﻿in 
  Positive 
  Rays 
  in 
  Hydrogen. 
  

  

  897 
  

  

  electrometer. 
  A 
  telephone 
  was 
  inserted 
  in 
  the 
  circuit 
  and 
  

   measurements 
  only 
  made 
  when 
  it 
  was 
  absolutely 
  silent. 
  

   Measurements 
  were 
  only 
  possible 
  before 
  disintegration 
  of 
  the 
  

   cathode 
  set 
  in, 
  for 
  as 
  soon 
  as 
  a 
  metallic 
  fihn 
  forms 
  on 
  the 
  

   walls 
  of 
  the 
  tube 
  the 
  discharge 
  is 
  altered 
  by 
  bringing 
  up 
  the 
  

   cathode. 
  

  

  The 
  values 
  of 
  the 
  electric 
  force 
  and 
  its 
  rate 
  of 
  change 
  

   along 
  the 
  discharge 
  were 
  obtained 
  from 
  the 
  potential 
  changes 
  

   w^hen 
  the 
  cathode 
  was 
  displaced 
  a 
  few 
  millimetres 
  on 
  each 
  

   side 
  of 
  the 
  point 
  where 
  the 
  value 
  w^as 
  required. 
  

  

  It 
  is 
  found 
  that 
  the 
  commencement 
  of 
  the 
  luminescence 
  of 
  

   the 
  cathode 
  glow 
  seems 
  to 
  depend 
  on 
  the 
  potential 
  fall 
  from 
  

   the 
  negative 
  glow 
  rather 
  than 
  on 
  the 
  values 
  of 
  the 
  electric 
  force 
  

   and 
  its 
  rate 
  of 
  change 
  at 
  this 
  point. 
  The 
  value 
  of 
  the 
  

   potential 
  fall 
  to 
  the 
  commencement 
  of 
  the 
  cathode 
  glow 
  is 
  

   independent 
  of 
  the 
  pressure 
  but 
  rises 
  slowing 
  according 
  to 
  a 
  

   straight 
  line 
  law 
  with 
  the 
  cathode 
  fall. 
  The 
  electric 
  force 
  

   and 
  its 
  rate 
  of 
  change 
  vary 
  between 
  wider 
  limits. 
  Some 
  of 
  

   the 
  values 
  obtained 
  are 
  given 
  in 
  the 
  accompanying 
  table. 
  

  

  Table 
  I. 
  

  

  Cathode 
  Fall. 
  

  

  800 
  volts. 
  

  

  1600 
  volts. 
  

  

  2400 
  volts. 
  

  

  , 
  Potential 
  fall 
  ... 
  

  

  Values 
  at 
  the 
  | 
  

   commence- 
  J 
  Electric 
  force 
  ... 
  

   ment 
  of 
  the 
  ] 
  

  

  cathode 
  glow, 
  j 
  Eate 
  of 
  change 
  of 
  

   1, 
  electric 
  force. 
  

  

  150 
  volts. 
  

   100 
  volts/cm. 
  

   50 
  volts/cm. 
  2 
  

  

  260 
  volts. 
  

   260 
  volts/cm. 
  

  

  360 
  volts. 
  

   500 
  volts/cm. 
  

   300 
  voltsVcm 
  . 
  

  

  The 
  Doppler 
  effect 
  was 
  observed 
  from 
  the 
  direction 
  F 
  

   (fig. 
  1) 
  by 
  focussing 
  the 
  cathode 
  glow 
  on 
  the 
  slit 
  of 
  a 
  grating 
  

   spectrograph. 
  The 
  grating 
  was 
  mounted 
  in 
  the 
  manner 
  

   described 
  by 
  Paschen 
  *. 
  The 
  camera 
  included 
  from 
  H^ 
  to 
  

   H^j 
  the 
  dispersion 
  varying 
  from 
  9-90 
  to 
  9*15 
  A.U. 
  per 
  mm. 
  

   The 
  density 
  of 
  the 
  photographs 
  was 
  not 
  very 
  different 
  for 
  

   H„, 
  H^, 
  and 
  Hy. 
  H^ 
  was 
  the 
  strongest, 
  H^ 
  being 
  sometimes 
  

   weaker 
  sometimes 
  stronger 
  with 
  different 
  batches 
  of 
  plates 
  

   than 
  H^. 
  

  

  The 
  Doppler 
  effect 
  when 
  the 
  cathode 
  without 
  holes 
  is 
  viewed 
  

   from 
  the 
  anode 
  side 
  has 
  already 
  been 
  observed 
  by 
  Paschen 
  f, 
  

  

  * 
  Pasclien, 
  Ann. 
  d. 
  Phys. 
  xxiii. 
  247 
  (1907). 
  

   t 
  Paschen, 
  Phys. 
  Zeits. 
  vii. 
  924 
  (1907). 
  

  

  