of　the　squared　figure。　That　would　make
  the　problem　as　follows：
  45　X　45　=　2025　/　200　=　10。125；　or；
  45　X　45　…　2025　X　。005　=　10。125。
  Again；　twenty…five　miles　per　hour　would　be
  25　X　25　=　625；　and　this　multiplied　by　。005　equals
  2　pounds　pressure。
  CONVERTING　HOURS　INTO　MINUTES。It　is　sometimes
  confusing　to　think　of　miles　per　hour；　when
  you　wish　to　express　it　in　minutes　or　seconds。　A
  simple　rule；　which　is　not　absolutely　accurate；　but
  is　correct　within　a　few　feet；　in　order　to　express
  the　speed　in　feet　per　minute；　is　to　multiply　the
  figure　indicating　the　miles　per　hour；　by　8　3/4。
  To　illustrate：　If　the　wind　is　moving　at　the
  rate　of　twenty　miles　an　hour；　it　will　travel　in　that
  time　105；600　feet　（5280　X　20）。　As　there　are　sixty
  minutes　in　an　hour；　105；600　divided　by　60；　equals
  1760　feet　per　minute。　Instead　of　going　through
  all　this　process　of　calculating　the　speed　per　minute；
  remember　to　multiply　the　speed　in　miles　per
  hour　by　90；　which　will　give　1800　feet。
  This　is　a　little　more　then　two　per　cent。　above
  the　correct　figure。　Again；　40　X　90　equals　3600。
  As　the　correct　figure　is　3520；　a　little　mental　calculation
  will　enable　you　to　correct　the　figures　so
  as　to　get　it　within　a　few　feet。
  CHANGING　SPEED　HOURS　TO　SECONDS。As　one…
  sixtieth　of　the　speed　per　minute　will　represent　the
  rate　of　movement　per　second；　it　is　a　comparatively
  easy　matter　to　convert　the　time　from　speed　in
  miles　per　hour　to　fraction　of　a　mile　traveled　in
  a　second；　by　merely　taking　one…half　of　the　speed
  in　miles；　and　adding　it；　which　will　very　nearly　express
  the　true　number　of　feet。
  As　examples；　take　the　following：　If　the　wind
  is　traveling　20　miles　an　hour；　it　is　easy　to　take
  one…half　of　20；　which　is　10；　and　add　it　to　20；　making
  30；　as　the　number　of　feet　per　second。　If　the
  wind　travels　50　miles　per　hour；　add　25；　making
  75；　as　the　speed　per　second。
  The　correct　speed　per　second　of　a　wind　traveling
  20　miles　an　hour　is　a　little　over　29　feet。　At
  50　miles　per　hour；　the　correct　figure　is　73　1/3　feet；
  which　show　that　the　figures　under　this　rule　are
  within　about　one　per　cent。　of　being　correct。
  With　the　table　before　you　it　will　be　an　easy
  matter；　by　observing　the　air　pressure　indicator；
  to　determine　the　proper　speed　for　the　anemometer。
  Suppose　it　shows　a　pressure　of　two　pounds；
  which　will　indicate　a　speed　of　twenty　miles　an
  hour。　You　have　thus　a　fixed　point　to　start　from。
  PRESSURE　AS　THE　SQUARE　OF　THE　SPEED。Now
  it　must　not　be　assumed　that　if　the　pressure　at
  twenty　miles　an　hour　is　two　pounds；　that　forty
  miles　an　hour　it　is　four　pounds。　The　pressure
  is　as　the　square　of　the　speed。　This　may　be　explained
  as　follows：　As　the　speed　of　the　wind
  increases；　it　has　a　more　effective　push　against　an
  object　than　its　rate　of　speed　indicates；　and　this
  is　most　simply　expressed　by　saying　that　each　time
  the　speed　is　doubled　the　pressure　is　four　times
  greater。
  As　an　example　of　this；　let　us　take　a　speed　of　ten
  miles　an　hour；　which　means　a　pressure　of　one…
  half　pound。　Double　this　speed；　and　we　have　20
  miles。　Multiplying　one…half　pound　by　4；　the　result
  is　2　pounds。　Again；　double　20；　which　means
  40　miles；　and　multiplying　2　by　4；　the　result　is　8。
  Doubling　forty　is　eighty　miles　an　hour；　and　again
  multiplying　8　by　4；　we　have　32　as　the　pounds　pressure
  at　a　speed　of　80　miles　an　hour。
  The　anemometer；　however；　is　constant　in　its
  speed。　If　the　pointer　should　turn　once　a　second
  at　10　miles　an　hour；　it　would　turn　twice　at　20　miles
  an　hour；　and　four　times　a　second　at　40　miles　an
  hour。
  GYROSCOPIC　BALANCE。Some　advance　has　been
  made　in　the　use　of　the　gyroscope　for　the　purpose
  of　giving　lateral　stability　to　an　aeroplane。　While
  the　best　of　such　devices　is　at　best　a　makeshift；
  it　is　well　to　understand　the　principle　on　which　they
  operate；　and　to　get　an　understanding　how　they　are
  applied。
  THE　PRINCIPLE　INVOLVED。The　only　thing
  known　about　the　gyroscope　is；　that　it　objects　to
  changing　the　plane　of　its　rotation。　This　statement
  must　be　taken　with　some　allowance；　however；
  as；　when　left　free　to　move；　it　will　change　in
  one　direction。
  To　explain　this　without　being　too　technical；　examine
  Fig。　63；　which　shows　a　gyroscopic　top；　one
  end　of　the　rim　A；　which　supports　the　rotating
  wheel　B；　having　a　projecting　finger　C；　that　is
  mounted　on　a　pin…point　on　the　upper　end　of　the
  pedestal　D。
  _Fig。　63。　The　Gyroscope。_
  When　the　wheel　B　is　set　in　rotation　it　will　maintain
