferencebetweentheelectricsparkandtheglow，althoughonthewholehiscontributionsinthisfieldareunimportant。Healsofirstpointedoutthatthemotionsoftheheavenlybodiesmustbelookeduponasamechanicalproblem，andwasalmostwithingraspingdistanceoftheexacttheoryofgravitation，himselforiginatingtheideaofmakinguseofthependuluminmeasuringgravity。Likewise，hefirstproposedthewavetheoryoflight；althoughitwasHuygenswhoestablisheditonitspresentfoundation。
　　Hookepublished，amongotherthings，abookofplatesanddescriptionsofhisMicroscopicalObservations，whichgivesanideaoftheadvancethathadalreadybeenmadeinmicroscopyinhistime。Twooftheseplatesaregivenhere，which，eveninthisageofmicroscopy，arebothinterestingandinstructive。TheseplatesaremadefromprintsofHooke’soriginalcopperplates，andshowthatexcellentlensesweremadeevenatthattime。Theyillustrate，also，howmuchmighthavebeenaccomplishedinthefieldofmedicineifmoreattentionhadbeengiventomicroscopybyphysicians。Evenacenturylater，hadphysiciansmadebetteruseoftheirmicroscopes，theycouldhardlyhaveoverlookedsuchaneasilyfoundparasiteastheitchmite，whichisquiteaseasilydetectedasthecheesemite，picturedinHooke’sbook。
　　InjusticetoHooke，andinextenuationofhisotherwiseinexcusablepeculiaritiesofmind，itshouldberememberedthatformanyyearshesufferedfromapainfulandwastingdisease。
　　Thismayhaveaffectedhismentalequilibrium，withoutappreciablyaffectinghisingenuity。Inhisowntimethisconditionwouldhardlyhavebeenconsideredadisease；butto-day，withouradvancedideasastomentaldiseases，weshouldbemoreinclinedtoascribehisunfortunateattitudeofmindtoapathologicalcondition，ratherthantoanymanifestationofnormalmentality。FromthispointofviewhismentaldeformityseemsnotunlikethatofCavendish’s，later，exceptthatinthecaseofCavendishitmanifesteditselfasanabnormalsensitivenessinsteadofanabnormalirritability。
　　CHRISTIANHUYGENS
　　Iffornothingelse，theworldisindebtedtothemanwhoinventedthependulumclock，ChristianHuygens1629-1695，oftheHague，inventor，mathematician，mechanician，astronomer，andphysicist。Huygenswasthedescendantofanobleanddistinguishedfamily，hisfather，SirConstantineHuygens，beingawell-knownpoetanddiplomatist。EarlyinlifeyoungHuygensbeganhiscareerinthelegalprofession，completinghiseducationinthejuridicalschoolatBreda；buthistasteformathematicssoonledhimtoneglecthislegalstudies，andhisaptitudeforscientificresearcheswassomarkedthatDescartespredictedgreatthingsofhimevenwhilehewasameretyrointhefieldofscientificinvestigation。
　　Oneofhisfirstendeavorsinsciencewastoattemptanimprovementofthetelescope。Reflectingupontheprocessofmakinglensestheninvogue，youngHuygensandhisbrotherConstantineattemptedanewmethodofgrindingandpolishing，wherebytheyovercameagreatdealofthesphericalandchromaticaberration。Withthisnewtelescopeamuchclearerfieldofvisionwasobtained，somuchsothatHuygenswasabletodetect，amongotherthings，ahithertounknownsatelliteofSaturn。Itwastheseastronomicalresearchesthatledhimtoapplythependulumtoregulatethemovementsofclocks。Theneedforsomemoreexactmethodofmeasuringtimeinhisobservationsofthestarswaskeenlyfeltbytheyoungastronomer，andafterseveralexperimentsalongdifferentlines，Huygenshitupontheuseofaswingingweight；andin1656madehisinventionofthependulumclock。Theyearfollowing，hisclockwaspresentedtothestates-general。Accuracyastotimeisabsolutelyessentialinastronomy，butuntiltheinventionofHuygens’sclocktherewasnoprecise，norevenapproximatelyprecise，meansofmeasuringshortintervals。
