the　wind　the　speed　must　be　greater　than　when　flying
  against　it。
  By　greater　speed　is　meant　relative　to　the　earth。
  If　the　machine　has　a　speed　of　thirty　miles　an　hour；
  in　still　air；　the　speed　would　be　forty　miles　an　hour
  going　with　the　wind；　but　only　twenty　miles　against
  the　wind。　Second；　the　banking　of　the　planes
  against　the　air　is　more　effective　when　going　into
  the　wind　than　when　traveling　with　it；　and；　therefore；
  the　speed　at　which　you　contact　with　the　earth
  is　lessened　to　such　an　extent　that　a　comparatively
  easy　landing　is　effected。
  THE　FOURTH　STAGE。After　sufficient　time　has
  been　devoted　to　the　long　turns　shorter　turns　may
  be　made；　and　these　also　require　the　same　care；
  and　will　give　an　opportunity　to　use　the　lateral
  controls　to　a　greater　extent。　Begin　the　turns；　not
  by　an　abrupt　throw　of　the　turning　rudder；　but
  bring　it　around　gently；　correcting　the　turning
  movement　to　a　straight　course；　if　you　find　the
  machine　inclined　to　tilt　too　much；　until　you　get　used
  to　the　sensation　of　keeling　over。　Constant　practice
  at　this　will　soon　give　confidence；　and　assure
  you　that　you　have　full　control　of　the　machine。
  THE　FIGURE　8。You　are　now　to　increase　the
  height　of　flying；　and　this　involves　also　the　ability
  to　turn　in　the　opposite　direction；　so　that　you　may
  be　able　to　experience　the　sensation　of　using　the
  stabilizers　in　the　opposite　direction。　You　will
  find　in　this　practice　that　the　senses　must　take　in
  the　course　of　the　wind　from　two　quarters　now；　as
  you　attempt　to　describe　the　figure　8。
  This　is　a　test　which　is　required　in　order　to　obtain
  a　pilot's　license。　It　means　that　you　shall
  be　able　to　show　the　ability　to　turn　in　either　direction
  with　equal　facility。　To　keep　an　even　flying
  altitude　while　describing　this　figure　in　a　wind；　is
  the　severest　test　that　can　be　exacted。
  THE　VOLPLANE。This　is　the　technical　term　for
  a　glide。　Many　accidents　have　been　recorded　owing
  to　the　stopping　of　the　motor；　which　in　the
  past　might　have　been　avoided　if　the　character　of
  the　glide　had　been　understood。　The　only　thing
  that　now　troubles　the　pilot　when　the　engine　〃goes
  dead；〃　is　to　select　a　landing　place。
  The　proper　course　in　such　a　case　is　to　urge
  the　machine　to　descend　as　rapidly　as　possible；　in
  order　to　get　a　headway；　for　the　time　being。　As
  there　is　now　no　propelling　force　the　glide　is　depended
  upon　to　act　as　a　substitute。　The　experienced
  pilot　will　not　make　a　straight…away　glide；
  but　like　the　vulture；　or　the　condor；　and　birds　of
  that　class；　soar　in　a　circle；　and　thus；　by　passing
  over　and　over　the　same　surfaces　of　the　earth；　enable
  him　to　select　a　proper　landing　place。
  THE　LANDING。The　pilot　who　can　make　a　good
  landing　is　generally　a　good　flyer。　It　requires
  nicety　of　judgment　to　come　down　properly。　One
  thing　which　will　appear　novel　after　the　first　altitude
  flights　are　attempted　is　the　peculiar　sensation
  of　the　apparently　increased　speed　as　the　earth
  comes　close　up　to　the　machine。
  At　a　height　of　one　hundred　feet；　flying　thirty
  miles　an　hour；　does　not　seem　fast；　because　the　surface
  of　the　earth　is　such　a　distance　away　that　particular
  objects　remain　in　view　for　some　moments；
  but　when　within　ten　feet　of　the　surface　the　same
  object　is　in　the　eye　for　an　instant　only。
  This　lends　a　sort　of　terror　to　the　novice。　He
  imagines　a　great　many　things；　but　forgets　some
  things　which　are　very　important　to　do　at　this
  time。　One　is；　that　the　front　of　the　machine　must
  be　thrown　up　so　as　to　bank　the　planes　against　the
  wind。　The　next　is　to　shut　off　the　power；　which
  is　to　be　done　the　moment　the　wheels　strike　the
  ground；　or　a　little　before。
  Upon　his　judgment　of　the　time　of　first　touching
  the　earth　depends　the　success　of　safely　alighting。
  He　may　bank　too　high；　and　come　down　on　the　tail
  with　disastrous　results。　If　there　is　plenty　of　field
  room　it　is　better　to　come　down　at　a　less　angle；　or
  even　keep　the　machine　at　an　even　keel；　and　the
  elevator　can　then　depress　the　tail　while　running
  over　the　ground；　and　thus　bring　the　machine　to
  rest。
  Frequently；　when　about　to　land　the　machine
  will　rock　from　side　to　side。　In　such　a　case　it　is
  far　safer　to　go　up　into　the　air　than　to　make　the
  land；　because；　unless　the　utmost　care　is　exercised；
  one　of　the　wing　tips　will　strike　the　earth　and
  wreck　the　machine。
  Another　danger　point　is　losing　headway；　as　the
  earth　is　neared；　due　to　flying　at　too　flat　an　angle；