  itself　so　that　its　axis　E　is　horizontal；　or　at
  any　other　angle　that　the　top　is　placed　in　when　the
  wheel　is　spun。　If　it　is　set　so　the　axis　is　horizontal
  the　wheel　B　will　rotate　on　a　vertical　plane；
  and　it　forcibly　objects　to　any　attempt　to　make　it
  turn　except　in　the　direction　indicated　by　the
  curved　arrows　F。
  The　wheel　B　will　cause　the　axis　E　to　swing
  around　on　a　horizontal　plane；　and　this　turning
  movement　is　always　in　a　certain　direction　in　relation
  to　the　turn　of　the　wheel　B；　and　it　is　obvious；
  therefore；　that　to　make　a　gyroscope　that
  will　not　move；　or　swing　around　an　axis；　the　placing
  of　two　such　wheels　side　by　side；　and　rotated
  in　opposite　directions；　will　maintain　them　in　a
  fixed　position；　this　can　also　be　accomplished　by
  so　mounting　the　two　that　one　rotates　on　a　plane
  at　right　angles　to　the　other。
  _Fig。　64。　Application　of　the　Gyroscope。_
  THE　APPLICATION　OF　THE　GYROSCOPE。Without
  in　any　manner　showing　the　structural　details　of
  the　device；　in　its　application　to　a　flying　machine；
  except　in　so　far　as　it　may　be　necessary　to　explain
  its　operation；　we　refer　to　Fig。　64；　which
  assumes　that　A　represents　the　frame　of　the　aeroplane；
  and　B　a　frame　for　holding　the　gyroscopic
  wheel　C；　the　latter　being　mounted　so　it　rotates　on
  a　horizontal　plane；　and　the　frame　B　being　hinged
  fore　and　aft；　so　that　it　is　free　to　swing　to　the　right
  or　to　the　left。
  For　convenience　in　explaining　the　action；　the
  planes　E　are　placed　at　right　angles　to　their　regular
  positions；　F　being　the　forward　margin　of　the
  plane；　and　G　the　rear　edge。　Wires　H　connect
  the　ends　of　the　frame　B　with　the　respective
  planes；　or　ailerons；　E；　and　another　wire　I　joins
  the　downwardly…projecting　arms　of　the　two
  ailerons；　so　that　motion　is　transmitted　to　both　at
  the　same　time；　and　by　a　positive　motion　in　either
  direction。
  _Fig。　65。　Action　of　the　Gyroscope。_
  In　the　second　figure；　65；　the　frame　of　the　aeroplane
  is　shown　tilted　at　an　angle；　so　that　its　right
  side　is　elevated。　As　the　gyroscopic　wheel　remains
  level　it　causes　the　aileron　on　the　right　side　to
  change　to　a　negative　angle；　while　at　the　same
  time　giving　a　positive　angle　to　the　aileron　on　the
  left　side；　which　would；　as　a　result；　depress　the
  right　side；　and　bring　the　frame　of　the　machine
  back　to　a　horizontal　position。
  FORE　AND　AFT　GYROSCOPIC　CONTROL。It　is
  obvious　that　the　same　application　of　this　force　may
  be　applied　to　control　the　ship　fore　and　aft；　although
  it　is　doubtful　whether　such　a　plan　would
  have　any　advantages；　since　this　should　be　wholly
  within　the　control　of　the　pilot。
  Laterally　the　ship　should　not　be　out　of　balance；
  fore　and　aft　this　is　a　necessity；　and　as　the　great
  trouble　with　all　aeroplanes　is　to　control　them
  laterally；　it　may　well　be　doubted　whether　it　would
  add　anything　of　value　to　the　machine　by　having
  an　automatic　fore　and　aft　control；　which　might；
  in　emergencies；　counteract　the　personal　control　of
  the　operator。
  ANGLE　INDICATOR。In　flight　it　is　an　exceedingly
  difficult　matter　for　the　pilot　to　give　an　accurate
  idea　of　the　angle　of　the　planes。　If　the　air　is
  calm　and　he　is　moving　over　a　certain　course；　and
  knows；　from　experience；　what　his　speed　is；　he　may
  be　able　to　judge　of　this　factor；　but　he　cannot　tell
  what　changes　take　place　under　certain　conditions
  during　the　flight。
  For　this　purpose　a　simple　little　indicator　may
  be　provided；　shown　in　Fig。　66；　which　is　merely　a
  vertical　board　A；　with　a　pendulum　B；　swinging
  fore　and　aft　from　a　pin　a　which　projects　out
  from　the　board　a　short　distance　above　its　center。
  The　upper　end　of　the　pendulum　has　a　heart…
  shaped　wire　structure　D；　that　carries　a　sliding
  weight　E。　Normally；　when　the　aeroplane　is　on
  an　even　keel；　or　is　even　at　an　angle；　the　weight
  E　rests　within　the　bottom　of　the　loop　D；　but
  should　there　be　a　sudden　downward　lurch　or　a
  quick　upward　inclination；　which　would　cause　the
  pendulum　below　to　rapidly　swing　in　either
  direction；　the　sliding　weight　E　would　at　once　move
  forward　in　the　same　direction　that　the　pendulum
  had　moved；　and　thus　counteract；　for　the　instant
  only；　the　swing；　when　it　would　again　drop　back
  into　its　central　position。
  _Fig。　66。　Angle　Indicator。_
  With　such　an　arrangement；　the　pendulum　would
  hang　vertically　at　all　times；　and　the　pointer　below；
  being　in　range　of　a　circle　with　degrees
  indicated　thereon；　and　the　base　attached　to　the
  frame