the dominion of the air-第10章

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ich　have　a　special　value　as　being　the　first　of　their　class。　　Rising　slowly；　a　difference　of　atmosphere　over　the　Neva　gave　the　balloon　a　downward　motion；　necessitating　the　discharge　of　ballast。　　As　late　as　8。45　p。m。　　a　fine　view　was　obtained　of　the　Newski　Islands；　and　the　whole　course　of　the　neighbouring　river。　　At　9。20　p。m。；　when　the　barometer　had　fallen　from　30　inches　to　23　inches；　a　canary　and　a　dove　were　dismissed；　the　former　falling　precipitately；　while　the　latter　sailed　down　to　a　village　below。　　All　available　ballast　was　now　thrown　out；　including　a　spare　great　coat　and　the　remains　of　supper；　with　the　result　that　at　9。30　the　barometer　had　fallen　to　22　inches；　and　at　this　height　they　caught　sight　of　the　upper　rim　of　the　sun。　　The　action　of　heart　and　lungs　remained　normal。　　No　stars　were　seen；　though　the　sky　was　mainly　clear；　such　clouds　as　were　visible　appearing　white　and　at　a　great　height。　　The　echo　of　a　speaking　trumpet　was　heard　after　an　interval　of　ten　seconds。　　This　was　substantially　the　outcome　of　the　experiments。　　The　practical　difficulties　of　carrying　out　prearranged　observations　amid　the　inconvenience　of　balloon　travel　were　much　felt。　　Their　instruments　were　seriously　damaged；　and　their　results；　despite　most　painstaking　and　praiseworthy　efforts；　must　be　regarded　as　somewhat　disappointing。

But　ere　the　autumn　of　the　same　year　two　other　scientific　ascents；　admirably　schemed　and　financed　at　the　public　expense；　had　been　successfully　carried　out　at　Paris　in　a　war　balloon　which；　as　will　be　told；　had　at　this　time　been　returned　from　military　operations　in　Egypt。　　In　the　first　of　these；　Gay　Lussac　ascended　in　company　with　M。　Biot；　with　very　complete　equipment。　　Choosing　ten　o'clock　in　the　morning　for　their　hour　of　departure；　they　quickly　entered　a　region　of　thin；　but　wet　fog；　after　which　they　shot　up　into　denser　cloud；　which　they　completely　surmounted　at　a　height　of　6；500　feet；　when　they　described　the　upper　surface　as　bearing　the　resemblance；　familiar　enough　to　aeronauts　and　mountaineers；　as　of　a　white　sea　broken　up　into　gently　swelling　billows；　or　of　an　extended　plain　covered　with　snow。

A　series　of　simple　experiments　now　embarked　upon　showed　the　behaviour　of　magnetised　iron；　as　also　of　a　galvanic　pile　or　battery；　to　remain　unaltered。　　As　their　altitude　increased　their　pulses　quickened；　though　beyond　feeling　keenly　the　contrast　of　a　colder　air　and　of　scorching　rays　of　the　sun　they　experienced　no　physical　discomfort。　　At　11；000　feet　a　linnet　which　they　liberated　fell　to　the　earth　almost　helplessly；　while　a　pigeon　with　difficulty　maintained　an　irregular　and　precipitate　flight。　　A　carefully　compiled　record　was　made　of　variations　of　temperature　and　humidity；　and　they　succeeded　in　determining　that　the　upper　air　was　charged　with　negative　electricity。　　In　all　this　these　two　accomplished　physicists　may　be　said　to　have　carried　out　a　brilliant　achievement；　even　though　their　actual　results　may　seem　somewhat　meagre。　　They　not　only　were　their　own　aeronauts；　but　succeeded　in　arranging　and　carrying　out　continuous　and　systematic　observations　throughout　the　period　of　their　remaining　in　the　sky。

This　voyage　was　regarded　as　such　a　pronounced　success　that　three　weeks　later；　in　mid…September；　Gay　Lussac　was　induced　to　ascend　again；　this　time　alone；　and　under　circumstances　that　should　enable　him　to　reach　an　exceptionally　high　altitude。　　Experience　had　taught　the　advisability　of　certain　modifications　in　his　equipment。　　A　magnet　was　ingeniously　slung　with　a　view　of　testing　its　oscillation　even　in　spite　of　accidental　gyrations　in　the　balloon。　　Thermometers　and　hygrometers　were　carefully　sheltered　from　the　direct　action　of　the　sun；　and　exhausted　flasks　were　supplied　with　the　object　of　bringing　down　samples　of　upper　air　for　subsequent　analysis。

