the mastery of the air(²Ù×Ý¿ÕÆø)-µÚ34ÕÂ
°´¼üÅÌÉÏ·½Ïò¼ü ¡û »ò ¡ú ¿É¿ìËÙÉÏÏ·ҳ£¬°´¼üÅÌÉ쵀 Enter ¼ü¿É»Øµ½±¾ÊéĿ¼ҳ£¬°´¼üÅÌÉÏ·½Ïò¼ü ¡ü ¿É»Øµ½±¾Ò³¶¥²¿£¡
¡ª¡ª¡ª¡ªÎ´ÔĶÁÍꣿ¼ÓÈëÊéÇ©ÒѱãÏ´μÌÐøÔĶÁ£¡
sink¡¡into¡¡the¡¡scenery¡£¡¡The¡¡magicians¡¡were¡¡men¡¡skilled¡¡in¡¡the¡¡use¡¡of¡¡brush¡¡
and¡¡¡¡¡¡paint¡pot£»¡¡¡¡¡¡and¡¡¡¡¡¡several¡¡¡¡¡¡leading¡¡¡¡¡¡figures¡¡¡¡¡¡in¡¡¡¡¡¡the¡¡¡¡¡¡world¡¡¡¡¡¡of¡¡¡¡¡¡art¡¡¡¡¡¡lent¡¡¡¡¡¡their¡¡
services¡¡¡¡¡¡¡¡¡¡¡¡to¡¡¡¡the¡¡¡¡¡¡military¡¡¡¡¡¡¡¡authorities¡¡¡¡¡¡¡¡¡¡as¡¡¡¡directors¡¡¡¡¡¡¡¡of¡¡¡¡¡¡this¡¡¡¡¡¡campaign¡¡¡¡¡¡¡¡¡¡¡¡of¡¡
concealment¡£¡¡In¡¡this¡¡connection¡¡it¡¡is¡¡interesting¡¡to¡¡note¡¡that¡¡both¡¡Admiralty¡¡
and¡¡War¡¡Office¡¡took¡¡measures¡¡to¡¡record¡¡the¡¡pictorial¡¡side¡¡of¡¡the¡¡Great¡¡War¡£¡¡
Special¡¡¡¡¡¡commissions¡¡¡¡¡¡were¡¡given¡¡¡¡¡¡to¡¡¡¡¡¡a¡¡¡¡¡¡notable¡¡band¡¡¡¡¡¡of¡¡¡¡¡¡artists¡¡¡¡¡¡working¡¡¡¡¡¡in¡¡
their¡¡¡¡¡¡different¡¡¡¡¡¡¡¨lines¡¨¡£¡¡¡¡¡¡An¡¡¡¡¡¡abiding¡¡¡¡¡¡record¡¡¡¡¡¡of¡¡¡¡¡¡the¡¡¡¡¡¡great¡¡¡¡¡¡struggle¡¡¡¡¡¡will¡¡¡¡¡¡be¡¡
afforded¡¡¡¡¡¡by¡¡¡¡the¡¡¡¡¡¡black¡and¡white¡¡¡¡¡¡work¡¡of¡¡¡¡¡¡Muirhead¡¡¡¡¡¡Bone£»¡¡¡¡James¡¡¡¡¡¡M'Bey£»¡¡
and¡¡¡¡¡¡Charles¡¡¡¡¡¡Pears£»¡¡¡¡¡¡the¡¡¡¡¡¡portraits£»¡¡¡¡¡¡landscapes£»¡¡¡¡¡¡and¡¡¡¡¡¡seascapes¡¡¡¡¡¡of¡¡¡¡¡¡Sir¡¡¡¡¡¡John¡¡
Lavery£»¡¡¡¡¡¡¡¡¡¡Philip¡¡¡¡¡¡¡¡Connard£»¡¡¡¡¡¡¡¡¡¡Norman¡¡¡¡¡¡¡¡¡¡¡¡¡¡Wilkinson£»¡¡¡¡¡¡¡¡¡¡and¡¡¡¡¡¡¡¡Augustus¡¡¡¡¡¡¡¡¡¡¡¡John£»¡¡¡¡¡¡who¡¡
received¡¡his¡¡commission¡¡from¡¡the¡¡Canadian¡¡Government¡£¡¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡122¡¡
¡¡¡Page¡¡123¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡THE¡¡MASTERY¡¡OF¡¡THE¡¡AIR¡¡
¡¡¡¡¡¡¡¡¡¡CHAPTER¡¡XL¡¡The¡¡Atmosphere¡¡and¡¡the¡¡Barometer¡¡
¡¡¡¡¡¡¡¡¡¡For¡¡¡¡¡¡the¡¡¡¡¡¡discovery¡¡¡¡¡¡of¡¡¡¡¡¡how¡¡¡¡¡¡to¡¡¡¡¡¡find¡¡¡¡¡¡the¡¡¡¡¡¡atmospheric¡¡¡¡¡¡pressure¡¡¡¡¡¡we¡¡¡¡¡¡are¡¡
