AmF™-J7h6*rm  \  Development  of  the  Chemical  Arts.  83 
drogen,  hitherto  employed,  must  be  condemned  if  anything  further  is  desired  than 
the  display  of  objects  and  transparencies  for  the  lecture-room  or  the  stage. 
Hydrogen  lighting  was  not  represented  at  the  Vienna  Exhibition — a  further  in- 
direct evidence  that  it  had  not  found  any  wider  application. 
An  objection,  long  known,  depends  on  the  high  coefficient  of  diffusion  of  hy- 
drogen, and  its  consequent  ready  escape  through  the  pores  and  fine  chinks  of  the 
mains,  a  circumstance  the  more  dangerous,  as  hydrogen  is  not,  like  coal-gas,  at  once 
detected  by  its  odor.  The  diffusion-coefficients  of  gases,  according  to  Graham's  ex- 
periments, are  inversely  as  the  square  roots  of  their  specific  gravities. 
But  if  lightness  is  a  disadvantage  for  the  delivery  of  hydrogen  through  pipes,  we 
have  now  to  consider  the  advantages  springing  from  the  same  attribute.  In  Novem- 
ber, 1782,  a  dream  long  cherished  seemed  on  the  point  of  fulfilment.  The  Brothers 
Etienne  and  Joseph  Montgolfier  sent  up  the  first  balloon  at  Avignon  by  means  of 
hot  air.* 
With  natural  enthusiasm  the  populace  of  Annonay  applauded  them  when,  on 
June  4,  they  repeated  the  experiment  of  the  previous  year  on  a  larger  scale,  and' 
king,  court  and  capital  congratulated  the  inventors  when  they  repeated  it  soon  after- 
wards at  Versailles.  The  dominion  of  the  air  seemed  won  for  mankind,  to  whom* 
space  had  now  no  limits.  To  day  we  look  back  upon  the  invention  with  a  cooler 
glance,  as,  in  spite  of  the  lapse  of  ninety  years,  it  has  remained  in  its  infancy.  Wc 
are  still  unable  to  speak  of  aerial  navigation,  since  the  balloon,  incapable  of  being 
steered,  has  remained  the  plaything  of  the  air  instead  of  becoming  its  ruler.  One 
step,  indeed,  towards  the  desired  end  was  taken  when  Charles,  Professor  of  Physics 
at  the  Conservatoire  des  Arts  et  Metiers,  at  Paris,  substituted  hydrogen  for  the 
heated  air  in  the  balloon.  On  August  27,  1783,  Charles,  in  concert  with  the 
Brothers  Robert,  skillful  mechanicians,  accomplished  the  ascent  of  the  first  hydrogen 
balloon  in  the  Champs-Elysees,  his  invention  being  known  as  the  Charliere  in  con- 
tradistinction to  the  Montgolfiere.  Both  systems  were  used  for  the  first  aerial  voy- 
age, the  one  in  November  and  the  other  in  December  of  the  same  year.  Previously 
the  balloons  had  been  sent  up  empty,  or  only  tenanted  by  some  animal.  The  first 
aerial  navigator,  Pilatre  de  Rozieres,  conceived  the  idea  of  combining  both  systems, 
which  was  the  occasion  of  his  death.  The  fire  in  the  Mongolfiere  was  communi- 
cated to  the  hydrogen  in  the  Charliere,  and  on  June  15,  1785,  balloon  and  aeronaut 
fell  shattered  on  the  limestone  rocks  of  the  coast,  near  Boulogne. 
The  motive  for  this  unfortunate  combination  was  the  wish  to  raise  or  lower  the 
balloon  by  stirring  up  or  extinguishing  the  fire — a  plan  which  makes  ballast  super- 
fluous, and  which  has  been  revived  in  a  recent  essayf  by  Captain  Gaede  (of  the 
Military  School  at  Hanover),  and  with  due  precautions  would  be  doubtless  practica- 
ble. Since  the  time  of  Pilatre  de  Rozieres  3,700  balloon  ascents  have  been  under- 
taken, and  only  sixteen  fatal  accidents  have  been  heard  of, J  due  chiefly  to  montgol- 
fieres,  though  the  sea  has  been  repeatedly  crossed  by  aeronauts.  Not  long  after  the 
discovery  of  balloons  they  were  used  both  for  practical  and  for  scientific  purposes. 
*  The  historical  details  concerning  aeronautics,  where  no  other  authorities  are  given,  are  taken  from 
the  excellent  summary  of  Louis  Figuier  in  "  Merveilles  de  la  Science,"  ii.,  426-626.  See  also  Marion, 
"  Les  Ballons,"  Paris,  1867;  and  Fonvielle,  "  La  Science  en  Ballon,"  Paris,  1869. 
t  Gaede,  :'  Ueber  den  Bau  Gefesselter  und  Lenkbarer  Luftschiffe."    Berlin  :  Mittler,  1873. 
%  Stephan,  "  Weltpost  und  LuftschifTahrt."    Berlin  :  1874. 
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