﻿164 
  

  

  Dr. 
  J. 
  Kunz 
  on 
  Cathode 
  and 
  

  

  much 
  fainter 
  when 
  the 
  vacuum 
  is 
  the 
  best 
  possible, 
  becoming 
  

   prolonged 
  through 
  the 
  centre 
  of 
  the 
  cathode 
  : 
  so 
  that 
  the 
  

   middle 
  of 
  this 
  tube 
  is 
  found 
  to 
  be 
  filled 
  with 
  bright 
  bluish 
  

   light. 
  The 
  phosphorescent 
  spots 
  at 
  the 
  poles 
  in 
  fig. 
  3 
  become 
  

   surrounded 
  by 
  a 
  system 
  of 
  circular 
  phosphorescent 
  rings, 
  

   separated 
  from 
  one 
  another 
  by 
  almost 
  dark 
  intervals. 
  The 
  

   limits 
  of 
  these 
  rings 
  are 
  sharply 
  defined 
  : 
  the 
  ring 
  which 
  

   appears 
  first 
  is 
  the 
  ring 
  a 
  in 
  fig. 
  4, 
  being 
  separated 
  from 
  the 
  

   central 
  spot 
  by 
  a 
  dark 
  band 
  with 
  limits 
  of 
  geometrical 
  

   distinctness. 
  With 
  decreasing 
  pressure, 
  a 
  fresh 
  ring 
  (b) 
  

  

  FiR-. 
  4. 
  

  

  appears, 
  followed 
  by 
  the 
  two 
  broad 
  faint 
  rings 
  c 
  and 
  d 
  ; 
  and 
  

   finally 
  the 
  central 
  spot 
  is 
  contracted 
  into 
  a 
  small 
  circle 
  

   distinctly 
  separated 
  from 
  a 
  ring 
  e 
  which 
  seems 
  much 
  fainter 
  

   than 
  the 
  ring 
  b. 
  The 
  limits 
  of 
  ring 
  d 
  art' 
  Ear 
  from 
  being 
  as 
  

   sharp 
  as 
  those 
  of 
  fche 
  other 
  rings. 
  

  

  At 
  the 
  most 
  complete 
  vacuum, 
  the 
  yellowish 
  light 
  sur- 
  

   rounding 
  the 
  cathode 
  nearly 
  disappears 
  : 
  but 
  there 
  is 
  to 
  be 
  

   found 
  a 
  very 
  thin 
  layer 
  of 
  red 
  light 
  quite 
  close 
  to 
  the 
  

   cylinder 
  visible 
  only 
  when 
  looked 
  at 
  in 
  a 
  direction 
  parallel 
  

  

  