﻿592 
  Messrs. 
  Cameron 
  and 
  Oettinger 
  on 
  Electromotive 
  

  

  The 
  apparatus 
  is 
  shown 
  in 
  the 
  accompanying 
  diagram 
  

  

  (fig- 
  !)• 
  

  

  The 
  electrometer 
  needle 
  was 
  always 
  charged 
  to 
  a 
  con- 
  

   venient 
  potential 
  by 
  means 
  o£ 
  a 
  Zamboni 
  pile. 
  One 
  pair 
  o£ 
  

   quadrants 
  was 
  earthed, 
  the 
  other 
  connected 
  with 
  the 
  electrode 
  

  

  nearest 
  the 
  free 
  end 
  o£ 
  the 
  capillary. 
  The 
  other 
  electrode 
  

   was 
  also 
  earthed. 
  It 
  was 
  found 
  that 
  the 
  connexions, 
  reversed, 
  

   did 
  not 
  lead 
  to 
  such 
  certain 
  results 
  ; 
  the 
  reason 
  was 
  probably 
  

   due 
  to 
  imperfect 
  insulation 
  of 
  the 
  second 
  electrode, 
  since 
  

   connexion 
  with 
  the 
  flask 
  was 
  allowed 
  by 
  the 
  liquid. 
  This 
  

   source 
  of 
  error 
  was 
  also 
  observed 
  by 
  Dorn. 
  The 
  sensibility 
  

   of 
  the 
  electrometer 
  was 
  always 
  determined 
  with 
  a 
  normal 
  

   cadmium 
  cell. 
  

  

  Preliminary 
  Experiments. 
  

  

  If 
  the 
  quantities 
  c^i 
  — 
  ^a, 
  77, 
  and 
  k 
  are 
  constant, 
  Helmholtz's 
  

   formula 
  simplifies 
  to 
  the 
  form 
  

  

  E 
  = 
  K.P, 
  

  

  where 
  E 
  and 
  P 
  are 
  respectively 
  the 
  differences 
  of 
  potential 
  

   and 
  pressure 
  between 
  two 
  electrodes, 
  and 
  K 
  is 
  a 
  constant. 
  

   Ordinary 
  distilled 
  water 
  of 
  specific 
  conductivity 
  between 
  

   10"^ 
  and 
  10"^ 
  was 
  used 
  to 
  test 
  the 
  formula 
  in 
  this 
  simple 
  

   form, 
  in 
  order 
  to 
  control 
  the 
  working 
  of 
  the 
  apparatus. 
  

  

  A 
  thin 
  capillary 
  tube 
  ah 
  of 
  diameter 
  0'65 
  and 
  length 
  

   270 
  mm. 
  was 
  taken, 
  and 
  four 
  electrodes 
  a, 
  (3, 
  7, 
  h. 
  inserted, 
  

   such 
  that 
  aa=29, 
  a^=^2, 
  fiy=97, 
  7^ 
  = 
  68, 
  Sb=U 
  mm. 
  

  

  