the unseen world and other essays-第4节

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different　from　what　they　are　in　our　own　system。　And　the　same　kind　of　inference　must　apply　to　all　the　matured　stars　which　we　see　in　the　heavens。

When　we　duly　take　all　these　things　into　the　account；　the　case　of　our　solar　system　will　appear　as　only　one　of　a　thousand　cases　of　evolution　and　dissolution　with　which　the　heavens　furnish　us。　Other　stars；　like　our　sun；　have　undoubtedly　started　as　vaporous　masses；　and　have　thrown　off　planets　in　contracting。　The　inference　may　seem　a　bold　one；　but　it　after　all　involves　no　other　assumption　than　that　of　the　continuity　of　natural　phenomena。　It　is　not　likely；　therefore；　that　the　solar　system　will　forever　be　left　to　itself。　Stars　which　strongly　gravitate　toward　each　other；　while　moving　through　a　perennially　resisting　medium；　must　in　time　be　drawn　together。　The　collision　of　our　extinct　sun　with　one　of　the　Pleiades；　after　this　manner；　would　very　likely　suffice　to　generate　even　a　grander　nebula　than　the　one　with　which　we　started。　Possibly　the　entire　galactic　system　may；　in　an　inconceivably　remote　future；　remodel　itself　in　this　way；　and　possibly　the　nebula　from　which　our　own　group　of　planets　has　been　formed　may　have　owed　its　origin　to　the　disintegration　of　systems　which　had　accomplished　their　career　in　the　depths　of　the　bygone　eternity。

When　the　problem　is　extended　to　these　huge　dimensions；　the　prospect　of　an　ultimate　cessation　of　cosmical　work　is　indefinitely　postponed；　but　at　the　same　time　it　becomes　impossible　for　us　to　deal　very　securely　with　the　questions　we　have　raised。　The　magnitudes　and　periods　we　have　introduced　are　so　nearly　infinite　as　to　baffle　speculation　itself：　One　point；　however；　we　seem　dimly　to　discern。　Supposing　the　stellar　universe　not　to　be　absolutely　infinite　in　extent；　we　may　hold　that　the　day　of　doom；　so　often　postponed；　must　come　at　last。　The　concentration　of　matter　and　dissipation　of　energy；　so　often　checked；　must　in　the　end　prevail；　so　that；　as　the　final　outcome　of　things；　the　entire　universe　will　be　reduced　to　a　single　enormous　ball；　dead　and　frozen；　solid　and　black；　its　potential　energy　of　motion　having　been　all　transformed　into　heat　and　radiated　away。　Such　a　conclusion　has　been　suggested　by　Sir　William　Thomson；　and　it　is　quite　forcibly　stated　by　the　authors　of　〃The　Unseen　Universe。〃　They　remind　us　that　〃if　there　be　any　one　form　of　energy　less　readily　or　less　completely　transformable　than　the　others；　and　if　transformations　constantly　go　on；　more　and　more　of　the　whole　energy　of　the　universe　will　inevitably　sink　into　this　lower　grade　as　time　advances。〃　Now　radiant　heat；　as　we　have　seen；　is　such　a　lower　grade　of　energy。　〃At　each　transformation　of　heat…energy　into　work；　a　large　portion　is　degraded；　while　only　a　small　portion　is　transformed　into　work。　So　that　while　it　is　very　easy　to　change　all　of　our　mechanical　or　useful　energy　into　heat；　it　is　only　possible　to　transform　a　portion　of　this　heat…energy　back　again　into　work。　After　each　change；　too；　the　heat　becomes　more　and　more　dissipated　or　degraded；　and　less　and　less　available　for　any　future　transformation。　In　other　words；〃　our　authors　continue；　〃the　tendency　of　heat　is　towards　equalization；　heat　is　par　excellence　the　communist　of　our　universe；　and　it　will　no　doubt　ultimately　bring　the　system　to　an　end。　。。。。　It　is　absolutely　certain　that　life；　so　far　as　it　is　physical；　depends　essentially　upon　transformations　of　energy；　it　is　also　absolutely　certain　that　age　after　age　the　possibility　of　such　transformations　is　becoming　less　and　less；　and；　so　far　as　we　yet　know；　the　final　state　of　the　present　universe　must　be　an　aggregation　（into　one　mass）　of　all　the　matter　it　contains；　i。　e。　the　potential　energy　gone；　and　a　practically　useless　state　of　kinetic　energy；　i。　e。　uniform　temperature　throughout　that　mass。〃　Thus　our　authors　conclude　that　the　visible　universe　began　in　time　and　will　in　time　come　to　an　end；　and　they　add　that　under　the　physical　conditions　of　such　a　universe　〃immortality　is　impossible。〃

