THEBEGINNINGSOFMODERNSCIENCE
ThestudiesofthepresentbookcovertheprogressofsciencefromthecloseoftheRomanperiodinthefifthcenturyA。D。toaboutthemiddleoftheeighteenthcentury。Intracingthecourseofeventsthroughsolongaperiod，adifficultybecomesprominentwhicheverywherebesetsthehistorianinlessdegree——adifficultyduetotheconflictbetweenthestrictlychronologicalandthetopicalmethodoftreatment。Wemustholdascloselyaspossibletotheactualsequenceofevents，since，asalreadypointedout，onediscoveryleadsontoanother。But，ontheotherhand，progressivestepsaretakencontemporaneouslyinthevariousfieldsofscience，andifweweretoattempttointroducetheseinstrictchronologicalorderweshouldloseallsenseoftopicalcontinuity。
Ourmethodhasbeentoadoptacompromise，followingthecourseofasinglescienceineachgreatepochtoaconvenientstopping-point，andthenturningbacktobringforwardthestoryofanotherscience。Thus，forexample，wetellthestoryofCopernicusandGalileo，bringingtherecordofcosmicalandmechanicalprogressdowntoaboutthemiddleoftheseventeenthcentury，beforeturningbacktotakeupthephysiologicalprogressofthefifteenthandsixteenthcenturies。Oncethelatterstreamisentered，however，wefollowitwithoutinterruptiontothetimeofHarveyandhiscontemporariesinthemiddleoftheseventeenthcentury，whereweleaveittoreturntothefieldofmechanicsasexploitedbythesuccessorsofGalileo，whowerealsothepredecessorsandcontemporariesofNewton。
Ingeneral，itwillaidthereadertorecallthat，sofaraspossible，weholdalwaystothesamesequencesoftopicaltreatmentofcontemporaryevents；asarulewetreatfirstthecosmical，thenthephysical，thenthebiologicalsciences。Thesameorderoftreatmentwillbeheldtoinsucceedingvolumes。
Severaloftheverygreatestofscientificgeneralizationsaredevelopedintheperiodcoveredbythepresentbook:forexample，theCopernicantheoryofthesolarsystem，thetruedoctrineofplanetarymotions，thelawsofmotion，thetheoryofthecirculationoftheblood，andtheNewtoniantheoryofgravitation。Thelaborsoftheinvestigatorsoftheearlydecadesoftheeighteenthcentury，terminatingwithFranklin’sdiscoveryofthenatureoflightningandwiththeLinnaeanclassificationofplantsandanimals，bringustothecloseofoursecondgreatepoch；or，toputitotherwise，tothethresholdofthemodernperiod，I。SCIENCEINTHEDARKAGE