﻿256 
  Prof. 
  More 
  and 
  Mr. 
  Mauchly: 
  Action 
  of 
  a 
  Magnetic 
  

  

  using 
  a 
  Wehnelt 
  cathode 
  in 
  the 
  tube, 
  as 
  we 
  can 
  then 
  get 
  a 
  

   large 
  current 
  with 
  a 
  low 
  and 
  steady 
  potential 
  from 
  storage- 
  

   cells. 
  

  

  The 
  modified 
  discharge-tube 
  is 
  shown 
  in 
  fig. 
  1. 
  The 
  

  

  No 
  magnetic 
  field, 
  neither 
  screen 
  nor 
  cathode 
  earthed, 
  j 
  

  

  main 
  part 
  of 
  the 
  tube, 
  BD, 
  is, 
  as 
  before, 
  a 
  metre 
  long 
  and 
  

   7 
  centimetres 
  in 
  diameter 
  ; 
  the 
  extension, 
  BA, 
  is 
  2'5 
  cm. 
  in 
  

   diameter 
  ; 
  and 
  the 
  cathode, 
  C, 
  is 
  15 
  cm. 
  from 
  A 
  and 
  8 
  cm. 
  

   from 
  B. 
  To 
  avoid 
  any 
  constriction 
  in 
  the 
  tube, 
  the 
  two 
  

   parts 
  are 
  so 
  joined 
  at 
  B 
  with 
  a 
  sealing-wax 
  joint 
  that 
  BD 
  

   slips 
  over 
  BA. 
  The 
  entire 
  main 
  portion 
  is 
  covered 
  with 
  a 
  

   close-fitting 
  screen 
  of 
  copper 
  gauze, 
  which 
  may 
  be 
  either 
  

   insulated 
  or 
  connected 
  to 
  earth. 
  

  

  The 
  anode, 
  A, 
  is 
  a 
  straight 
  aluminium 
  rod 
  and 
  the 
  cathode, 
  

   C, 
  is 
  of 
  the 
  Wehnelt 
  hot 
  lime 
  type. 
  The 
  cathode 
  is 
  shown 
  

   In 
  detail 
  in 
  fig. 
  2. 
  Two 
  open 
  glass 
  tubes, 
  and 
  P, 
  are 
  sealed 
  

  

  Fig. 
  2. 
  

  

  p 
  ^ 
  r 
  '^^VTT?'"TS^!S5SSais 
  

  

  to 
  the 
  extension 
  tube. 
  Stout 
  brass 
  rods 
  with 
  brass 
  heads, 
  

   J, 
  G, 
  H, 
  and 
  I, 
  are 
  inserted 
  in 
  these 
  tubes, 
  and 
  are 
  kept 
  

   accurately 
  coaxial 
  by 
  the 
  short 
  lengths 
  of 
  barometer 
  tubing, 
  

   Q, 
  and 
  the 
  spiral 
  brass 
  springs, 
  T. 
  The 
  heads, 
  J 
  and 
  I, 
  

   serve 
  as 
  terminals 
  for 
  the 
  heating 
  current 
  and 
  for 
  the 
  

   cathode 
  end 
  of 
  the 
  discharge-current, 
  and, 
  when 
  sealed 
  with 
  

   wax* 
  close 
  the 
  ends 
  of 
  the 
  tubes. 
  The 
  other 
  heads, 
  G 
  and 
  

  

  