﻿660 
  Prof. 
  J. 
  J. 
  Thomson 
  on 
  

  

  soon 
  as 
  the 
  obstacle 
  had 
  advanced 
  into 
  such 
  a 
  position 
  that 
  

   its 
  normal 
  went 
  down 
  the 
  aperture 
  in 
  A, 
  the 
  phosphorescence 
  

   on 
  the 
  screen 
  due 
  to 
  the 
  positive 
  rays 
  appeared. 
  The 
  con- 
  

   trast 
  between 
  the 
  brightness 
  of 
  the 
  phosphorescence 
  when 
  the 
  

   normal 
  to 
  the 
  obstacle 
  went 
  down 
  the 
  hole 
  in 
  A 
  and 
  when 
  

   it 
  did 
  not 
  was 
  very 
  sharp, 
  though 
  there 
  was 
  very 
  little 
  

   variation 
  in 
  the 
  number 
  of 
  cathode 
  rays 
  striking 
  against 
  the 
  

   anode 
  as 
  a 
  whole. 
  These 
  experiments 
  show 
  that 
  the 
  positive 
  

   rays 
  under 
  discussion 
  are 
  not 
  due 
  to 
  reversals 
  of 
  the 
  induc- 
  

   tion-coil 
  nor 
  to 
  the 
  negative 
  electrification 
  of 
  A 
  by 
  the 
  

   bombardment 
  of 
  cathode 
  rays, 
  but 
  that 
  they 
  originate 
  at 
  the 
  

   cathode 
  and 
  travel 
  away 
  from 
  it 
  down 
  the 
  tube. 
  

  

  By 
  means 
  of 
  the 
  rotating 
  cathode 
  B 
  we 
  can 
  determine 
  

   whether 
  the 
  positive 
  rays 
  coining 
  from 
  the 
  cathode 
  are 
  

   emitted 
  normally 
  to 
  its 
  surface, 
  or 
  whether, 
  like 
  some 
  of 
  the 
  

   rays 
  observed 
  by 
  Goldstein, 
  they 
  come 
  off 
  in 
  all 
  directions. 
  

   "When 
  the 
  normal 
  to 
  the 
  cathode 
  went 
  down 
  the 
  tube 
  in 
  A, 
  

   a 
  plentiful 
  supply 
  of 
  positive 
  rays 
  went 
  down 
  the 
  tube. 
  When 
  

   the 
  cathode 
  was 
  rotated, 
  the 
  phosphorescence 
  due 
  to 
  the 
  

   positive 
  rays 
  did 
  not 
  immediately 
  disappear, 
  although 
  it 
  

   became 
  very 
  much 
  fainter 
  ; 
  it 
  could, 
  however, 
  be 
  detected 
  

   until 
  the 
  normal 
  to 
  the 
  cathode 
  made 
  an 
  angle 
  of 
  about 
  15° 
  

   with 
  the 
  axis 
  of 
  the 
  tube. 
  The 
  positive 
  rays 
  under 
  discussion 
  

   appear 
  to 
  follow 
  much 
  the 
  same 
  path 
  as 
  the 
  cathode 
  rays, 
  

   for 
  it 
  was 
  found 
  that 
  the 
  angle 
  of 
  rotation 
  required 
  to 
  prevent 
  

   these 
  getting 
  down 
  the 
  tube 
  was 
  much 
  the 
  same 
  as 
  that 
  

   required 
  to 
  extinguish 
  the 
  phosphorescence 
  due 
  to 
  the 
  positive 
  

   rays. 
  

  

  Properties 
  of 
  these 
  Positive 
  Rays. 
  

  

  These 
  rays 
  get 
  exceedingly 
  faint 
  at 
  very 
  low 
  pressures,. 
  

   and 
  cease 
  to 
  be 
  observable 
  at 
  pressures 
  when 
  the 
  Canal- 
  

   strahlen 
  are 
  still 
  quite 
  bright. 
  It 
  is 
  probably 
  due 
  to 
  this 
  

   that 
  I 
  have 
  never 
  been 
  able 
  to 
  observe 
  the 
  resolution 
  of 
  the 
  

   phosphorescence, 
  under 
  the 
  action 
  of 
  electric 
  and 
  magnetic 
  

   forces, 
  into 
  separate 
  patches 
  as 
  in 
  the 
  case 
  of 
  Canalstrahlen 
  

   (Phil. 
  Mag. 
  xiii. 
  p. 
  561, 
  1907) 
  when 
  the 
  pressure 
  is 
  low. 
  

   The 
  spot 
  of 
  phosphorescence 
  due 
  to 
  the 
  positive 
  rays 
  coming- 
  

   out 
  in 
  front 
  of 
  the 
  cathode 
  is, 
  under 
  the 
  action 
  of 
  electric 
  and 
  

   magnetic 
  deflexion 
  of 
  the 
  rays, 
  drawn 
  out 
  into 
  a 
  continuous 
  

   band, 
  even 
  when 
  the 
  pressure 
  is 
  such 
  that 
  the 
  phosphor- 
  

   escence 
  due 
  to 
  the 
  Canalstrahlen 
  shows 
  well 
  -developed 
  

   patches. 
  In 
  the 
  case 
  of 
  the 
  Canalstrahlen, 
  there 
  are 
  some 
  

   rays 
  whose 
  deflexion 
  shows 
  that 
  they 
  are 
  negatively 
  charged 
  

   and 
  have 
  a 
  mass 
  comparable 
  with 
  that 
  of 
  the 
  positive 
  rays. 
  

   We 
  find, 
  too, 
  in 
  the 
  case 
  of 
  the 
  rays 
  travelling 
  in 
  the 
  opposite 
  

  

  