WhenBiela’scometgavetheinhabitantsoftheearthsuchafrightin1832，itreallydidnotcomewithinfiftymillionsofmilesofus。Eventhegreatcometthroughwhosefilmytailtheearthpassedin1861wasitselffourteenmillionsofmilesaway。Theordinarymind，schooledtomeasurespacebythetinystretchesofapygmyplanet，cannotgrasptheimportofsuchdistances；yetthesearemereunitsofmeasurecomparedwiththevaststretchesofsiderealspace。Werethecometwhichhurtlespastusataspeedof，say，ahundredmilesasecondtocontinueitsmadflightuncheckedstraightintothevoidofspace，itmustflyonitsfrigidwayeightthousandyearsbeforeitcouldreachtheverynearestofourneighborstars；andeventhenitwouldhavepenetratedbutamerearm’s-lengthintothevistaswhereliethedozenorsoofsiderealresidentsthatarenextbeyond。Eventothetrainedmindsuchdistancesareonlyvaguelyimaginable。Yettheastronomerofourcenturyhasreachedoutacrossthisunthinkablevoidandbroughtbackmanyasecretwhichourpredecessorsthoughtforeverbeyondhumangrasp。
AtentativeassaultuponthisstrongholdofthestarswasbeingmadebyHerschelatthebeginningofthecentury。In1802thatgreatestofobservingastronomersannouncedtotheRoyalSocietyhisdiscoverythatcertaindoublestarshadchangedtheirrelativepositionstowardsoneanothersincehefirstcarefullychartedthemtwentyyearsbefore。Hithertoithadbeensupposedthatdoublestarsweremereopticaleffects。Nowitbecameclearthatsomeofthem，atanyrate，aretrue\"binarysystems，\"linkedtogetherpresumablybygravitationandrevolvingaboutoneanother。Halleyhadshown，three-quartersofacenturybefore，thatthestarshaveanactualor\"proper\"motioninspace；
Herschelhimselfhadprovedthatthesunsharesthismotionwiththeotherstars。Herewasanothershiftofplace，hithertoquiteunsuspected，tobereckonedwithbytheastronomerinfathomingsiderealsecrets。
DoubleStarsWhenJohnHerschel，theonlysonandtheworthysuccessorofthegreatastronomer，beganstar-gazinginearnest，aftergraduatingseniorwrangleratCambridge，andmakingtwoorthreetentativeprofessionalstartsinotherdirectionstowhichhisversatilegeniusimpelledhim，hisfirstextendedworkwastheobservationofhisfather’sdoublestars。Hisstudies，inwhichatfirsthehadthecollaborationofMr。JamesSouth，broughttolightscoresofhithertounrecognizedpairs，andgavefreshdataforthecalculationoftheorbitsofthoselongerknown。SoalsodidtheindependentresearchesofF。G。W。Struve，theenthusiasticobserverofthefamousRussianobservatoryattheuniversityofDorpat，andsubsequentlyatPulkowa。Utilizingdatagatheredbytheseobservers，M。Savary，ofParis，showed，in1827，thattheobservedellipticalorbitsofthedoublestarsareexplicablebytheordinarylawsofgravitation，thusconfirmingtheassumptionthatNewton’slawsapplytothesesiderealbodies。Henceforththerecouldbenoreasontodoubtthatthesameforcewhichholdsterrestrialobjectsonourglobepullsateachandeveryparticleofmatterthroughoutthevisibleuniverse。
Thepioneerexplorersofthedoublestarsearlyfoundthatthesystemsintowhichthestarsarelinkedarebynomeansconfinedtosinglepairs。Oftenthreeorfourstarsarefoundthuscloselyconnectedintogravitationsystems；indeed，thereareallgradationsbetweenbinarysystemsandgreatclusterscontaininghundredsoreventhousandsofmembers。Itisknown，forexample，thatthefamiliarclusterofthePleiadesisnotmerelyanopticalgrouping，aswasformerlysupposed，butanactualfederationofassociatedstars，sometwothousandfivehundredinnumber，onlyafewofwhicharevisibletotheunaidedeve。Andthemorecarefullythemotionsofthestarsarestudied，themoreevidentitbecomesthatwidelyseparatedstarsarelinkedtogetherintoinfinitelycomplexsystems，asyetbutlittleunderstood。Atthesametime，allinstrumentaladvancestendtoresolvemoreandmoreseeminglysinglestarsintoclosepairsandminorclusters。ThetwoHerschelsbetweenthemdiscoveredsomethousandsoftheseclosemultiplesystems；Struveandothersincreasedthelisttoabovetenthousand；andMr。S。W。