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andwouldsorenderittothatextentheterogeneous。Takeapieceofred—hot
matter，andhoweverevenlyheateditmayatfirstbe，itwillquicklycease
tobeso:theexterior，coolingfasterthantheinteriorwillbecomedifferent
fromitintemperature。Andthelapseintoheterogeneityoftemperature，
soobvious。inthisextremecase，takesplacemoreorlessinthecasesof
allsurroundingobjects，whichareeverbeingwarmedorcooled。Theaction
ofchemicalforcessuppliesotherillustrations。Exposeafragmentofmetal
toairorwater，andincourseoftimeitwillbecoatedwithafilmofoxide，
carbonate，orothercompound:itsouterpartswillbecomeunlikeitsinner
parts。Oftentheheterogeneityproducedbytheactionsofchemicalforces
onthesurfacesofmasses，isnotstriking，becausethechangedportions
aresoonwashedaway，orotherwiseremoved。Butifthisbepreventedcomparatively
complexstructuresresult。Insomequarriesoftrap—rocktherearestriking
examples。Notunfrequentlyapieceoftrapmaybefoundreduced，bytheaction
oftheweather，toanumberofloosely—adherentcoats，likethoseofanonion。
Wheretheblockhasbeenundisturbed，wemaytracethewholeseriesofthese，
fromtheangular，irregularouterone，throughsuccessivelyincludedones
inwhichtheshapebecomesgraduallyrounded，endingatlengthinaspherical
nucleus。Oncomparingtheoriginalmassofstonewiththisgroupofconcentric
coats，eachdifferingfromtherestinform，andprobablyinthestateof
decompositionithasarrivedat，wegetamarkedillustrationofthemultiformity
towhich，inlapseoftime，auniformbodymaybebroughtbyexternalchemical
action。Theinstabilityofthehomogeneousisequallyseeninthechanges
setupthroughouttheinteriorofamass，whenitconsistsofunitsthat
arenotrigidlyboundtogether。Themoleculesofaslowly—settlingprecipitate
donotremainseparate，andequablydistributedthroughthefluidinwhich
theymaketheirappearance。Theyaggregateeitherintocrystallinegrains
orintoflocculi;andwherethemassoffluidisgreatandtheprocessprolonged，
theseflocculidonotcontinueequi—distant，butasSembleintogroups。That
istosay，thereisadestructionofthebalanceatfirstsubsistingamong
thediffusedparticles，andalsoofthebalanceatfirstsubsistingamongthegroupsintowhichtheseparticlesunite。Theinstabilitythusvariouslyillustratedisconsequentonthefactthat
theseveralpartsofanyhomogeneousaggregateareexposedtodifferentforces
——forceswhichdiffereitherinkindoramount;andareofnecessitydifferently
modified。Therelationsofoutsideandinside，andofcomparativenearness
ofthepartstoneighbouringsourcesofinfluence，implythereceptionof
influencesthatareunlikeinquantityorquality，orboth:unlikechanges，nowtemporarynowpermanent，beingcaused。Forlikereasonstheprocessmustrepeatitselfineachofthecomponent
massesofunitsthataredifferentiatedbythemodifyingforces。Eachof
theseminorgroups，likethemajorgroup，mustgradually，inobedienceto
theunlikeinfluencesactingonit，loseitsbalanceofparts，andpassfrom
auniformintoamultiformstate。Andsooncontinuously。Whence，indeed，
itfollowsthatnotonlymustthehomogeneouslapseintonon—homogeneous，
butthemorehomogeneousmusttendevertobecomelesshomogeneous。Ifany
givenwhole，insteadofbeingabsolutelyuniformthroughout，consistofparts
distinguishablefromoneanother——ifeachoftheseparts，whilesomewhat
unlikeotherparts，isuniformwithinitself;then，eachofthembeingin
unstableequilibrium，itfollowsthatwhilethechangessetupwithinit
mustrenderitmultiform，theymustatthesametimerenderthewholemore
multiformthanbefore。Thegeneralprinciple，nowtobefollowedoutinits
applications，isthussomewhatmorecomprehensivethanthetitleofthechapterimplies。Nodemurrertotheconclusionsdrawn，canbebasedonthetruththatperfect
homogeneitynowhereexists;since，whetherthatstatewithwhichwecommence
