Am^Kr;sP76"rm'}  'Development  of  the  Chemical  Arts.  85 
Port  Natal,  in  South-eastern  Africa.  All  the  others  descended  safely  beyond  the 
radius  of  the  besieging  army  in  France,  or  upon  neutral  territory  :  one  in  Belgium  ; 
three  in  Holland  ;  and  one  upon  a  snowfield  in  Norway,  60  (German)  miles  to  the 
north  of  Christiana,  and  180  from  Paris,  which  had  been  traversed  in  fifteen 
hours.  * 
At  that  time,  the  power  of  steering  balloons  was  more  than  ever  felt  to  be 
necessary.  Many  of  Montgolfier's  contemporaries,  including  well-known  physicists 
and  mathematicians,  such  as  Meusnier,  Monge,  Lelande,  Sec,  had  pronounced  this 
problem  to  be  practicable.  Fruitless  and  partially  absurd  attempts  at  its  solution 
were  not  wanting.  The  celebrated  inventor  of  the  injector,  Henry  Giffard,  was 
not  deterred  from  carrying  out  new  experiments  in  this  direction  in  the  year  1852, 
and  the  most  recent  attempts  are  based  upon  his  ideas  and  those  of  Meusnier. 
Instead  of  the  ordinary  form,  Giffard  gave  his  balloon  the  fish-like  shape  of  a  ship, 
for  the  convenience  of  steering.  A  steam  engine,  with  its  chimney  turned  down- 
wards to  obviate  the  risk  of  fire,  and  whose  steam  was  simultaneously  employed  to 
maintain  the  draught,  turned  a  screw  sufficient  to  turn  the  balloon,  but  certainly  too 
weak  to  overcome  the  strong  wind  which,  on  September  25th,  drove  Giffard's  aerial 
ship  before  it.  Public  opinion  then  turned  in  favor  of  a  project  of  aerial  navigation 
opposed  to  all  previous  methods.  Ponton  d'Amecourt,  De  la  Landell  and  Nader 
wished  to  attempt  by  mere  mechanical  force,  without  the  aid  of  light  gases,  to 
navigate  the  air  in  all  directions.  The  authority  of  Babinet  supported  this  scheme, 
which,  however,  according  to  Helmholtz,f  had  no  sound  physical  basis,  and  which, 
when  carried  into  execution,  proved  a  failure. 
When  the  Paris  Exhibition  of  1867  drew  general  attention  to  every  industrial 
advance,  Giffard  received  a  commission  to  make  aeronautics  available  for  the 
"  million  "  by  means  of  a  hydrogen  balloon.  He  constructed  a  balloon  of  5,000 
cubic  metres  capacity,  the  inflation  of  which,  with  hydrogen,  generated  by  iron  and 
sulphuric  acid  in  wooden  casks,  cost  5,000  francs.  The  gas  was  subsequently 
prepared  by  him  for  a  twentieth  part  of  the  cost  of  conducting  steam  over  ignited 
charcoal,  a  method  of  which  Coutelle  had  made  use  in  1794.  The  balloon  was 
attached  to  a  wire  rope  300  metres  in  length,  and  was  very  skillfully  secured.  A 
steam  engine  of  50  horse  power  uncoiled  the  rope,  and  drew  down  the  balloon 
with  its  passengers  when  the  permitted  height  had  been  reached.  This  height  was 
not  great  enough  to  occasion  any  danger  from  the  expansion  of  the  gas,  hence 
Giffard  was  able  to  close  the  balloon  with  valves  instead  of  leaving  it  open  below. 
Thus,  the  loss  of  gas  by  diffusion  did  not  exceed  15  cubic  metres  daily,  and  was 
easily  replaced  at  intervals  of  three  days. 
The  next  impulse  to  aeronautics  was  given,  not  by  festivity,  but  by  the  terrors  of 
war  and  the  siege  of  Paris.  The  Academie  des  Sciences  commissioned  one  of  its 
members,  Dupuy  de  Lome,  to  make  experiments  on  steering  balloons,  and  the 
government  furnished  the  requisite  means.  Dupuy  gave  his  balloon  the  fish  shape,;!: 
and,  in  order  to  render  its  shape  stable  in  the  wind,  he  fitted  it  with  an  internal 
secondary  balloon  {ballonet),  containing  more  or  less  air,  and  equal  in  bulk  to  one- 
tenth  part  of  the  main  balloon.  The  air  could  be  let  out  of  this  inner  balloon  by 
valves,  or  driven  in  again  by  means  of  a  bellows  in  the  car,  according  to  a  plan 
*Stephan,  "  Weltpost  und  Luftschiffahrt."    Berlin,  1874. 
fHelmholtz,  "Berl.  Akad.  Ber.  u.  Verhand.  d.  Ver.  fiir  Gewerbfleiss  in  Preussen,"  1873,  326. 
%  Dupuy  de  Lome,  "  Note  sur  1' Aerostat."    Paris:  Gautier-Villars.  1872. 