　　Huygenswasoneofthefirsttoadaptthemicrometertothetelescope——amechanicaldeviceonwhichallthenicedeterminationofminutedistancesdepends。HealsotookupthecontroversyagainstHookeastothesuperiorityoftelescopicoverplainsightstoquadrants，Hookecontendinginfavoroftheplain。Inthiscontroversy，thesubjectofwhichattractedwideattention，Huygenswascompletelyvictorious；andHooke，beingunabletorefuteHuygens’sarguments，exhibitedsuchirritabilitythatheincreasedhisalreadygeneralunpopularity。Alloftheargumentsforandagainstthetelescopesightaretoonumeroustobegivenhere。IncontendinginitsfavorHuygenspointedoutthattheunaidedeyeisunabletoappreciateanangularspaceintheskylessthanaboutthirtyseconds。Eveninthebestquadrantwithaplainsight，therefore，thealtitudemustbeuncertainbythatquantity。Ifinplaceoftheplainsightatelescopeissubstituted，evenifitmagnifyonlythirtytimes，itwillenabletheobservertofixthepositiontoonesecond，withprogressivelyincreasedaccuracyasthemagnifyingpowerofthetelescopeisincreased。ThiswasonlyoneofthemanytellingargumentsadvancedbyHuygens。
　　Inthefieldofoptics，also，Huygenshasaddedconsiderablytoscience，andhiswork，Dioptrics，issaidtohavebeenafavoritebookwithNewton。Duringthelaterpartofhislife，however，Huygensagaindevotedhimselftoinventingandconstructingtelescopes，grindingthelenses，anddevising，ifnotactuallymaking，theframeforholdingthem。Thesetelescopeswereofenormouslengths，threeofhisobject-glasses，nowinpossessionoftheRoyalSociety，beingof123，180，and210feetfocallengthrespectively。Suchinstruments，ifconstructedintheordinaryformofthelongtube，wereveryunmanageable，andtoobviatethisHuygensadoptedtheplanofdispensingwiththetubealtogether，mountinghislensesonlongpolesmanipulatedbymachinery。Eventhesewereunwieldyenough，butthedifficultiesofmanipulationwerefullycompensatedbytheresultsobtained。
　　Ithadbeendiscovered，amongotherthings，thatinobliquerefractionlightisseparatedintocolors。Therefore，anysmallportionoftheconvexlensofthetelescope，beingaprism，theraysproceedtothefocus，separatedintoprismaticcolors，whichmaketheimagethusformededgedwithafringeofcolorandindistinct。But，fortunatelyfortheearlytelescopemakers，thedegreeofthisaberrationisindependentofthefocallengthofthelens；sothat，byincreasingthisfocallengthandusingtheappropriateeye-piece，theimagecanbegreatlymagnified，whilethefringeofcolorsremainsaboutthesameaswhenalesspowerfullensisused。HencetheadvantageofHuygens’slongtelescope。Hedidnotconfinehiseffortstosimplylengtheningthefocallengthofhistelescopes，however，butalsoaddedtotheirefficiencybyinventinganalmostperfectachromaticeye-piece。
　　In1663hewaselectedafellowoftheRoyalSocietyofLondon，andin1669hegavetothatbodyaconcisestatementofthelawsgoverningthecollisionofelasticbodies。AlthoughthesameviewshadbeengivenbyWallisandWrenafewweeksearlier，thereisnodoubtthatHuygens’sviewswerereachedindependently；anditisprobablethathehadarrivedathisconclusionsseveralyearsbefore。InthePhilosophicalTransactionsfor1669itisrecordedthatthesociety，beinginterestedinthelawsoftheprinciplesofmotion，arequestwasmadethatM。Huygens，Dr。Wallis，andSirChristopherWrensubmittheirviewsonthesubject。Wallissubmittedhispaperfirst，November15，1668。Amonthlater，December17th，Wrenimpartedtothesocietyhislawsastothenatureofthecollisionofbodies。
　　Andafewdayslater，January5，1669，Huygenssentinhis"RulesConcerningtheMotionofBodiesafterMutualImpulse。"AlthoughHuygens’sreportwasreceivedlast，hewasanticipatedbysuchabriefspaceoftime，andhisviewsaresoclearlystated——onthewholerathermoresothanthoseoftheothertwo——thatwegivetheminparthere:
　　"1。Ifahardbodyshouldstrikeagainstabodyequallyhardatrest，aftercontacttheformerwillrestandthelatteracquireavelocityequaltothatofthemovingbody。
　　"2。Butifthatotherequalbodybelikewiseinmotion，andmovinginthesamedirection，aftercontacttheywillmovewithreciprocalvelocities。
　　"3。Abody，howevergreat，ismovedbyabodyhoweversmallimpelledwithanyvelocitywhatsoever。