beorbenotoneofperfecthomogeneity，theprocessmustequallybetowardsarelativeheterogeneity。§150。Thestarsaredistributedwithathreefoldirregularity。There
isfirstthemarkedcontrastbetweentheMilkyWayandotherpartsofthe
heavens，inrespectofthequantitiesofstarswithingivenvisualareas。
TherearesecondarycontrastsoflikekindintheMilkyWayitself，which
hasitsthickandthinplaces;aswellasthroughoutthecelestialspaces
ingeneral，whicharemorecloselystrewninsomeregionsthaninothers。
Andthereisathirdorderofcontrastsproducedbytheaggregationofstars
intosmallclusters。Besidesthisheterogeneityinthedistributionofstars，
consideredwithoutdistinctionsofkind，afurtherheterogeneityisdisclosed
whentheyareclassifiedbytheirdifferencesofcolour，whichanswerto
differencesofphysicalconstitution。Whileyellowstarsarefoundinall
partsoftheheavens，redandbluestarsarenotso:therearewideregions
inwhichbothredandbluestarsarerare;thereareregionsinwhichthe
blueoccurinconsiderablenumbers，andthereareotherregionsinwhich
theredarecomparativelyabundant。Yetonemoreirregularityoflikesignificance
ispresentedbythenebulae。Thesearenotdispersedwithanythinglikeuniformity，
butarefarmorenumerousaroundthepolesofthegalacticcirclethanintheneighbourhoodofitsplane。Noonewillexpectthatanythinglikeadefiniteinterpretationofthis
structurecanbegivenonthehypothesisofEvolution，oranyotherhypothesis。
Suchaninterpretationwouldimplysomereasonableassumptionrespecting
thepre—existingdistributionofthestellarmatterandofthematterforming
nebulae，andwehavenowarrantforanyassumption。Ifweallowimagination
torangebackthroughantecedentPossibilitiesandprobabilities，wesee
ittobeunlikelythathomogeneousmatterfilledthespacewhichourSidereal
Systemnowfills，atatimeimmediatelyprecedingitsinitiation。Rather
theevidencewhichtheheavenspresentimpliesthatthedistributionout
ofwhichthepresentdistributionarose，wasirregularinallrespects。Though
certaintraitsofourgalaxysuggestthatithasavagueindividuality，and
that，alongwiththeirspecialmotions，itsstarshavesomegeneralmotion;
yettheevidenceforcesonustheconclusionthatmanyvarietiesofchanges
havebeensimultaneouslygoingoninitsdifferentparts。Wefindnebulae
inallstagesofconcentration，star—clustersvariouslycondensed，groups
oflargerstarsapproximatingindifferentdegrees，aswellasregionslike
thosewhichthenubeculaeoccupy，presentingcomplexstructuresandapparently
activechanges。Themostwhichcanbesaidrespectingthistotaldistribution
isthat，subjectasallpartsofourSiderealSystemaretothelawofgravitation，
theheterogeneitiesitexhibits，everywhereimplyingaprogressingconcentration，
thatis，integration，pointbackwardtoalessheterogeneousstateandpoint
forwardtoamoreheterogeneousstate。But，leavingasidethistootranscendent
question，wemaywithoutunduerashnessconsiderfromtheevolutionpoint
ofviewthechangestobeanticipatedinoneofthosecollectionsofmatter
describedasadiffusednebulosity，oroneofthosemoredistinctonesof
whichtheoutlyingpartsarecomparedtowispsofcloudblownaboutbythe
wind。Theonlyevolutionalprocesswhichcanatfirstbedisplayedisthe
primaryoneofintegration——thegatheringtogetherthroughmutualattraction
oftheparts;forinthisearlystageinwhichindefinitenessandincoherence
aresofullyexemplified，theredoesnotyetexistsuchanaggregateasis
capableofexhibitingsecondaryre—distributions:wehaveonlythedispersed
componentsofsuchanaggregate。Contemplating，then，onlytheprocessof
integration，wemay，withoutaskinganythingabouttheprevioushistoryof
anirregularnebula，safelyassumethatitspartshavetheirrespectiveproper
motions;forthechancesareinfinitytooneagainstastateofrestrelatively
