sh；　he　recorded　how；　as　he　constantly　and　somewhat　rapidly　rose；　the　wind　changed　its　direction　from　N。W。　through　N。　to　N。E。；　while　he　remained　over　the　metropolis；　the　balloon　all　the　while　rotating　on　its　axis。　　This　continual　swinging　or　revolving　of　the　balloon　Green　considers　an　accompaniment　of　either　a　rapid　ascent　or　descent；　but　it　may　be　questioned　whether　it　is　not　merely　a　consequence　of　changing　currents；　or；　sometimes；　of　an　initial　spin　given　inadvertently　to　the　balloon　at　the　moment　of　its　being　liberated。　　The　phenomenon　of　marked　change　which　he　describes　in　the　upper　currents　is　highly　interesting；　and　tallies　with　what　the　writer　has　frequently　experienced　over　London　proper。　　Such　higher　currents　may　be　due　to　natural　environment；　and　to　conditions　necessarily　prevailing　over　so　vast　and　varied　a　city；　and　they　may　be　able　to　play　an　all…important　part　in　the　dispersal　of　London　smoke　or　fog。　　This　point　will　be　touched　on　later。　　In　this　particular　voyage　Green　records　that　as　he　was　rising　at　the　moment　when　his　barometer　reached　19　inches；　the　thermometer　he　carried　registered　46　degrees；　while　on　coming　down；　when　the　barometer　again　marked　19　inches；　the　same　thermometer　recorded　only　22　degrees。　　It　will　not　fail　to　be　recognised　that　there　is　doubtless　here　an　example　of　the　errors　alluded　to　above；　inseparable　from　readings　taken　in　ascent　and　descent。
  A　calculation　made　by　Green　in　his　earlier　years　has　a　certain　value。　　By　the　time　he　had　accomplished　200　ascents　he　was　at　pains　to　compute　that　he　had　travelled　across　country　some　6；000　miles；　which　had　been　traversed　in　240　hours。　　From　this　it　would　follow　that　the　mean　rate　of　travel　in　aerial　voyages　will　be　about　twenty…five　miles　per　hour。　　Towards　the　end　of　his　career　we　find　it　stated　by　Lieutenant　G。　Grover；　R。E。；　that　〃the　Messrs。　Green；　Father　and　Son；　have　made　between　them　some　930　ascents；　in　none　of　which　have　they　met　with　any　material　accident　or　failure。〃　　This　is　wonderful　testimony；　indeed；　and　we　may　here　add　the　fact　that　the　father　took　up　his　own　father；　then　at　the　age　of　eighty…three；　in　a　balloon　ascent　of　1845；　without　any　serious　consequences。　　But　it　is　time　that　some　account　should　be　given　of　a　particular　occasion　which　at　least　provided　the　famous　aeronaut　with　an　adventure　spiced　with　no　small　amount　of　risk。　　It　was　on　the　5th　of　July；　1850；　that　Green　ascended；　with　Rush　as　his　companion；　from　Vauxhall；　at　the　somewhat　late　hour　of　7。50　p。m。；　using；　as　always；　the　great　Nassau　balloon。　　The　rate　of　rise　must　have　been　very　considerable；　and　they　presently　record　an　altitude　of　no　less　than　20；000　feet；　and　a　temperature　of　12　degrees　below　freezing。　　They　were　now　above　the　clouds；　where　all　view　of　earth　was　lost；　and；　not　venturing　to　remain　long　in　this　situation；　they　commenced　a　rapid　descent；　and　on　emerging　below　found　themselves　sailing　down　Sea　Reach　in　the　direction　of　Nore　Sands；　when　they　observed　a　vessel。　　Their　chance　of　making　land　was；　to　say　the　least；　uncertain；　and　Green；　considering　that　his　safety　lay　in　bespeaking　the　vessel's　assistance；　opened　the　valve　and　brought　the　car　down　in　the　water　some　two　miles　north　of　Sheerness；　the　hour　being　8。45；　and　only　fifty…five　minutes　since　the　start。　　The　wind　was　blowing　stiffly；　and；　catching　the　hollow　of　the　half…inflated　balloon；　carried　the　voyagers　rapidly　down　the　river；　too　fast；　indeed；　to　allow　of　the　vessel's　overtaking　them。　　This　being　soon　apparent；　Green　cast　out　his　anchor；　and　not　without　result；　for　it　shortly　became　entangled　in　a　sunken　wreck；　and　the　balloon　was　promptly　〃brought　up；〃　though　struggling　and　tossing　in　the　broken　water。　　A　neighbouring　barge　at　once　put　off　a　boat　to　the　rescue；　and　other　boats　were　despatched　by　H。M。　cutter　Fly；　under　Commander　Gurling。　　Green　and　Rush　were　speedily　rescued；　but　the　balloon　itself　was　too　restive　and　dangerous　an　object　to　approach　with　safety。　　At　Green's　suggestion；　therefore；　a　volley　of　musketry　was　fired　into　the　silk'　after　which　it　became　possible　to　pass　a　rope　around　it　and　expel　the　gas。　　Green　subsequently　relates　how　it　took　a　fortnight　to　restore　the　damage；　consisting　of　sixty…two　bullet　rents　and　nineteen　torn　gores。
  Green's　name　will　always　be　famous；　if　only　for　the　fact　that　it　was　he　who　first　adopted　the　use　of　coal　gas　in　his　calling。　　This；　it　will　be　remembered；　was　in　1821；　and　it　should　be　borne　in　mind　that　at　that　time　household　gas　had　only　recently　been　introduced。　　In　point　of　fact；　it　first　lighted　Pall　Mall　in　1805；　and　it　was　not　used　for　the　general　lighting　of　London　till　1814。