　　"5。Thequantityofmotionoftwobodiesmaybeeitherincreasedordiminishedbytheirshock；butthesamequantitytowardsthesamepartremains，aftersubtractingthequantityofthecontrarymotion。
　　"6。Thesumoftheproductsarisingfrommultiplyingthemassofanyhardbodyintothesquaresofitsvelocityisthesamebothbeforeandafterthestroke。
　　"7。Ahardbodyatrestwillreceiveagreaterquantityofmotionfromanotherhardbody，eithergreaterorlessthanitself，bytheinterpositionofanythirdbodyofameanquantity，thanifitwasimmediatelystruckbythebodyitself；andiftheinterposingbodybeameanproportionalbetweentheothertwo，itsactionuponthequiescentbodywillbethegreatestofall。"[10]
　　ThiswasonlyoneofseveralinterestingandimportantcommunicationssenttotheRoyalSocietyduringhislifetime。Oneofthesewasareportonwhathecalls"PneumaticalExperiments。"
　　"Uponincludinginavacuumaninsectresemblingabeetle，butsomewhatlarger，"hesays，"whenitseemedtobedead，theairwasreadmitted，andsoonafteritrevived；puttingitagaininthevacuum，andleavingitforanhour，afterwhichtheairwasreadmitted，itwasobservedthattheinsectrequiredalongertimetorecover；includingitthethirdtimefortwodays，afterwhichtheairwasadmitted，itwastenhoursbeforeitbegantostir；but，puttingitinafourthtime，foreightdays，itneverafterwardsrecovered……Severalbirds，rats，mice，rabbits，andcatswerekilledinavacuum，butiftheairwasadmittedbeforetheenginewasquiteexhaustedsomeofthemwouldrecover；yetnonerevivedthathadbeeninaperfectvacuum……Uponputtingtheweightofeighteengrainsofpowderwithagaugeintoareceiverthatheldseveralpoundsofwater，andfiringthepowder，itraisedthemercuryaninchandahalf；fromwhichitappearsthatthereisone-fifthofairingunpowder，uponthesuppositionthatairisaboutonethousandtimeslighterthanwater；forinthisexperimentthemercuryrosetotheeighteenthpartoftheheightatwhichtheaircommonlysustainsit，andconsequentlytheweightofeighteengrainsofpowderyieldedairenoughtofilltheeighteenthpartofareceiverthatcontainedsevenpoundsofwater；nowthiseighteenthpartcontainsforty-ninedrachmsofwater；whereforetheair，thattakesupanequalspace，beingathousandtimeslighter，weighsone-thousandthpartofforty-ninedrachms，whichismorethanthreegrainsandahalf；itfollows，therefore，thattheweightofeighteengrainsofpowdercontainsmorethanthreeandahalfofair，whichisaboutone-fifthofeighteengrains……"
　　From1665to1681，acceptingthetemptingoffermadehimthroughColbert，byLouisXIV。，HuygenspursuedhisstudiesattheBibliothequeduRoiasaresidentofFrance。HerehepublishedhisHorologiumOscillatorium，dedicatedtotheking，containing，amongotherthings，hissolutionoftheproblemofthe"centreofoscillation。"Thisinitselfwasanimportantstepinthehistoryofmechanics。Assumingastruethatthecentreofgravityofanynumberofinterdependentbodiescannotrisehigherthanthepointfromwhichitfalls，hereachedcorrectconclusionsastothegeneralprincipleoftheconservationofvisviva，althoughhedidnotactuallyprovehisconclusions。Thiswasthefirstattempttodealwiththedynamicsofasystem。Inthiswork，also，wasthetruedeterminationoftherelationbetweenthelengthofapendulumandthetimeofitsoscillation。
　　In1681hereturnedtoHolland，influenced，itisbelieved，bytheattitudethatwasbeingtakeninFranceagainsthisreligion。
　　Herehecontinuedhisinvestigations，builthisimmensetelescopes，and，amongotherthings，discovered"polarization，"
　　whichisrecordedinTraitedelaLumiere，publishedatLeydenin1690。Fiveyearslaterhedied，bequeathinghismanuscriptstotheUniversityofLeyden。ItisinterestingtonotethatheneveracceptedNewton’stheoryofgravitationasauniversalpropertyofmatter。
　　XI。NEWTONANDTHECOMPOSITIONOFLIGHT