tooneanother。Further，thechancesareinfinitytooneagainsttheirproper
motionsbeingsuchthatduringconcentrationtheywillcanceloneanother:
themotionofsomepart，ortheresultantofthemotionsofseveralparts，
willconstituteapropermotiondistinctfromthatwhichmutualgravitation
generates——amotionwhich，unlessjustcounterbalancedbyanoppositeone
（againaninfiniteimprobability）willgeneraterotation。Itmay，indeed，
bearguedthat，apartfromanypre—existingpropermotionsofitsparts，
anebulousmass，ifirregular，willacquirerotationwhileintegrating;since
eachoutlyingfragment，arrivingaftertheresthavebeengatheredtogether，
isinfinitelyunlikelytofallintothemassinsuchamannerthatitsmotion
willbeentirelycancelledbyresistance;but，fallingintoitsoastobe
deflectedlaterally，willhaveitsmotionofapproachsochangedindirection
astobecomeinpartamotionofrevolution:aresultantofallsuchmotions，
largelyconflicting，beinganeventualrotationofthemass。Itmustnot，
however，beassumedthatthiswillnecessarilybetherotationofasolitary
aggregate。ThegreatnebulainAndromedadoesnotappearonthewaytoform
asinglebody;andisanadvancedspiralofwhichthethatinCanesVenatici
outerpartshaveatangentialmotiontoogreattopermitoftheirbeingdrawn
intothecentre。Rathertheapparentimplicationofthestructureisthat
therewillbeformedaclusterofmassesrevolvingroundacommoncentre
ofgravity。Suchcases，joinedwiththoseoftheannularnebula，suggest
thatoftentheprocessesofintegrationresultincompoundstructures，various
intheirkinds，whileinothercases，andperhapsmostfrequently，singlemassesofrotatingnebulousmatterareformed。Ignoringallsuchpossibilitiesandprobabilities，however，andlimiting
ourattentiontothatformofthenebularhypothesiswhichregardsthesolar
systemashavingresultedfromarotatingspheroidofdiffusedsubstance;
letusconsiderwhatconsequencetheinstabilityofthehomogeneousnecessitates。
Beingoblateinfigure，unlikeinthedensitiesofitscentreandsurface，
unlikeintheirtemperatures，andprobablyunlikeintheangularvelocities
ofitsparts，suchamasscannotbecalledhomogeneous;andanyfurtherchanges
exhibitedbyitcanillustratethegenerallaw，onlyasbeingchangesfrom
amorehomogeneoustoalesshomogeneousstate。Justnotingthatoneofthese
changesistheincreasingoblatenessofform，letusgoontoobservethose
whicharetobefoundinthetransformationsofsuchofitspartsasare
atfirsthomogeneouswithinthemselves。Ifweaccepttheconclusionthat
theequatorialportionofthisrotatingandcontractingspheroidwill，at
successivestages，haveacentrifugalforcegreatenoughtopreventnearer
approachtothecentreofrotation，andwillsobeleftbehind;weshall
find，inthefateofthedetachedring，anexemplificationoftheprinciple
wearefollowingout。Consistingofgaseousmattersucharing，evenifuniform
atthetimeofitsdetachment，couldnotcontinueso。Intheabsenceofequality
amongtheforces，internalandexternal，actingonit，theremustbeapoint
orpointsatwhichthecohesionofitspartswouldbelessthanelsewhere
——apointorpointsatwhichrupturewouldthereforetakeplace。Theoriginal
assumptionwasthattheringwouldruptureatoneplaceonly，andwouldthen
collapseonitself。Butthiswasamorethanquestionableassumption:such，
atleast，IknowtohavebeentheopinionofthelateSirJohnHerschel。
Sovastaring，consistingofmatterhavingsuchfeeblecohesion，mustbreak
upintomanyparts。Nevertheless，appealtoanotherhighauthority——the
lateSirG。B。Airy——yieldedverificationforthebeliefthattheultimate
resultwhichLaplacepredictedwouldtakeplace。Andhereisfurnisheda
furtherillustrationoftheinstabilityofthehomogeneous。Forevensupposing
themassesofnebulousmatterintowhichsucharingseparated，weresomuch
alikeintheirsizesanddistancesastoattractoneanotherwithexactly
