﻿Canal 
  Rays 
  from 
  Hollow 
  Cathodes. 
  169 
  

  

  taking 
  place 
  mostly 
  outside 
  the 
  cathode, 
  penetrates 
  the 
  tube 
  

   for 
  only 
  a 
  short 
  distance 
  ; 
  and 
  the 
  negative 
  corpuscles 
  driven 
  

   by 
  the 
  electric 
  field 
  in 
  the 
  direction 
  o£ 
  the 
  axis 
  constitute 
  the 
  

   blue 
  beam 
  represented 
  in 
  fig. 
  3. 
  

  

  According 
  to 
  this 
  view, 
  the 
  intense 
  blue 
  beams 
  are 
  to 
  be 
  

   considered 
  as 
  the 
  negative 
  glow 
  of 
  the 
  inner 
  surface 
  of 
  the 
  

   tube. 
  The 
  negative 
  glow 
  belonging 
  to 
  the 
  outer 
  surface 
  gets 
  

   fainter 
  and 
  more 
  uniformly 
  blue 
  as 
  it 
  recedes 
  from 
  the 
  outer 
  

   surface. 
  The 
  total 
  amount 
  of 
  ionization 
  taking 
  place 
  all 
  over 
  

   the 
  region 
  of 
  the 
  negative 
  glow, 
  however, 
  may 
  remain 
  nearly 
  

   constant 
  with 
  decreasing 
  pressure. 
  The 
  narrow 
  region 
  in 
  

   which 
  the 
  central 
  blue 
  beam 
  occurs 
  is 
  a 
  place 
  of 
  strong 
  

   ionization 
  and 
  weak 
  electric 
  field. 
  The 
  ionization 
  is 
  due 
  to 
  

   corpuscles 
  moving 
  from 
  the 
  inner 
  surface 
  of 
  the 
  metal. 
  

  

  The 
  faint 
  blue 
  luminosity 
  filling 
  almost 
  the 
  whole 
  glass 
  

   bulb, 
  and 
  produced 
  by 
  cathode 
  rays 
  starting 
  from 
  the 
  outer 
  

   surface, 
  is 
  as 
  it 
  were 
  concentrated 
  for 
  the 
  inner 
  surface 
  into 
  a 
  

   sharp 
  beam 
  whose 
  colour 
  is 
  found 
  to 
  coincide 
  with 
  that 
  of 
  the 
  

   misty 
  luminosity. 
  In 
  pure 
  air 
  the 
  blue 
  colour 
  is 
  predominant; 
  

   in 
  damp 
  air 
  a 
  change 
  into 
  a 
  reddish 
  colour 
  takes 
  place; 
  while 
  

   in 
  the 
  presence 
  of: 
  mercury 
  vapour 
  the 
  rays 
  appear 
  to 
  be 
  of 
  a 
  

   bluish-white 
  colour. 
  The 
  polar 
  visible 
  beams, 
  being 
  a 
  con- 
  

   tinuation 
  of 
  the 
  negative 
  glow 
  of 
  the 
  inner 
  surface 
  of 
  the 
  

   cylinder, 
  appear 
  in 
  the 
  same 
  interval 
  of 
  pressure 
  as 
  that 
  faint 
  

   misty 
  luminosity 
  due 
  to 
  secondary 
  cathode 
  rays. 
  As 
  the 
  

   bright 
  central 
  beam 
  and 
  the 
  faint 
  luminosity 
  of 
  the 
  negative 
  

   glow 
  of 
  the 
  outer 
  surface 
  die 
  away 
  together 
  with 
  decreasing 
  

   pressure, 
  the 
  yellow 
  phosphorescence 
  caused 
  by 
  the 
  primary 
  

   cathode 
  rays 
  gets 
  brighter. 
  The 
  fact 
  that 
  with 
  decreasing 
  

   pressure 
  the 
  blue 
  central 
  beams 
  enter 
  deeper 
  into 
  the 
  hole 
  of 
  

   the 
  cathode, 
  is 
  connected 
  with 
  the 
  change 
  in 
  direction 
  of 
  the 
  

   lines 
  of 
  electric 
  force 
  and 
  with 
  the 
  appearance 
  of 
  the 
  bright 
  

   rings 
  of 
  phosphorescence 
  on 
  the 
  glass 
  wall. 
  

  

  The 
  positive 
  ions 
  are 
  mostly 
  attracted 
  by 
  the 
  negative 
  

   metal 
  cylinder 
  just 
  in 
  the 
  inner 
  edge 
  of 
  the 
  cylinder, 
  giving 
  

   rise 
  to 
  primary 
  cathode 
  rays 
  which 
  get 
  more 
  and 
  more 
  

   deflected 
  as 
  the 
  pressure 
  decreases 
  and 
  the 
  length 
  of 
  the 
  

   dark 
  space 
  becomes 
  greater. 
  Since 
  the 
  strength 
  of 
  the 
  field 
  

   only 
  changes 
  slowly 
  as 
  we 
  recede 
  from 
  the 
  cathode, 
  the 
  

   velocity 
  acquired 
  by 
  the 
  corpuscles 
  will 
  be 
  smaller 
  than 
  at 
  

   higher 
  pressure. 
  In 
  addition, 
  the 
  deflecting 
  electric 
  force 
  

   will 
  be 
  greater 
  at 
  a 
  greater 
  distance 
  from 
  the 
  cathode. 
  For 
  

   both 
  reasons, 
  the 
  cathode 
  rays 
  get 
  more 
  and 
  more 
  deflected 
  

   from 
  the 
  path 
  perpendicular 
  to 
  the 
  inner 
  surface 
  of 
  the 
  

   cathode. 
  

  

  At 
  a 
  certain 
  stage 
  of 
  pressure 
  these 
  primary 
  rays 
  start 
  

  

  