　　Galileo，thatgiantinphysicalscienceoftheearlyseventeenthcentury，diedin1642。OnChristmasdayofthesameyeartherewasborninEnglandanotherintellectualgiantwhowasdestinedtocarryforwardtheworkofCopernicus，Kepler，andGalileotoamarvellousconsummationthroughthediscoveryofthegreatunifyinglawinaccordancewithwhichtheplanetarymotionsareperformed。Werefer，ofcourse，tothegreatestofEnglishphysicalscientists，IsaacNewton，theShakespeareofthescientificworld。Bornthusbeforethemiddleoftheseventeenthcentury，Newtonlivedbeyondthefirstquarteroftheeighteenth1727。Forthelastfortyyearsofthatperiodhiswasthedominatingscientificpersonalityoftheworld。Withfullproprietythattimehasbeenspokenofasthe"AgeofNewton。"
　　Yetthemanwhowastoachievesuchdistinctiongavenoearlypremonitionoffuturegreatness。Hewasasicklychildfrombirth，andaboyoflittleseemingpromise。Hewasanindifferentstudent，yet，ontheotherhand，hecaredlittleforthecommonamusementsofboyhood。Heearlyexhibited，however，atasteformechanicalcontrivances，andspentmuchtimeindevisingwindmills，water-clocks，sun-dials，andkites。Whileotherboyswereinterestedonlyinhavingkitesthatwouldfly，Newton——atleastsothestoriesofalatertimewouldhaveusunderstand——caredmorefortheinvestigationoftheseemingprinciplesinvolved，orfortestingthebestmethodsofattachingthestrings，orthebestmaterialstobeusedinconstruction。
　　Meanwhilethefuturephilosopherwasacquiringatasteforreadingandstudy，delvingintooldvolumeswheneverhefoundanopportunity。Thesehabitsconvincedhisrelativesthatitwasuselesstoattempttomakeafarmeroftheyouth，ashadbeentheirintention。Hewasthereforesentbacktoschool，andinthesummerof1661hematriculatedatTrinityCollege，Cambridge。
　　EvenatcollegeNewtonseemstohaveshownnounusualmentalcapacity，andin1664，whenexaminedforascholarshipbyDr。
　　Barrow，thatgentlemanissaidtohaveformedapooropinionoftheapplicant。ItissaidthattheknowledgeoftheestimateplaceduponhisabilitiesbyhisinstructorpiquedNewton，andledhimtotakeupinearnestthemathematicalstudiesinwhichheafterwardsattainedsuchdistinction。ThestudyofEuclidandDescartes’s"Geometry"rousedinhimalatentinterestinmathematics，andfromthattimeforwardhisinvestigationswerecarriedonwithenthusiasm。In1667hewaselectedFellowofTrinityCollege，takingthedegreeofM。A。thefollowingspring。
　　ItwillthusappearthatNewton’sboyhoodandearlymanhoodwerepassedduringthattroubloustimeinBritishpoliticalannalswhichsawtheoverthrowofCharlesI。，theautocracyofCromwell，andtheeventualrestorationoftheStuarts。HismatureryearswitnessedtheoverthrowofthelastStuartandthereignoftheDutchman，WilliamofOrange。InhisoldagehesawthefirstoftheHanoveriansmountthethroneofEngland。Withinadecadeofhisdeathsuchscientificpath-findersasCavendish，Black，andPriestleywereborn——menwholivedontothecloseoftheeighteenthcentury。Inafullsense，then，theageofNewtonbridgesthegapfromthatearlytimeofscientificawakeningunderKeplerandGalileotothetimewhichweofthetwentiethcenturythinkofasessentiallymodern。
　　THECOMPOSITIONOFWHITELIGHT
　　InDecember，1672，NewtonwaselectedaFellowoftheRoyalSociety，andatthismeetingapaperdescribinghisinventionoftherefractingtelescopewasread。Afewdayslaterhewrotetothesecretary，makingsomeinquiriesastotheweeklymeetingsofthesociety，andintimatingthathehadanaccountofaninterestingdiscoverythathewishedtolaybeforethesociety。
　　Whenthiscommunicationwasmadepublic，itprovedtobeanexplanationofthediscoveryofthecompositionofwhitelight。