equalforces（whichisinfinitelyimprobable）;yettheunequalactionsof
externaldisturbingforceswouldinevitablydestroytheirequilibrium——
therewouldbeoneormorepointsatwhichadjacentmasseswouldbeginto
partcompany。Separation，oncecommenced，wouldwithacceleratingspeedlead
toagroupingofthemasses。Alikeresultwouldeventuallytakeplacewiththegroupsthusformed;untiltheyatlengthaggregatedintoasinglemass。§151。Alreadysomanyreferenceshavebeenmadetotheformation
ofacrustovertheoriginallyincandescentEarth，thatitmaybethought
superfluousagaintonameit。Ithasnot，however，beenthusfarconsidered
inconnexionwiththegeneralprincipleunderdiscussion。Hereitmustbe
notedasanecessaryconsequenceoftheinstabilityofthehomogeneous。In
thiscoolingandsoldificationoftheEarth\'ssurface，wehaveoneofthe
simplest，aswellasoneofthemostimportant，instancesofthatchange
fromauniformtoamultiformstatewhichoccursinanymassthroughexposure
ofitscomponentpartstounlikeconditions。Tothedifferentiationofthe
Earth\'sexteriorfromitsinterior，thusbroughtabout，wemustaddoneof
themostconspicuousdifferentiationswhichtheexterioritselfafterwards
undergoes，asbeingsimilarlybroughtabout。Weretheforcestowhichthe
surfaceoftheEarthissubject，alikeinalldirections，therewouldbe
noreasonwhycertainofitspartsshouldbecomepermanentlyunliketherest。
Butbeingunequallyexposedtothechiefexternalcentreofforce——the
Sun——itsmaindivisionsbecomeunequallymodified。Whilethecrustthickens
andcools，therearisesthatcontrast，nowsodecided，betweenthepolarandequatorialregions。AlongwiththesemostmarkedphysicaldifferentiationsoftheEarth，there
havebeengoingonnumerouschemicaldifferentiations，admittingofsimilar
interpretation。Leavingasideallspeculationsconcerningtheoriginofthe
so—calledsimplesubstances，itwillsufficetoshowhowinplaceofthat
comparativehomogeneityoftheEarth\'scrust，chemicallyconsidered，which
musthaveexistedwhenitstemperaturewashigh，therehasarisen，during
itscooling，anincreasingchemicalheterogeneity。Letuscontemplatethis
changesomewhatindetail。Atanextremeheatthebodieswecallelements
cannotcombine。Evenundersuchheatascanbegeneratedartificially，some
verystrongaffinitiesyield;andthegreatmajorityofchemicalcompounds
aredecomposedatmuchlowertemperatures。Probably，therefore，whenthe
Earthwasinitsfirststateofincandescence，therewerenochemicalcombinations。
Butwithoutdrawingthisinference，letussetoutwiththeunquestionable
factthatthecompoundswhichcanexistatthehighesttemperatures，and
whichmustthereforehavebeenthefirstformedastheEarthcooled，are
thoseofthesimplestconstitutions。Theprotoxides（includingunderthat
headthealkalies，earths，etc。）are，asaclass，themoststablecompounds
known——theleastchangeablebyheat。These，consistingseverallyofone
atomofeachcomponentelement，arebutonedegreelesshomogeneousthan
theelementsthemselves。Moreheterogeneousthanthese，moredecomposable
byheat，andthereforelaterintheEarth\'shistory，arethedeutoxides，
tritoxides，peroxides，etc。;inwhichtwo，three，four，ormoreatomsof
oxygenareunitedwithoneatomofmetalorotherbase。Stilllessableto
resistheatarethesalts，whichpresentuswithcompoundatomseachmade
upoffive，six，seven，eight，ten，twelve，ormoreatoms，ofthreeormore
kinds。Thentherearethehydratedsaltsofayetgreaterheterogeneity，
whichundergopartialdecompositionatmuchlowertemperatures。Afterthem
comethefurther—complicatedsupersaltsanddoublesalts，havingastability
againdecreased;andsothroughout。Aftermakingafewunimportantqualifications
demandedbypeculiaraffinities，itmaybeassertedasagenerallawofthese
inorganiccombinationsthat，otherthingsequal，thestabilitydecreases
asthecomplexityincreases。Whenwepasstothecompoundswhichmakeup