indebted¡¡to¡¡an¡¡Italian¡¡named¡¡Torricelli£»¡¡a¡¡pupil¡¡of¡¡Galileo£»¡¡who¡¡carried¡¡out¡¡
numerous¡¡experiments¡¡on¡¡the¡¡atmosphere¡¡toward¡¡the¡¡close¡¡of¡¡the¡¡sixteenth¡¡
century¡£¡¡
¡¡¡¡¡¡¡¡¡¡Torricelli¡¡argued¡¡that£»¡¡as¡¡air¡¡is¡¡a¡¡fluid£»¡¡if¡¡it¡¡had¡¡weight¡¡it¡¡could¡¡be¡¡made¡¡
to¡¡balance¡¡another¡¡fluid¡¡of¡¡known¡¡weight¡£¡¡In¡¡his¡¡experiments¡¡he¡¡found¡¡that¡¡
if¡¡a¡¡glass¡¡tube¡¡about¡¡3¡¡feet¡¡in¡¡length£»¡¡open¡¡at¡¡one¡¡end¡¡only£»¡¡and¡¡filled¡¡with¡¡
mercury£»¡¡were¡¡placed¡¡vertically¡¡with¡¡the¡¡open¡¡end¡¡submerged¡¡in¡¡a¡¡cup¡¡of¡¡
mercury£»¡¡some¡¡of¡¡the¡¡mercury¡¡in¡¡the¡¡tube¡¡descended¡¡into¡¡the¡¡cup£»¡¡leaving¡¡
a¡¡column¡¡of¡¡mercury¡¡about¡¡30¡¡inches¡¡in¡¡height¡¡in¡¡the¡¡tube¡£¡¡From¡¡this¡¡¡¡¡¡it¡¡
was¡¡deduced¡¡that¡¡the¡¡pressure¡¡of¡¡air¡¡on¡¡the¡¡surface¡¡of¡¡the¡¡mercury¡¡in¡¡the¡¡
cup¡¡¡¡¡¡forced¡¡¡¡¡¡it¡¡¡¡¡¡up¡¡¡¡¡¡the¡¡¡¡¡¡tube¡¡¡¡¡¡to¡¡¡¡¡¡the¡¡¡¡¡¡height¡¡¡¡¡¡Of¡¡¡¡¡¡30¡¡¡¡¡¡inches£»¡¡¡¡¡¡and¡¡¡¡¡¡this¡¡¡¡¡¡was¡¡¡¡¡¡so¡¡
because¡¡¡¡¡¡the¡¡¡¡¡¡weight¡¡¡¡¡¡of¡¡¡¡¡¡a¡¡¡¡¡¡column¡¡¡¡¡¡of¡¡¡¡¡¡air¡¡¡¡¡¡from¡¡¡¡¡¡the¡¡¡¡¡¡cup¡¡¡¡¡¡to¡¡¡¡¡¡the¡¡¡¡¡¡top¡¡¡¡¡¡of¡¡¡¡¡¡the¡¡
atmosphere¡¡¡¡¡¡was¡¡¡¡¡¡only¡¡¡¡equal¡¡¡¡¡¡to¡¡¡¡¡¡that¡¡¡¡¡¡of¡¡¡¡¡¡a¡¡¡¡¡¡column¡¡¡¡¡¡of¡¡¡¡¡¡mercury¡¡¡¡of¡¡¡¡¡¡the¡¡¡¡¡¡same¡¡
base¡¡and¡¡30¡¡inches¡¡high¡£¡¡
¡¡¡¡¡¡¡¡¡¡Torricelli's¡¡experiment¡¡can¡¡be¡¡easily¡¡repeated¡£¡¡Take¡¡a¡¡glass¡¡tube¡¡about¡¡
3¡¡¡¡¡¡feet¡¡¡¡¡¡long£»¡¡¡¡¡¡closed¡¡¡¡¡¡at¡¡¡¡¡¡one¡¡¡¡¡¡end¡¡¡¡¡¡and¡¡¡¡¡¡open¡¡¡¡¡¡at¡¡¡¡¡¡the¡¡¡¡¡¡other£»¡¡¡¡¡¡fill¡¡¡¡¡¡it¡¡¡¡¡¡as¡¡¡¡¡¡full¡¡¡¡¡¡as¡¡
possible¡¡with¡¡mercury¡£¡¡Then¡¡close¡¡the¡¡open¡¡end¡¡with¡¡the¡¡thumb£»¡¡and¡¡invert¡¡
