626  Prof.  "W.  H.  Bragg  on  the  Ionization  of 
Plotting  these  values  it  is  found  that  R  =  4*57,  I  (less 
copper  leak)  =635.  Hence  HI,  corrected  for  want  of 
saturation,  =298. 
Hence, 
Total  ionization  for  C2H2  _  298  _-,.9Q 
Total  ionization  lor  air         231  —  " 
Also  stopping-power 
483    760    3105 
457  '  763  *  2930 
lvll. 
In  the  paper  by  Mr.  Kleeman  and  myself,  to  which  I 
have  already  referred,  it  was  pointed  out  that  Rutherford 
had  found  it  more  easy  to  obtain  the  saturation  current 
from  a  gas  when  it  was  removed  from  the  influence  of  the 
ionizing  agent.  We  observed  that  this  could  be  easilv 
explained  by  supposing  initial  recombination  to  be  completed 
before  the  gas  was  subjected  to  the  electric  field.  It  is 
nevertheless  no  essential  feature  of  the  initial  recombination 
hypothesis  that  the  act  of  recombination  should  take  place 
within  any  set  time.  The  one  important  point  is  that  the 
recombination  takes  place  between  two  ions  originally 
forming  parts  of  one  molecule.  It  is  quite  conceivable  that 
for  a  certain  time  the  positive  and  negative  may  remain 
"  semi-detached/'  their  recombination  in  suspense  until 
precipitated  by  some  change  of  conditions.  Curiously 
enough  Mr.  Mad  sen,  working  in  this  laboratory,  has  not  vet 
been  able  to  repeat  Prof.  Rutherford's  experiment  ;  and  his 
results  point  to  a  prolonged  existence  of  these  pairs.  He 
finds  it  hard  to  saturate  a  mixture  of  air  and  ether  vapour 
which  has  been  ionized  by  radium  and  then  drawn  away 
into  a  separate  ionization  chamber.  It  is  not  easy  to 
reconcile  this  result  with  that  of  Prof.  Rutherford  :  and  it 
will  be  necessary  to  repeat  the  experiment  under  varying 
conditions.  The  point  is  one  of  considerable  interest,  for 
the  existence  of  these  pairs  would  help  to  explain  much  of 
the  mechanism  of  phosphorescence.  They  would  appear  to 
be  connected  with  the  clusters  of  J.  B.  B.  Burke,  which 
were  produced  by  ionization,  gave  rise  to  phosphorescent 
glow,  contained  energy,  yet  were  not  electrified.  It  is 
of    interest  in  this   connexion   that   the   photograph    which 
