the dominion of the air-第26章

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culminating　point　of　6；200　feet。　　Then；　during　the　descent；　the　temperature　increased；　though　not　uniformly；　till　he　was　nearly　brushing　the　tops　of　the　trees；　where　it　was　some　3　degrees　　colder　than　at　starting。

It　was　now　that　the　balloon；　showing　a　little　waywardness；　slightly　upset　a　portion　of　the　experiment；　for；　instead　of　getting　to　the　neighbourhood　of　earth　just　at　the　moment　of　sunset；　the　travellers　found　themselves　at　that　epoch　600　feet　above　the　ground；　and　over　the　ridge　of　a　hill；　on　passing　which　the　balloon　became　sucked　down　with　a　down　draught；　necessitating　a　liberal　discharge　of　sand　to　prevent　contact　with　the　ground。　　This　circumstance；　slight　in　itself；　caused　the　lowest　point　of　the　descent　to　be　reached　some　minutes　late；　and；　still　more　unfortunate；　occasioned　the　ascent　which　immediately　followed　to　be　a　rapid　one；　too　rapid；　doubtless；　to　give　the　registering　instruments　a　fair　chance；　but　one　principal　record　aimed　at　was　obtained　at　least　with　sufficient　truth；　namely；　that　at　the　culminating　point；　which　again　was　6；200　feet；　the　temperature　read　35　degrees；　or　about　6　degrees　　warmer　than　when　the　balloon　was　at　the　same　altitude　a　little　more　than　an　hour　before。　　This　comparatively　warm　temperature　was　practically　maintained　for　a　considerable　portion　of　the　descent。

We　may　summarise　the　principal　of　Mr。　Glaisher's　generalisations　thus；　using　as　nearly　as　possible　his　own　words：

〃The　decrease　of　temperature；　with　increase　of　elevation；　has　a　diurnal　range；　and　depends　upon　the　hour　of　the　day；　the　changes　being　the　greatest　at　mid…day　and　the　early　part　of　the　afternoon；　and　decreasing　to　about　sunset；　when；　with　a　clear　sky；　there　is　little　or　no　change　of　temperature　for　several　hundred　feet　from　the　earth；　whilst；　with　a　cloudy　sky；　the　change　decreases　from　the　mid…day　hours　at　a　less　rapid　rate　to　about　sunset；　when　the　decrease　is　nearly　uniform　and　at　the　rate　of　1　degree　in　2；000　feet。

〃Air　currents　differing　in　direction　are　almost　always　to　be　met　with。　　The　thicknesses　of　these　were　found　to　vary　greatly。　　The　direction　of　the　wind　on　the　earth　was　sometimes　that　of　the　whole　mass　of　air　up　to　20；000　feet　nearly；　whilst　at　other　times　the　direction　changed　within　500　feet　of　the　earth　Sometimes　directly　opposite　currents　were　met　with。〃

With　regard　to　the　velocity　of　upper　currents；　as　shown　by　the　travel　of　balloons；　when　the　distances　between　the　places　of　ascent　and　descent　are　measured；　it　was　always　found　that　these　distances　were　very　much　greater　than　the　horizontal　movement　of　the　air；　as　measured　by　anemometers　near　the　ground。



CHAPTER　XVI。　SOME　FAMOUS　FRENCH　AERONAUTS。


By　this　period　a　revival　of　aeronautics　in　the　land　of　its　birth　had　fairly　set　in。　　Since　the　last　ascents　of　Gay　Lussac；　in　1804；　already　recorded；　there　had　been　a　lull　in　ballooning　enterprise　in　France；　and　no　serious　scientific　expeditions　are　recorded　until　the　year　1850；　when　MM。　Baral　and　Bixio　undertook　some　investigations　respecting　the　upper　air；　which　were　to　deal　with　its　laws　of　temperature　and　humidity；　with　the　proportion　of　carbonic　acid　present　in　it；　with　solar　heat　at　different　altitudes；　with　radiation　and　the　polarisation　of　light；　and　certain　other　interesting　enquiries。

The　first　ascent；　made　in　June　from　the　Paris　Observatory；　though　a　lofty　one；　was　attended　with　so　much　danger　and　confusion　as　to　be　barren　of　results。　　The　departure；　owing　to　stormy　weather；　was　hurried　and　illordered；　so　that　the　velocity　in　rising　was　excessive；　the　net　constricted　the　rapidly…swelling　globe；　and　the　volumes　of　out…rushing　gas　half…suffocated　the　voyagers。　　Then　a　large　rent　occurred；　which　caused　an　alarmingly　rapid　fall；　and　the　two　philosophers　were　reduced　to　the　necessity　of　flinging　away　all　they　possessed；　their　instruments　only　excepted。　　The　landing；　in　a　vineyard；　was　happily　not　attended　with　disaster；　and　within　a　month　the　same　two　colleagues　attempted　a　second　aerial　excursion；　again　in　wet　weather。