the¡¡¡¡¡¡tube¡¡¡¡¡¡in¡¡¡¡¡¡a¡¡¡¡¡¡basin¡¡¡¡¡¡of¡¡¡¡¡¡mercury¡¡¡¡¡¡so¡¡¡¡¡¡that¡¡¡¡¡¡the¡¡¡¡¡¡open¡¡¡¡¡¡end¡¡¡¡¡¡dips¡¡¡¡¡¡beneath¡¡¡¡¡¡the¡¡
surface¡£¡¡The¡¡mercury¡¡in¡¡the¡¡tube¡¡will¡¡be¡¡found¡¡to¡¡fall¡¡a¡¡short¡¡distance£»¡¡and¡¡
if¡¡the¡¡height¡¡of¡¡the¡¡column¡¡from¡¡the¡¡surface¡¡of¡¡the¡¡mercury¡¡in¡¡the¡¡basin¡¡be¡¡
measured¡¡you¡¡will¡¡find¡¡it¡¡will¡¡be¡¡about¡¡30¡¡inches¡£¡¡As¡¡the¡¡tube¡¡is¡¡closed¡¡at¡¡
the¡¡top¡¡there¡¡is¡¡no¡¡downward¡¡pressure¡¡of¡¡air¡¡at¡¡that¡¡point£»¡¡and¡¡the¡¡space¡¡
above¡¡the¡¡mercury¡¡in¡¡the¡¡tube¡¡is¡¡quite¡¡empty£º¡¡it¡¡forms¡¡a¡¡VACUUM¡£¡¡This¡¡
vacuum¡¡is¡¡generally¡¡known¡¡as¡¡the¡¡TORRICELLIAN¡¡VACUUM£»¡¡after¡¡the¡¡
name¡¡of¡¡its¡¡discoverer¡£¡¡
¡¡¡¡¡¡¡¡¡¡Suppose£»¡¡now£»¡¡a¡¡hole¡¡be¡¡bored¡¡through¡¡the¡¡top¡¡of¡¡the¡¡tube¡¡above¡¡the¡¡
column¡¡of¡¡mercury£»¡¡the¡¡mercury¡¡will¡¡immediately¡¡fall¡¡in¡¡the¡¡tube¡¡until¡¡it¡¡
stands¡¡at¡¡the¡¡same¡¡level¡¡as¡¡the¡¡mercury¡¡in¡¡the¡¡basin£»¡¡because¡¡the¡¡upward¡¡
pressure¡¡of¡¡air¡¡through¡¡the¡¡liquid¡¡in¡¡the¡¡basin¡¡would¡¡be¡¡counterbalanced¡¡by¡¡
the¡¡downward¡¡pressure¡¡of¡¡the¡¡air¡¡at¡¡the¡¡top£»¡¡and¡¡the¡¡mercury¡¡would¡¡fall¡¡by¡¡
its¡¡own¡¡weight¡£¡¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡123¡¡
¡¡¡Page¡¡124¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡THE¡¡MASTERY¡¡OF¡¡THE¡¡AIR¡¡
¡¡¡¡¡¡¡¡¡¡A¡¡¡¡few¡¡¡¡years¡¡¡¡¡¡later¡¡¡¡Professor¡¡¡¡Boyle¡¡¡¡¡¡proposed¡¡¡¡¡¡to¡¡¡¡¡¡use¡¡¡¡¡¡the¡¡instrument¡¡¡¡¡¡to¡¡
measure¡¡the¡¡height¡¡of¡¡mountains¡£¡¡He¡¡argued¡¡that£»¡¡since¡¡the¡¡pressure¡¡of¡¡the¡¡
atmosphere¡¡balanced¡¡a¡¡column¡¡of¡¡mercury¡¡30¡¡inches¡¡high£»¡¡it¡¡followed¡¡that¡¡
if¡¡one¡¡could¡¡find¡¡the¡¡weight¡¡of¡¡the¡¡mercury¡¡column¡¡one¡¡would¡¡also¡¡find¡¡
