the unseen world and other essays-第5节

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　Jevons　observes；　we　might　as　well　regard　it　as　an　infinitely　solid　〃adamant。〃　〃Sir　John　Herschel　has　calculated　the　amount　of　force　which　may　be　supposed；　according　to　the　undulatory　theory　of　light；　to　be　exerted　at　each　point　in　space；　and　finds　it　to　be　1；148；000；000；000　times　the　elastic　force　of　ordinary　air　at　the　earth's　surface；　so　that　the　pressure　of　the　ether　upon　a　square　inch　of　surface　must　be　about　17；000；000；000；000；　or　seventeen　billions　of　pounds。〃＇4＇　Yet　at　the　same　time　the　resistance　offered　by　the　ether　to　the　planetary　motions　is　too　minute　to　be　appreciable。　〃All　our　ordinary　notions；〃　says　Professor　Jevons；　〃must　be　laid　aside　in　contemplating　such　an　hypothesis；　yet　＇it　is＇　no　more　than　the　observed　phenomena　of　light　and　heat　force　us　to　accept。　We　cannot　deny　even　the　strange　suggestion　of　Dr。　Young；　that　there　may　be　independent　worlds；　some　possibly　existing　in　different　parts　of　space；　but　others　perhaps　pervading　each　other；　unseen　and　unknown；　in　the　same　space。　For　if　we　are　bound　to　admit　the　conception　of　this　adamantine　firmament；　it　is　equally　easy　to　admit　a　plurality　of　such。〃

＇4＇　Jevons's　Principles　of　Science；　Vol。　II。　p。　145。　The　figures；　which　in　the　English　system　of　numeration　read　as　seventeen　billions；　would　in　the　American　system　read　as　seventeen　trillions。


The　ether；　therefore；　is　unlike　any　of　the　forms　of　matter　which　we　can　weigh　and　measure。　In　some　respects　it　resembles　a　fluid；　in　some　respects　a　solid。　It　is　both　hard　and　elastic　to　an　almost　inconceivable　degree。　It　fills　all　material　bodies　like　a　sea　in　which　the　atoms　of　the　material　bodies　are　as　islands；　and　it　occupies　the　whole　of　what　we　call　empty　space。　It　is　so　sensitive　that　a　disturbance　in　any　part　of　it　causes　a　〃tremour　which　is　felt　on　the　surface　of　countless　worlds。〃　Our　old　experiences　of　matter　give　us　no　account　of　any　substance　like　this；　yet　the　undulatory　theory　of　light　obliges　us　to　admit　such　a　substance；　and　that　theory　is　as　well　established　as　the　theory　of　gravitation。　Obviously　we　have　here　an　enlargement　of　our　experience　of　matter。　The　analysis　of　the　phenomena　of　light　and　radiant　heat　has　brought　us　into　mental　relations　with　matter　in　a　different　state　from　any　in　which　we　previously　knew　it。　For　the　supposition　that　the　ether　may　be　something　essentially　different　from　matter　is　contradicted　by　all　the　terms　we　have　used　in　describing　it。　Strange　and　contradictory　as　its　properties　may　seem；　are　they　any　more　strange　than　the　properties　of　a　gas　would　seem　if　we　were　for　the　first　time　to　discover　a　gas　after　heretofore　knowing　nothing　but　solids　and　liquids？　I　think　not；　and　the　conclusion　implied　by　our　authors　seems　to　me　eminently　probable；　that　in　the　so…called　ether　we　have　simply　a　state　of　matter　more　primitive　than　what　we　know　as　the　gaseous　state。　Indeed；　the　conceptions　of　matter　now　current；　and　inherited　from　barbarous　ages；　are　likely　enough　to　be　crude　in　the　extreme。　It　is　not　strange　that　the　study　of　such　subtle　agencies　as　heat　and　light　should　oblige　us　to　modify　them；　and　it　will　not　be　strange　if　the　study　of　electricity　should　entail　still　further　revision　of　our　ideas。

