the aeroplane speaks-第6部分

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t　I've　got　naturalized　since　the　War　began。''

Then　the　Air　Speed　Indicator　catches　the　eye　of　the　Pilot。　‘‘Good　enough；''　he　says　as　he　gently　deflects　the　Elevator　and　points　the　nose　of　the　Aeroplane　upwards　in　search　of　the　elusive　Best　Climbing　Angle。

‘‘Ha！　ha！''　shouts　the　Drift；　growing　stronger　with　the　increased　Angle　of　Incidence。　‘‘Ha！　ha！''　he　laughs　to　the　Thrust。　‘‘Now　I've　got　you。　Now　who's　Master？''

And　the　Propeller　shrieks　hysterically；　‘‘Oh！　look　at　me。　I'm　a　helicopter。　That's　not　fair。　Where's　Efficiency？''　And　she　can　only　sadly　reply；　‘‘Yes；　indeed；　but　you　see　we're　a　Compromise。''

And　the　Drift　has　hopes　of　reaching　the　Maximum　Angle　of　Incidence　and　vanquishing　the　Thrust　and　the　Lift。　And　he　grows　very　bold　as　he　strangles　the　Thrust；　but　the　situation　is　saved　by　the　Propeller；　who　is　now　bravely　helicopting　skywards；　somewhat　to　the　chagrin　of　Efficiency。

‘‘Much　ado　about　nothing；''　quotes　the　Aeroplane　learnedly。　‘‘Compromise　or　not；　I'm　climbing　a　thousand　feet　a　minute。　Ask　the　Altimeter。　He'll　confirm　it。''

And　so　indeed　it　was。　The　vacuum　box　of　the　Altimeter　was　steadily　expanding　under　the　decreased　pressure　of　the　rarefied　air；　and　by　means　of　its　little　levers　and　its　wonderful　chain　no　larger　than　a　hair　it　was　moving　the　needle　round　the　gauge　and　indicating　the　ascent　at　the　rate　of　a　thousand　feet　a　minute。

And　lo！　the　Aeroplane　has　almost　reached　the　clouds！　But　what's　this？　A　sudden　gust；　and　down　sinks　one　wing　and　up　goes　the　other。　‘‘Oh；　my　Horizontal　Equivalent！''　despairingly　call　the　Planes：　‘‘it's　eloping　with　the　Lift；　and　what　in　the　name　of　Gravity　will　happen？　Surely　there　was　enough　scandal　in　the　Factory　without　this；　too！''　For　the　lift　varies　with　the　horizontal　equivalent　of　the　planes；　so　that　if　the　aeroplane　tilts　sideways　beyond　a　certain　angle；　the　lift　becomes　less　than　the　weight　of　the　machine；　which　must　then　fall。　A　fall　in　such　a　position　is　known　as　a　‘‘side…slip。''

But　the　ever…watchful　Pilot　instantly　depresses　one　aileron；　elevating　the　other；　with　just　a　touch　of　the　rudder　to　keep　on　the　course；　and　the　Planes　welcome　back　their　precious　Lift　as　the　Aeroplane　flicks　back　to　its　normal　position。

‘‘Bit　bumpy　here　under　these　clouds；''　is　all　the　Pilot　says　as　he　heads　for　a　gap　between　them；　and　the　next　minute　the　Aeroplane　shoots　up　into　a　new　world　of　space。

‘‘My　eye！''　ejaculates　the　Wind…screen；　‘‘talk　about　a　view！''　And　indeed　mere　words　will　always　fail　to　express　the　wonder　of　it。　Six　thousand　feet　up　now；　and　look！　The　sun　is　rising　quicker　than　ever　mortal　on　earth　witnessed　its　ascent。　Far　below　is　Mother　Earth；　wrapt　in　mists　and　deep　blue　shadows；　and　far　above　are　those　light；　filmy；　ethereal　clouds　now　faintly　tinged　with　pink　And　all　about　great　mountains　of　cloud；　lazily　floating　in　space。　The　sun　rises　and　they　take　on　all　colours；　blending　one　with　the　other；　from　dazzling　white　to　crimson　and　deep　violet…blue。　Lakes　and　rivers　here　and　there　in　the　enormous　expanse　of　country　below　refract　the　level　rays　of　the　sun　and；　like　so　many　immense　diamonds；　send　dazzling　shafts　of　light　far　upwards。　The　tops　of　the　hills　now　laugh　to　the　light　of　the　sun；　but　the　valleys　are　still　mysterious　dark　blue　caverns；　clowned　with　white　filmy　lace…like　streaks　of　vapour。　And　withal　the　increasing　sense　with　altitude　of　vast；　clean；　silent　solitudes　of　space。