  or　against　a　wind　that　happens　to　be　blowing　particularly
  hard　at　the　landing　place。　If　the　motor
  is　still　going　this　does　not　make　so　much　difference；
  but　in　a　volplane　it　means　that　the　descent
  must　be　so　steep；　at　the　last　moment　of　flight；　that
  the　chassis　is　liable　to　be　crushed　by　the　impact。
  FLYING　ALTITUDE。It　is　doubtful　whether　the
  disturbed　condition　of　the　atmosphere；　due　to
  the　contour　of　the　earth's　surface；　reaches　higher
  than　500　feet。　Over　a　level　area　it　is　certain　that
  it　is　much　less；　but　in　some　sections　of　the　country；
  where　the　hill　ranges　extend　for　many　miles；
  at　altitudes　of　three　and　four　hundred　feet；　the
  upper　atmosphere　may　be　affected　for　a　thousand
  feet　above。
  Prof。　Lowe；　in　making　a　flight　with　a　balloon；
  from　Cincinnati　to　North　Carolina；　which　lasted
  a　day　and　all　of　one　night；　found　that　during　the
  early　morning　the　balloon；　for　some　reason；　began
  to　ascend；　and　climbed　nearly　five　thousand
  feet　in　a　few　hours；　and　as　unaccountably
  began　to　descend　several　hours　before　he　landed。
  Before　it　began　to　ascend；　he　was　on　the　western
  side　of　the　great　mountain　range　which　extends
  south　from　Pennsylvania　and　terminates　in
  Georgia。　He　was　actually　climbing　the　mountain
  in　a　drift　of　air　which　was　moving　eastwardly；
  and　at　no　time　was　he　within　four　thousand　feet
  of　the　earth　during　that　period；　which　shows　that
  air　movements　are　of　such　a　character　as　to　exert
  their　influence　vertically　to　great　heights。
  For　cross　country　flying　the　safest　altitude　is
  1000　feet；　a　distance　which　gives　ample　opportunity
  to　volplane；　if　necessary；　and　it　is　a　height
  which　enables　the　pilot　to　make　observations　of　the
  surface　so　as　to　be　able　to　judge　of　its　character。
  But　explanations　and　statements；　and　the　experiences
  of　pilots　might　be　detailed　in　pages；　and
  still　it　would　be　ineffectual　to　teach　the　art　of　flying。
  The　only　sure　course　is　to　do　the　work　on
  an　actual　machine。
  Many　of　the　experiences　are　valuable　to　the
  learner；　some　are　merely　in　the　nature　of　cautions；
  and　it　is　advisable　for　the　beginner　to　learn　what
  the　experiences　of　others　have　been；　although　they
  may　never　be　called　upon　to　duplicate　them。
  All　agree　that　at　great　elevations　the　flying
  conditions　are　entirely　different　from　those　met
  with　near　the　surface　of　the　ground；　and　the　history
  of　accidents　show　that　in　every　case　where
  a　mishap　was　had　at　high　altitude　it　came　about
  through　defect　in　the　machine；　and　not　from　gusts
  or　bad　air　condition。
  On　the　other　hand；　the　uptilting　of　machines；
  the　accidents　due　to　the　so…called　〃Holes　in　the
  air；〃　which　have　dotted　the　historic　pages　with
  accidents；　were　brought　about　at　low　altitudes。
  At　from　two　to　five　thousand　feet　the　air　may　be
  moving　at　speeds　of　from　twenty　to　forty　miles
  an　hour；great　masses　of　winds；　like　the　trade
  stream；　which　are　uniform　over　vast　areas。　To
  the　aviator　flying　in　such　a　field；　with　the　earth
  hidden　from　him；　there　would　be　no　wind　to　indicate
  that　he　was　moving　in　any　particular　direction。
  He　would　fly　in　that　medium；　in　any　direction；
  without　the　slightest　sense　that　he　was　in　a　gale。
  It　would　not　affect　the　control　of　the　machine；
  because　the　air；　though　moving　as　a　mass；　would
  be　the　same　as　flying　in　still　air。　It　is　only　when
  he　sees　fixed　objects　that　he　is　conscious　of　the
  movement　of　the　wind。
  CHAPTER　XIII
  THE　PROPELLER
  BY　far　the　most　difficult　problem　connected
  with　aviation　is　the　propeller。　It　is　the　one　great
  vital　element　in　the　science　and　art　pertaining　to
  this　subject　which　has　not　advanced　in　the　slightest
  degree　since　the　first　machine　was　launched。
  The　engine　has　come　in　for　a　far　greater　share
  of　expert　experimental　work；　and　has　advanced
  most　rapidly　during　the　past　ten　years。　But；
  strange　to　say；　the　propeller　is；　essentially；　the
  same　with　the　exception　of　a　few　small　changes。
  PROPELLER　CHANGES。The　changes　which　have
  been　made　pertaining　to　the　form　of　structure；
  principally；　and　in　the　use　of　new　materials。　The
  kind　of　wood　most　suitable　has　been　discovered；
  but　the　lines　are　the　same；　and　nothing　has　been
  done　to　fill　the　requirement　which　grows　out　of
  the　difference　in　speed　when　a　machine　is　in　the
  act　of　launching　and　when　it　is　in　full　flight。
  PROPELLER　SHAPE。It　cannot　be　possible　that
  the　present　shape　of　the　propeller　will　be　its　ultimate
  form。　It　is　inconceivabl