﻿834 
  Sir 
  J. 
  J. 
  Thomson 
  

  

  on 
  

  

  rays. 
  The 
  phosphorescence 
  at 
  these 
  pressures 
  is 
  very 
  diffuse 
  

   and 
  faint 
  and 
  the 
  rays 
  are 
  evidently 
  much 
  scattered 
  in 
  their 
  

   journey 
  to 
  the 
  screen. 
  I 
  think 
  the 
  increased 
  deflexion 
  is 
  

   due 
  more 
  to 
  this 
  and 
  their 
  loss 
  of 
  velocity 
  during 
  the 
  journey^ 
  

   than 
  to 
  any 
  considerable 
  falling 
  off 
  in 
  their 
  initial 
  velocity 
  

   of 
  projection. 
  

  

  Though 
  the 
  equivalent 
  spark-length 
  has 
  changed 
  in 
  the 
  

   ratio 
  of 
  nearly 
  8 
  : 
  1 
  and 
  the 
  deflexion 
  of 
  the 
  cathode 
  rays 
  

   as 
  3 
  : 
  1, 
  there 
  has 
  been 
  hardly 
  any 
  change 
  in 
  the 
  deflexions 
  

   of 
  the 
  Canalstrahlen. 
  This 
  makes 
  it 
  very 
  improbable 
  that 
  they 
  

   owe 
  any 
  considerable 
  part 
  of 
  their 
  velocity 
  to 
  the 
  action 
  of 
  the 
  

   electric 
  field 
  upon 
  them 
  whilst 
  they 
  approach 
  the 
  cathode. 
  

  

  We 
  must 
  remember 
  that 
  the 
  bundle 
  of 
  Canalstrahlen 
  when 
  

   it 
  passes 
  through 
  the 
  hole 
  is 
  a 
  mixture 
  of 
  rays 
  of 
  different 
  

   kinds. 
  With 
  such 
  an 
  apparatus 
  as 
  that 
  just 
  described 
  the 
  

   only 
  rays 
  investigated 
  are 
  those 
  which 
  can 
  traverse 
  the 
  very 
  

   considerable 
  distance 
  between 
  the 
  cathode 
  and 
  the 
  screen 
  

   and 
  yet 
  retain 
  their 
  power 
  of 
  producing 
  phosphorescence. 
  

   Coming 
  through 
  the 
  hole 
  there 
  may 
  be, 
  in 
  fact 
  in 
  certain 
  

   cases 
  we 
  know 
  there 
  are, 
  positive 
  particles 
  which 
  have 
  been 
  

   set 
  in 
  motion 
  by 
  the 
  electric 
  field, 
  with 
  velocities 
  depending 
  

   on 
  those 
  of 
  the 
  molecules 
  of 
  the 
  gas 
  in 
  the 
  tube. 
  

  

  These, 
  in 
  the 
  experiment 
  I 
  am 
  describing, 
  have 
  disappeared 
  

   before 
  travelling 
  as 
  far 
  as 
  the 
  screen, 
  their 
  " 
  range,"" 
  to 
  use 
  

   an 
  expression 
  familiar 
  to 
  those 
  who 
  study 
  the 
  a 
  particles, 
  is 
  

   less 
  than 
  the 
  distance 
  between 
  the 
  screen 
  and 
  cathode. 
  The 
  

   existence 
  of 
  this 
  range 
  in 
  the 
  case 
  of 
  the 
  a 
  particles 
  may 
  be 
  

   explained 
  by 
  supposing 
  that 
  when 
  the 
  velocity 
  of 
  the 
  particle 
  

   falls 
  below 
  a 
  certain 
  value, 
  the 
  particle 
  is 
  no 
  longer 
  able 
  to 
  

   escape 
  from 
  the 
  negative 
  corpuscles 
  which 
  it 
  has 
  to 
  pass 
  

   through 
  on 
  its 
  travels. 
  The 
  same 
  argument 
  will 
  apply 
  to 
  

   Canalstrahlen 
  ; 
  if 
  they 
  move 
  with 
  less 
  than 
  a 
  certain 
  speed 
  

   they 
  may 
  not 
  be 
  able 
  to 
  escape 
  from 
  corpuscles 
  near 
  which 
  

   they 
  pass. 
  Since 
  the 
  a 
  particle 
  has 
  twice 
  the 
  charge 
  of 
  a 
  

   particle 
  in 
  the 
  Canalstrahlen, 
  the 
  velocity, 
  other 
  circumstances 
  

   being 
  the 
  same, 
  required 
  for 
  the 
  escape 
  of 
  an 
  a 
  particle 
  will 
  

   be 
  greater 
  than 
  for 
  one 
  in 
  the 
  Canalstrahlen. 
  The 
  velocity 
  

   of 
  the 
  latter, 
  in 
  round 
  numbers 
  2 
  x 
  10^ 
  cm. 
  per 
  sec, 
  is 
  

   about 
  that 
  required 
  for 
  a 
  particle 
  of 
  unit 
  charge 
  and 
  10 
  ~|^ 
  cm. 
  

   in 
  radius 
  to 
  escape 
  from 
  a 
  corpuscle. 
  

  

  In 
  the 
  preceding 
  experiments 
  the 
  velocity 
  of 
  the 
  cathode 
  

   rays 
  at 
  the 
  lowest 
  pressure 
  was 
  6 
  x 
  10^ 
  cm./sec, 
  taking 
  

   elm 
  = 
  l'l 
  xlQi^. 
  The 
  velocity 
  of 
  the 
  Canalstrahlen 
  particle 
  

   is 
  thus 
  considerably 
  less 
  than 
  that 
  of 
  a 
  cathode 
  ray 
  particle 
  ; 
  

   the 
  energy 
  of 
  a 
  cathode 
  particle 
  is, 
  however, 
  less 
  than 
  that 
  

   of 
  a 
  particle 
  in 
  the 
  Canalstrahlen. 
  

  

  