Lives　there　the　man　who　can　adequately　describe　this　Wonder？　‘‘Never；''　says　the　Pilot；　who　has　seen　it　many　times；　but　to　whom　it　is　ever　new　and　more　wonderful。

Up；　up；　up；　and　still　up；　unfalteringly　speeds　the　Pilot　and　his　mount。　Sweet　the　drone　of　the　Engine　and　steady　the　Thrust　as　the　Propeller　exultingly　battles　with　the　Drift。

And　look！　What　is　that　bright　silver　streak　all　along　the　horizon？　It　puzzled　the　Pilot　when　first　he　saw　it；　but　now　he　knows　it　for　the　Sea；　full　fifty　miles　away！

And　on　his　right　is　the　brightness　of　the　Morn　and　the　smiling　Earth　unveiling　itself　to　the　ardent　rays　of　the　Sun；　and　on　his　left；　so　high　is　he；　there　is　yet　black　Night；　hiding　innumerable　Cities；　Towns；　Villages　and　all　those　places　where　soon　teeming　multitudes　of　men　shall　awake；　and　by　their　unceasing　toil　and　the　spirit　within　them　produce　marvels　of　which　the　Aeroplane　is　but　the　harbinger。

And　the　Pilot's　soul　is　refreshed；　and　his　vision；　now　exalted；　sees　the　Earth　a　very　garden；　even　as　it　appears　at　that　height；　with　discord　banished　and　a　happy　time　come；　when　the　Designer　shall　have　at　last　captured　Efficiency；　and　the　Man…who…takes…the…credit　is　he　who　has　earned　it；　and　when　kisses　are　the　only　things　that　go　by　favour。

Now　the　Pilot　anxiously　scans　the　Barograph；　which　is　an　instrument　much　the　same　as　the　Altimeter；　but　in　this　case　the　expansion　of　the　vacuum　box　causes　a　pen　to　trace　a　line　upon　a　roll　of　paper。　This　paper　is　made　by　clockwork　to　pass　over　the　point　of　the　pen；　and　so　a　curved　line　is　made　which　accurately　registers　the　speed　of　the　ascent　in　feet　per　minute。　No　longer　is　the　ascent　at　the　rate　of　a　thousand　feet　a　minute；　and　the　Propeller　complains　to　the　Engine；　‘‘I'm　losing　my　Revs。　and　the　Thrust。　Buck　up　with　the　Power；　for　the　Lift　is　decreasing；　though　the　Weight　remains　much　the　same。''

Quoth　the　Engine：　‘‘I　strangle　for　Air。　A　certain　proportion；　and　that　of　right　density；　I　must　have　to　one　part　of　Petrol；　in　order　to　give　me　full　power　and　compression；　and　here　at　an　altitude　of　ten　thousand　feet　the　Air　is　only　two…thirds　as　dense　as　at　sea…level。　Oh；　where　is　he　who　will　invent　a　contrivance　to　keep　me　supplied　with　Air　of　right　density　and　quality？　It　should　not　be　impossible　within　certain　limits。''

‘‘We　fully　agree；''　said　the　dying　Power　and　Thrust。　‘‘Only　maintain　Us　and　you　shall　be　surprised　at　the　result。　For　our　enemy　Drift　decreases　in　respect　of　distance　with　the　increase　of　altitude　and　rarity　of　air；　and　there　is　no　limit　to　the　speed　through　space　if　only　our　strength　remains。　And　with　oxygen　for　Pilot　and　Passengers　and　a　steeper　pitch＇＇11＇＇　for　the　Propeller　we　may　then　circle　the　Earth　in　a　day！''


＇＇11＇＇　A　propeller　screws　through　the　air；　and　the　distance　it　advances　during　one　revolution；　supposing　the　air　to　be　solid；　is　known　as　the　pitch。　The　pitch；　which　depends　upon　the　angle　of　the　propeller　blades；　must　be　equal　to　the　speed　of　the　aeroplane；　plus　the　slip；　and　if；　on　account　of　the　rarity　of　the　air　the　speed　of　the　aeroplane　increases；　then　the　angle　and　pitch　should　be　correspondingly　increased。　Propellers　with　a　pitch　capable　of　being　varied　by　the　pilot　are　the　dream　of　propeller　designers。　For　explanation　of　‘‘slip''　see　Chapter　IV。　on　propellers。