　　WehaveseenthatthequestionastothenatureofcolorhadcommandedtheattentionofsuchinvestigatorsasHuygens，butthatnoverysatisfactorysolutionofthequestionhadbeenattained。Newtonprovedbydemonstrativeexperimentsthatwhitelightiscomposedoftheblendingoftheraysofdiversecolors，andthatthecolorthatweascribetoanyobjectismerelyduetothefactthattheobjectinquestionreflectsraysofthatcolor，absorbingtherest。Thatwhitelightisreallymadeupofmanycolorsblendedwouldseemincrediblehadnottheexperimentsbywhichthiscompositionisdemonstratedbecomefamiliartoeveryone。TheexperimentswereabsolutelynovelwhenNewtonbroughtthemforward，andhisdemonstrationofthecompositionoflightwasoneofthemoststrikingexpositionseverbroughttotheattentionoftheRoyalSociety。Itishardlynecessarytoaddthat，notwithstandingtheconclusivecharacterofNewton’swork，hisexplanationsdidnotforalongtimemeetwithgeneralacceptance。
　　Newtonwasledtohisdiscoverybysomeexperimentsmadewithanordinaryglassprismappliedtoaholeintheshutterofadarkenedroom，therefractedraysofthesunlightbeingreceivedupontheoppositewallandformingtherethefamiliarspectrum。
　　"Itwasaverypleasingdiversion，"hewrote，"toviewthevividandintensecolorsproducedthereby；andafteratime，applyingmyselftoconsiderthemverycircumspectly，Ibecamesurprisedtoseetheminvaryingform，which，accordingtothereceivedlawsofrefraction，Iexpectedshouldhavebeencircular。Theywereterminatedatthesideswithstraightlines，butattheendsthedecayoflightwassogradualthatitwasdifficulttodeterminejustlywhatwastheirfigure，yettheyseemedsemicircular。
　　"Comparingthelengthofthiscoloredspectrumwithitsbreadth，Ifounditalmostfivetimesgreater；adisproportionsoextravagantthatitexcitedmetoamorethanordinarycuriosityofexaminingfromwhenceitmightproceed。Icouldscarcethinkthatthevariousthicknessesoftheglass，ortheterminationwithshadowordarkness，couldhaveanyinfluenceonlighttoproducesuchaneffect；yetIthoughtitnotamiss，first，toexaminethosecircumstances，andsotriedwhatwouldhappenbytransmittinglightthroughpartsoftheglassofdiversthickness，orthroughholesinthewindowofdiversbigness，orbysettingtheprismwithoutsothatthelightmightpassthroughitandberefractedbeforeitwastransmittedthroughthehole；
　　butIfoundnoneofthosecircumstancesmaterial。Thefashionofthecolorswasinallthesecasesthesame。
　　"ThenIsuspectedwhetherbyanyunevennessoftheglassorothercontingentirregularitythesecolorsmightbethusdilated。AndtotrythisItookanotherprismliketheformer，andsoplaceditthatthelight，passingthroughthemboth，mightberefractedcontraryways，andsobythelatterreturnedintothatcoursefromwhichtheformerdivertedit。For，bythismeans，Ithought，theregulareffectsofthefirstprismwouldbedestroyedbythesecondprism，buttheirregularonesmoreaugmentedbythemultiplicityofrefractions。Theeventwasthatthelight，whichbythefirstprismwasdiffusedintoanoblongform，wasbythesecondreducedintoanorbicularonewithasmuchregularityaswhenitdidnotallpassthroughthem。Sothat，whateverwasthecauseofthatlength，’twasnotanycontingentirregularity。
　　"Ithenproceededtoexaminemorecriticallywhatmightbeeffectedbythedifferenceoftheincidenceofrayscomingfromdiverspartsofthesun；andtothatendmeasuredtheseverallinesandanglesbelongingtotheimage。Itsdistancefromtheholeorprismwas22feet；itsutmostlength131/4inches；itsbreadth25/8；thediameterofthehole1/4ofaninch；theanglewhichtherays，tendingtowardsthemiddleoftheimage，madewiththoselines，inwhichtheywouldhaveproceededwithoutrefraction，was44degrees56’；andtheverticalangleoftheprism，63degrees12’。Alsotherefractionsonbothsidesoftheprism——thatis，oftheincidentandemergentrays——were，asnearasIcouldmakethem，equal，andconsequentlyabout54degrees4’；andtheraysfellperpendicularlyuponthewall。Now，subductingthediameteroftheholefromthelengthandbreadthoftheimage，thereremains13inchesthelength，and23/8thebreadth，comprehendedbythoserays，which，passingthroughthecentreofthesaidhole，whichthatbreadthsubtended，wasabout31’，answerabletothesun’sdiameter；buttheanglewhichitslengthsubtendedwasmorethanfivesuchdiameters，namely2
　　degrees49’。
