﻿628 
  Prof. 
  E. 
  M. 
  Wellisch 
  on 
  the 
  Distribution 
  of 
  the 
  

  

  percentage 
  cathode 
  activities. 
  The 
  values 
  obtained 
  for 
  the 
  

   percentage 
  cathode 
  activity 
  for 
  air 
  at 
  210 
  mm. 
  pressure 
  are 
  

   greater 
  than 
  those 
  obtained 
  in 
  the 
  previous 
  research. 
  It 
  is 
  

   probable 
  that 
  this 
  discrepancy 
  is 
  due 
  to 
  the 
  fact 
  that 
  in 
  

   the 
  previous 
  experiment 
  some 
  of 
  the 
  ebonite 
  insulation 
  was 
  

   exposed 
  to 
  the 
  emanation, 
  so 
  that 
  the 
  central 
  electrode 
  did 
  

   not 
  receive 
  all 
  the 
  positive 
  carriers. 
  The 
  insulation 
  would 
  

   probably 
  act 
  as 
  a 
  partial 
  conductor, 
  especially 
  at 
  the 
  lower 
  

   pressures 
  when 
  it 
  would 
  be 
  exposed 
  to 
  the 
  a. 
  radiation 
  pro- 
  

   ceeding 
  from 
  a 
  considerable 
  distance. 
  In 
  the 
  present 
  ex- 
  

   periment 
  this 
  source 
  of 
  error 
  was 
  carefully 
  avoided, 
  and 
  the 
  

   result 
  appears 
  to 
  be 
  that 
  the 
  same 
  maximum 
  value 
  is 
  obtained 
  

   for 
  the 
  percentage 
  cathode 
  activity 
  both 
  for 
  the 
  lower 
  and 
  

   the 
  higher 
  pressure. 
  

  

  In 
  the 
  previous 
  work 
  the 
  assumption 
  was 
  made 
  that 
  100 
  

   per 
  cent, 
  was 
  the 
  limiting 
  value 
  which 
  the 
  cathode 
  deposit 
  

   approached 
  as 
  the 
  potential 
  was 
  increased, 
  and 
  that 
  even 
  at 
  

   the 
  low 
  pressures 
  the 
  saturation 
  attained 
  was 
  merely 
  apparent. 
  

   This 
  assumption 
  was 
  made 
  chiefly 
  as 
  a 
  result 
  of 
  the 
  experi- 
  

   mental 
  observation 
  that 
  the 
  percentage 
  cathode 
  activity 
  was 
  

   greater 
  at 
  the 
  higher 
  than 
  the 
  lower 
  pressures. 
  Since, 
  

   however, 
  it 
  has 
  now 
  been 
  shown 
  that 
  the 
  percentage 
  cathode 
  

   activity 
  has 
  the 
  same 
  value 
  (89*2) 
  at 
  the 
  higher 
  potentials 
  

   for 
  both 
  pressures, 
  it 
  appears 
  much 
  better 
  to 
  regard 
  this 
  as 
  

   the 
  true 
  limiting 
  value. 
  The 
  gradual 
  increase 
  of 
  the 
  values 
  

   for 
  one 
  atmosphere 
  for 
  potentials 
  above 
  40 
  volts 
  shows 
  that 
  

   the 
  phenomenon 
  of 
  columnar 
  recombination 
  is 
  present 
  : 
  the 
  

   active 
  deposit 
  particle 
  recoils 
  into 
  the 
  gas 
  after 
  the 
  expulsion 
  

   of 
  the 
  a-particle 
  from 
  the 
  atom 
  of 
  emanation 
  and 
  tends 
  to 
  

   recombine 
  with 
  the 
  negative 
  ions 
  which 
  it 
  forms 
  along 
  its 
  

   path. 
  

  

  Experiments 
  made 
  with 
  a 
  steel 
  instead 
  of 
  a 
  brass 
  central 
  

   electrode 
  gave 
  the 
  same 
  limiting 
  value 
  for 
  the 
  percentage 
  

   cathode 
  activity, 
  indicating 
  that 
  this 
  valne 
  does 
  not 
  depend 
  

   upon 
  the 
  nature 
  of 
  the 
  material 
  of 
  which 
  the 
  electrodes 
  are 
  

   composed. 
  

  

  At 
  low 
  pressures, 
  as 
  is 
  well 
  known, 
  a 
  considerable 
  number 
  

   of 
  the 
  active 
  deposit 
  particles 
  may 
  reach 
  the 
  walls 
  of 
  the 
  

   containing 
  vessel 
  before 
  their 
  velocity 
  is 
  sufficiently 
  reduced 
  

   to 
  enable 
  them 
  to 
  be 
  directed 
  by 
  the 
  electric 
  field. 
  With 
  

   air 
  at 
  a 
  pressure 
  of 
  6 
  mm. 
  and 
  with 
  180 
  volts 
  the 
  percentage 
  

   cathode 
  activity 
  was 
  found 
  to 
  be 
  66*7. 
  

  

  Experiments 
  with 
  Small 
  Applied 
  Potentials. 
  

   5. 
  The 
  experiments 
  described 
  in 
  the 
  preceding 
  section 
  

   refer 
  to 
  potentials 
  for 
  which 
  the 
  distribution 
  of 
  the 
  active 
  

  

  