﻿Lime 
  for 
  the 
  Wehnelt 
  Cathode. 
  

  

  595 
  

  

  gradually 
  increased 
  until 
  the 
  disc 
  of 
  lime 
  became 
  white. 
  The 
  

   lime 
  was 
  thus 
  deposited 
  on 
  the 
  platinum 
  strip. 
  The 
  tube 
  was 
  

   then 
  placed 
  in 
  position, 
  sealed, 
  and 
  the 
  apparatus 
  evacuated 
  

   until 
  the 
  pressure 
  was 
  -Ol^ 
  111111 
  of 
  mercury 
  or 
  less. 
  Pressures 
  

   ranging 
  from 
  -003 
  to 
  *04 
  mm 
  were 
  used. 
  'The 
  apparatus 
  was 
  

   usually 
  allowed 
  to 
  stand 
  over 
  night 
  after 
  evacuating 
  to 
  allow 
  

   the 
  P„0 
  5 
  to 
  absorb 
  the 
  moisture. 
  

  

  The 
  heating 
  current 
  was 
  adjusted 
  until 
  the 
  temperature 
  of 
  

   the 
  platinum 
  was 
  that 
  corresponding 
  to 
  a 
  light 
  cherry 
  -red. 
  

  

  Fig. 
  6. 
  

  

  'OOfr 
  

  

  OT2 
  

  

  OSf 
  

  

  09? 
  

  

  0+? 
  

  

  00? 
  

  

  091 
  021 
  08 
  0+ 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  «< 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  .. 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  c 
  

   r 
  3 
  

  

  3 
  

   x 
  

  

  Since 
  it 
  was 
  necessary 
  to 
  renew 
  the 
  lime 
  frequently, 
  a 
  reliable 
  

   thertno-junction 
  connection 
  was 
  nearly 
  impossible 
  and 
  hence 
  

   no 
  attempt 
  was 
  made 
  to 
  determine 
  the 
  temperature. 
  It 
  was, 
  

   however, 
  kept 
  strictly 
  constant 
  during 
  any 
  given 
  run 
  or 
  set 
  of 
  

   runs. 
  The 
  discharge 
  circuit 
  was 
  closed, 
  the 
  time 
  noted, 
  and 
  

   the 
  galvanometer 
  watched 
  for 
  the 
  current 
  to 
  start. 
  When 
  a 
  

   cathode 
  with 
  fresh 
  lime 
  was 
  heated 
  the 
  first 
  time 
  the 
  discharge 
  

   did 
  not 
  start 
  immediately 
  but 
  only 
  after 
  from 
  ten 
  to 
  thirty 
  

   minutes 
  if 
  conditions 
  were 
  favorable. 
  An 
  induction 
  coil 
  may 
  

   be 
  used 
  to 
  start 
  the 
  discharge, 
  but 
  this 
  complicates 
  matters 
  as 
  

   there 
  seems 
  to 
  be 
  a 
  gradual 
  rise 
  due 
  to 
  the 
  ionization 
  caused 
  by 
  

   the 
  induction 
  coil 
  discharge. 
  The 
  cathode 
  stream 
  may 
  also 
  be 
  

   started 
  more 
  quickly 
  by 
  making 
  the 
  heating 
  current 
  larger 
  for 
  

   a 
  short 
  time 
  ; 
  however 
  if 
  this 
  is 
  done 
  the 
  increase 
  to 
  a 
  maximum 
  

   and 
  the 
  maximum 
  itself 
  are 
  not 
  shown, 
  — 
  only 
  the 
  part 
  of 
  the 
  

   curve 
  due 
  to 
  the 
  clecav 
  is 
  obtained. 
  

  

  Discussio7i 
  of 
  Curves. 
  

  

  The 
  effect 
  of 
  changes 
  in 
  the 
  heating 
  current 
  is 
  shown 
  by 
  

   curve 
  1, 
  fig. 
  2. 
  A 
  very 
  small 
  change 
  in 
  this 
  current, 
  in 
  fact 
  

   one 
  which 
  the 
  eye 
  could 
  scarcely 
  detect 
  on 
  the 
  ammeter 
  

   where 
  two 
  scale 
  divisions 
  read 
  1/10 
  of 
  an 
  ampere, 
  produced 
  

   quite 
  an 
  appreciable 
  effect 
  upon 
  the 
  galvanometer 
  deflections. 
  

  

  