﻿Gaseous 
  Ionization 
  and 
  Pressure. 
  887 
  

  

  To 
  sum 
  up, 
  it 
  is 
  to 
  be 
  expected 
  that 
  : 
  

  

  (a) 
  the 
  ionization 
  produced 
  by 
  the 
  7 
  rays 
  and 
  the 
  

   secondary 
  ft 
  radiation 
  from 
  the 
  walls 
  will 
  vary 
  

   as 
  the 
  pressure 
  ; 
  

   (7>) 
  the 
  ionization 
  due 
  to 
  the 
  secondary 
  ft 
  radiation 
  from 
  

   the 
  gas 
  will 
  be 
  small 
  in 
  amount 
  and 
  vary 
  as 
  the 
  

   square 
  o£ 
  the 
  pressure. 
  

   It 
  will 
  be 
  shown 
  below 
  how 
  the 
  above 
  factors 
  partly 
  

   account 
  for 
  the 
  pressure-ionization 
  curves 
  we 
  have 
  obtained 
  

   for 
  hydrogen, 
  air, 
  and 
  carbon 
  dioxide. 
  To 
  completely 
  account 
  

   for 
  the 
  curves 
  it 
  is 
  necessary 
  to 
  assume 
  the 
  presence 
  of 
  soft 
  

   tertiary 
  ft 
  radiation 
  in 
  the 
  ionizing 
  vessel, 
  

  

  Soft 
  Tertiary 
  ft 
  Radiation. 
  

  

  The 
  convexity 
  of 
  the 
  ionization 
  axis 
  of 
  the 
  curves 
  of 
  

   ionization 
  and 
  pressure 
  (which 
  is 
  slight, 
  however, 
  in 
  the 
  case 
  

   of 
  hydrogen) 
  indicates 
  the 
  presence 
  of 
  soft 
  tertiary 
  ft 
  radia- 
  

   tion 
  of 
  considerable 
  ionizing 
  power. 
  For 
  if 
  such 
  radiation 
  is 
  

   excited 
  in 
  the 
  ionization 
  chamber, 
  and 
  the 
  gas 
  present 
  is 
  

   sufficiently 
  transparent 
  to 
  it, 
  then 
  the 
  ionization 
  produced 
  by 
  

   it 
  will 
  vary 
  at 
  first 
  as 
  the 
  pressure 
  of 
  the 
  gas. 
  But 
  as 
  the 
  

   pressure 
  increases 
  the 
  absorption 
  of 
  this 
  radiation 
  in 
  the 
  gas 
  

   will 
  increase 
  until 
  some 
  of 
  the 
  tertiary 
  ft 
  rays 
  are 
  completely 
  

   absorbed. 
  The 
  tertiary 
  ft 
  rays 
  remaining 
  will 
  contribute 
  

   less 
  and 
  less 
  ionization 
  for 
  each 
  equal 
  increment 
  of 
  the 
  pres- 
  

   sure, 
  and 
  so 
  the 
  ionization-pressure 
  curves 
  will 
  bend 
  towards 
  

   the 
  pressure 
  axis. 
  

  

  The 
  excitation 
  in 
  the 
  walls 
  and 
  gas 
  of 
  this 
  radiation 
  by 
  the 
  

   secondary 
  ft 
  radiation 
  is 
  certainly 
  to 
  be 
  expected 
  from 
  what 
  

   is 
  known 
  of 
  cathode 
  radiation. 
  Gehrcke 
  *, 
  for 
  example, 
  has 
  

   shown 
  that 
  cathode 
  rays, 
  when 
  incident 
  on 
  a 
  magnesium 
  

   plate, 
  produce 
  reflected 
  or 
  secondary 
  rays 
  with 
  a 
  wide 
  range 
  

   of 
  velocities 
  up 
  to 
  that 
  of 
  the 
  primary 
  rays. 
  

  

  The 
  increase 
  in 
  the 
  convexity 
  of 
  the 
  ionization-pressure 
  

   curves 
  with 
  the 
  opacity 
  of 
  the 
  gases 
  H 
  2 
  , 
  air, 
  C0 
  2 
  , 
  is 
  the 
  most 
  

   striking 
  evidence 
  in 
  favour 
  of 
  the 
  existence 
  of 
  this 
  soft 
  radia- 
  

   tion. 
  Lenard 
  f 
  found 
  that 
  cathode 
  rays 
  were 
  less 
  absorbed 
  

   by 
  H 
  2 
  than 
  by 
  air 
  or 
  C0 
  2 
  : 
  with 
  rays 
  having 
  1/10 
  of 
  the 
  

   velocity 
  of 
  light, 
  X 
  for 
  H 
  2 
  is 
  '19, 
  for 
  air 
  *85, 
  for 
  C0 
  2 
  2, 
  each 
  

   gas 
  being 
  at 
  1 
  mm. 
  pressure. 
  These 
  numbers 
  are 
  just 
  in 
  the 
  

   order 
  required 
  by 
  the 
  curves 
  C, 
  D, 
  E 
  of 
  fig. 
  6 
  (PI. 
  XXVI.), 
  

   where 
  the 
  C0 
  2 
  curve 
  is 
  more 
  bent 
  than 
  the 
  air 
  one, 
  and 
  both 
  

   are 
  much 
  more 
  bent 
  than 
  the 
  one 
  for 
  H 
  2 
  ; 
  in 
  other 
  words, 
  the 
  

  

  * 
  Ann. 
  der 
  Phijsik, 
  viii. 
  p. 
  81 
  (1902). 
  

   t 
  Ann. 
  der 
  Physik, 
  xii. 
  p. 
  732 
  (1903). 
  

  

  