﻿Ions 
  in 
  Gases 
  under 
  Different 
  Pressures, 
  

  

  285 
  

  

  spark-gap 
  connexion, 
  and 
  was 
  driven 
  by 
  a 
  large 
  Ruhmkorff 
  

   induction-coil. 
  The 
  coil 
  was 
  run 
  by 
  the 
  current 
  from 
  the 
  

   110-volt 
  circuit, 
  with 
  a 
  Wehnelt 
  interrupter 
  of 
  slow 
  frequency 
  

   in 
  series. 
  In 
  order 
  to 
  intensify 
  the 
  discharge 
  in 
  the 
  focus- 
  

   tube, 
  a 
  spark-gap 
  o£ 
  about 
  a 
  centimetre 
  and 
  a 
  half 
  was 
  placed 
  

   directly 
  in 
  series 
  with 
  the 
  secondary 
  of 
  the 
  coil 
  and 
  the 
  

   electrodes 
  of 
  the 
  tube. 
  

  

  The 
  induction-coil 
  and 
  A'-ray 
  bulb 
  were 
  completely 
  inclosed 
  

   in 
  a 
  small 
  metal 
  room 
  connected 
  to 
  earth 
  and 
  the 
  rays 
  issued 
  

   through 
  a 
  small 
  orifice 
  A 
  in 
  a 
  thick 
  lead 
  plate 
  B 
  B'. 
  A 
  short 
  

   distance 
  in 
  front 
  of 
  this 
  was 
  placed 
  another 
  thick 
  lead 
  plate 
  C 
  C 
  

   The 
  rays 
  passed 
  through 
  a 
  small 
  rectangular 
  orifice 
  H 
  in 
  this 
  

   plate 
  and 
  then 
  into 
  a 
  brass 
  cylinder 
  through 
  an 
  aluminium 
  

   window. 
  This 
  cylinder, 
  which 
  is 
  shown 
  more 
  in 
  detail 
  in 
  

   fig. 
  2, 
  contained 
  the 
  electrodes 
  between 
  which 
  the 
  leak 
  was 
  

   measured. 
  

  

  Fig-. 
  2. 
  

  

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  The 
  electrodes 
  employed 
  consisted 
  of 
  extremely 
  thin 
  alumi- 
  

   nium-foil, 
  stretched 
  on 
  narrow 
  zinc 
  rings, 
  the 
  rings 
  being 
  

   for 
  the 
  purpose 
  of 
  support. 
  These 
  rings 
  were 
  supported 
  

   on 
  ebonite 
  blocks, 
  which 
  were 
  rigidly 
  fastened 
  to 
  a 
  metal 
  

   frame, 
  which 
  could 
  easily 
  be 
  removed 
  from 
  the 
  cylinder. 
  

   These 
  thin 
  plates 
  were 
  eleven 
  in 
  number, 
  and 
  were 
  placed 
  

   at 
  distances 
  of 
  about 
  two 
  centimetres 
  apart. 
  Six 
  of 
  them, 
  

   namely 
  the 
  two 
  end 
  ones 
  and 
  the 
  four 
  alternate 
  ones 
  of 
  the 
  

   remainder, 
  were 
  all 
  connected 
  together 
  and 
  also 
  to 
  the 
  

   terminal 
  E, 
  while 
  the 
  other 
  five 
  alternate 
  plates 
  were 
  con- 
  

   nected 
  to 
  W 
  . 
  

  

  This 
  arrangement 
  of 
  electrodes 
  was 
  adopted 
  in 
  order 
  to 
  

   secure 
  a 
  large 
  volume 
  of 
  gas 
  to 
  be 
  ionized, 
  and 
  thus 
  obtain 
  

   a 
  larger 
  effect 
  than 
  could 
  be 
  obtained 
  otherwise, 
  while 
  at 
  

   the 
  same 
  time 
  the 
  electrodes 
  were 
  close 
  enough 
  together 
  to 
  

   secure 
  a 
  saturation-current 
  with 
  a 
  reasonable 
  voltage. 
  All 
  

   the 
  ions 
  could 
  thus 
  reach 
  the 
  electrodes 
  in 
  a 
  very 
  short 
  

   time. 
  This 
  precaution 
  was 
  essential 
  as 
  it 
  was 
  necessary 
  that 
  

   all 
  the 
  ions 
  should 
  reach 
  the 
  electrodes 
  before 
  disappearing 
  

   by 
  recombination. 
  An 
  arrangement 
  consisting 
  of 
  a 
  guard- 
  

  

  