Recombination  of  Ions  in  Air  and  other  Gases.         4:11 
He  has  found  by  experiment  that  when  I  is  1  cm.,  and  F0  is 
151  volts  per  cm.,  then  (in  amperes) 
C  =8-03  x  10-8/200  (area  of  electrode  -  200  sq.cm.) 
=  4-01xl0-10, 
c=  3-94  xl0~10. 
Therefore, 
C  —  c       .  K      1AT 
— k—  —  4*0  xlO, 
cr 
and  by  substitution  in  the   equation  it  can   be  found  that 
a/e  =  4434  {loccit.  p.  530). 
Now,  in  a  similar  experiment,  with  far  smaller  currents,  we 
find  that  when  /  is  1  cm.  and  F0  is  150  volts  per  cm., 
C  =  4-23  x  10-'3, 
c  =  3-90  x  10-13. 
Therefore 
°~^=2-2xl011, 
cr 
and  substitution  in  the  equation  gives  a  value  of  ot/e  about 
5000  times  greater  than  Retschinsky's,  or  about  2  x  107. 
In  the  second  formula  (Stark's)  the  values  of  a.  are  more 
correct,  because  the  current  values  used  are  taken,  one  from 
the  lower  part  of  the  curve,  and  one  from  the  saturation 
values,  so  that  their  difference  depends  less  on  the  effects  of 
initial  recombination.  Retschinsky  draws  attention  to  these 
anomalies  in  his  results,  but  ascribes  them  to  absorption  of 
ions  by  the  electrodes.  He  argues  that  in  a  shallow  ionization 
chamber  this  effect  must  be  greater  than  in  a  deeper  one  ; 
and  so  he  accounts  for  the  lack  of  saturation  in  the  small 
chamber,  a  lack  which  is  excessive  if  attempt  is  made  to 
explain  it  as  wholly  due  to  general  recombination.  But  we 
think  that  a  more  reasonable  explanation  is  to  be  found  in 
the  hypothesis  and  results  described  in  this  paper,  in  con- 
nection with  which  Retscbinsky's  results  fall  naturally  into 
place. 
When,  therefore,  the  ionizing  agent  is  feeble,  the  only 
part  of  the  curve  which  can  be  altered  by  varying  the  current 
is  that  where  the  potential  gradient  is  small ;  the  feebler 
the  agent,  the  smaller  the  gradient.  Let  us  now  consider 
whether  our  hypothesis  makes  it  probable  that  we  can  alter 
the  shape  of  the  rest  of  the  curve  by  any  variation  of  the 
conditions  of  the  experiment. 
Now,    if   initial    recombination    takes   place   because    the 