It　would　seem　as　if　on　this　occasion；　as　on　the　former　one；　there　was　some　lack　of　due　management；　for　the　car；　suspended　at　a　long　distance　from　the　balloon　proper；　acquired　violent　oscillations　on　leaving　the　ground；　and　dashing　first　against　a　tree；　and　then　against　a　mast；　broke　some　of　the　instruments。　　A　little　later　there　occurred　a　repetition　on　a　minor　scale　of　the　aeronauts'　previous　mishap；　for　a　rent　appeared　in　the　silk；　though；　luckily；　so　low　down　in　the　balloon　as　to　be　of　small　consequence；　and　eventually　an　altitude　of　some　19；000　feet　was　attained。　At　one　time　needles　of　ice　were　encountered　settling　abundantly　with　a　crackling　sound　upon　their　notebooks。　　But　the　most　remarkable　observation　made　during　this　voyage　related　to　an　extraordinary　fall　of　temperature　which；　as　recorded；　is　without　parallel。　　It　took　place　in　a　cloud　mass；　15；000　feet　thick；　and　amounted　to　a　drop　of　from　15　degrees　to　…39　degrees。

In　1867　M。　C。　Flammarion　made　a　few　balloon　ascents；　ostensibly　for　scientific　research。　　His　account　of　these；　translated　by　Dr。　T。　L。　Phipson；　is　edited　by　Mr。　Glaisher；　and　many　of　the　experiences　he　relates　will　be　found　to　contrast　with　those　of　others。　　His　physical　symptoms　alone　were　remarkable；　for　on　one　occasion；　at　an　altitude　of　apparently　little　over　10；000　feet；　he　became　unwell　being　affected　with　a　sensation　of　drowsiness；　palpitation；　shortness　of　breath；　and　singing　in　the　ears；　which；　after　landing　gave　place　to　a　〃fit　of　incessant　gaping〃　while　he　states　that　in　later　voyages；　at　but　slightly　greater　altitudes；　his　throat　and　lungs　became　affected；　and　he　was　troubled　with　presence　of　blood　upon　the　lips。　　This　draws　forth　a　footnote　from　Mr。　Glaisher；　which　should　be　commended　to　all　would…be　sky　voyagers。　　It　runs　thus：〃I　have　never　experienced　any　of　these　effects　till　I　had　long　passed　the　heights　reached　by　M。　Flammarion；　and　at　no　elevation　was　there　the　presence　of　blood。〃　　However；　M。　Flammarion　adduces；　at　least；　one　reassuring　fact；　which　will　be　read　with　interest。　　Once；　having；　against　the　entreaties　of　his　friends；　ascended　with　an　attack　of　influenza　upon　him；　he　came　down　to　earth　again　an　hour　or　two　afterwards　with　this　troublesome　complaint　completely　cured。

It　would　seem　as　if　the　soil　of　France　supplied　the　aeronaut　with　certain　phenomena　not　known　in　England；　one　of　these　apparently　being　the　occasional　presence　of　butterflies　hovering　round　the　car　when　at　considerable　heights。　　M。　Flammarion　mentions　more　than　one　occasion　when　he　thus　saw　them；　and　found　them　to　be　without　sense　of　alarm　at　the　balloon　or　its　passengers。　　Again；　the　French　observer　seems　seldom　to　have　detected　those　opposite　airstreams　which　English　balloonists　may　frequently　observe；　and　have　such　cause　to　be　wary　of。　　His　words；　as　translated；　are：〃　t　appears　to　me　that　two　or　more　currents；　flowing　in　different　directions；　are　very　rarely　met　with　as　we　rise　in　the　air；　and　when　two　layers　of　cloud　appear　to　travel　in　opposite　directions　the　effect　is　generally　caused　by　the　motion　of　one　layer　being　more　rapid　than　the　other；　when　the　latter　appears　to　be　moving　in　a　contrary　direction。〃　　In　continuation　of　these　experiences；　he　speaks　of　an　occasion　when；　speeding　through　the　air　at　the　rate　of　an　ordinary　express　train；　he　was　drawn　towards　a　tempest　by　a　species　of　attraction。

