the unseen world and other essays-第2节

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ing　a　haphazard　mental　proceeding　that　it　is　perhaps　hardly　fair　to　classify　it　with　guesses。　It　is　lifted　out　of　the　plane　of　guesswork；　in　so　far　as　it　has　acquired　the　character　of　inevitable　inference　from　that　which　now　is　to　that　which　has　been　or　will　be。　Instead　of　the　innumerable　particular　assumptions　which　were　once　admitted　into　cosmic　philosophy；　we　are　now　reduced　to　the　one　universal　assumption　which　has　been　variously　described　as　the　〃principle　of　continuity；〃　the　〃uniformity　of　nature；〃　the　〃persistence　of　force；〃　or　the　〃law　of　causation；〃　and　which　has　been　variously　explained　as　a　necessary　datum　for　scientific　thinking　or　as　a　net　result　of　all　induction。　I　am　not　unwilling；　however；　to　adopt　the　language　of　a　book　which　has　furnished　the　occasion　for　the　present　discussion；　and　to　say　that　this　grand　assumption　is　a　supreme　act　of　faith；　the　definite　expression　of　a　trust　that　the　infinite　Sustainer　of　the　universe　〃will　not　put　us　to　permanent　intellectual　confusion。〃　For　in　this　mode　of　statement　the　harmony　between　the　scientific　and　the　religious　points　of　view　is　well　brought　out。　It　is　as　affording　the　only　outlet　from　permanent　intellectual　confusion　that　inquirers　have　been　driven　to　appeal　to　the　principle　of　continuity；　and　it　is　by　unswerving　reliance　upon　this　principle　that　we　have　obtained　such　insight　into　the　past；　present；　and　future　of　the　world　as　we　now　possess。

The　work　just　mentioned＇1＇　is　especially　interesting　as　an　attempt　to　bring　the　probable　destiny　of　the　human　soul　into　connection　with　the　modern　theories　which　explain　the　past　and　future　career　of　the　physical　universe　in　accordance　with　the　principle　of　continuity。　Its　authorship　is　as　yet　unknown；　but　it　is　believed　to　be　the　joint　production　of　two　of　the　most　eminent　physicists　in　Great　Britain；　and　certainly　the　accurate　knowledge　and　the　ingenuity　and　subtlety　of　thought　displayed　in　it　are　such　as　to　lend　great　probability　to　this　conjecture。　Some　account　of　the　argument　it　contains　may　well　precede　the　suggestions　presently　to　be　set　forth　concerning　the　Unseen　World；　and　we　shall　find　it　most　convenient　to　begin；　like　our　authors；　with　a　brief　statement　of　what　the　principle　of　continuity　teaches　as　to　the　proximate　beginning　and　end　of　the　visible　universe。　I　shall　in　the　main　set　down　only　results；　having　elsewhere＇2＇　given　a　simple　exposition　of　the　arguments　upon　which　these　results　are　founded。

＇1＇　The　Unseen　Universe；　or；　Physical　Speculations　on　a　Future　State。　＇Attributed　to　Professors　TAIT　and　BALFOUR　STEWART。＇　New　York：　Macmillan　&　Co。　1875。　8vo。　pp。　212。

＇2＇　Outlines　of　Cosmic　Philosophy；　based　on　the　Doctrine　of　Evolution。　Boston：　J。　R。　Osgood　&　Co。　1875。　2　vols。　8vo。


