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。（*）