﻿produced 
  in 
  Gases 
  by 
  Ultra-Violet 
  Light. 
  559 
  

  

  tube 
  about 
  33 
  inches 
  long, 
  which 
  dipped 
  into 
  a 
  vessel 
  con- 
  

   taining 
  mercury. 
  

  

  Some 
  of 
  the 
  ebonite 
  tube 
  E 
  was 
  cut 
  away 
  so 
  as 
  to 
  allow 
  

   the 
  gas 
  a 
  free 
  passage 
  from 
  the 
  space 
  between 
  the 
  plates 
  to 
  

   the 
  other 
  parts 
  of 
  the 
  apparatus. 
  

  

  Fio-. 
  1. 
  

  

  Fig. 
  2. 
  

  

  A 
  short 
  piece 
  of 
  ebonite 
  was 
  fixed 
  to 
  the 
  screw 
  S, 
  and 
  the 
  

   rod 
  R, 
  coming 
  through 
  the 
  mercury 
  column 
  below 
  D, 
  fitted 
  

   into 
  a 
  notch 
  cut 
  in 
  the 
  ebonite. 
  The 
  distance 
  between 
  the 
  

   plates 
  A 
  and 
  B 
  could 
  be 
  altered, 
  without 
  changing 
  the 
  pres- 
  

   sure, 
  by 
  turning 
  the 
  end 
  of 
  the 
  rod 
  R, 
  which 
  was 
  bent 
  as 
  

   shown 
  in 
  figure 
  2. 
  

  

  The 
  apparatus 
  was 
  connected 
  to 
  a 
  Toepler 
  pump 
  and 
  a 
  

   McLeod 
  gauge. 
  A 
  small 
  variation 
  of 
  pressure 
  could 
  be 
  

   detected 
  by 
  means 
  of 
  the 
  gauge, 
  and 
  it 
  was 
  found 
  that 
  the 
  

   pressure 
  only 
  altered 
  by 
  about 
  a 
  five-hundredth 
  of 
  a 
  milli- 
  

   metre 
  during 
  a 
  set 
  of 
  observations. 
  

  

  When 
  experimenting 
  with 
  hydrogen 
  and 
  carbonic 
  acid, 
  a 
  

   fresh 
  supply 
  of 
  gas 
  was 
  introduced 
  into 
  the 
  apparatus 
  before 
  

   each 
  set 
  of 
  experiments, 
  so 
  that 
  the 
  small 
  leakage 
  could 
  not 
  

   have 
  produced 
  any 
  appreciable 
  effect 
  in 
  the 
  results. 
  

  

  2P2 
  

  

  