The　first　great　cosmological　speculation　which　has　been　raised　quite　above　the　plane　of　guesswork　by　making　no　other　assumption　than　that　of　the　uniformity　of　nature；　is　the　well…known　Nebular　Hypothesis。　Every　astronomer　knows　that　the　earth；　like　all　other　cosmical　bodies　which　are　flattened　at　the　poles；　was　formerly　a　mass　of　fluid；　and　consequently　filled　a　much　larger　space　than　at　present。　It　is　further　agreed；　on　all　hands；　that　the　sun　is　a　contracting　body；　since　there　is　no　other　possible　way　of　accounting　for　the　enormous　quantity　of　heat　which　he　generates。　The　so…called　primeval　nebula　follows　as　a　necessary　inference　from　these　facts。　There　was　once　a　time　when　the　earth　was　distended　on　all　sides　away　out　to　the　moon　and　beyond　it；　so　that　the　matter　now　contained　in　the　moon　was　then　a　part　of　our　equatorial　zone。　And　at　a　still　remoter　date　in　the　past；　the　mass　of　the　sun　was　diffused　in　every　direction　beyond　the　orbit　of　Neptune；　and　no　planet　had　an　individual　existence；　for　all　were　indistinguishable　parts　of　the　solar　mass。　When　the　great　mass　of　the　sun；　increased　by　the　relatively　small　mass　of　all　the　planets　put　together；　was　spread　out　in　this　way；　it　was　a　rare　vapour　or　gas。　At　the　period　where　the　question　is　taken　up　in　Laplace's　treatment　of　the　nebular　theory；　the　shape　of　this　mass　is　regarded　as　spheroidal；　but　at　an　earlier　period　its　shape　may　well　have　been　as　irregular　as　that　of　any　of　the　nebulae　which　we　now　see　in　distant　parts　of　the　heavens；　for；　whatever　its　primitive　shape；　the　equalization　of　its　rotation　would　in　time　make　it　spheroidal。　That　the　QUANTITY　of　rotation　was　the　same　then　as　now　is　unquestionable；　for　no　system　of　particles；　great　or　small；　can　acquire　or　lose　rotation　by　any　action　going　on　within　itself；　any　more　than　a　man　could　pick　himself　up　by　his　waistband　and　lift　himself　over　a　stone　wale　So　that　the　primitive　rotating　spheroidal　solar　nebula　is　not　a　matter　of　assumption；　but　is　just　what　must　once　have　existed；　provided　there　has　been　no　breach　of　continuity　in　nature's　operations。　Now　proceeding　to　reason　back　from　the　past　to　the　present；　it　has　been　shown　that　the　abandonment　of　successive　equatorial　belts　by　the　contracting　solar　mass　must　have　ensued　in　accordance　with　known　mechanical　laws；　and　in　similar　wise；　under　ordinary　circumstances。　each　belt　must　have　parted　into　fragments；　and　the　fragments　chasing　each　other　around　the　same　orbit；　must　have　at　last　coalesced　into　a　spheroidal　planet。　Not　only　this；　but　it　has　also　been　shown　that　as　the　result　of　such　a　process　the　relative　sizes　of　the　planets　would　be　likely　to　take　the　order　which　they　now　follow；　that　the　ring　immediately　succeeding　that　of　Jupiter　would　be　likely　to　abort　and　produce　a　great　number　of　tiny　planets　instead　of　one　good…sized　one；　that　the　outer　planets　would　be　likely　to　have　many　moons；　and　that　Saturn；　besides　having　the　greatest　number　of　moons；　would　be　likely　to　retain　some　of　his　inner　rings　unbroken；　that　the　earth　would　be　likely　to　have　a　long　day　and　Jupiter　a　short　one；　that　the　extreme　outer　planets　would　be　not　unlikely　to　rotate　in　a　retrograde　direction；　and　so　on；　through　a　long　list　of　interesting　and　striking　details。　Not　only；　therefore；　are　we　driven　to　the　inference　that　our　solar　system　was　once　a　vaporous　nebula；　but　we　find　that　the　mere　contraction　of　such　a　nebula；　under　the　influence　of　the　enormous　mutual　gravitation　of　its　particles；　carries　with　it　the　explanation　of　both　the　more　general　and　the　more　particular　features　of　the　present　system。　So　that　we　may　fairly　regard　this　stupendous　process　as　veritable　matter　of　history；　while　we　proceed　to　study　it　under　some　further　aspects　and　to　consider　what　consequences　are　likely　to　follow。

Our　attention　should　first　be　directed　to　the　enormous　waste　of　energy　which　has　accompanied　this　contraction　of　the　solar　nebula。　The　first　result　of　such　a　contraction　is　the　generation　of　a　great　quantity　of　heat；　and　when　the　heat　thus　generated　has　been　lost　by　radiation　into　surrounding　space　it　becomes　possible　for　the　contraction　to　continue。　Thus；　as　concentration　goes　on；　heat　is　incessantly　generated　and　incessantly　dissipated。　How　long　this　process　is　to　endure　depends　chiefly　on　the　size　of　the　contracting　mass；　as　small　bodies　radiate　heat　much　faster　than

large　ones。　The　moon　seems　to　be　already　thoroughly　refrigerated；　while　Jupiter　and　Saturn　are　very　much　hotter　than　the　earth；　as　is　shown　by　the　tremendous　atmospheric　phenomena　which　occur　on　their　surfaces。　The　sun；　again；　generates　heat　so　rapidly；　owing　to　his　great　energy　of　contraction；　and　loses　it　so　slowly；　owing　to　his　great　size；　that　his　surface　is　always　kept　in　a　state　of　incandescence。　His　surface…temperature　is　estimated　at　some　three　million　degrees　of　Fahrenheit；　and　a　diminution　of　his　diameter　far　too　small　to　be　detected　by　the　finest　existing　instruments　would　suffice　to　maintain　the　present　supply　of　heat　for　more　than　fifty　centuries。　These　facts　point　to　a　very　long　future　during　which　the　sun　will　continue　to　warm　the　earth　and　its　companion　planets；　but　at　the　same　time　they　carry　on　their　face　the　story　of　inevitable　ultimate　doom。　If　things　continue　to　go　on　as　they　have　all　along　gone　on；　the　sun　must　by　and　by　grow　black　and　cold；　and　all　life　whatever　throughout　the　solar　system　must　come　to　an　end。　Long　before　this　consummation；　however；　life　will　probably　have　become　extinct　through　the　refrigeration　of　each　of　the　planets　into　a　state　like　the　present　state　of　the　moon；　in　which　the　atmosphere　and　oceans　have　disappeared　from　the　surface。　No　doubt　the　sun　will　continue　to　give　out　heat　a　long　time　after　heat　has　ceased　to　be　needed　for　the　support　of　living　organisms。　For　the　final　refrigeration　of　the　sun　will　long　be　postponed　by　the　fate　of　the　planets　themselves。　The　separation　of　the　planets　from　their　parent　solar　mass　seems　to　be　after　all　but　a　temporary　separation。　So　nicely　balanced　are　they　now　in　their　orbits　that　they　may　well　seem　capable　of　rolling　on　in　their　present　courses　forever。　But　this　is　not　the　case。　Two　sets　of　circumstances　are　all　the　while　striving；　the　one　to　drive　the　planets　farther　away　from　the　sun；　the　other　to　draw　them　all　into　it。　On　the　one　hand；　every　body　in　our　system　which　contains　fluid　matter　has　tides　raised　upon　its　surface　by　the　attraction　of　neighbouring　bodies。　All　the　planets　raise　tides　upon　the　surface　of　the　sun　and　the　periodicity　of　sun…spots　（or　sola