Ah；　Reader；　smile　not　unbelievingly；　as　you　smiled　but　a　few　years　past。　There　may　be　greater　wonders　yet。　Consider　that　as　the　speed　increases；　so　does　the　momentum　or　stored…up　force　in　the　mass　of　the　aeroplane　become　terrific。　And；　bearing　that　in　mind；　remember　that　with　altitude　gravity　decreases。　There　may　yet　be　literally　other　worlds　to　conquer。＇＇12＇＇


＇＇12＇＇　Getting　out　of　my　depth？　Invading　the　realms　of　fancy？　Well；　perhaps　so；　but　at　any　rate　it　is　possible　that　extraordinary　speed　through　space　may　be　secured　if　means　are　found　to　maintain　the　impulse　of　the　engine　and　the　thrust…drift　efficiency　of　the　propeller　at　great　altitude。


Now　at　fifteen　thousand　feet　the　conditions　are　chilly　and　rare；　and　the　Pilot；　with　thoughts　of　breakfast　far　below；　exclaims；　‘‘High　enough！　I　had　better　get　on　with　the　Test。''　And　then；　as　he　depresses　the　Elevator；　the　Aeroplane　with　relief　assumes　its　normal　horizontal　position。　Then；　almost　closing　the　Throttle；　the　Thrust　dies　away。　Now；　the　nose　of　the　Aeroplane　should　sink　of　its　own　volition；　and　the　craft　glide　downward　at　flying　speed；　which　is　in　this　case　a　hundred　miles　an　hour。　That　is　what　should　happen　if　the　Designer　has　carefully　calculated　the　weight　of　every　part　and　arranged　for　the　centre　of　gravity　to　be　just　the　right　distance　in　front　of　the　centre　of　lift。　Thus　is　the　Aeroplane　‘‘nose…heavy''　as　a　glider；　and　just　so　to　a　degree　ensuring　a　speed　of　glide　equal　to　its　flying　speed。　And　the　Air　Speed　Indicator　is　steady　at　one　hundred　miles　an　hour；　and　‘‘That's　all　right！''　exclaims　the　Pilot。　‘‘And　very　useful；　too；　in　a　fog　or　a　cloud；''　he　reflects；　for　then　he　can　safely　leave　the　angle　of　the　glide　to　itself；　and　give　all　his　attention；　and　he　will　need　it　all；　to　keeping　the　Aeroplane　horizontal　from　wing…tip　to　wing…tip；　and　to　keeping　it　straight　on　its　course。　The　latter　he　will　manage　with　the　rudder；　controlled　by　his　feet；　and　the　Compass　will　tell　him　whether　a　straight　course　is　kept。　The　former　he　will　control　by　the　Ailerons；　or　little　wings　hinged　to　the　tips　of　the　planes；　and　the　bubble　in　the　Inclinometer　in　front　of　him　must　be　kept　in　the　middle。

A　Pilot；　being　only　human；　may　be　able　to　do　two　things　at　once；　but　three　is　a　tall　order；　so　was　this　Pilot　relieved　to　find　the　Design　not　at　fault　and　his　craft　a　‘‘natural　glider。''　To　correct　this　nose…heavy　tendency　when　the　Engine　is　running；　and　descent　not　required；　the　centre　of　Thrust　is　arranged　to　be　a　little　below　the　centre　of　Drift　or　Resistance；　and　thus　acts　as　a　counter…balance。

But　what　is　this　stream　of　bad　language　from　the　Exhaust　Pipe；　accompanied　by　gouts　of　smoke　and　vapour？　The　Engine；　now　revolving　at　no　more　than　one…tenth　its　normal　speed；　has　upset　the　proportion　of　petrol　to　air；　and　combustion　is　taking　place　intermittently　or　in　the　Exhaust　Pipe；　where　it　has　no　business　to　be。

‘‘Crash；　Bang；　Rattle！！！''　and　worse　than　that；　yells　the　Exhaust；　and　the　Aeroplane；　who　is　a　gentleman　and　not　a　box　kite；＇＇13＇＇　remonstrates　with　the　severity　of　a　Senior　Officer。　‘‘See　the　Medical　Officer；　you　young　Hun。　Go　and　see　a　doctor。　Vocal　diarrhoea；　that's　your　complaint；　and　a　very　nasty　one　too。　Bad　form；　bad　for　discipline；　and　a　nuisance　in　the　Mess。　What's　your　Regiment？　Special　Reserve；　you　say？　Humph！　Sounds　like　Secondhand　Bicycle　Trade　to　me！''


＇＇13＇＇　Box…kite。　The　first　crude　form　of　biplane。


Now　the　Pilot　decides　to　change　the　straight　gliding　descent　to　a　spiral　one；　and；　obedient　to　the　Rudder；　the　Aeroplane　turns　to　the　left。　Bu