  We　are　not　surprised　to　find　that　the　great　aeronaut　at　one　time　turned　his　attention　to　the　construction　of　models；　and　this　with　no　inconsiderable　success。　　A　model　of　his　was　exhibited　in　1840　at　the　Polytechnic　Institution；　and　is　described　in　the　Times　as　consisting　of　a　miniature　balloon　of　three　feet　diameter；　inflated　with　coal　gas。　　It　was　acted　on　by　fans；　which　were　operated　by　mechanism　placed　in　the　car。　　A　series　of　three　experiments　was　exhibited。　　First；　the　balloon　being　weighted　so　as　to　remain　poised　in　the　still　air　of　the　building；　the　mechanism　was　started；　and　the　machine　rose　steadily　to　the　ceiling。　　The　fans　were　then　reversed；　when　the　model；　equally　gracefully；　descended　to　the　floor。　　Lastly；　the　balloon；　with　a　weighted　trail　rope；　being　once　more　balanced　in　mid…air；　the　fans　were　applied　laterally；　when　the　machine　would　take　a　horizontal　flight；　pulling　the　trail　rope　after　it；　with　an　attached　weight　dragging　along　the　floor　until　the　mechanism　had　run　down；　when　it　again　remained　stationary。　　The　correspondent　of　the　Times　continues；　〃Mr。　Green　states　that　by　these　simple　means　a　voyage　across　the　Atlantic　may　be　performed　in　three　or　four　days；　as　easily　as　from　Vauxhall　Gardens　to　Nassau。〃
  We　can　hardly　attribute　this　statement　seriously　to　one　who　knew　as　well　as　did　Green　how　fickle　are　the　winds；　and　how　utterly　different　are　the　conditions　between　the　still　air　of　a　room　and　those　of　the　open　sky。　　His　insight　into　the　difficulties　of　the　problem　cannot　have　been　less　than　that　of　his　successor；　Coxwell；　who；　as　the　result　of　his　own　equally　wide　experience；　states　positively；　〃I　could　never　imagine　a　motive　power　of　sufficient　force　to　direct　and　guide　a　balloon；　much　less　to　enable　a　man　or　a　machine　to　fly。〃　　Even　when　modern　invention　had　produced　a　motive　power　undreamed　of　in　the　days　we　are　now　considering；　Coxwell　declares　his　conviction　that　inherent　difficulties　would　not　be　overcome　〃unless　the　air　should　invariably　remain　in　a　calm　state。〃
  It　would　be　tedious　and　scarcely　instructive　to　inquire　into　the　various　forms　of　flying　machines　that　were　elaborated　at　this　period；　but　one　that　was　designed　in　America　by　Mr。　Henson；　and　with　which　it　was　seriously　contemplated　to　attempt　to　cross　the　Atlantic；　may　be　briefly　described。　　In　theory　it　was　supposed　to　be　capable　of　being　sustained　in　the　air　by　virtue　of　the　speed　mechanically　imparted　to　it；　and　of　the　angle　at　which　its　advancing　under　surface　would　meet　the　air。　　The　inventor　claimed　to　have　produced　a　steam　engine　of　extreme　lightness　as　well　as　efficiency；　and　for　the　rest　his　machine　consisted　of　a　huge　aero…plane　propelled　by　fans　with　oblique　vanes；　while　a　tail　somewhat　resembling　that　of　a　bird　was　added；　as　also　a　rudder；　the　functions　of　which　were　to　direct　the　craft　vertically　and　horizontally　respectively。　　Be　it　here　recorded　that　the　machine　did　not　cross　the　Atlantic。
  One　word　as　to　the　instruments　used　up　to　this　time　for　determining　altitudes。　　These　were；　in　general；　ordinary　mercurial　barometers；　protected　in　various　ways。　　Green　encased　his　instrument　in　a　simple　metal　tube；　which　admitted　of　the　column　of　mercury　being　easily　read。　　This　instrument；　which　is　generally　to　be　seen　held　in　his　hand　in　Green's　old　portraits；　might　be　mistaken　for　a　mariner's　telescope。　　It　is　now　in　the　possession　of　the　family　of　Spencers；　the　grandchildren　of　his　old　aeronautical　friend　and　colleague；　and　it　is　stated　that　with　all　his　care　the　glass　was　not　infrequently　broken　in　a　descent。
  Wise；　with　characteristic　ingenuity；　devised　a　rough…and…ready　height　instrument；　which　he　claims　to　have　answered　well。　　It　consisted　simply　of　a　common　porter　bottle；　to　the　neck　of　which　was　joined　a　bladder　of　the　same　capacity。　　The　bottle　being　filled　with　air　of　the　density　of　that　on　the　ground；　and　the　bladder　tied　on　in　a　collapsed　state；　the　expansion　of　the　air　in　the　bottle　would　gradually　fill　the　bladder　as　it　rose　into　the　rarer　regions　of　the　atmosphere。　　Experience　would　then　be　trusted　to　enable　the　aeronaut　to　judge　his　height　from　the　amount　of　inflation　noticeable　in　the　bladder。
  CHAPTER　XII。　HENRY　COXWELL　AND　HIS　CONTEMPORARIES。
  Mention　should　be　made　in　these　pages　of　a　night　sail　of　a　hundred　miles；　boldly　carried　out　in　1849　by　M。　Arban；　which　took　the　voyager　from　Marseilles　to　Turin　fairly　over　the　Alps。　　The　main　summit　was　reached　at　11　p。m。；　when　the　〃snow；　cascades；　and　rivers　were　all　sparkling　under　the　moon；　and　the　ravines　and　rocks　produced　masses　of　darkness　which　served　as　shadows　to　the　gigantic　picture。〃　　Ar