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。