S4  Development  of  the  Chemical  Arts  {Am-fc8P76frm- 
Coutelle  used  them  for  military  reconnoitering,  and,  according  to  Carnot's  testimony, 
contributed  essentially  to  the  result  of  the  battle  of  Fleurus.  On  the  other  hand, 
Captain  Gaede  considers  the  results  attained  by  means  of  balloons,  especially  in 
reconnoitering  fortified  places,  both  in  earlier  campaigns  and  in  the  Franco-Prussian 
war  of  1870-71,  as  insignificant.  Napoleon  I.  regarded  the  military  efficiency  of  the 
balloons  of  his  time  not  more  favorably.  After  his  return  from  Egypt — where  the 
attempt  to  convince  the  natives  of  the  superiority  of  Europeans  by  means  of  a 
balloon  ascent  had  failed,  owing  to  their  fatalistic  indolence — he  closed  the  military- 
aerostatic  school  which  had  been  founded  at  Meudon  under  the  management  of 
Coutelle  and  Conti,  evidently  holding  its  military  results  as  unimportant. 
Ballooning  has  been  made  subservient  to  the  purposes  of  meteorology  and 
physics  before  it  was  enlisted  in  the  service  of  the  war-spirit.  Charles  utilized  his 
expedition  for  scientific  purposes.  On  July  18,  1803,  he  was  imitated  by  Robert- 
son, who  ascended  from  Hamburg  to  the  height  of  7,400  metres,  and  who  imagined 
that  he  perceived  at  this  altitude  a  decrease  in  the  intensity  not  merely  of  terrestrial 
magnetism,  but  also  of  fractional  electricity.  These  statements  induced  the  great 
physicists,  Biot  and  Gay-Lussac,  to  undertake  two  ascents  the  next  year.  They 
refuted  the  above-mentioned  views  of  Robertson,  remarked  the  decrease  of  atmos- 
pheric moisture  with  increasing  altitude,  and  made  numerous  and  valuable  meteor- 
ological observations.  From  the  greatest  height  which  they  attained,  6,500  metres, 
Oay-Lussac  brought  back  a  specimen  of  air,  and  found  that  it  had  the  same 
composition  as  the  air  of  lower  regions — a  result,  at  that  time,  of  capital  importance. 
The  last-mentioned  ascents  were  all  made  with  hydrogen  gas.  As  the  use  of  gas- 
lighting  became  more  and  more  general  the  greater  power  which  the  lightest  of  all 
known  bodies  offers  was  sacrificed  to  the  convenience  which  coal-gas  afforded.  In 
France,  Barral  and  Bixio  made  their  scientific  ascent,  in  1850,  with  the  aid  of  coal- 
gas.  In  England,  Glaisher  adopted  the  same  plan  in  1864,  and  the  numerous 
balloon  voyages  which  have  been  made  for  the  amusement  of  the  public,  from  the 
love  of  adventure  or  for  some  especial  purpose,  have  been  undertaken  with  the 
same  material.  With  coal-gas  Green  traveled  in  sixteen  hours  from  London  to 
Weilburg,  in  Nassau,  in  18365  Flammarion  and  Godard,  in  1867,  from  Paris  to 
Solingen,  performing  70  German  miles  in  twelve  and  a  half  hours.  Nader,  who 
hoped  to  take  photographic  maps  whilst  floating  in  the  air,  had  filled  his  balloon, 
"  Le  Geant,"  with  6,000  cubic  metres  of  coal-gas,  on  his  somewhat  dangerous 
journey  from  Paris  to  Hanover,  October  18,  1863.  More  recently  aeronauts  have 
returned  to  the  use  of  hydrogen.  But  even  in  those  four  months  of  the  greatest 
siege  of  a  metropolis  of  which  history  bears  record,  when  Paris  depended  exclu- 
sively, for  its  intercourse  with  the  outer  world,  upon  carrier  pigeons  and  balloons, 
which  had  never  before  been  called  to  so  important  a  service,  even  then  necessity 
compelled  the  use  of  coal-gas,  because  it  was  procurable  with  the  least  difficulty.* 
65  balloons  went  up  from  Paris  between  September  28  and  January  22,  carrying  91 
passengers,  363  pigeons  and  2^  million  letters,  and  for  the  most  part  with  success. 
Only  five  balloons  fell  into  the  hands  of  the  German  armies  :  one  descended  in 
Munich  ;  another  at  Wetzlar  ;  one  disappeared  entirely,  perhaps  in  the  sea,-  whilst 
the  fragments  of  another  were  found,  in  the  autumn  of  1873,  clinging  to  a  tree  at 
*  Saint-Edme,  "  La  Science  pendant  le  Siege  de  Paris,"  1871,  62. 
