Equallycertain，iflessfamiliar，isthefactthatintropicalclimatesdecayproceeds
　　muchmorerapidlythanintemperateclimates。Thus，dispersionofthedead
　　bodyintogasesisrapidinproportionasthemolecularmotionreceivedfrom
　　withoutisgreat。Thestill—quickerdecompositionsproducedbyexposureto
　　artificially—raisedtemperatures，affordfurtherproofs:instancethosewhich
　　occurincooking。Thecharredsurfacesofpartsmuchheated，showusthat
　　themolecularmotionabsorbedhasservedtodissipateingaseousformsalltheelementsbutthecarbon。ThenatureandcausesofDissolutionarethusclearlydisplayedbythe
　　aggregateswhichsoclearlydisplaythenatureandcausesofEvolution。One
　　oftheseaggregatesbeingmadeofthatpeculiarmattertowhichalargequantity
　　ofconstitutionalmotiongivesgreatplasticity，andtheabilitytoevolve
　　intoahighlycomplexform，（§103）;itresultsthatafterevolution
　　hasceased，asmallamountofmolecularmotionaddedtothatalreadycontained
　　initspeculiarmatter，sufficestocausedissolution。Thoughatdeaththere
　　isreachedanequilibriumamongthesensiblemasses，ororgans，whichmake
　　upthebody;yet，astheinsensibleunitsormoleculesofwhichtheseorgans
　　consistarechemicallyunstable，smallincidentforcessufficetooverthrowthem，andhencedisintegrationproceedsrapidly。§180。Mostinorganicaggregates，havingarrivedatdenseformsin
　　whichcomparativelylittlemotionisretained，remainlongwithoutmarked
　　changes。Eachhaslostsomuchmotioninpassingfromtheunintegratedto
　　theintegratedstate，thatmuchmotionmustbegiventoittocauseresumption
　　oftheunintegratedstate;andanimmensetimemayelapsebeforethereoccur
　　intheenvironment，changesgreatenoughtocommunicatetoittherequisite
　　quantityofmotion。Wewilllookfirstatthosefewinorganicaggregateswhichretainmuchmotion，andthereforereadilyundergodissolution。Amongthesearetheliquidsandvolatilesolidswhichdissipateunder
　　ordinaryconditions——waterthatevaporates，camphorthatwastesawayby
　　thedispersionofitsmolecules。Inallsuchcasesmotionisabsorbed;and
　　alwaysthedissolutionisrapidinproportionasthequantityofheator
　　motionwhichthemassreceivesfromitsenvironmentisgreat。Nextcomethe
　　casesinwhichthemoleculesofahighlyintegratedorsolidaggregate，are
　　dispersedamongthemoleculesofalessintegratedorliquidaggregate;as
　　inaqueoussolutions。Oneevidencethatthisdisintegrationofmatterhas
　　foritsconcomitanttheabsorptionofmotion，isthatsolublesubstances
　　dissolvethemorequicklythehotterthewater:supposingalwaysthatno
　　electiveaffinitycomesintoplay。Anotherandstillmoreconclusiveevidence
　　is，thatwhencrystalsofagiventemperatureareplacedinwaterofthe
　　sametemperature，theprocessofsolutionisaccompaniedbyafalloftemperature
　　——oftenaverygreatone。Omittinginstancesinwhichsomechemicalaction
　　takesplacebetweenthesaltandthewater，itisauniformlawthatthe
　　motionwhichdispersesthemoleculesofthesaltthroughthewater，isat
　　theexpenseofthemolecularmotionpossessedbythewater。Analliedand
　　stillbetterexampleisfurnishedbycasesinwhichthedissolutionoftwo
　　solidsresultsfrommixingthem，ashappenswithsnowandsalt。Heredissolution
　　necessitatessogreatanabsorptionofmolecularmotionasgreatlytolowerthetemperatureoftheliquidproduced。Massesofsedimentaccumulatedintostrata，afterwardscompressedbymany
　　thousandsoffeetofsuperincumbentstrata，andreducedincourseoftime
　　toasolidstate，mayremainforuntoldmillionsofyearsunchanged;but
　　insubsequentmillionsofyearstheyareinevitablyexposedtodisintegrating
　　actions。Raisedalongwithothersuchmassesintoacontinent，denudedand
　　exposedtorain，frost，andthegrindingactionsofglaciers，theyhavetheir
　　particlesgraduallyseparated，carriedaway，andwidelydispersed。Orwhen，
　　asotherwisehappens，theencroachingseaarrives，theunderminedcliffs
　　formedofthemfallfromtimetotime;thewaves，rollingaboutthesmall
　　pieces，andinstormsknockingtogetherthelargerblocks，reducethemto
　　bouldersandpebbles，andatlasttosandandmud。Evenifportionsofthe
　　disintegratedstrataaccumulateintoshinglebankswhichafterwardsbecome
　　solidified，theprocessofdissolution，arrestedthoughitmaybeforsome
