﻿Besistance 
  of 
  Mixtures 
  of 
  Xylol 
  and 
  Alcohol. 
  1047 
  

  

  connexions 
  is 
  shown 
  in 
  fig. 
  2. 
  The 
  resistances 
  r^ 
  r 
  2 
  , 
  are 
  taken 
  

   from 
  a 
  Post 
  Office 
  box, 
  the 
  greater 
  of 
  them 
  being 
  always 
  

  

  Fig. 
  2. 
  

  

  Earth 
  

  

  Fig. 
  3. 
  

  

  Earth 
  

  

  2000 
  ohms. 
  When 
  the 
  ratio 
  a?/R 
  is 
  greater 
  than 
  20 
  the 
  

   arrangement 
  shown 
  in 
  fig. 
  3 
  is 
  more 
  sensitive 
  ; 
  the 
  potential 
  

   of 
  the 
  battery 
  Vi 
  may 
  be 
  100 
  volts 
  or 
  more 
  and 
  compared 
  with 
  

   that 
  of 
  V 
  2 
  (2 
  volts) 
  by 
  means 
  of 
  a 
  standard 
  voltmeter. 
  These 
  

   methods 
  of 
  comparison 
  are 
  certainly 
  more 
  accurate 
  than 
  those 
  

   based 
  on 
  the 
  use 
  of 
  a 
  constant 
  current 
  provided 
  by 
  a 
  radio- 
  

   active 
  preparation, 
  because 
  when 
  two 
  of 
  the 
  resistances 
  

   investigated 
  are 
  balanced 
  against 
  each 
  other 
  there 
  are 
  no 
  

  

  observable 
  " 
  Schweidler's 
  fluctuations. 
  

  

  In 
  fig. 
  2 
  the 
  fulfil- 
  

  

  ment 
  of 
  Ohm's 
  law 
  is 
  easily 
  tested 
  by 
  changing 
  the 
  E.M.F. 
  

   of 
  the 
  battery. 
  

  

  It 
  was 
  usually 
  found 
  that 
  the 
  bridge 
  was 
  not 
  completely 
  

   balanced 
  even 
  when 
  the 
  battery 
  switch 
  was 
  open 
  and, 
  conse- 
  

   quently, 
  that 
  the 
  values 
  of 
  r 
  1? 
  r 
  2 
  necessary 
  to 
  obtain 
  a 
  balance 
  

   varied 
  with 
  the 
  direction 
  of 
  the 
  current. 
  I 
  think 
  it 
  is 
  this 
  

  

  : 
  

  

  

  