﻿Positive 
  Rays. 
  699 
  

  

  phosphorescence 
  appeared 
  suddenly 
  at 
  wave-length 
  380 
  metres 
  

   and 
  increased 
  to 
  a 
  maximum 
  at 
  wave-length 
  620, 
  the 
  curve 
  

   then 
  continued 
  parallel 
  to 
  the 
  axis 
  of 
  X. 
  In 
  determining 
  

   the 
  wave-lengths 
  I 
  employed 
  the 
  admirable 
  wave 
  -meter 
  of 
  

   Professor 
  G. 
  W. 
  Pierce 
  *. 
  This 
  instrument 
  enabled 
  me 
  to 
  

   make 
  measurements 
  in 
  a 
  few 
  moments 
  which 
  otherwise 
  would 
  

   have 
  required 
  days 
  of 
  labour. 
  

  

  On 
  placing 
  the 
  tube 
  C 
  between 
  the 
  poles 
  of 
  an 
  electro- 
  

   magnet, 
  which 
  produced 
  a 
  field 
  just 
  sufficient 
  to 
  divert 
  the 
  

   cathode 
  rays 
  from 
  the 
  screen, 
  I 
  found 
  that 
  the 
  changes 
  in 
  

   the 
  phosphorescence 
  represented 
  in 
  fig. 
  2 
  were 
  produced 
  by 
  

   the 
  cathode 
  rays 
  ; 
  for 
  the 
  phosphorescence 
  due 
  to 
  the 
  positive 
  

   rays 
  remained 
  constant 
  through 
  the 
  range 
  measured. 
  The 
  

   positive 
  rays 
  were 
  deflected 
  in 
  the 
  direction 
  opposite 
  to 
  that 
  

   in 
  which 
  the 
  cathode 
  rays 
  were 
  thrown 
  by 
  a 
  field 
  of 
  530 
  lines 
  

   to 
  the 
  centimetre, 
  and 
  produced 
  a 
  narrow 
  band 
  on 
  the 
  wil- 
  

   lemite 
  screen 
  which 
  showed 
  a 
  slight 
  discontinuity, 
  fig. 
  3, 
  

   although 
  the 
  pressure 
  did 
  not 
  exceed 
  J 
  mm. 
  I 
  was 
  surprised 
  

   to 
  find 
  that 
  the 
  group 
  of 
  positive 
  rays 
  were 
  so 
  readily 
  de- 
  

   flected 
  by 
  a 
  comparatively 
  weak 
  magnetic 
  field. 
  The 
  length 
  

  

  Fig. 
  3. 
  

  

  of 
  the 
  band 
  of 
  phosphorescence 
  was 
  1*5 
  cm. 
  It 
  is 
  to 
  be 
  

   noted 
  that 
  the 
  band 
  occurred 
  only 
  on 
  one 
  side 
  of 
  the 
  middle 
  

   point 
  of 
  the 
  phosphorescent 
  screen. 
  

  

  On 
  discovering 
  that 
  changes 
  in 
  self-induction 
  had 
  no 
  effect 
  

   upon 
  the 
  intensity 
  of 
  the 
  phosphorescence 
  produced 
  by 
  this 
  

  

  Contributions 
  from 
  the 
  Jefferson 
  Physical 
  Laboratory, 
  vol. 
  iv. 
  190G. 
  

  

  