﻿Canal 
  Rays 
  from 
  Hollow 
  Catjiodei 
  

  

  163 
  

  

  also 
  very 
  bright 
  just 
  at 
  the 
  points 
  a, 
  and 
  two 
  spots 
  of 
  green 
  

   phosphorescence 
  appear 
  at 
  b, 
  where 
  the 
  prolonged 
  axis 
  o£ 
  

   the 
  tube 
  cuts 
  the 
  glass 
  bulb 
  (fig. 
  2). 
  

  

  On 
  the 
  outside 
  of 
  the 
  cathode, 
  the 
  boundary 
  of 
  the 
  dark 
  

   space 
  is 
  approximately 
  the 
  surface 
  traced 
  out 
  by 
  normals 
  of 
  

   constant 
  length 
  drawn 
  to 
  the 
  surface 
  of 
  the 
  cathode 
  ; 
  in 
  the 
  

   tube 
  itself, 
  however, 
  the 
  width 
  of 
  the 
  dark 
  space 
  is 
  much 
  

   smaller 
  than 
  outside. 
  

  

  As 
  the 
  pressure 
  is 
  decreased, 
  there 
  appear 
  two 
  beautiful 
  

   well-defined 
  rays 
  of 
  bright 
  blue 
  light 
  starting 
  from 
  both 
  ends 
  

   of 
  the 
  cathode, 
  spreading 
  out 
  as 
  they 
  approach 
  the 
  wall 
  of 
  

   the 
  tube, 
  and 
  producing 
  the 
  yellow-green 
  phosphorescence 
  

   due 
  to 
  cathode 
  rays. 
  The 
  rays 
  start 
  from 
  a 
  short 
  distance 
  

   within 
  either 
  end 
  of 
  the 
  tube, 
  the 
  centre 
  appearing 
  quite 
  

   empty 
  except 
  for 
  a 
  faint 
  yellow 
  light 
  enveloping 
  the 
  cathode 
  

   inside 
  and 
  out. 
  The 
  very 
  sharply 
  defined 
  bright 
  central 
  

   beam 
  of 
  blue 
  light 
  is 
  deflected 
  by 
  a 
  magnet 
  in 
  the 
  same 
  way 
  

   as 
  ordinary 
  cathode 
  rays. 
  Under 
  the 
  given 
  pressure, 
  a 
  pale 
  

   bluish 
  misty 
  luminosity 
  fills 
  the 
  whole 
  tube, 
  due 
  to 
  secondary 
  

   cathode 
  rays 
  produced 
  by 
  the 
  ionization 
  of 
  the 
  gas 
  by 
  the 
  

   primary 
  rays. 
  At 
  the 
  same 
  time, 
  a 
  band 
  of 
  weak 
  phos- 
  

   phorescence 
  appears 
  round 
  about 
  the 
  meridian 
  of 
  the 
  bulb, 
  

  

  Fiff. 
  3. 
  

  

  if 
  we 
  consider 
  the 
  axis 
  of 
  the 
  cathode-tube 
  as 
  polar 
  axis 
  of 
  

   the 
  sphere. 
  This 
  phosphorescence 
  is 
  produced 
  by 
  cathode 
  

   rays, 
  which 
  are 
  invisible 
  in 
  the 
  gas 
  and 
  which 
  start 
  nearly 
  

   at 
  right 
  angles 
  from 
  the 
  outer 
  surface 
  of 
  the 
  cylindrical 
  

   cathode. 
  

  

  When 
  the 
  vacuum 
  advances, 
  all 
  the 
  phosphorescent 
  spots 
  

   on 
  the 
  glass 
  wall 
  become 
  brighter 
  ; 
  the 
  general 
  dim 
  bluish 
  

   luminosity 
  gradually 
  disappears. 
  The 
  bright 
  blue 
  polar 
  

   cathode 
  rays 
  remain 
  visible 
  for 
  a 
  long 
  time, 
  but 
  get 
  verv 
  

  

  M2 
  

  

  

  