﻿286 
  Mr. 
  McClung 
  on 
  the 
  Rate 
  of 
  Recombination 
  of 
  

  

  ring 
  was 
  tried, 
  but 
  the 
  effect 
  produced 
  was 
  so 
  small 
  that 
  

   it 
  was 
  not 
  suitable 
  for 
  measurement, 
  and 
  so 
  was 
  abandoned. 
  

  

  Thin 
  aluminium-foil 
  was 
  used 
  in 
  the 
  first 
  place 
  because, 
  

   being 
  so 
  very 
  thin, 
  it 
  would 
  not 
  absorb 
  the 
  rays 
  to 
  any 
  

   appreciable 
  extent, 
  and, 
  secondly, 
  because 
  the 
  secondary 
  

   radiation 
  produced 
  at 
  the 
  surface 
  of 
  metals 
  is 
  small 
  in 
  the 
  

   case 
  of 
  aluminium. 
  The 
  actual 
  thickness 
  of 
  the 
  foil 
  used 
  

   was 
  only 
  '00036 
  of 
  a 
  centimetre. 
  Before 
  finally 
  adopting 
  

   the 
  aluminium 
  a 
  set 
  ol: 
  electrodes 
  consisting 
  of 
  paper 
  covered 
  

   with 
  powdered 
  graphite 
  and 
  then 
  soaked 
  with 
  dilute 
  acid 
  so 
  

   as 
  to 
  make 
  them 
  conductors, 
  was 
  tried. 
  These 
  gave 
  very 
  

   satisfactory 
  results 
  while 
  they 
  lasted 
  ; 
  but 
  they 
  were 
  not 
  

   durable, 
  and 
  so 
  had 
  to 
  be 
  abandoned 
  also. 
  The 
  final 
  arrange- 
  

   ment 
  of 
  the 
  aluminium 
  plates 
  seemed 
  to 
  be 
  the 
  most 
  satisfactory, 
  

   and 
  was 
  therefore 
  adopted. 
  The 
  terminals 
  connected 
  to 
  the 
  

   electrodes 
  passed 
  through 
  ebonite 
  corks 
  in 
  the 
  end 
  of 
  the 
  

   cylinder 
  to 
  secure 
  insulation. 
  

  

  The 
  cylinder 
  was 
  made 
  so 
  that 
  the 
  air 
  might 
  be 
  exhausted 
  

   from 
  it 
  through 
  the 
  opening 
  F, 
  and 
  it 
  was 
  also 
  made 
  strong- 
  

   enough 
  to 
  stand 
  considerable 
  internal 
  pressure. 
  

  

  In 
  order 
  to 
  measure 
  the 
  maximum 
  number 
  of 
  ions 
  in 
  a 
  

   given 
  volume 
  of 
  the 
  gas 
  when 
  a 
  steady 
  state 
  had 
  been 
  

   reached, 
  and 
  also 
  the 
  number 
  remaining 
  at 
  the 
  end 
  of 
  any 
  

   given 
  interval 
  of 
  time, 
  it 
  was 
  necessary 
  to 
  be 
  able 
  to 
  apply 
  the 
  

   electromotive 
  force 
  to 
  the 
  electrode 
  E 
  at 
  the 
  same 
  instant 
  that 
  

   the 
  rays 
  ceased, 
  and 
  also 
  at 
  any 
  given 
  time 
  after 
  the 
  cessation 
  

   of 
  the 
  rays. 
  For 
  this 
  purpose 
  the 
  following 
  method 
  was 
  

   used. 
  L 
  and 
  L' 
  were 
  two 
  contact-breakers, 
  pivoted 
  at 
  P 
  

   and 
  P' 
  and 
  making 
  contact 
  with 
  Q 
  and 
  Q' 
  respectively. 
  The 
  

   primary 
  circuit 
  of 
  the 
  induction-coil 
  was 
  closed 
  through 
  the 
  

   contact-maker 
  L. 
  The 
  lever 
  L' 
  was 
  connected 
  to 
  earth, 
  while 
  

   Q' 
  was 
  connected 
  to 
  the 
  electrode 
  E 
  and 
  also, 
  through 
  a 
  very 
  

   large 
  resistance 
  B, 
  to 
  one 
  pole 
  of 
  a 
  battery 
  of 
  small 
  accu- 
  

   mulators, 
  the 
  other 
  pole 
  of 
  the 
  battery 
  being 
  connected 
  to 
  

   earth. 
  The 
  resistance 
  R 
  which 
  was 
  used 
  was 
  a 
  carbon 
  one 
  

   of 
  nbout 
  a 
  megohm. 
  

  

  Now 
  since 
  the 
  resistance 
  between 
  Q' 
  and 
  E 
  was 
  extremely 
  

   small 
  compared 
  with 
  E, 
  then, 
  if 
  the 
  lever 
  L' 
  were 
  closed 
  

   against 
  Q', 
  the 
  plates 
  connected 
  with 
  E 
  would 
  be 
  practically 
  

   at 
  zero 
  potential, 
  since 
  L' 
  is 
  connected 
  to 
  earth. 
  But 
  as 
  soon 
  

   as 
  the 
  contact 
  was 
  broken 
  between 
  L' 
  and 
  Q', 
  then 
  E 
  would 
  

   be 
  instantly 
  charged 
  up 
  to 
  the 
  potential 
  of 
  the 
  battery. 
  The 
  

   contacts 
  at 
  Q 
  and 
  Q' 
  were 
  broken 
  by 
  means 
  of 
  a 
  heavy 
  pen- 
  

   dulum 
  which 
  swung 
  along 
  the 
  path 
  xy. 
  If 
  the 
  levers 
  were 
  

   placed 
  directly 
  opposite 
  to 
  each 
  other, 
  the 
  rays 
  could 
  be 
  

   stopped 
  and 
  the 
  electromotive 
  force 
  applied 
  to 
  E 
  at 
  the 
  same' 
  

  

  