﻿822 
  

  

  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  cathode, 
  and, 
  secondly, 
  the 
  rays 
  shot 
  out 
  from 
  the 
  cathode 
  in 
  

   the 
  same 
  direction 
  as 
  the 
  cathode 
  rays 
  but 
  which 
  are 
  deflected 
  

   much 
  less 
  than 
  those 
  rays 
  by 
  magnetic 
  forces, 
  and 
  which 
  

   instead 
  of 
  carrying 
  a 
  negative 
  charge 
  are 
  some 
  of 
  them 
  

   positively 
  charged 
  while 
  others 
  are 
  electrically 
  neutral. 
  

  

  To 
  take 
  the 
  Canalstrahlen 
  first. 
  These 
  can 
  be 
  studied 
  by 
  

   an 
  apparatus 
  like 
  that 
  represented 
  by 
  fig. 
  1. 
  It 
  consists 
  of 
  a» 
  

  

  Fi-. 
  1. 
  

  

  vacuum-tube 
  with 
  a 
  perforated 
  cathode 
  through 
  which 
  a 
  

   beam 
  of 
  Canalstrahlen 
  is 
  streaming. 
  The 
  rays 
  strike 
  against 
  

   a 
  willemite 
  screen 
  at 
  the 
  end 
  of 
  the 
  discharge-tube 
  and 
  

   produce 
  phosphorescence 
  when 
  they 
  reach 
  the 
  screen. 
  In 
  

   their 
  path 
  to 
  the 
  screen 
  the 
  rays 
  pass 
  between 
  the 
  poles 
  of 
  an 
  

   electromagnet 
  which 
  deflects 
  them 
  in 
  a 
  vertical 
  direction 
  

   and 
  simultaneously 
  between 
  two 
  parallel 
  metal 
  plates 
  con- 
  

   nected 
  with 
  the 
  terminals 
  of 
  a 
  large 
  number 
  of 
  storage-cells 
  ; 
  

   the 
  electrostatic 
  field 
  deflects 
  the 
  spot 
  horizontally. 
  The 
  

   magnetic 
  deflexion 
  is 
  equal 
  to 
  ^e/mv, 
  where 
  e, 
  m, 
  v 
  are 
  

   respectively 
  the 
  charge, 
  mass^ 
  and 
  velocity 
  of 
  the 
  particles, 
  

   and 
  B 
  a 
  constant 
  depending 
  upon 
  the 
  strength 
  of 
  the 
  

   magnetic 
  field 
  and 
  the 
  distance 
  of 
  the 
  screen 
  from 
  the 
  cathode. 
  

   The 
  electrostatic 
  deflexion 
  is 
  equal 
  to 
  Ae/mv'^, 
  where 
  A 
  depends 
  

   on 
  the 
  strength 
  of 
  the 
  electric 
  field 
  and 
  the 
  size 
  of 
  the 
  apparatus. 
  

   When 
  both 
  these 
  fields 
  are 
  in 
  activity, 
  the 
  appearance 
  pre- 
  

   sented 
  by 
  the 
  willemite 
  screen 
  when 
  the 
  rays 
  strike 
  against 
  

   it 
  is, 
  when 
  the 
  pressure 
  is 
  not 
  very 
  low, 
  somewhat 
  like 
  fig. 
  2. 
  

   The 
  small 
  spot 
  which 
  marks 
  the 
  place 
  of 
  incidence 
  of 
  the 
  

   pencil 
  when 
  the 
  magnetic 
  and 
  electrostatic 
  fields 
  are 
  not 
  on, 
  

   is 
  drawn 
  out 
  into 
  a 
  ribbon 
  the 
  edges 
  of 
  which 
  are 
  often 
  very 
  

   approximately 
  straight. 
  In 
  some 
  cases 
  the 
  original 
  position 
  

   of 
  the 
  spot, 
  even 
  when 
  the 
  magnet 
  is 
  on, 
  is 
  more 
  brightly 
  

  

  