Concerning　the　latter　inference　we　shall　by　and　by　have　something　to　say。　Meanwhile　this　whole　speculation　as　to　the　final　cessation　of　cosmical　work　seems　to　meas　it　does　to　my　friend；　Professor　Clifford＇3＇by　no　means　trustworthy。　The　conditions　of　the　problem　so　far　transcend　our　grasp　that　any　such　speculation　must　remain　an　unverifiable　guess。　I　do　not　go　with　Professor　Clifford　in　doubting　whether　the　laws　of　mechanics　are　absolutely　the　same　throughout　eternity；　I　cannot　quite　reconcile　such　a　doubt　with　faith　in　the　principle　of　continuity。　But　it　does　seem　to　me　needful；　before　we　conclude　that　radiated　energy　is　absolutely　and　forever　wasted；　that　we　should　find　out　what　becomes　of　it。　What　we　call　radiant　heat　is　simply　transverse　wave…motion；　propagated　with　enormous　velocity　through　an　ocean　of　subtle　ethereal　matter　which　bathes　the　atoms　of　all　visible　or　palpable　bodies　and　fills　the　whole　of　space；　extending　beyond　the　remotest　star　which　the　telescope　can　reach。　Whether　there　are　any　bounds　at　all　to　this　ethereal　ocean；　or　whether　it　is　as　infinite　as　space　itself；　we　cannot　surmise。　If　it　be　limited；　the　possible　dispersion　of　radiant　energy　is　limited　by　its　extent。　Heat　and　light　cannot　travel　through　emptiness。　If　the　ether　is　bounded　by　surrounding　emptiness；　then　a　ray　of　heat；　on　arriving　at　this　limiting　emptiness；　would　be　reflected　back　as　surely　as　a　ball　is　sent　back　when　thrown　against　a　solid　wall。　If　this　be　the　case；　it　will　not　affect　our　conclusions　concerning　such　a　tiny　region　of　space　as　is　occupied　by　the　solar　system；　but　it　will　seriously　modify　Sir　William　Thomson's　suggestion　as　to　the　fate　of　the　universe　as　a　whole。　The　radiance　thrown　away　by　the　sun　is　indeed　lost　so　far　as　the　future　of　our　system　is　concerned；　but　not　a　single　unit　of　it　is　lost　from　the　universe。　Sooner　or　later；　reflected　back　in　all　directions；　it　must　do　work　in　one　quarter　or　another；　so　that　ultimate　stagnation　be　comes　impossible。　It　is　true　that　no　such　return　of　radiant　energy　has　been　detected　in　our　corner　of　the　world；　but　we　have　not　yet　so　far　disentangled　all　the　force…relations　of　the　universe　that　we　are　entitled　to　regard　such　a　return　as　impossible。　This　is　one　way　of　escape　from　the　consummation　of　things　depicted　by　our　authors。　Another　way　of　escape　is　equally　available；　if　we　suppose　that　while　the　ether　is　without　bounds　the　stellar　universe　also　extends　to　infinity。　For　in　this　case　the　reproduction　of　nebulous　masses　fit　for　generating　new　systems　of　worlds　must　go　on　through　space　that　is　endless；　and　consequently　the　process　can　never　come　to　an　end　and　can　never　have　had　a　beginning。　We　have；　therefore；　three　alternatives：　either　the　visible　universe　is　finite；　while　the　ether　is　infinite；　or　both　are　finite；　or　both　are　infinite。　Only　on　the　first　supposition；　I　think；　do　we　get　a　universe　which　began　in　time　and　must　end　in　time。　Between　such　stupendous　alternatives　we　have　no　grounds　for　choosing。　But　it　would　seem　that　the　third；　whether　strictly　true　or　not；　best　represents　the　state　of　the　case　relatively　to　our　feeble　capacity　of　comprehension。　Whether　absolutely　infinite　or　not；　the　dimensions　of　the　universe　must　be　taken　as　practically　infinite；　so　far　as　human　thought　is　concerned。　They　immeasurably　transcend　the　capabilities　of　any　gauge　we　can　bring　to　bear　on　them。　Accordingly　all　that　we　are　really　entitled　to　hold；　as　the　outcome　of　sound　speculation；　is　the　conception　of　innumerable　systems　of　worlds　concentrating　out　of　nebulous　masses；　and　then　rushing　together　and　dissolving　into　similar　masses；　as　bubbles　unite　and　break　upnow　here；　now　therein　their　play　on　the　surface　of　a　pool；　and　to　this　tremendous　series　of　events　we　can　assign　neither　a　beginning　nor　an　end。

＇3＇　Fortnightly　Review；　April；　1875。


We　must　now　make　some　more　explicit　mention　of　the　ether　which　carries　through　space　the　rays　of　heat　and　light。　In　closest　connection　with　the　visible　stellar　universe；　the　vicissitudes　of　which　we　have　briefly　traced；　the　all…pervading　ether　constitutes　a　sort　of　unseen　world　remarkable　enough　from　any　point　of　view；　but　to　which　the　theory　of　our　authors　ascribes　capacities　hitherto　unsuspected　by　science。　The　very　existence　of　an　ocean　of　ether　enveloping　the　molecules　of　material　bodies　has　been　doubted　or　denied　by　many　eminent　physicists；　though　of　course　none　have　called　in　question　the　necessity　for　some　interstellar　medium　for　the　transmission　of　thermal　and　luminous　vibrations。　This　scepticism　has　been；　I　think；　partially　justified　by　the　many　difficulties　encompassing　the　conception；　into　which；　however；　we　need　not　here　enter。　That　light　and　heat　cannot　be　conveyed　by　any　of　the　ordinary　sensible　forms　of　matter　is　unquestionable。　None　of　the　forms　of　sensible　matter　can　be　imagined　sufficiently　elastic　to　propagate　wave…motion　at　the　rate　of　one　hundred　and　eighty…eight　thousand　miles　per　second。　Yet　a　ray　of　light　is　a　series　of　waves；　and　implies　some　substance　in　which　the　waves　occur。　The　substance　required　is　one　which　seems　to　possess　strangely　contradictory　properties。　It　is　commonly　regarded　as　an　〃ether〃　or　infinitely　rare　substance；　but；　as　Professor　Jevons　observes；　we　might　as　well　regard　it　as　an　infinitely　solid　〃adamant。〃　〃Sir　John　Herschel　ha