﻿Canal 
  Rays 
  from 
  Hollow 
  Cathodes* 
  

  

  171 
  

  

  than 
  those 
  producing 
  the 
  ring 
  a 
  of 
  fig. 
  4. 
  As 
  they 
  pass 
  

   through 
  a 
  longer 
  interval 
  of 
  air 
  than 
  the 
  latter 
  ones, 
  their 
  

   ring 
  b 
  of 
  phosphorescence 
  will 
  only 
  appear 
  at 
  a 
  pressure 
  a 
  

   little 
  lower 
  than 
  those 
  of 
  the 
  ring 
  a. 
  The 
  same 
  consideration 
  

   applies 
  to 
  the 
  rays 
  of 
  the 
  ring 
  b 
  as 
  well 
  as 
  to 
  those 
  of 
  ring 
  a 
  

   of 
  fig. 
  4, 
  and 
  shows 
  us 
  that 
  at 
  a 
  still 
  lower 
  pressure 
  we 
  should 
  

   expect 
  a 
  further 
  dark 
  ring 
  inside 
  the 
  ring 
  b, 
  and 
  afterwards 
  

   a 
  central 
  bright 
  spot 
  of 
  phosphorescence 
  : 
  and 
  that 
  indeed 
  

   happens. 
  

  

  This 
  explanation 
  seems 
  to 
  account 
  for 
  all 
  the 
  phenomena 
  

   observed, 
  and 
  recalls 
  the 
  distribution 
  of 
  the 
  phosphorescent 
  

   patch 
  observed 
  by 
  Campbell 
  Swinton. 
  

  

  The 
  positive 
  particles 
  playing 
  an 
  important 
  part 
  in 
  this 
  

   interpretation, 
  we 
  might 
  expect 
  to 
  find 
  the 
  same 
  outside 
  the 
  

   hollow 
  cathode 
  as 
  within. 
  Positive 
  rays 
  have 
  not 
  been 
  

   directly 
  observed 
  so 
  far 
  in 
  the 
  above 
  experiments. 
  An 
  

   interesting 
  observation, 
  however, 
  wants 
  mentioning. 
  If 
  the 
  

   discharges 
  take 
  place 
  at 
  a 
  high 
  degree 
  of 
  exhaustion, 
  the 
  

   brass 
  cathode 
  will 
  be 
  disintegrated 
  to 
  a 
  large 
  amount 
  and 
  a 
  

   brown 
  deposit 
  will 
  spread 
  over 
  the 
  glass 
  bulb 
  with 
  a 
  uniform 
  

   thickness 
  except 
  at 
  the 
  poles. 
  If 
  now 
  the 
  cylindrical 
  cathode 
  

   is 
  turned, 
  say, 
  60° 
  about 
  the 
  supporting 
  axis, 
  a 
  small 
  circular 
  

   part 
  of 
  the 
  deposit 
  will 
  be 
  found 
  to 
  get 
  swept 
  out 
  at 
  the 
  new 
  

   poles 
  of 
  the 
  bulb 
  under 
  the 
  action 
  of 
  the 
  discharges. 
  This 
  

   effect 
  may 
  be 
  due 
  to 
  canal-rays. 
  E. 
  Goldstein 
  showed, 
  

   indeed, 
  that 
  the 
  positive 
  rays 
  have 
  the 
  property 
  of 
  sweeping 
  

   away 
  metallic 
  deposits. 
  If 
  a 
  conical 
  hollow 
  cathode 
  was 
  

   used, 
  rays 
  different 
  in 
  colour 
  and 
  magnetic 
  deflexion 
  were 
  

   found 
  to 
  start 
  from 
  the 
  narrower 
  end 
  at 
  a 
  very 
  low 
  pressure 
  ; 
  

   the 
  yellowish- 
  white 
  colour 
  and 
  the 
  absence 
  of 
  magnetic 
  

   deflexion 
  of 
  one 
  part 
  of 
  these 
  rays 
  seem 
  to 
  indicate 
  that 
  we 
  

   are 
  dealing 
  with 
  a 
  mixture 
  of 
  positive 
  and 
  negative 
  rays. 
  

   The 
  blue 
  beam 
  starting 
  from 
  the 
  wider 
  end 
  goes 
  deeper 
  back 
  

   to 
  the 
  point 
  of 
  the 
  cone 
  with 
  decreasing 
  pressure, 
  and 
  is 
  

   continued 
  by 
  a 
  faint 
  yellowish 
  ray. 
  The 
  central 
  patch 
  of 
  

   phosphorescence 
  due 
  to 
  the 
  blue 
  beam 
  is 
  surrounded 
  by 
  two 
  

   bright 
  rings, 
  whereas 
  at 
  the 
  opposite 
  pole 
  of 
  the 
  glass 
  bulb 
  

   we 
  find 
  only 
  a 
  faint 
  central 
  spot 
  surrounded 
  by 
  the 
  outer 
  

   ring. 
  This 
  is 
  exactly 
  what 
  we 
  should 
  expect 
  from 
  the 
  view 
  

   given 
  above, 
  because 
  the 
  rays 
  which 
  would 
  produce 
  the 
  inner 
  

   ring 
  cannot 
  escape 
  from 
  the 
  pointed 
  end 
  of 
  the 
  cone. 
  

  

  If 
  we 
  draw 
  perpendicular 
  lines 
  from 
  the 
  coating 
  of 
  the 
  cone 
  

   outwards, 
  a 
  certain 
  zone 
  of 
  the 
  spherical 
  bulb 
  will 
  be 
  cast 
  

   out, 
  and 
  this 
  zone 
  is 
  found 
  to 
  glow 
  in 
  a 
  dim 
  phosphorescent 
  

   light 
  due 
  to 
  cathode 
  rays. 
  If 
  the 
  middle 
  of 
  the 
  cylindrical 
  

   tube 
  used 
  for 
  the 
  above 
  experiments 
  is 
  surrounded 
  by 
  a 
  metal 
  

   wire, 
  this 
  meridional 
  band 
  will 
  be 
  divided 
  into 
  two 
  parts 
  

  

  