Method　for　Determining　the　Movement　of　a　Bomb。
  The　Great　Extent　of　Modern　Battle　Lines。　The　Aeroplane
  Detecting　the　Movements　of　Armies。　The　Effective
  Height　for　Scouting。　Sizes　of　Objects　at　Great
  Distances。　Some　Daring　Feats　in　War。　The　German
  Taube。　How　Aeroplanes　Report　Observations。　Signal
  Flags。　How　Used。　Casualties　Due　to　Bombs
  From　Aeroplanes。
  GLOSSARY
  INTRODUCTORY
  In　preparing　this　volume　on　Flying　Machines
  the　aim　has　been　to　present　the　subject　in　such　a
  manner　as　will　appeal　to　boys；　or　beginners；　in
  this　field　of　human　activity。
  The　art　of　aviation　is　in　a　most　primitive　state。
  So　many　curious　theories　have　been　brought　out
  that；　while　they　furnish　food　for　thought；　do　not；
  in　any　way；　advance　or　improve　the　structure　of
  the　machine　itself；　nor　are　they　of　any　service
  in　teaching　the　novice　how　to　fly。
  The　author　considers　it　of　far　more　importance
  to　teach　right　principles；　and　correct　reasoning
  than　to　furnish　complete　diagrams　of　the　details
  of　a　machine。　The　former　teach　the　art；　whereas
  the　latter　merely　point　out　the　mechanical
  arrangements；　independently　of　the　reasons　for
  making　the　structures　in　that　particular　way。
  Relating　the　history　of　an　art；　while　it　may　be
  interesting　reading；　does　not　even　lay　the　foundations
  of　a　knowledge　of　the　subject；　hence　that
  field　has　been　left　to　others。
  The　boy　is　naturally　inquisitive；　and　he　is　interested
  in　knowing　WHY　certain　things　are
  necessary；　and　the　reasons　for　making　structures　in
  particular　ways。　That　is　the　void　into　which
  these　pages　are　placed。
  The　author　knows　from　practical　experience；
  while　experimenting　with　and　building　aeroplanes；
  how　eagerly　every　boy　inquires　into　details。
  They　want　the　reasons　for　things。
  One　such　instance　is　related　to　evidence　this
  spirit　of　inquiry。　Some　boys　were　discussing　the
  curved　plane　structure。　One　of　them　ventured
  the　opinion　that　birds'　wings　were　concaved　on　the
  lower　side。　〃But；〃　retorted　another；　〃why　are
  birds'　wings　hollowed？〃
  This　was　going　back　to　first　principles　at　one
  leap。　It　was　not　satisfying　enough　to　know　that
  man　was　copying　nature。　It　was　more　important
  to　know　why　nature　originated　that　type　of　formation；
  because；　it　is　obvious；　that　if　such　structures
  are　universal　in　the　kingdom　of　flying　creatures；
  there　must　be　some　underlying　principle
  which　accounted　for　it。
  It　is　not　the　aim　of　the　book　to　teach　the　art
  of　flying；　but　rather　to　show　how　and　why　the
  present　machines　fly。　The　making　and　the　using
  are　separate　and　independent　functions；　and　of
  the　two　the　more　important　is　the　knowledge　how
  to　make　a　correct　machine。
  Hundreds　of　workmen　may　contribute　to　the
  building　of　a　locomotive；　but　one　man；　not　a
  builder；　knows　better　how　to　handle　it。　To
  manipulate　a　flying　machine　is　more　difficult　to
  navigate　than　such　a　ponderous　machine；　because
  it　requires　peculiar　talents；　and　the　building　is
  still　more　important　and　complicated；　and　requires
  the　exercise　of　a　kind　of　skill　not　necessary
  in　the　locomotive。
  The　art　is　still　very　young；　so　much　is　done
  which　arises　from　speculation　and　theories；　too
  much　dependence　is　placed　on　the　aviator；　the
  desire　in　the　present　condition　of　the　art　is　to　exploit
  the　man　and　not　the　machine；　dare…devil　exhibitions
  seem　to　be　more　important　than　perfecting
  the　mechanism；　and　such　useless　attempts　as
  flying　upside　down；　looping　the　loop；　and　characteristic
  displays　of　that　kind；　are　of　no　value　to
  the　art。
  THE　AUTHOR。
  AEROPLANES
  CHAPTER　I
  THEORIES　AND　FACTS　ABOUT　FLYING
  THE　〃SCIENCE〃　OF　AVIATION。It　may　be
  doubted　whether　there　is　such　a　thing　as　a　〃science
  of　aviation。〃　Since　Langley；　on　May　6；
  1896；　flew　a　motor…propelled　tandem　monoplane
  for　a　minute　and　an　half；　without　a　pilot；　and　the
  Wright　Brothers　in　1903　succeeded　in　flying　a
  bi…plane　with　a　pilot　aboard；　the　universal　opinion
  has　been；　that　flying　machines；　to　be　successful；
  must　follow　the　structural　form　of　birds；　and
  that　shape　has　everything　to　do　with　flying。
  We　may　be　able　to　learn　something　by　carefully
  examining　the　different　views　presented　by
  those　interested　in　the　art；　and　then　see　how　they
  conform　to　the　facts　as　brought　out　by　the　actual
  experiments。
  MACHINE　TYPES。There　is　really　but　one　type
  of　plane　machine。　While　technically　two　forms