The　French　aeronaut's　estimate　of　what　constitutes　a　terrific　rate　of　fall　differs　somewhat　from　that　of　others　whose　testimony　we　have　been　recording。　　In　one　descent；　falling　（without　reaching　earth；　however）　a　distance　of　2；130　feet　in　two　minutes；　he　describes　the　earth　rising　up　with　frightful　rapidity；　though；　as　will　be　observed；　this　is　not　nearly　half　the　speed　at　which　either　Mr。　Glaisher　or　Albert　Smith　and　his　companions　were　precipitated　on　to　bare　ground。　　Very　many　cases　which　we　have　cited　go　to　show　that　the　knowledge　of　the　great　elasticity　of　a　well…made　wicker　car　may　rob　a　fall　otherwise　alarming　of　its　terrors；　while　the　practical　certainty　that　a　balloon　descending　headlong　will　form　itself　into　a　natural　parachute；　if　properly　managed；　reduces　enormously　the　risk　attending　any　mere　impact　with　earth。　　It　will　be　allowed　by　all　experienced　aeronauts　that　far　worse　chances　lie　in　some　awkward　alighting　ground；　or　in　the　dragging　against　dangerous　obstacles　after　the　balloon　has　fallen。

Many　of　M。　Flammarion's　experiments　are　remarkable　for　their　simplicity。　　Indeed；　in　some　cases　he　would　seem　to　have　applied　himself　to　making　trials　the　result　of　which　could　not　have　been　seriously　questioned。　　The　following；　quoting　from　Dr。　Phipson's　translation；　will　serve　as　an　example：

〃Another　mechanical　experiment　was　made　in　the　evening；　and　renewed　next　day。　　I　wished　to　verify　Galileo's　principle　of　the　independence　of　simultaneous　motions。　　According　to　this　principle；　a　body　which　is　allowed　to　fall　from　another　body　in　motion　participates　in　the　motion　of　the　latter；　thus；　if　we　drop　a　marble　from　the　masthead　of　a　ship；　it　preserves　during　its　fall　the　rate　of　motion　of　the　vessel；　and　falls　at　the　foot　of　the　mast　as　if　the　ship　were　still。　　Now；　if　a　body　falls　from　a　balloon；　does　it　also　follow　the　motion　of　the　latter；　or　does　it　fall　directly　to　the　earth　in　a　line　which　is　perpendicular　to　the　point　at　which　we　let　it　fall？　　In　the　first　case　its　fall　would　be　described　by　an　oblique　line。　The　latter　was　found　to　be　the　fact；　as　we　proved　by　letting　a　bottle　fall。　　During　its　descent　it　partakes　of　the　balloon's　motion；　and　until　it　reaches　the　earth　is　always　seen　perpendicularly　below　the　car。〃

An　interesting　phenomenon；　relating　to　the　formation　of　fog　was　witnessed　by　M。　Flammarion　in　one　of　his　voyages。　　He　was　flying　low　with　a　fast　wind；　and　while　traversing　a　forest　he　noticed　here　and　there　patches　of　light　clouds；　which；　remaining　motionless　in　defiance　of　the　strong　wind；　continued　to　hang　above　the　summits　of　the　trees。　　The　explanation　of　this　can　hardly　be　doubtful；　being　analogous　to　the　formation　of　a　night…cap　on　a　mountain　peak　where　warm　moist　air…currents　become　chilled　against　the　cold　rock　surface；　forming；　momentarily；　a　patch　of　cloud　which；　though　constantly　being　blown　away；　is　as　constantly　re…formed；　and　thus　is　made　to　appear　as　if　stationary。

The　above　instructive　phenomenon　could　hardly　have　been　noticed　save　by　an　aeronaut；　and　the　same　may　be　said　of　the　following。　　Passing　in　a　clear　sky　over　the　spot　where　the　Marne　flows　into　the　Seine；　M。　Flammarion　notes　that　the　water　of　the　Marne；　which；　as　he　says；　is　as　yellow　now　as　it　was　in　the　time　of　Julius　Caesar；　does　not　mix　with　the　green　water　of　the　Seine；　which　flows　to　the　left　of　the　current；　nor　with　the　blue　water　of　the　canal；　which　flows　to　the　right。　　Thus；　a　yellow　river　was　seen　flowing　between　two　distinct　brooks；　green　and　blue　respectively。

Here　was　optical　evidence　of　the　way　in　which　streams　of　water　which　actually　unite　may　continue　to　maintain　independent　courses。　　We　have　seen　that　the　same　is　true　of　streams　of　air；　and；　where　these　traverse　one　another　in　a　copious　and　complex　manner；　we　find；　as　will　be　shown；　conditions　produced　that　cause　a　great　deadening　of　sound；　thus；　great　differences　in　the