Wearenowbroughttooneoftheprofoundestspeculationsofmoderntimes，thevortex-atomtheoryofHelmholtzandThomson，inwhichtheevolutionofordinarymatterfrometherisplainlyindicated。Thereaderfirstneedstoknowwhatvortex-motionis；
andthishasbeensobeautifullyexplainedbyProfessorClifford，thatIquotehisdescriptionentire:“Imaginearingofindia-rubber，madebyjoiningtogethertheendsofacylindricalpiecelikealead-pencilbeforeitiscut，tobeputuponaroundstickwhichitwilljustfitwithalittlestretching。Letthestickbenowpulledthroughtheringwhilethelatteriskeptinitsplacebybeingpulledtheotherwayontheoutside。Theindia-rubberhasthenwhatiscalledvortex-motion。Beforetheendswerejoinedtogether，whileitwasstraight，itmighthavebeenmadetoturnaroundwithoutchangingposition，byrollingitbetweenthehands。Justthesamemotionofrotationithasonthestick，onlythattheendsarenowjoinedtogether。Alltheinsidesurfaceoftheringisgoingoneway，namely，thewaythestickispulled；andalltheoutsideisgoingtheotherway。Suchavortex-ringismadebythesmokerwhopurseshislipsintoaroundholeandsendsoutapuffofsmoke。Theoutsideoftheringiskeptbackbythefrictionofhislipswhiletheinsideisgoingforwards；thusarotationissetupallroundthesmoke-ringasittravelsoutintotheair。“Inthesecases，andinothersaswecommonlyfindit，vortex-motionowesitsorigintofrictionandisafterawhilebroughttoanendbyfriction。
Butin1858theequationsofmotionofanincompressiblefrictionlessfluidwerefirstsuccessfullysolvedbyHelmholtz，andamongotherthingsheprovedthat，thoughvortex-motioncouldnotbeoriginatedinsuchafluid，yetsupposingitoncetoexist，itwouldexisttoalleternityandcouldnotbediminishedbyanymechanicalactionwhatever。Avortex-ring，forexample，insuchafluid，wouldforeverpreserveitsownrotation，andwouldthusforeverretainitspeculiarindividuality，being，asitwere，markedofffromitsneighbourvortex-rings。UponthismechanicaltruthSirWilliamThomsonbasedhiswonderfullysuggestivetheoryoftheconstitutionofmatter。Thatwhichispermanentorindestructibleinmatteristheultimatehomogeneousatom；andthisisprobablyallthatispermanent，sincechemistsnowalmostunanimouslyholdthatso-calledelementarymoleculesarenotreallysimple，butowetheirsensibledifferencestothevariousgroupingsofanultimateatomwhichisalikeforall。
Relativelytoourpowersofcomprehensiontheatomendureseternally；thatis，itretainsforeverunalterableitsdefinitemassanditsdefiniterateofvibration。Nowthisisjustwhatavortex-ringwoulddoinanincompressiblefrictionlessfluid。
Thusthestartlingquestionissuggested，Whymaynottheultimateatomsofmatterbevortex-ringsforeverexistinginsuchafrictionlessfluidfillingthewholeofspace？SuchahypothesisisnotlessbrilliantthanHuyghens’sconjecturalidentificationoflightwithundulatorymotion；anditismoreoveralegitimatehypothesis，sinceitcanbebroughttothetestofverification。SirWilliamThomsonhasshownthatitexplainsagreatmanyofthephysicalpropertiesofmatter:itremainstobeseenwhetheritcanexplainthemall。