﻿Canal 
  Kays 
  from 
  Hollow 
  Cathodes. 
  Ifi7 
  

  

  increasing 
  vacuum, 
  the 
  central 
  blue 
  beams 
  and 
  the 
  spots 
  of 
  

   yellow-green 
  phosphorescence 
  surrounded 
  by 
  a 
  bright 
  ring 
  on 
  

  

  Fig-. 
  Qa. 
  

  

  r 
  

  

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  r 
  

  

  the 
  glass 
  wall 
  gradually 
  appear. 
  The 
  blue 
  polar 
  beam 
  and 
  the 
  

   P 
  io 
  . 
  7 
  central 
  spot 
  are, 
  however, 
  not 
  so 
  intense 
  

  

  as 
  in 
  the 
  first 
  experiment, 
  owing 
  to 
  the 
  

   fact 
  that 
  the 
  rays 
  starting 
  from 
  the 
  central 
  

   parts 
  of 
  the 
  tube 
  are 
  cut 
  off 
  by 
  the 
  glass 
  

   tube. 
  The 
  ring 
  b 
  of 
  fig. 
  4 
  does 
  not 
  appear 
  

   until 
  we 
  reduce 
  the 
  length 
  of 
  the 
  glass 
  

   tube 
  to 
  about 
  half 
  that 
  of 
  the 
  cathodic 
  

   cylinder 
  and 
  introduce 
  it 
  into 
  the 
  middle 
  

   of 
  the 
  cathode. 
  

  

  