　　"Havingmadetheseobservations，Ifirstcomputedfromthemtherefractivepoweroftheglass，andfounditmeasuredbytheratioofthesines20to31。Andthen，bythatratio，Icomputedtherefractionsoftworaysflowingfromoppositepartsofthesun’sdiscus，soastodiffer31’intheirobliquityofincidence，andfoundthattheemergentraysshouldhavecomprehendedanangleof31’，astheydid，beforetheywereincident。
　　"Butbecausethiscomputationwasfoundedonthehypothesisoftheproportionalityofthesinesofincidenceandrefraction，whichthoughbymyownexperienceIcouldnotimaginetobesoerroneousastomakethatanglebut31’，whichinrealitywas2
　　degrees49’，yetmycuriositycausedmeagaintomakemyprism。
　　Andhavingplaceditatmywindow，asbefore，Iobservedthatbyturningitalittleaboutitsaxistoandfro，soastovaryitsobliquitytothelightmorethananangleof4degreesor5
　　degrees，thecolorswerenottherebysensiblytranslatedfromtheirplaceonthewall，andconsequentlybythatvariationofincidencethequantityofrefractionwasnotsensiblyvaried。Bythisexperiment，therefore，aswellasbytheformercomputation，itwasevidentthatthedifferenceoftheincidenceofraysflowingfromdiverspartsofthesuncouldnotmakethemafterdecussationdivergeatasensiblygreateranglethanthatatwhichtheybeforeconverged；whichbeing，atmost，butabout31’
　　or32’，therestillremainedsomeothercausetobefoundout，fromwhenceitcouldbe2degrees49’。"
　　AllthiscausedNewtontosuspectthattherays，aftertheirtrajectionthroughtheprism，movedincurvedratherthaninstraightlines，thustendingtobecastuponthewallatdifferentplacesaccordingtotheamountofthiscurve。Hissuspicionswereincreased，also，byhappeningtorecallthatatennis-ballsometimesdescribessuchacurvewhen"cut"byatennis-racketstrikingtheballobliquely。
　　"Foracircularaswellasaprogressivemotionbeingcommunicatedtoitbythestroke，"hesays，"itspartsonthatsidewherethemotionsconspiremustpressandbeatthecontiguousairmoreviolentlythanontheother，andthereexciteareluctancyandreactionoftheairproportionatelygreater。Andforthesamereason，iftheraysoflightshouldpossiblybeglobularbodies，andbytheirobliquepassageoutofonemediumintoanotheracquireacirculatingmotion，theyoughttofeelthegreaterresistancefromtheambientetheronthatsidewherethemotionsconspire，andthencebecontinuallybowedtotheother。
　　Butnotwithstandingthisplausiblegroundofsuspicion，whenI
　　cametoexamineitIcouldobservenosuchcurvityinthem。And，besideswhichwasenoughformypurpose，Iobservedthatthedifference’twixtthelengthoftheimageanddiameteroftheholethroughwhichthelightwastransmittedwasproportionabletotheirdistance。
　　"Thegradualremovalofthesesuspicionsatlengthledmetotheexperimentumcrucis，whichwasthis:Itooktwoboards，and，placingoneofthemclosebehindtheprismatthewindow，sothatthelightmustpassthroughasmallhole，madeinitforthepurpose，andfallontheotherboard，whichIplacedatabouttwelvefeetdistance，havingfirstmadeasmallholeinitalso，forsomeoftheincidentlighttopassthrough。ThenIplacedanotherprismbehindthissecondboard，sothatthelighttrajectedthroughboththeboardsmightpassthroughthatalso，andbeagainrefractedbeforeitarrivedatthewall。Thisdone，Itookthefirstprisminmyhandsandturnedittoandfroslowlyaboutitsaxis，somuchastomaketheseveralpartsoftheimage，castonthesecondboard，successivelypassthroughtheholeinit，thatImightobservetowhatplacesonthewallthesecondprismwouldrefractthem。AndIsawbythevariationoftheseplacesthatthelight，tendingtothatendoftheimagetowardswhichtherefractionofthefirstprismwasmade，didinthesecondprismsufferarefractionconsiderablygreaterthanthelighttendingtotheotherend。AndsothetruecauseofthelengthofthatimagewasdetectedtobenootherthanthatLIGHT
　　consistsofRAYSDIFFERENTLYREFRANGIBLE，which，withoutanyrespecttoadifferenceintheirincidence，were，accordingtotheirdegreesofrefrangibility，transmittedtowardsdiverspartsofthewall。"[1]