the¡¡¡¡¡¡weight¡¡¡¡¡¡of¡¡¡¡¡¡a¡¡¡¡¡¡column¡¡¡¡¡¡of¡¡¡¡¡¡air¡¡¡¡¡¡standing¡¡¡¡¡¡on¡¡¡¡¡¡a¡¡¡¡¡¡base¡¡¡¡¡¡of¡¡¡¡¡¡the¡¡¡¡¡¡same¡¡¡¡¡¡size£»¡¡¡¡¡¡and¡¡
stretching¡¡¡¡¡¡away¡¡¡¡¡¡indefinitely¡¡¡¡¡¡into¡¡¡¡¡¡space¡£¡¡¡¡¡¡It¡¡¡¡¡¡was¡¡¡¡¡¡found¡¡¡¡¡¡that¡¡¡¡¡¡a¡¡¡¡¡¡column¡¡¡¡¡¡of¡¡
mercury¡¡in¡¡a¡¡tube¡¡having¡¡a¡¡sectional¡¡area¡¡of¡¡1¡¡square¡¡inch£»¡¡and¡¡a¡¡height¡¡of¡¡
30¡¡inches£»¡¡weighed¡¡15¡¡pounds£»¡¡therefore¡¡the¡¡weight¡¡of¡¡the¡¡atmosphere£»¡¡or¡¡
air¡¡¡¡¡¡pressure£»¡¡¡¡¡¡¡¡at¡¡¡¡sea¡level¡¡¡¡¡¡is¡¡¡¡about¡¡¡¡¡¡¡¡15¡¡¡¡pounds¡¡¡¡¡¡¡¡¡¡to¡¡¡¡the¡¡¡¡square¡¡¡¡¡¡¡¡inch¡£¡¡¡¡¡¡The¡¡
ordinary¡¡mercury¡¡barometer¡¡is¡¡essentially¡¡a¡¡Torricellian¡¡tube¡¡graduated¡¡so¡¡
that¡¡the¡¡varying¡¡heights¡¡of¡¡the¡¡mercury¡¡column¡¡can¡¡be¡¡used¡¡as¡¡a¡¡measure¡¡
of¡¡¡¡¡¡the¡¡varying¡¡¡¡¡¡atmospheric¡¡¡¡¡¡pressure¡¡due¡¡to¡¡¡¡¡¡change¡¡¡¡¡¡of¡¡¡¡¡¡weather¡¡or¡¡¡¡¡¡due¡¡¡¡¡¡to¡¡
alteration¡¡¡¡¡¡of¡¡¡¡¡¡altitude¡£¡¡¡¡¡¡If¡¡¡¡¡¡we¡¡¡¡¡¡take¡¡¡¡¡¡a¡¡¡¡¡¡mercury¡¡¡¡¡¡barometer¡¡¡¡¡¡up¡¡¡¡¡¡a¡¡¡¡¡¡hill¡¡¡¡¡¡we¡¡¡¡¡¡will¡¡
observe¡¡that¡¡the¡¡mercury¡¡falls¡£¡¡The¡¡weight¡¡of¡¡atmosphere¡¡being¡¡less¡¡as¡¡we¡¡
ascend£»¡¡the¡¡column¡¡of¡¡mercury¡¡supported¡¡becomes¡¡smaller¡£¡¡
¡¡¡¡¡¡¡¡¡¡Although¡¡the¡¡atmosphere¡¡has¡¡been¡¡proved¡¡to¡¡be¡¡over¡¡200¡¡miles¡¡high£»¡¡it¡¡
has¡¡by¡¡no¡¡means¡¡the¡¡same¡¡density¡¡throughout¡£¡¡Like¡¡all¡¡gases£»¡¡air¡¡is¡¡subject¡¡
to¡¡the¡¡law¡¡that¡¡the¡¡density¡¡increases¡¡directly¡¡as¡¡the¡¡pressure£»¡¡and¡¡thus¡¡the¡¡
densest¡¡and¡¡heaviest¡¡layers¡¡are¡¡those¡¡nearest¡¡the¡¡sea¡level£»¡¡because¡¡the¡¡air¡¡
near¡¡the¡¡earth's¡¡surface¡¡has¡¡to¡¡support¡¡the¡¡pressure¡¡of¡¡all¡¡the¡¡air¡¡above¡¡it¡£¡¡
As¡¡airmen¡¡rise¡¡into¡¡the¡¡highest¡¡portions¡¡of¡¡the¡¡atmosphere¡¡the¡¡height¡¡of¡¡the¡¡
