﻿produced 
  in 
  Air 
  by 
  the 
  Motion 
  of 
  Negative 
  Ions. 
  213 
  

  

  and 
  for 
  this 
  purpose 
  the 
  following 
  experiments 
  were 
  under- 
  

   taken. 
  

  

  1. 
  The 
  form 
  of 
  the 
  apparatus 
  is 
  shown 
  in 
  the 
  accompanying 
  

   figure. 
  It 
  consisted 
  of 
  two 
  coaxial 
  cylinders. 
  The 
  outer 
  one 
  

   was 
  of 
  aluminium 
  in 
  order 
  that 
  the 
  Rontgen 
  rays, 
  which 
  were 
  

   used 
  to 
  ionize 
  the 
  air 
  within, 
  might 
  pass 
  freely 
  through 
  it. 
  

   The 
  internal 
  diameter 
  was 
  41/5 
  mm. 
  A 
  copper 
  wire 
  formed 
  

   the 
  inner 
  cylinder 
  : 
  its 
  diameter 
  was 
  *206 
  mm. 
  The 
  ends 
  of 
  

   the 
  external 
  cylinder 
  were 
  cemented 
  into 
  grooves 
  turned 
  in 
  

   pieces 
  of 
  ebonite 
  E 
  1? 
  E 
  2 
  , 
  as 
  shown 
  in 
  fig. 
  1. 
  Brass 
  tubes, 
  

   T„ 
  T 
  2 
  , 
  coaxial 
  with 
  the 
  aluminium 
  cylinder 
  projected 
  from 
  

  

  Fig. 
  1. 
  

  

  Al/f 
  PuMf 
  

  

  £L£CrAOM£T£ft 
  

  

  the 
  ebonite 
  pieces 
  Ej, 
  E 
  2 
  , 
  and 
  carried 
  the 
  ebonite 
  plugs 
  P 
  1} 
  P 
  2 
  , 
  

   into 
  the 
  centres 
  of 
  which 
  metallic 
  rods 
  R 
  1? 
  R 
  2 
  were 
  fastened. 
  

   The 
  copper 
  wire 
  was 
  stretched 
  between 
  these 
  rods. 
  The 
  

   brass 
  tubes 
  T 
  l5 
  T 
  2 
  , 
  which 
  were 
  permanently 
  earthed, 
  formed 
  a 
  

   divided 
  insulation 
  which 
  effectually 
  prevented 
  any 
  leakage 
  

   between 
  the 
  cylinders 
  when 
  the 
  outer 
  cylinder 
  was 
  charged 
  

   to 
  a 
  high 
  potential. 
  The 
  space 
  within 
  the 
  aluminium 
  cylinder 
  

   was 
  exhausted 
  to 
  the 
  required 
  amount 
  by 
  means 
  of 
  the 
  thin 
  

   vertical 
  tube 
  shown 
  in 
  the 
  diagram, 
  which 
  was 
  soldered 
  into 
  

   the 
  brass 
  tube 
  T,. 
  The 
  pressure 
  was 
  determined 
  by 
  a 
  Macleod 
  

   gauge 
  which 
  was 
  in 
  permanent 
  connexion 
  with 
  the 
  aluminium 
  

   cylinder. 
  

  

  The 
  Rontgen 
  rays 
  passed 
  through 
  a 
  slit 
  in 
  a 
  lead-covered 
  

   box 
  which 
  contained 
  the 
  Crookes 
  tube 
  and 
  the 
  Ruhmkorf 
  

   coil. 
  The 
  aluminium 
  cylinder 
  was 
  placed 
  over 
  the 
  slit. 
  

  

  2. 
  The 
  method 
  of 
  conducting 
  the 
  experiments 
  was 
  similar 
  

   to 
  that 
  adopted 
  in 
  the 
  paper 
  already 
  referred 
  to. 
  One 
  pair 
  

   of 
  quadrants 
  of 
  the 
  electrometer 
  was 
  permanently 
  connected 
  

   to 
  the 
  copper 
  wire. 
  The 
  other 
  pair 
  was 
  permanently 
  to 
  

   earth. 
  The 
  potential 
  of 
  the 
  aluminium 
  cylinder 
  was 
  raised 
  

   to 
  any 
  required 
  amount 
  by 
  connecting 
  it 
  to 
  one 
  terminal 
  of 
  a 
  

   battery 
  of 
  small 
  Leclanche 
  cells, 
  the 
  other 
  terminal 
  being 
  to 
  

   earth. 
  The 
  voltage 
  used 
  ranered 
  in 
  general 
  from 
  37 
  to 
  370. 
  

  

  