86  Development  of  the  Chemical  Arts.  {Am-FJe°buri8P76arm- 
which  Meusnier  had  devised  as  early  as  1783  to  supercede  the  use  of  ballast. 
Dupuy's  balloon  was  further  distinguished  by  a  very  firm  method  of  suspending  the 
car,  and  by  the  use  of  a  varnish  impermeable  to  gases,  and  made  of  gelatin  and 
tannin  dissolved  in  pyroligneous  acid.  The  propelling  screw  was  not  turned  by  a 
steam  engine,  but  by  eight  men  in  the  car.  The  balloon,  containing  3,450  cubic 
metres,  was  filled  with  hydrogen  obtained  from  iron  and  sulphuric  acid,  and  went 
up  at  Vincennes  on  February  1st,  1872,  carrying  fourteen  persons.  After  a  flight  of 
two  hours  it  was  let  down  at  Noyon,  a  distance  of  106  kilometres.  By  means  of  an 
anemometer,  Dupuy  was  able  to  determine  the  independent  speed  of  the  balloon  at 
2*82  metres  per  second,  whilst  that  of  the  wind  was  16  to  17  metres,  and  the  course 
of  the  balloon  made  an  angle  of  120  with  the  direction  of  the  wind.  The  problem 
of  steering  had,  therefore,  been  solved,  though  only  to  a  very  slight  degree — suffi- 
cient for  a  calm,  but  insufficient  for  overcoming  even  moderate  winds.  The  speed 
attained  was  slight.  Both  conditions  of  success  depend  on  the  employment  of 
stronger  sources  of  mechanical  power,  and  this,  again,  requires  an  increase  of  its 
power  of  ascent,  i.  e.,  of  its  relative  levity  with  an  enlarged  volume. 
The  calculations  which  Helmholtz  *  has  lately  put  forward  concerning  the  re- 
spective ratio  of  bulk  to  resistance  and  to  speed  in  ships  and  balloons  are  therefore 
of  great  value.  According  to  him  the  speed  of  Dupuy's  balloon  nearly  attained  the 
maximum  possible  for  its  size.  In  order  to  proceed  slowly  against  a  fresh  breeze, 
with  the  sources  of  mechanical  power  at  present  available,  the  volume  of  the  balloon 
must  be  three  and  a-half  times  larger  than  that  of  the  largest  ship  of  the  line.  This 
demands  of  the  tissue  with  which  the  balloon  is  to  be  constructed  a  degree  of 
strength  scarcely  possible.  In  fajt,  the  expectations  of  the  inventors  did  not  go  be- 
yond the  hope  of  steering  the  balloon  when  the  air  is  tranquil.  If  the  screws  or 
paddle-wheels  are  enlarged  they  must  also  be  made  thicker  and  stronger,  in  order  to 
preserve  the  necessary  firmness.  "  We  can  only  work  sparingly  with  slowly-moving 
propellers  of  large  surface,  and  to  produce  these  of  the  requisite  size  without  burden- 
ing the  balloon  too  much,  will  constitute  one  of  the  greatest  practical  difficulties." 
With  this  sentence  Helmholtz  concludes  his  memoir,  and  the  prospects  to  which 
he  points  fall  very  far  short  of  the  enthusiastic  prophecies  of  such  as  are  guided  by 
their  wishes  rather  than  by  sober  scientific  considerations. 
The  problem  of  steering  balloons  turns  on  three  conditions  :  the  production  of 
balloons  of  the  lowest  specific  gravity  5  the  construction  of  propellers,  light,  but 
capable  of  resistance,  and  of  sources  of  power  at  once  light  and  capable  of  perform- 
ing a  high  duty.  In  how  far  chemistry  has  prepared  the  way  towards  the  fulfilment 
of  the  last  condition,  e.  g.,  by  means  of  aluminium,  the  future  must  decide.  The 
first  condition  she  has  accomplished  ninety  years  ago,  by  means  of  hydrogen,  as  is 
now  fully  recognized. 
Upon  the  consideration  of  hydrogen  and  oxygen  should  follow  an  account  of  the 
industrial  applications  of  water.  These,  however,  are  so  many-sided,  not  to  say 
omnipresent,  that  they  escape  our  reach.  The  most  important  will  be  considered  in 
especial  chapters. 
The  elements  oxygen  and  hydrogen  form,  however,  as  is  well  known,  a  second 
compound,  peroxide  of  hydrogen,  H202,  which  has  latterly  begun  to  acquire  a  cer- 
tain industrial  importance. — Chem.  News,  Oct.  15-Dec.  3. 
To  be  continued. 
-*  Helmholtz,  "Berl.  Akad.  Ber.,"  1873.  501. 