　　enormousgeologicperiod，isfinallyresumed。Asmanyashoreshowsus，the
　　conglomerateitselfissoonerorlatersubjecttothelikeprocesses;and
　　itscementedmassesofheterogeneouscomponentsarebrokenupandwornawaybyimpactandattrition——thatis，bycommunicatedmechanicalmotion。Whennotthuseffected，thedisintegrationiseffectedbycommunicated
　　molecularmotion。Aconsolidatedstratuminsomeareaofsubsidence，brought
　　downnearerandnearertotheregionsoccupiedbymoltenmatter，comeseventually
　　tohaveitsparticlesbroughttoaplasticstatebyheat，orfinallymelted
　　downintoliquid。Whatevermaybeitssubsequenttransformations，thetransformationthenexhibitedbyitisanabsorptionofmotionanddisintegrationofmatter。Thusbeitsimpleorcompound，smallorlarge，acrystaloramountain—chat，
　　everyinorganicaggregateontheEarthundergoes，atsometimeorother，
　　areversalofthosechangesundergoneduringitsevolution。Notthatitusually
　　passesbackfromtheperceptibleintotheimperceptible，duringanyperiod
　　inwhichitisorcanbeexposedtohumanobservation。Itdoesnotbecome
　　aeriformandinvisible，asorganicaggregatesdoingreatpart，thoughnot
　　wholly。Butstillitsdisintegrationanddispersioncarryitsomedistance
　　onthewaytowardstheimperceptible;andtherearereasonsforthinking
　　thatitsarrivalthereisbutdelayed。Ataperiodimmeasurablyremote，every
　　suchinorganicaggregate，alongwithallundissipatedremnantsoforganic
　　aggregates，mustbereducedtoastateofgaseousdiffusion，andsocompletethecycleofitschanges。§181。FortheEarthasawhole，whenithasgonethroughtheentire
　　seriesofitsascendingtransformations，mustremainexposedtothecontingencies
　　ofitsenvironment;andinthecourseofthoseceaselesschangesgoingon
　　throughoutaUniverseofwhichallpartsareinmotion，must，atsomeperiod
　　beyondtheutmoststretchofimagination，besubjecttoenergiessufficient
　　tocauseitscompletedisintegration。Letusglanceattheenergiescompetenttodisintegrateit。Inhisessayon"TheInter—actionofNaturalForces，"Prof。
　　HelmholtzstatesthethermalequivalentoftheEarth'smovementthroughspace，
　　ascalculatedonthenowreceiveddatumofMr。Joule。"IfourEarth，"
　　hesays，"werebyasuddenshockbroughttorestinherorbit——which
　　isnottobefearedintheexistingarrangementofoursystem——bysuch
　　ashockaquantityofheatwouldbegeneratedequaltothatproducedbythe
　　combustionoffourteensuchEarthsofsolidcoal。Makingthemostunfavourable
　　assumptionastoitscapacityforheat，thatis，placingitequaltothat
　　ofwater，themassoftheEarthwouldtherebybeheated11，200degrees;it
　　wouldthereforebequitefused，andforthemostpartreducedtovapour。
　　IfthentheEarth，afterhavingbeenthusbroughttorest，shouldfallinto
　　theSun，whichofcoursewouldbethecase，thequantityofheatdeveloped
　　bytheshockwouldbe400timesgreater。"Nowthoughthiscalculation
　　seemstobenothingtothepurpose，sincetheEarthisnotlikelytobesuddenly
　　arrestedinitsorbitandnotlikelythereforesuddenlytofallintothe
　　Sun;yet，asbeforepointedout（§171），thereisaforceatworkwhich
　　itisheldmustatlastbringtheEarthintotheSun。Thisforceistheresistance
　　oftheetherealmedium。Frometherealresistanceisinferredaretardation
　　ofallmovingbodiesintheSolarSystem——aretardationwhichsomeastronomers
　　contendevennowshowsitseffectsintherelativenearnesstooneanother
　　oftheorbitsoftheolderplanets。If，then，retardationisgoingon，there
　　mustcomeatime，nomatterhowremote，whentheslowlydiminishingorbit
　　oftheEarthwillendintheSun;andthoughthequantityofmolarmotion
　　tobethentransformedintomolecularmotion，willnotbesogreatasthat
　　whichthecalculationofHelmholtzsupposes，itwillbegreatenoughtoreducethesubstanceoftheEarthtoagaseousstate。ThisdissolutionoftheEarthand，atintervals，ofeveryotherplanet，
　　isnot，however，adissolutionoftheSolarSystem。Allthechangesexhibited
　　throughouttheSolarSystem，areincidentsaccompanyingtheintegrationof
　　theentiremattercomposingit:thelocalintegrationofwhicheachplanet
　　isthescene，completingitselflongbeforethegeneralintegrationiscomplete。
　　Buteachsecondarymassleavinggonethroughitsevolutionandreacheda
