StanleySpencerinthecar，shesailedgracefullydownthefootballfield，wheeledroundinacircle——asmallcircle，too——andforperhapsaquarterofanhoursailedatortuouscourseovertheheadsofasmallbutenthusiasticcrowdofspectators。Theshipwashandicappedtosomeextentbythefactthatintheiranxietytomakethetrialtheaeronautshadnotwaitedtoinflateitfully，butstillitdiditsworkwell，answereditshelmreadily，showednosignsofrolling，and，inshort，appearedtogiveentiresatisfactiontoeverybodyconcerned——somuchso，indeed，thatMr。StanleySpencerinformedthecrowdaftertheascentthathewasquitereadytotakeupanychallengethatM。SantosDumontmightthrowdown。"
　　WithinafewweeksofthishisfirstsuccessMr。Spencerwasabletoprovetotheworldthathehadonlyclaimedforhismachinewhatitspowersfullyjustified。OnastillSeptemberafternoon，ascendingalone，hesteeredhisaerialshipinaneasyandgracefulflightoverLondon，fromtheCrystalPalacetoHarrow。
　　CHAPTERXXIX。CONCLUSION。
　　Thefuturedevelopmentofaerostationisnecessarilydifficulttoforecast。Havingrevieweditshistoryfromitsinceptionwehavetoallowthattheballooninitself，asaninstrumentofaeriallocomotion，remainspracticallyonlywhereitwas120
　　yearsago。Nor，inthenatureofthecase，isthistobewonderedat。Thewind，whichaloneguidestheballoon，isbeyondman’scontrol，while，asasourceofliftingpower，alighterandthereforemoresuitablegasthanhydrogenisnottobefoundinnature。
　　Itis，however，conceivablethatasuperiormodeofinflationmayyetbediscovered。Nowthattheliquefactionofgaseshasbecomeanaccomplishedfact，itseemsalmosttheoreticallypossiblethataballoonistmaypresentlybeabletoprovidehimselfwithanunlimitedreserveofpotentialenergysoastobefittedfortravelofindefiniteduration。Endowedwithincreasedpowersofthisnature，theaeronautcouldutiliseaballoonforvoyagesofdiscoveryoverregionsoftheearthwhichbarman’sprogressbyanyothermodeoftravel。AfutureAndree，providedwithameansofmaintaininghisgassupplyforsixweeks，needhavenohesitationinlayinghiscoursetowardstheNorthPole，beingconfidentthatthewindsmustultimatelywafthimtosomesafehaven。Hecould，indeed，wellafford，havingreachedthePole，todescendandbuildhiscairn，oreventostopaweek，ifhesodesired，beforecontinuingonhisway。
　　Butitmayfairlybeclaimedfortheballoon，evenasitnowis，thatagreatandimportantfutureisopentoitasameansforexploringinaccessiblecountry。Itmay，indeed，beurgedthatAndree’staskwas，intheverynatureofthecase，wellnighimpracticable，andhisunfortunatemiscarriagewillbeusedasargumentagainstsuchamethodofexploration。ButitmustalwaysberememberedthatinAndree’scasetherigoursofclimatewhichhewascompelledtofacewerethemostseriousofallobstaclestoballoontravel。Theextremecoldwouldnotonlycauseconstantshrinkageofthegas，butwouldentailthedepositionofaweightofmoisture，ifnotofsnow，uponthesurfaceoftheballoon，whichmustgreatlyshortenitslife。
　　Itwouldbeentirelyotherwiseifthecountryitweresoughttoexplorewereinlowerlatitudes，inAustralia，orwithinthevastunknownbeltofearthlyingnearertheequator。Thewriter’sschemeforexploringthewhollyunknownregionsofArabiaisalreadybeforethepublic。Thefact，thoughttobeestablishedbythemostexperiencedaeronautsofoldtimes，andalreadyreferredtointhesepages，thatatsomeheightastrongwestwindistobefoundblowingwithgreatconstancyallroundtheglobe，isinaccordancewiththeviewentertainedbymodernmeteorologists。