organicbodes，wefindthisgenerallawfurtherexemplified;wefindmuch
greatercomplexityandmuchlessstability。Amoleculeofalbumen，forinstance，
consistsofmorethantwohundredultimateunitsoffivedifferentkinds。
Accordingtothelatestanalysesitcontainsineachmolecule，72ofcarbon，
18ofnitrogen，1ofsulphur，112ofhydrogen，and22ofoxygen——inall，
225atoms;or，morestrictlyspeaking，equivalents。Andthissubstanceis
sounstableastodecomposeatquitemoderatetemperatures;asthattowhich
theoutsideofajointofroastingmeatisexposed。Possiblyitwillbeobjected
thatsomeinorganiccompounds，asphosphurettedhydrogen，chlorideofnitrogen，
andthenitrogen—explosivesingeneral，aremoredecomposablethanmostorganic
compounds。Thisistrue。Buttheadmissionmaybemadewithoutdamageto
theargument。Thepropositionisnotthatallsimplecombinationsaremore
stablethanallcomplexones。Toestablishourinferenceitisnecessary
onlytoshowthat，asanaveragefact，thesimplecombinationscanexist
atahighertemperaturethanthecomplexones。Andthisisbeyondquestion。
ThusitismanifestthatthepresentchemicalheterogeneityoftheEarth\'s
surface，andofthebodiesuponit，hasarisenbydegreesasthedecrease
ofheathaspermitted;andthatithasshownitselfinthreeforms:——first，
inthemultiplicationofchemicalcompounds;second，inthegreaternumber
ofdifferentelementscontainedinthemoremodernofthesecompounds;and
third，inthehigherandmorevariedmultiplesinwhichthesemorenumerouselementscombine。Withoutspecifyingthem，itwillsufficejusttonamethemeteorologic
processeseventuallysetupintheEarth\'satmosphere，asfurtherillustrating
theallegedlaw。Theyequallydisplaythatdestructionofahomogeneousstatewhichresultsfromunequalexposuretoincidentforces。§152。Takeamassofunorganizedbutorganizablematter——either
thebodyofoneofthelowestlivingforms，orthegermofoneofthehigher:
bothcomparativelyhomogeneous。Consideritscircumstances。Eitheritis
immersedinwaterorairoriscontainedwithinaparentorganism。Wherever
placed，however，itsouterandinnerpartsstanddifferentlyrelatedtosurrounding
agencies——nutriment，oxygen，andthevariousstimuli。Butthisisnotall。
Whetheritliesquiescentatthebottomofapoolorontheleafofaplant;
whetheritmovesthroughthewaterpreservingsomedefiniteattitude;or
whetheritisintheinsideofanadult;itequallyhappensthatcertain
partsofitssurfacearemoreexposedtosurroundingagenciesthanother
parts——insomecasesmoreexposedtolight，heat，oroxygen，andinother
casestothematernaltissuesandtheircontents。Hencemustfollowtheloss
ofitsoriginalequilibrium。Thismaytakeplaceinoneoftwoways。Either
thedisturbingforcesmaybesuchastoover—balancetheaffinitiesofthe
organicelements，andthereresultsdecomposition;or，asordinarilyoccurs，
suchchangesareinducedasdonotdestroytheorganiccompoundsbutonly
modifythem:thepartsmostexposedtothemodifyingforcesbeingmostmodified。Toelucidatethisafewcasesarerequired。Observefirstwhatappeartobeexceptions。Certainminuteanimalforms
presenteithernoappreciabledifferentiationsordifferentiationssoobscure
astobemadeoutwithgreatdifficulty。Concerningtheseforms，however，
notethefactthatinallcases（somesayinnearlyall）thepresenceof
anucleusshowsconformitytothegenerallaw，sinceitimpliesacontrast
betweentheinnermostprotoplasmandtheprotoplasmsurroundingit。Butlet
uspassontotheseeminglyexceptionalfactthatthesurroundingprotoplasm
doesnotexhibitthekindofdifferentiationbetweeninnerandouterabove
alleged。Tothisobjection，thereimmediatelypresentsitselftheanswer
thatthishomogeneousbody—substancedoesnotbecomeheterogeneousbecause
itspartsarenotsubjecttoanypermanentheterogeneityofconditions:it
hasnofixedsurface。Inallmembersofthelowestgroup，Proteomyxa，the