Again　it　was　an　early　morning　ascent；　with　a　barometer　on　the　ground　standing　at　30。6　inches；　and　a　slightly　misty　air。　　Lussac　appears　to　have　accomplished　the　exceedingly　difficult　task　of　counting　the　oscillations　of　his　magnet　with　satisfaction　to　himself。　　At　10；000　feet　twenty　vibrations　occupied　83　seconds；　as　compared　with　84。33　seconds　at　the　earth's　surface。　　The　variation　of　the　compass　remained　unaltered；　as　also　the　behaviour　of　magnetised　iron　at　all　altitudes。　　Keeping　his　balloon　under　perfect　control；　and　maintaining　a　uniform　and　steady　ascent；　he　at　the　same　time　succeeded　in　compiling　an　accurate　table　of　readings　recording　atmospheric　pressure；　temperature　and　humidity；　and　it　is　interesting　to　find　that　he　was　confronted　with　an　apparent　anomaly　which　will　commonly　present　itself　to　the　aeronaut　observer。　　Up　to　12；000　feet　the　temperature　had　decreased　consistently　from　82　degrees　to　47　degrees；　after　which　it　increased　6　degrees　in　the　next　2；000　feet。　　This　by　no　means　uncommon　experience　shall　be　presently　discussed。　　The　balloon　was　now　steadily　manoeuvred　up　to　18；636　feet；　at　which　height　freezing　point　was　practically　reached。　　Then　with　a　further　climb　20；000　feet　is　recorded；　at　which　altitude　the　ardent　philosopher　could　still　attend　to　his　magnetic　observations；　nor　is　his　arduous　and　unassisted　task　abandoned　here；　but　with　marvellous　pertinacity　he　yet　struggled　upwards　till　a　height　of　no　less　than　23；000　feet　is　recorded；　and　the　thermometer　had　sunk　to　14　degrees　F。　　Four　miles　and　a　quarter　above　the　level　of　the　sea；　reached　by　a　solitary　aerial　explorer；　whose　legitimate　training　lay　apart　from　aeronautics；　and　whose　main　care　was　the　observation　of　the　philosophical　instruments　he　carried！　　The　achievement　of　this　French　savant　makes　a　brilliant　record　in　the　early　pages　of　our　history。

It　is　not　surprising　that　Lussac　should　own　to　having　felt　no　inconsiderable　personal　discomfort　before　his　venture　was　over。　　In　spite　of　warm　clothing　he　suffered　greatly　from　cold　and　benumbed　fingers；　not　less　also　from　laboured　breathing　and　a　quickened　pulse；　headache　supervened；　and　his　throat　became　parched　and　unable　to　swallow　food。　　In　spite　of　all；　he　conducted　the　descent　with　the　utmost　skill；　climbing　down　quietly　and　gradually　till　he　alighted　with　gentle　ease　at　St。　　Gourgen；　near　Rouen。　　It　may　be　mentioned　here　that　the　analysis　of　the　samples　of　air　which　he　had　brought　down　proved　them　to　contain　the　normal　proportion　of　oxygen；　and　to　be　essentially　identical；　as　tested　in　the　laboratory；　with　the　free　air　secured　at　the　surface　of　the　earth。

The　sudden　and　apparently　unaccountable　variation　in　temperature　recorded　by　Lussac　is　a　striking　revelation　to　an　aerial　observer；　and　becomes　yet　more　marked　when　more　sensitive　instruments　are　used　than　those　which　were　taken　up　on　the　occasion　just　related。　　It　will　be　recorded　in　a　future　chapter　how　more　suitable　instruments　came　in　course　of　time　to　be　devised。　　It　is　only　necessary　to　point　out　at　this　stage　that　instruments　which　lack　due　sensibility　will　unavoidably　read　too　high　in　ascents；　and　too　low　in　descents　where；　according　to　the　general　law；　the　air　is　found　to　grow　constantly　colder　with　elevation　above　the　earth's　surface。　　It　is　strong　evidence　of　considerable　efficiency　in　the　instruments；　and　of　careful　attention　on　the　part　of　the　observer；　that　Lussac　was　able　to　record　the　temporary　inversion　of　the　law　of　change　of　temperature　above…mentioned。　　Had　he　possessed　modern　instrumental　equipment　he　would　have　brought　down　a　yet　more　remarkable　account　of　the　upper　regions　which　he　visited；　and　learned　that　the　variations　of　heat　and　cold　were　considerably　more　striking　than　he　supposed。

With　a　specially　devised　instrument　used　with　special　precautions；　the　writer；　as　will　be　shown　hereafter；　has　been　able　to　prove　that　the　temperature　of　the　air；　as　traversed　in　the　wayward　course　of　a　balloon；　is　probably　far　more　variable　and　complex　than　has　been　recorded　by　most　observers。

The　exceptional　height　claimed　to　have　been　reached　by　Gay　Lassac　need　not　for　a　moment　be　questioned；　and　the　fact　that　he　did　not　experience　the　same　personal　inconvenience　as　has　been　complained　of　by　mountain　climbers　at　far　less　altitudes　admits　of　ready　explanation。　　The　physical　exertion　demanded　of　the　mountaineer　is　entirely　absent　in　the　case　of　an　aeronaut　who　is　sailing　at　perfect　ease　in　a　free　balloon