﻿674 
  Prof. 
  J. 
  J. 
  Thomson 
  on 
  

  

  being 
  ionized 
  by 
  cathode 
  rays 
  coming 
  down 
  through 
  the 
  

   tube 
  C 
  which 
  was 
  connected 
  with 
  the 
  earth. 
  The 
  cathode 
  

   was 
  at 
  D 
  in 
  front 
  of 
  the 
  tube, 
  the 
  anode 
  in 
  a 
  side 
  tube 
  F. 
  

   Three 
  parallel 
  electrodes, 
  L, 
  M, 
  N, 
  were 
  put 
  in 
  the 
  ionization 
  

   chamber. 
  The 
  first, 
  L, 
  was 
  a 
  plate 
  at 
  the 
  top 
  of 
  the 
  tube 
  ; 
  the 
  

   second, 
  M, 
  near 
  the 
  bottom 
  of 
  the 
  tube 
  was 
  a 
  piece 
  of 
  wire 
  

   gauze 
  about 
  a 
  millimetre 
  above 
  N, 
  which 
  was 
  the 
  top 
  of 
  an 
  

   earth-connected 
  cylinder, 
  with 
  a 
  small 
  hole 
  '9 
  mm. 
  in 
  diameter 
  

   bored 
  through 
  the 
  centre, 
  the 
  thickness 
  of 
  this 
  plate 
  was 
  

   1*6 
  mm. 
  By 
  means 
  of 
  these 
  electrodes 
  ions 
  could 
  be 
  collected 
  

   and 
  some 
  of 
  them 
  sent 
  through 
  the 
  hole 
  with 
  a 
  definite 
  and 
  

   known 
  velocity. 
  Suppose 
  for 
  example 
  we 
  wish 
  to 
  send 
  a 
  

   stream 
  of 
  positive 
  ions 
  through 
  the 
  hole. 
  A 
  small 
  difference 
  

   of 
  potential 
  (in 
  our 
  experiments 
  generally 
  that 
  due 
  to 
  two 
  

   Leclanche 
  cells) 
  was 
  maintained 
  between 
  the 
  plates 
  L, 
  M, 
  

   L 
  being 
  at 
  the 
  higher 
  potential. 
  The 
  electric 
  field 
  produced 
  

   in 
  this 
  way 
  caused 
  a 
  stream 
  of 
  slowdy 
  moving 
  positive 
  ions 
  

   to 
  pass 
  downwards 
  through 
  the 
  gauze 
  ; 
  by 
  means 
  of 
  a 
  potential 
  

   divider 
  any 
  potential-difference 
  between 
  10 
  and 
  800 
  volts 
  could 
  

   be 
  established 
  between 
  the 
  gauze 
  and 
  the 
  top 
  of 
  the 
  cylinder, 
  

   the 
  gauze 
  being 
  positive 
  to 
  the 
  cylinder. 
  The 
  ions 
  collected 
  

   by 
  the 
  upper 
  plates 
  thus 
  entered 
  into 
  a 
  much 
  stronger 
  field 
  

   which 
  gave 
  to 
  them 
  a 
  velocity 
  much 
  greater 
  than 
  that 
  with 
  

   which 
  they 
  entered 
  it, 
  so 
  that 
  when 
  they 
  passed 
  through 
  

   the 
  hole 
  they 
  were 
  all 
  moving 
  with 
  practically 
  the 
  same 
  

   velocity. 
  

  

  Beneath 
  the 
  top 
  of 
  the 
  box 
  there 
  was 
  an 
  insulated 
  Faraday 
  

   cylinder 
  (P) 
  connected 
  with 
  a 
  Wilson 
  electroscope. 
  The 
  

   distance 
  between 
  the 
  top 
  of 
  the 
  cylinder 
  and 
  the 
  bottom 
  of 
  

   the 
  plate 
  was 
  1 
  mm. 
  in 
  one 
  piece 
  of 
  apparatus, 
  \5 
  mm. 
  in 
  

   another 
  ; 
  the 
  diameter 
  of 
  the 
  hole 
  in 
  the 
  Faraday 
  cylinder 
  

   was 
  2*3 
  mm. 
  Beneath 
  this 
  hole 
  there 
  was 
  a 
  metal 
  disk 
  

   insulated 
  and 
  connected 
  with 
  another 
  Wilson 
  electroscope; 
  

   the 
  plane 
  of 
  the 
  disk 
  was 
  parallel 
  to 
  N 
  and 
  thus 
  at 
  right 
  

   angles 
  to 
  the 
  undeviated 
  path 
  of 
  the 
  ions, 
  the 
  axis 
  of 
  

   the 
  hole 
  in 
  N 
  passed 
  through 
  the 
  centre 
  of 
  the 
  disk. 
  

   The 
  part 
  of 
  the 
  tube 
  below 
  N 
  was 
  placed 
  between 
  the 
  poles 
  

   of 
  a 
  powerful 
  electromagnet, 
  the 
  lines 
  of 
  magnetic 
  force 
  

   being 
  at 
  right 
  angles 
  to 
  the 
  undeviated 
  path 
  of 
  the 
  ions, 
  and 
  

   parallel 
  to 
  the 
  direction 
  of 
  the 
  cathode 
  rays. 
  To 
  protect 
  the 
  

   cathode 
  rays 
  coming 
  from 
  D 
  from 
  the 
  magnetic 
  field, 
  a 
  deep 
  

   catting 
  was 
  made 
  in 
  one 
  of 
  the 
  poles 
  of 
  the 
  electromagnet 
  

   and 
  the 
  portion 
  from 
  C 
  to 
  D 
  of 
  the 
  tube 
  placed 
  in 
  this 
  and 
  

   then 
  covered 
  over 
  with 
  layers 
  of 
  soft 
  iron. 
  This 
  tube 
  was 
  

   sealed 
  on 
  to 
  the 
  tube 
  T 
  of 
  the 
  kind 
  already 
  described, 
  for 
  the 
  

   determination 
  of 
  e/m 
  for 
  the 
  Canalstrahlen. 
  

  

  

  