the unseen world and other essays-第6章

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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。　Scientifically　speaking；　Helmholtz　and　Thomson　are　as　well　entitled　to　reason　upon　the　assumption　of　a　perfectly　frictionless　fluid　as　geometers　in　general　are　entitled　to　assume　perfect　lines　without　breadth　and　perfect　surfaces　without　thickness。　Perfect　lines　and　surfaces　do　not　exist　within　the　region　of　our　experience；　yet　the　conclusions　of　geometry　are　none　the　less　true　ideally；　though　in　any　particular　concrete　instance　they　are　only　approximately　realized。　Just　so　with　the　conception　of　a　frictionless　fluid。　So　far　as　experience　goes；　such　a　thing　has　no　more　real　existence　than　a　line　without　breadth；　and　hence　an　atomic　theory　based　upon　such　an　assumption　may　be　as　true　ideally　as　any　of　the　theorems　of　Euclid；　but　it　can　give　only　an　approximatively　true　account　of　the　actual　universe。　These　considerations　do　not　at　all　affect　the　scientific　value　of　the　theory；　but　they　will　modify　the　tenour　of　such　transcendental　inferences　as　may　be　drawn　from　it　regarding；　the　probable　origin　and　destiny　of　the　universe。

The　conclusions　reached　in　the　first　part　of　this　paper；　while　we　were　dealing　only　with　gross　visible　matter；　may　have　seemed　bold　enough；　but　they　are　far　surpassed　by　the　inference　which　our　authors　draw　from　the　vortex　theory　as　they　interpret　it。　Our　authors　exhibit　various　reasons；　more　or　less　sound；　for　attributing　to　the　primordial　fluid　some　slight　amount　of　friction；　and　in　support　of　this　view　they　adduce　Le　Sage's　explanation　of　gravitation　as　a　differential　result　of　pressure；　and　Struve's　theory　of　the　partial　absorption　of　light…rays　by　the　ether；questions　with　which　our　present　purpose　does　not　require　us　to　meddle。　Apart　from　such　questions　it　is　every　way　probable　that　the　primary　assumption　of　Helmholtz　and　Thomson　is　only　an　approximation　to　the　truth。　But　if　we　accredit　the　primordial　fluid　with　even　an　infinitesimal　amount　of　friction；　then　we　are　required　to　conceive　of　the　visible　universe　as　developed　from　the　invisible　and　as　destined　to　return　into　the　invisible。　The　vortex…atom；　produced　by　infinitesimal　friction　operating　through　wellnigh　infinite　time；　is　to　be　ultimately　abolished　by　the　agency　which　produced　it。　In　the　words　of　our　authors；　〃If　the　visible　universe　be　developed　from　an　invisible　which　is　not　a　perfect　fluid；　then　the　argument　deduced　by　Sir　William　Thomson　in　favour　of　the　eternity　of　ordinary　matter　disappears；　since　this　eternity　depends　upon　the　perfect　fluidity　of　the　invisible。　In　fine；　if　we　suppose　the　material　universe　to　be　composed　of　a　series　of　vortex…rings　developed　from　an　invisible　universe　which　is　not　a　perfect　fluid；　it　will　be　ephemeral；　just　as　the　smoke…ring　which　we　develop　from　air；　or　that　which　we　develop　from　water；　is　ephemeral；　the　only　difference　being　in　duration；　these　lasting　only　for　a　few　seconds；　and　the　others　it　may　be　for　billions　of　years。〃　Thus；　as　our　authors　suppose　that　〃the　available　energy　of　the　visible　universe　will　ultimately　be　appropriated　by　the　invisible；〃　they　go　on　to　imagine；　〃at　least　as　a　possibi