We　are　now　brought　to　one　of　the　profoundest　speculations　of　modern　times；　the　vortex…atom　theory　of　Helmholtz　and　Thomson；　in　which　the　evolution　of　ordinary　matter　from　ether　is　plainly　indicated。　The　reader　first　needs　to　know　what　vortex…motion　is；　and　this　has　been　so　beautifully　explained　by　Professor　Clifford；　that　I　quote　his　description　entire：　〃Imagine　a　ring　of　india…rubber；　made　by　joining　together　the　ends　of　a　cylindrical　piece　（like　a　lead…pencil　before　it　is　cut）；　to　be　put　upon　a　round　stick　which　it　will　just　fit　with　a　little　stretching。　Let　the　stick　be　now　pulled　through　the　ring　while　the　latter　is　kept　in　its　place　by　being　pulled　the　other　way　on　the　outside。　The　india…rubber　has　then　what　is　called　vortex…motion。　Before　the　ends　were　joined　together；　while　it　was　straight；　it　might　have　been　made　to　turn　around　without　changing　position；　by　rolling　it　between　the　hands。　Just　the　same　motion　of　rotation　it　has　on　the　stick；　only　that　the　ends　are　now　joined　together。　All　the　inside　surface　of　the　ring　is　going　one　way；　namely；　the　way　the　stick　is　pulled；　and　all　the　outside　is　going　the　other　way。　Such　a　vortex…ring　is　made　by　the　smoker　who　purses　his　lips　into　a　round　hole　and　sends　out　a　puff　of　smoke。　The　outside　of　the　ring　is　kept　back　by　the　friction　of　his　lips　while　the　inside　is　going　forwards；　thus　a　rotation　is　set　up　all　round　the　smoke…ring　as　it　travels　out　into　the　air。〃　In　these　cases；　and　in　others　as　we　commonly　find　it；　vortex…motion　owes　its　origin　to　friction　and　is　after　a　while　brought　to　an　end　by　friction。　But　in　1858　the　equations　of　motion　of　an　incompressible　frictionless　fluid　were　first　successfully　solved　by　Helmholtz；　and　among　other　things　he　proved　that；　though　vortex…motion　could　not　be　originated　in　such　a　fluid；　yet　supposing　it　once　to　exist；　it　would　exist　to　all　eternity　and　could　not　be　diminished　by　any　mechanical　action　whatever。　A　vortex…ring；　for　example；　in　such　a　fluid；　would　forever　preserve　its　own　rotation；　and　would　thus　forever　retain　its　peculiar　individuality；　being；　as　it　were；　marked　off　from　its　neighbour　vortex…rings。　Upon　this　mechanical　truth　Sir　William　Thomson　based　his　wonderfully　suggestive　theory　of　the　constitution　of　matter。　That　which　is　permanent　or　indestructible　in　matter　is　the　ultimate　homogeneous　atom；　and　this　is　probably　all　that　is　permanent；　since　chemists　now　almost　unanimously　hold　that　so…called　elementary　molecules　are　not　really　simple；　but　owe　their　sensible　differences　to　the　various　groupings　of　an　ultimate　atom　which　is　alike　for　all。　Relatively　to　our　powers　of　comprehension　the　atom　endures　eternally；　that　is；　it　retains　forever　unalterable　its　definite　mass　and　its　definite　rate　of　vibration。　Now　this　is　just　what　a　vortex…ring　would　do　in　an　incompressible　frictionless　fluid。　Thus　the　startling　question　is　suggested；　Why　may　not　the　ultimate　atoms　of　matter　be　vortex…rings　forever　existing　in　such　a　frictionless　fluid　filling　the　whole　of　space？　Such　a　hypothesis　is　not　less　brilliant　than　Huyghens's　conjectural　identification　of　light　with　undulatory　motion；　and　it　is　moreover　a　legitimate　hypothesis；　since　it　can　be　brought　to　the　test　of　verification。　Sir　William　Thomson　has　shown　that　it　explains　a　great　many　of　the　physical　properties　of　matter：　it　remains　to　be　seen　whether　it　can　explain　them　all。

Of　course　the　ether　which　conveys　thermal　and　luminous　undulations　is　not　the　frictionless　fluid　postulated　by　Sir　William　Thomson。　The　most　conspicuous　property　of　the　ether　is　its　enormous　elasticity；　a　property　which　we　should　not　find　in　a　frictionless　fluid。　〃To　account　for　such　elasticity；〃　says　Professor　Clifford　（whose　exposition　of　the　subject　is　still　more　lucid　than　that　of　our　authors）；　〃it　has　to　be　supposed　that　even　where　there　are　no　material　molecules　the　universal　fluid　is　full　of　vortex…motion；　but　that　the　vortices　are　smaller　and　more　closely　packed　than　those　of　＇ordinary＇　matter；　forming　altogether　a　more　finely　grained　structure。　So　that　the　difference　between　matter　and　ether　is　reduced　to　a　mere　difference　in　the　size　and　arrangement　of　the　component　vortex…rings。　Now；　whatever　may　turn　out　to　be　the　ultimate　nature　of　the　ether　and　of　molecules；　we　know　that　to　some　extent　at　least　they　obey　the　same　dynamic　laws；　and　that　they　act　upon　one　another　in　accordance　with　these　laws。　Until；　therefore；　it　is　absolutely　disproved；　it　must　remain　the　simplest　and　most　probable　assumption　that　they　are　finally　made　of　the　same　stuff；　that　the　material　molecule　is　some　kind　of　knot　or　coagulation　of　ether。〃＇5＇

＇5＇　Fortnightly　Review；　June；　1875；　p。　784。


Another　interesting　consequence　of　Sir　William　Thomson's　pregnant　hypothesis　is　that　the　absolute　hardness　which　has　been　attributed　to　material　atoms　from　the　time　of　Lucretius　downward　may　be　dispensed　with。　Somewhat　in　the　same　way　that　a　loosely　suspended　chain　becomes　rigid　with　rapid　rotation；　the　hardness　and　elasticity　of　the　vortex…atom　are　explained　as　due　to　the　swift　rotary　motion　of　a　soft　and　yielding　fluid。　So　that　the　vortex…atom　is　really　indivisible；　not　by　reason　of　its　hardness　or　solidity；　but　by　reason　of　the　indestructibleness　of　its　motion。

Supposing；　now；　that　we　adopt　provisionally　the　vortex　theory；the　great　power　of　which　is　well　shown　by　the　consideration　just　mentioned；we　must　not　forget　that　it　is　absolutely　essential　to　the　indestructibleness　of　the　material　atom　that　the　universal　fluid　in　which　it　has　an　existence　as　a　vortex…ring　should　be　entirely　destitute　of　friction。　Once　admit　even　the　most　infinitesimal　amount　of　friction；　while　retaining　the　conception　of　vortex…motion　in　a　universal　fluid；　and　the　whole　case　is　so　far　altered　that　the　material　atom　can　no　longer　be　regarded　as　absolutely　indestructible；　but　only　as　indefinitely　enduring。　It　may　have　been　generated；　in　bygone　eternity；　by　a　natural　process　of　evolution；　and　in　future　eternity　may　come　to　an　end。　Relatively　to　our　powers　of　comprehension　the　practical　difference　is　perhaps　not　great。　Scient