column¡¡of¡¡air¡¡above¡¡them¡¡decreases£»¡¡and¡¡it¡¡follows¡¡that£»¡¡having¡¡a¡¡shorter¡¡
column¡¡¡¡¡¡of¡¡¡¡¡¡air¡¡¡¡to¡¡support£»¡¡¡¡those¡¡¡¡¡¡portions¡¡¡¡¡¡are¡¡¡¡less¡¡¡¡¡¡dense¡¡than¡¡those¡¡¡¡¡¡lower¡¡
down¡£¡¡¡¡¡¡¡¡¡¡So¡¡¡¡¡¡rare¡¡¡¡¡¡does¡¡¡¡¡¡the¡¡¡¡¡¡atmosphere¡¡¡¡¡¡¡¡¡¡¡¡become£»¡¡¡¡¡¡¡¡¡¡when¡¡¡¡¡¡¡¡great¡¡¡¡¡¡altitudes¡¡¡¡¡¡are¡¡
reached£»¡¡that¡¡at¡¡a¡¡height¡¡of¡¡seven¡¡miles¡¡breathing¡¡is¡¡well¡nigh¡¡impossible£»¡¡
and¡¡¡¡¡¡¡¡at¡¡¡¡far¡¡¡¡lower¡¡¡¡¡¡¡¡altitudes¡¡¡¡¡¡¡¡than¡¡¡¡¡¡this¡¡¡¡airmen¡¡¡¡¡¡¡¡have¡¡¡¡¡¡¡¡to¡¡¡¡be¡¡¡¡¡¡supported¡¡¡¡¡¡¡¡¡¡by¡¡
inhalations¡¡of¡¡oxygen¡£¡¡
¡¡¡¡¡¡¡¡¡¡One¡¡of¡¡the¡¡greatest¡¡altitudes¡¡was¡¡reached¡¡by¡¡two¡¡famous¡¡balloonists£»¡¡
Messrs¡£¡¡Coxwell¡¡and¡¡Glaisher¡£¡¡They¡¡were¡¡over¡¡seven¡¡miles¡¡in¡¡the¡¡air¡¡when¡¡
the¡¡latter¡¡fell¡¡unconscious£»¡¡and¡¡the¡¡plucky¡¡aeronauts¡¡were¡¡only¡¡saved¡¡by¡¡
Mr¡£¡¡¡¡¡¡Coxwell¡¡¡¡¡¡pulling¡¡¡¡¡¡the¡¡¡¡¡¡valve¡¡¡¡¡¡line¡¡¡¡¡¡with¡¡¡¡¡¡his¡¡¡¡¡¡teeth£»¡¡¡¡¡¡as¡¡¡¡¡¡all¡¡¡¡¡¡his¡¡¡¡¡¡limbs¡¡¡¡¡¡were¡¡
disabled¡£¡¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡124¡¡
¡¡¡Page¡¡125¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡THE¡¡MASTERY¡¡OF¡¡THE¡¡AIR¡¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡CHAPTER¡¡XLI¡¡How¡¡an¡¡Airman¡¡Knows¡¡what¡¡
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡Height¡¡he¡¡Reaches¡¡
¡¡¡¡¡¡¡¡¡¡One¡¡of¡¡the¡¡first¡¡questions¡¡the¡¡visitor¡¡to¡¡an¡¡aerodrome£»¡¡when¡¡watching¡¡
the¡¡altitude¡¡tests£»¡¡asks¡¡is£º¡¡¡¨How¡¡is¡¡it¡¡known¡¡that¡¡the¡¡airman¡¡has¡¡risen¡¡to¡¡a¡¡
height¡¡¡¡¡¡of¡¡¡¡¡¡so¡¡¡¡¡¡many¡¡¡¡¡¡feet£¿¡¨¡¡¡¡¡¡Does¡¡¡¡¡¡he¡¡¡¡¡¡guess¡¡¡¡¡¡at¡¡¡¡¡¡the¡¡¡¡¡¡distance¡¡¡¡¡¡he¡¡¡¡¡¡is¡¡¡¡¡¡above¡¡¡¡¡¡the¡¡
earth£¿¡¡
¡¡¡¡¡¡¡¡¡¡If¡¡¡¡this¡¡¡¡were¡¡¡¡¡¡¡¡so£»¡¡¡¡then¡¡¡¡¡¡it¡¡¡¡is¡¡¡¡very¡¡¡¡¡¡evident¡¡¡¡that¡¡¡¡there¡¡¡¡¡¡would¡¡¡¡¡¡¡¡be¡¡¡¡¡¡great¡¡