Suchawind，too，maybeexpectedtobeafairlyfastwind，thecalculationbeingthat，asageneralrule，thevelocityofcurrentsincreasesfromthegroundattherateofaboutthreemilesperhourforeachthousandfeetofheight;thusthechanceofaballoondriftingspeedilyacrossthebreadthofArabiaisastrongone，and，regardedinthislight，thedistancetobetraversediscertainlynotexcessive，beingprobablywellwithinthelastingpowerofsuchaballoonasthatemployedbyAndree。If，forthesakeofgassupply，Adenwerechosenforthestartingground，then1，200milesE。N。E。wouldcarrythevoyagertoMuscat;1，100milesN。E。byE。wouldlandhimatSohar;whilesome800mileswouldsufficetotakehimtotheseaboardifhiscourselayN。E。ItmustalsobeborneinmindthattheArabiansunbyday，andtheheatradiatedoffthedesertbynight，wouldbeallinfavourofthebuoyancyoftheballoon。
　　Butthereareotherpersistentwindsthat，forpurposesofexploration，wouldproveequallyserviceableandsure。FromtimeimmemorialthedwellerontheNilehasbeenledtoregardhisriverinthelightofabenignantdeity。Ifhewishedtotraveldownitscoursehehadbuttoentrusthisvesseltothestream，andthiswouldcarryhim。If，again，hewishedtoretracehiscourse，hehadbuttoraiseasail，andtheprevalentwind，conqueringtheflood，wouldbearhimagainstthestream。Thisconstantnorthwind，followingtheNilevalley，andthencetrendingstillsouthwardtowardsUganda，hasbeenregardedasameanstohandwelladaptedfortheexplorationofimportantunsurveyedcountrybyballoon。ThisschemehasbeenconceivedandelaboratedbyMajorB。F。S。
　　Baden—Powell，and，sofar，theonlyapparentobstacleinthewayhasprovedthelackofnecessaryfunds。
　　Itwillbeurged，however，thatforpurposesofexplorationsomeformofdirigibleballoonisdesirable，andwehavealreadyhadproofthatwhereitisnotsoughttocombatwindsstronglyopposedtotheircoursesuchairshipsasSantos—DumontorMessrs。Spencerhavealreadyconstructedacquitthemselveswell;anditrequiresnostretchofimaginationtoconceivethatbeforethepresentcenturyisclosedmanygreatgapsinthemapoftheworldwillhavebeenfilledinbyaerialsurvey。
　　But，leavingtheballoontoitsproperfunction，weturntotheflyingmachineproperlysocalledwithmoresanguinehopesofseeingtherealconquestoftheairachieved。Itwasasitwerebutyesterdaywhentheairship，unhamperedbyhugeglobesofgas，andcontrolledbymechanicalmeansalone，wasfirstfairlytried，yetitisalreadyconsideredbythosebestabletojudgethatitsultimatesuccessisassured。
　　Thissuccessrestsnowsolelyinthehandsofthemechanicalengineer。Hemust，andsurelycan，buildtheshipofsuchstrengththatsomeessentialpartdoesnotatthecriticalmomentbreakdownorcarryaway。Hemayhavetoimprovehismotivepower，andhere，again，wedonotdoubthiscunning。
　　Motorengines，self—containedandburningliquidfuel，areyetintheirinfancy，andtheextraordinaryemulationnowexistingintheirproductionputsitbeyonddoubtthateveryyearwillseerapidimprovementintheirefficiency。
　　Wedonotexpect，nordowedesire，thattheworldmayseethefulfilmentofthepoet’sdream，"Argosiesofmagicsails"or"Airynaviesgrapplinginthecentralblue。"Wewouldnotbefogourvisionofthefuturewithanywildimaginings，seeking，assomehavedone，toseeintheelectricityorotherhiddenpowerofheaventhemeansforitssubjugationbyman;
　　butitisfarfromunreasonabletohopethatbutalittlewhileshallpass，andweshallhavemoreperfectandreliableknowledgeofthetidesandcurrentsinthevastoceanofair，andwhenthatdaymayhavecomethenitmaybeclaimedthatthegrandproblemofaerialnavigationwillbealreadysolved。