﻿446 
  

  

  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  The 
  wires 
  a, 
  h 
  (fig. 
  3) 
  were 
  replaced 
  by 
  cathode 
  rays 
  gene- 
  

   rated 
  in 
  the 
  side 
  tube 
  S 
  (fig, 
  4) 
  by 
  a 
  small 
  induction-coil; 
  

  

  Fiff. 
  4. 
  

  

  the 
  cathode 
  C 
  is 
  at 
  the 
  end 
  of 
  the 
  tube, 
  the 
  anode 
  is 
  the 
  

   metal 
  plug 
  A 
  connected 
  with 
  the 
  earth; 
  a 
  very 
  fine 
  hole 
  was 
  

   bored 
  in 
  this 
  plug 
  and 
  through 
  it 
  a 
  pencil 
  of 
  rays 
  passed 
  

   across 
  the 
  discharge 
  and 
  then 
  entered 
  the 
  side 
  tube 
  T. 
  In 
  

   this 
  tube 
  there 
  was 
  a 
  screen 
  W, 
  covered 
  by 
  a 
  phosphorescent 
  

   substance, 
  in 
  some 
  cases 
  willemite; 
  in 
  others 
  the 
  screen 
  was 
  

   a 
  zinc 
  sulphide 
  one 
  procured 
  from 
  Mr. 
  Glew. 
  The 
  place 
  

   of 
  impact 
  of 
  the 
  cathode 
  rays 
  against 
  the 
  screen 
  is 
  marked 
  

   by 
  a 
  luminous 
  spot, 
  and 
  by 
  measuring 
  with 
  a 
  cathetometer 
  

   the 
  deflexion 
  of 
  this 
  spot 
  the 
  magnitude 
  and 
  direciion 
  of 
  the 
  

   electric 
  force 
  acting 
  on 
  the 
  cathode 
  rays 
  as 
  they 
  pass 
  across 
  

   the 
  discharge-tube 
  can 
  be 
  determined. 
  Tinfoil 
  was 
  wrapped 
  

   round 
  the 
  outside 
  of 
  the 
  discharge-tube 
  to 
  neutrahze 
  the 
  

   effect 
  of 
  electric 
  charges 
  on 
  the 
  glass 
  walls 
  of 
  the 
  tube. 
  The 
  

   use 
  of 
  cathode 
  rays 
  not 
  only 
  avoids 
  the 
  disturbance 
  due 
  to 
  

   the 
  presence 
  of 
  the 
  vvires, 
  but 
  inasmuch 
  as 
  the 
  cathode 
  rays 
  

   are 
  negatively 
  electrified 
  particles 
  it 
  enables 
  us 
  to 
  measure 
  

   the 
  effect 
  of 
  the 
  field 
  on 
  such 
  particles, 
  and 
  as 
  it 
  is 
  the 
  

   corpuscles 
  which 
  carry 
  practically 
  all 
  the 
  current 
  in 
  the 
  

   discharge, 
  the 
  method 
  enables 
  us 
  to 
  observe 
  in 
  a 
  very 
  

   direct 
  way 
  the 
  most 
  important 
  factor 
  in 
  the 
  discharge. 
  

  

  The 
  method 
  is, 
  however, 
  limited 
  to 
  the 
  case 
  where 
  the 
  

   pressure 
  in 
  the 
  discharge-tube 
  is 
  low, 
  as 
  it 
  is 
  only 
  at 
  low 
  

   pressures 
  that 
  the 
  cathode 
  rays 
  produce 
  a 
  wxll-defined 
  spot 
  on 
  

   the 
  screen. 
  

  

  Observations 
  made 
  with 
  this 
  method 
  showed 
  unmistakably 
  

   the 
  existence 
  of 
  negative 
  forces 
  in 
  certain 
  parts 
  of 
  the 
  dis- 
  

   charge, 
  and 
  in 
  fact 
  the 
  distribution 
  of 
  electric 
  force 
  along 
  

  

  