protoplasmcontinuallyprotrudesitself，nowinthickernowinthinnerprocesses
——pseudopodia;provedtohavenolimitingmembranesbyoftencoalescing。
These，whentheytouchfragmentsofnutriment，contractanddrawtheminto
themassofthebody;sothatwhatwasjustbeforeexternalnowbecomesinternal。
Thustherearenofixedrelationsofpartsandthereforenodifferentiations。
AnditisnoteworthythatincertainoftheAmoebae，lessexcursivethan
othersofthetypeinthemovementsoftheirsubstance，weseeanincipient
differentiation:sometimesthereisaninvestingfilm，"delicateand
evanescent，"implyingthatanouterpartwhichisforashorttimestationary，
beginstobedifferentiated。Perceiving，then，thatthisapparentexception
isinfactaverification，wegoontoobservethatpermanentrelationsof
innerandouterarefollowedbypermanentdifferentiations。Elsewhere（Essays，
i，439）IhavequotedfromSachsvariousproofsthataportionofprotoplasm，
whethernormallydetached，asinaspore，orabnormallydetached，asbya
rupture，forthwithbecomingglobular，atonceacquiresasurfacedenserthan
theinterior;andKernersimilarlydescribestheprotoplasmofazoospore
as"fixingitselfandputtingonadelicatecell—wall。"Thesecases，
joinedwiththoseofvariousProtozoawhich，ceasingtheiractivechanges
ofform，passintoarestingstageandbecomeenclosedinacyst，andjoined
withthecasesofProtophyta，likeSphaerellanivalisor"RedSnow，"
which，initsyoungstageovoid，flagellate，locomotive，andsecretinga
skin，presentlypassesintoarestingstageandbecomessphericalandcovered
byasubstantialcell—membrane，yieldclearevidencethatintheselowest
typesthereisalapsefromamorehomogeneousstateintoalesshomogeneous
state。AndthroughoutthehigherProtozoaandProtophyta，theprimarycontrast
isbetweencell—membraneandcell—contents——betweenthepartexposedtoenvironingforcesandthepartshelteredfromthem。Thetransition——themostimportanttransitionwhichtheorganicworld
presents——betweenthesimpleformsaboveexemplifiedandthosecompound
formsinwhichanumberofsuchareunitedintoacolony，iswellseenin
certainminutealgae，PandorinaandEudorina:eachbeingaspherically—arranged
colonyofsixteenorthirty—twomembers。Inthisfirstadvancefromunicellular
typestomulticellulartypeswefindconformitytothegenerallawinso
farthatthehollowsphereconspicuouslydisplaystheprimarycontrastbetween
outerandinner;aprimitiveamorphousclusterhasundergoneamarkeddifferentiation
ofpartscorrespondingtothedifferenceofconditions。Stillmoreinstructive
istheevidencefurnishedbytypesslightlyinadvanceofthese——Pleodorina
andVolvox;thefirstconsistingofsome128cellsandthesecondof10，000
ormore。Hollowspheresliketheforegoing，theypresentincommonthesignificant
traitthat，revolving，astheydo，onaconstantaxisandmovingforward
approximatelyinthelineofthataxis，theirtwoendsareexposedtoslightly
differentconditions，andtheprimitivehomogeneityofthemembersofthe
colonyhas，inconsequence，lapsedintoappropriateheterogeneity。These
ciliatedalga—cells，whetherlivingsinglyorjoinedintogroups，severally
haveaminuteredspeckwhichisprovedtobesensitivetolight，andcauses
motiontowardsit。Nowinthesecompoundformsjustnamed，theeye—spots
aremoredevelopedinthosecellsformingtheanteriorpartofthespherical
colony—cellswhichalsocarryonmoreactivelythenutritivefunction;while
thosecellswhichformtheposteriorpartofthesphere，andcarryonthe
reproductivefunction，havesmallereye—spots。Onpassingtotheanimalkingdom
（whichatitsrootissolittledifferentiatedfromthevegetalkingdomthat
thereareunsettleddisputesrespectingtheinclusionofthelowestforms
intheoneortheother）wemeetwithparallelillustrations。Thenucleated
cell，whichisthecommonstartingpointforallorganisms，animalandvegetal，
presentsusasbeforewiththeprimarycontrastbetweeninnerandouter。