　　stateofequilibriumamongitsparts（supposingthattheavailabletimesuffices，
　　whichinthecasesofJupiterandSaturnitmaynot），thereaftercontinues
　　initsextinctstate，until，bythestill—progressinggeneralintegration，
　　itisbroughtintothecentralmass。Andthougheachsuchunionofasecondary
　　masswiththecentralmass，implyingtransformationofmolarmotioninto
　　molecularmotion，causespartialdiffusionofthetotalmassformed，and
　　addstothequantityofmotionthathastobedispersedintheshapeoflight
　　andheat;yetitdoesbutpostponetheperiodatwhichthetotalmassmust
　　becomecompletelyintegrated，anditsexcessofcontainedmotionradiatedintospace。§182。Herewecometothequestionraisedatthecloseofthelast
　　chapter——DoesEvolutionasawhole，likeEvolutionindetail，advancetowards
　　completequiescience？Isthatmotionlessstatecalleddeath，whichendsEvolution
　　inorganicbodies，typicaloftheuniversaldeathinwhichEvolutionatlarge
　　mustend？Andhavewethustocontemplateastheoutcomeofthings，aboundless
　　spaceholdinghereandthereextinctSuns，fatedtoremainforeverwithoutfurtherchange？Tosospeculativeaninquiry，nonebutaspeculativeansweristobeexpected。
　　Suchanswerasmaybeventured，mustbetakenlessasapositiveanswerthan
　　asademurrertotheconclusionthattheproximateresultmustbetheultimate
　　result。If，pushingtoitsextremetheargumentthatEvolutionmustcome
　　toacloseincompleteequilibriumorrest，thereadersuggeststhatfor
　　aughtwhichappearstothecontrarytheremustresultaUniversalDeathwhich
　　willcontinueindefinitely，tworepliesmaybemade。Thefirstisthatthe
　　evidencepresentedintheheavensatlargeimpliesthatwhileofthemultitudinous
　　aggregatesofmatteritpresents，mostarepassingthroughthosestages——
　　whichmustendinlocalrest，thereareotherswhich，havingbarelycommenced
　　theseriesofchangesconstitutingEvolution，areonthewaytobecometheatres
　　oflife。ThesecondreplyisthatwhenwecontemplateourSiderealSystem
　　asawhole，certainofthegreatfactswhichsciencehasestablishedimply
　　potentialrenewalsoflife，nowinoneregionnowinanother，followed，possibly，
　　ataperiodunimaginablyremotebyamoregeneralrenewal。Thisconclusionissuggestedwhenwetakeintoaccountafactornotyetmentioned。Forhithertowehaveconsideredonlythatequilibrationwhichistaking
　　placewithinourSolarSystemandwithinsimilarsystems;takingnonote
　　ofthatimmeasurablygreaterequilibrationwhichremainstotakeplace:ending
　　thosemotionsthroughspacewhichsuchsystemspossess。Thatthestars，in
　　oldtimescalledfixed，areallinmotion，hasnowbecomeafamiliartruth，
　　andthattheyaremovingwithvelocitiesrangingfromsay10milespersecond
　　uptosome70milespersecond（whichlastisthevelocityofa"runaway
　　star"supposedtobepassingthroughourSiderealSystem）isatruth
　　deducedfromobservationsbymodernastronomers。Tobejoinedwiththisis
　　thefactthattherearedyingstarsandprobablydeadstars。Beyondtheevidence
　　furnishedbythevariouskindsoflighttheyemit，ofwhichtheredindicates
　　relativelyadvancedage，thereistheevidencethatinsomecasesbright
　　starshaveattendantswhicharedarkoralmostdark:themostconspicuous
　　casebeingthatofSirius，roundwhichrevolvesabodyofaboutone—third
　　itssizebutyieldingonly1/30000thpartofitslight——astarapproaching
　　toourSuninsize，whichhasgoneout。Theimplicationappearstobethat
　　beyondtheluminousmassesconstitutingthevisibleSiderealSystem，there
　　arenon—luminousmasses，perhapsfewerinnumberperhapsmorenumerous，which
　　incommonwiththeluminousonesareimpelledbymutualgravitation。How
　　thenaretobeequilibratedthemotionsofthesevastmasses，luminousandnonluminous，havinghighvelocities？Thisquestionmaybedividedintotwo，amajorandaminor，ofwhichtheminoradmitsofsomethinglikeananswer，whilethemajorseemsunanswerable。§182a。Scatteredthroughimmensurablespace，butmoreespecially
　　inandabouttheregionoftheMilkyWay，arenumerousstar—clusters，varying
　　intheircharactersfromthosewhicharehardlydistinguishablefromunusually
　　richportionsoftheheavens，tothosewhichconstitutecondensedswarms
　　ofstars;kindsofwhichmaybenamed，asattheoneextreme，24Persei，
　　103Cassiopeiaand32Cygni，andattheotherextreme，13Herculisand2
　　Aquarei。（*）