  are　known；　namely；　the　monoplane　and　the
  bi…plane；　they　are　both　dependent　on　outstretched
  wings；　longer　transversely　than　fore　and　aft；　so
  far　as　the　supporting　surfaces　are　concerned；　and
  with　the　main　weight　high　in　the　structure；　thus；
  in　every　particular；　conforming　to　the　form
  pointed　out　by　nature　as　the　apparently　correct
  type　of　a　flying　structure。
  SHAPE　OR　FORM　NOT　ESSENTIAL。It　may　be
  stated　with　perfect　confidence；　that　shape　or　form
  has　nothing　to　do　with　the　mere　act　of　flying。　It
  is　simply　a　question　of　power。　This　is　a　broad
  assertion；　and　its　meaning　may　be　better　understood
  by　examining　the　question　of　flight　in　a
  broad　sense。
  A　STONE　AS　A　FLYING　MACHINE。When　a　stone
  is　propelled　through　space；　shape　is　of　no　importance。
  If　it　has　rough　and　jagged　sides　its　speed
  or　its　distance　may　be　limited；　as　compared　with
  a　perfectly　rounded　form。　It　may　be　made　in
  such　a　shape　as　will　offer　less　resistance　to　the　air
  in　flight；　but　its　actual　propulsion　through　space
  does　not　depend　on　how　it　is　made；　but　on　the
  power　which　propelled　it；　and　such　a　missile　is　a
  true　heavier…than…air　machine。
  A　flying　object　of　this　kind　may　be　so　constructed
  that　it　will　go　a　greater　distance；　or　require
  less　power；　or　maintain　itself　in　space　at
  less　speed；　but　it　is　a　flying　machine；　nevertheless；
  in　the　sense　that　it　moves　horizontally　through　the
  air。
  POWER　THE　GREAT　ELEMENT。Now；　let　us　examine
  the　question　of　this　power　which　is　able　to
  set　gravity　at　naught。　The　quality　called　energy
  resides　in　material　itself。　It　is　something　within
  matter；　and　does　not　come　from　without。　The
  power　derived　from　the　explosion　of　a　charge　of
  powder　comes　from　within　the　substance；　and　so
  with　falling　water；　or　the　expansive　force　of
  steam。
  GRAVITY　AS　POWER。Indeed；　the　very　act　of　the
  ball　gradually　moving　toward　the　earth；　by　the
  force　of　gravity；　is　an　illustration　of　a　power
  within　the　object　itself。　Long　after　Galileo
  firmly　established　the　law　of　falling　bodies　it　began
  to　dawn　on　scientists　that　weight　is　force。
  After　Newton　established　the　law　of　gravitation
  the　old　idea；　that　power　was　a　property　of　each
  body；　passed　away。
  In　its　stead　we　now　have　the　firmly　established
  view；　that　power　is　something　which　must　have
  at　least　two　parts；　or　consist　in　pairs；　or　two　elements
  acting　together。　Thus；　a　stone　poised　on
  a　cliff；　while　it　exerts　no　power　which　can　be
  utilized；　has；　nevertheless；　what　is　called　potential
  energy。　When　it　is　pushed　from　its　lodging　place
  kinetic　energy　is　developed。　In　both　cases；
  gravity；　acting　in　conjunction　with　the　mass　of
  the　stone；　produced　power。
  So　in　the　case　of　gunpowder。　It　is　the　unity　of
  two　or　more　substances；　that　causes　the　expansion
  called　power。　The　heat　of　the　fuel　converting
  water　into　steam；　is　another　illustration　of　the
  unity　of　two　or　more　elements；　which　are　necessary
  to　produce　energy。
  MASS　AN　ELEMENT　IN　FLYING。The　boy　who
  reads　this　will　smile；　as　he　tells　us　that　the　power
  which　propelled　the　ball　through　the　air　came
  from　the　thrower　and　not　from　the　ball　itself。
  Let　us　examine　this　claim；　which　came　from　a　real
  boy；　and　is　another　illustration　how　acute　his　mind
  is　on　subjects　of　this　character。
  We　have　two　balls　the　same　diameter；　one　of
  iron　weighing　a　half　pound；　and　the　other　of　cotton
  weighing　a　half　ounce。　The　weight　of　one
  is；　therefore；　sixteen　times　greater　than　the　other。
  Suppose　these　two　balls　are　thrown　with　the
  expenditure　of　the　same　power。　What　will　be　the
  result！　The　iron　ball　will　go　much　farther；　or；
  if　projected　against　a　wall　will　strike　a　harder
  blow　than　the　cotton　ball。
  MOMENTUM　A　FACTOR。Each　had　transferred
  to　it　a　motion。　The　initial　speed　was　the　same；
  and　the　power　set　up　equal　in　the　two。　Why　this
  difference；　The　answer　is；　that　it　is　in　the
  material　itself。　It　was　the　mass　or　density　which　accounted
  for　the　difference。　It　was　mass　multiplied
  by　speed　which　gave　it　the　power；　called；　in
  this　case；　momentum。
  The　iron　ball　weighing　eight　ounces；　multiplied
  by　the　assumed　speed　of　50　feet　per　second；　equals
  400　units　of　work。　The　cotton　ball；　weighing　1/2
  ounce；　with　the　same　initial　speed；　represents　25
  units　of　work。　The　term　〃unit　of　work〃　means
  a　measurement；　or　a　factor　which　may　be　used　to
  measure　force。
  It　will　thus　be　seen　that　it　was　not　the　throw