difficulty¡¡in¡¡¡¡¡¡awarding¡¡¡¡¡¡a¡¡prize¡¡to¡¡¡¡¡¡a¡¡number¡¡¡¡¡¡of¡¡¡¡¡¡competitors¡¡each¡¡trying¡¡to¡¡
ascend¡¡higher¡¡than¡¡his¡¡rivals¡£¡¡
¡¡¡¡¡¡¡¡¡¡No£»¡¡the¡¡pilot¡¡does¡¡not¡¡guess¡¡at¡¡his¡¡flying¡¡height£»¡¡but¡¡he¡¡finds¡¡it¡¡by¡¡a¡¡
height¡recording¡¡instrument¡¡called¡¡the¡¡BAROGRAPH¡£¡¡
¡¡¡¡¡¡¡¡¡¡In¡¡the¡¡last¡¡chapter¡¡we¡¡saw¡¡how¡¡the¡¡ordinary¡¡mercurial¡¡barometer¡¡can¡¡
be¡¡¡¡¡¡used¡¡¡¡¡¡to¡¡¡¡¡¡ascertain¡¡¡¡¡¡fairly¡¡¡¡¡¡accurately¡¡¡¡¡¡the¡¡¡¡¡¡height¡¡¡¡¡¡of¡¡¡¡¡¡mountains¡£¡¡¡¡¡¡But¡¡¡¡¡¡the¡¡
airman¡¡does¡¡not¡¡take¡¡a¡¡mercurial¡¡barometer¡¡up¡¡with¡¡him¡£¡¡There¡¡is¡¡for¡¡his¡¡
use¡¡another¡¡form¡¡of¡¡barometer¡¡much¡¡more¡¡suited¡¡to¡¡his¡¡purpose£»¡¡namely£»¡¡
the¡¡barograph£»¡¡which¡¡is¡¡really¡¡a¡¡development¡¡of¡¡the¡¡aneroid¡¡barometer¡£¡¡
¡¡¡¡¡¡¡¡¡¡The¡¡aneroid¡¡barometer¡¡£¨Gr¡£¡¡a£»¡¡not£»¡¡neros£»¡¡moist£©¡¡is¡¡so¡¡called¡¡because¡¡it¡¡
requires¡¡¡¡¡¡¡¡neither¡¡¡¡¡¡¡¡mercury£»¡¡¡¡¡¡¡¡glycerine£»¡¡¡¡¡¡¡¡water£»¡¡¡¡¡¡nor¡¡¡¡any¡¡¡¡¡¡other¡¡¡¡¡¡liquid¡¡¡¡¡¡in¡¡¡¡its¡¡
construction¡£¡¡It¡¡consists¡¡essentially¡¡of¡¡a¡¡small£»¡¡flat£»¡¡metallic¡¡box¡¡made¡¡of¡¡
elastic¡¡metal£»¡¡and¡¡from¡¡which¡¡the¡¡air¡¡has¡¡been¡¡partially¡¡exhausted¡£¡¡In¡¡the¡¡
interior¡¡¡¡¡¡there¡¡¡¡¡¡is¡¡¡¡¡¡an¡¡¡¡¡¡ingenious¡¡¡¡¡¡arrangement¡¡¡¡¡¡of¡¡¡¡¡¡springs¡¡¡¡¡¡and¡¡¡¡¡¡levers£»¡¡¡¡¡¡which¡¡
respond¡¡¡¡¡¡to¡¡¡¡¡¡atmospheric¡¡¡¡¡¡pressure£»¡¡¡¡¡¡and¡¡¡¡¡¡the¡¡¡¡¡¡depression¡¡¡¡¡¡or¡¡¡¡¡¡elevation¡¡¡¡¡¡of¡¡¡¡¡¡the¡¡
surface¡¡¡¡¡¡¡¡¡¡is¡¡¡¡registered¡¡¡¡¡¡by¡¡¡¡¡¡an¡¡¡¡index¡¡¡¡¡¡on¡¡¡¡¡¡the¡¡¡¡dial¡£¡¡¡¡As¡¡¡¡¡¡the¡¡¡¡pressure¡¡¡¡¡¡¡¡of¡¡¡¡the¡¡
atmosphere¡¡increases£»¡¡the¡¡sides¡¡of¡¡the¡¡box¡¡are¡¡squeezed¡¡in¡¡by¡¡the¡¡w