﻿Roioland 
  and 
  Penniman 
  — 
  ElectTical 
  Measurements. 
  43 
  

  

  necessary 
  that 
  I 
  and 
  C 
  should 
  be 
  exactly 
  known 
  as 
  the 
  last 
  

   term 
  in 
  the 
  equation 
  above 
  plays 
  the 
  part 
  of 
  a 
  correction 
  term, 
  

   and 
  is 
  in 
  all 
  cases 
  below 
  small 
  and 
  in 
  some 
  cases 
  negligible. 
  

   The 
  capacities 
  that 
  were 
  used 
  in 
  the 
  experiments 
  were 
  the 
  2 
  

   and 
  3 
  microfarads, 
  the 
  \ 
  microfarad 
  Elliott 
  condenser, 
  and 
  the 
  

   -J 
  microfarad 
  Troy 
  condenser. 
  

  

  Experiments 
  — 
  The 
  process 
  of 
  experimenting 
  was 
  to 
  apply 
  a 
  

   periodic 
  electromotive 
  force 
  to 
  a 
  and 
  d.^ 
  and 
  to 
  adjust 
  the 
  dif- 
  

   ferent 
  resistances 
  until 
  there 
  was 
  no 
  deflection 
  of 
  the 
  coil 
  in 
  

  

  the 
  same 
  way 
  as 
  in 
  the 
  ordinary 
  measurement 
  of 
  resistance 
  on 
  

   a 
  Wheatstone 
  bridge. 
  The 
  different 
  resistances 
  R', 
  R^', 
  R^^ 
  

   and 
  r 
  being 
  known, 
  the 
  apparent 
  value 
  of 
  the 
  resistance 
  R, 
  was 
  

   found, 
  and 
  knowing 
  the 
  ohmic 
  resistance 
  of 
  the 
  R^ 
  circuit, 
  the 
  

   absorption 
  resistance 
  appears 
  as 
  the 
  difference. 
  

  

  Some 
  interest 
  lies 
  not 
  alone 
  in 
  that 
  the 
  method 
  is 
  applica- 
  

   ble, 
  but 
  that 
  it 
  confirmed 
  the 
  supposition 
  that 
  absorption 
  

   resistance 
  acts 
  as 
  an 
  ordinary 
  ohmic 
  resistance 
  in 
  series 
  in 
  

   the 
  circuit. 
  This 
  was 
  confirmed 
  by 
  the 
  fact 
  that 
  when 
  con- 
  

   densers 
  were 
  in 
  series 
  and 
  in 
  parallel, 
  their 
  absorption 
  resist- 
  

   ances 
  acted 
  under 
  these 
  conditions 
  like 
  ohmic 
  resistances, 
  being 
  

   increased 
  in 
  the 
  one 
  case 
  and 
  decreased 
  in 
  the 
  other, 
  and 
  in 
  the 
  

   right 
  ratio. 
  This 
  agreement 
  was 
  not 
  exact, 
  as 
  the 
  absorption 
  

   resistance 
  was 
  extremely 
  sensitive 
  both 
  to 
  change 
  of 
  period 
  

   and 
  change 
  of 
  temperature. 
  The 
  great 
  sensitiveness 
  to 
  change 
  

   of 
  temperature 
  was 
  shown 
  either 
  by 
  letting 
  the 
  current 
  go 
  

   through 
  the 
  condensers 
  for 
  a 
  little 
  time, 
  or 
  placing 
  the 
  con- 
  

   densers 
  before 
  a 
  hot 
  air 
  flue 
  ; 
  in 
  either 
  case 
  after 
  cooling, 
  the 
  

   absorption 
  resistance 
  returned 
  to 
  its 
  original 
  value. 
  The 
  cool- 
  

   ing 
  was 
  very 
  slow, 
  as 
  there 
  was 
  very 
  little 
  radiation 
  from 
  the 
  

   condensers 
  inclosed 
  in 
  wooden 
  boxes. 
  

  

  The 
  results 
  are 
  now 
  given 
  for 
  the 
  condensers 
  2 
  and 
  3 
  micro- 
  

   farads. 
  In 
  the 
  calculation 
  of 
  the 
  results 
  the 
  last 
  term 
  of 
  the 
  

  

  ZR'^R'+R'O 
  

  

  equation, 
  that 
  is 
  

  

  has 
  been 
  left 
  

  

  c?RXR''+R,j-t-KR'+JR'0 
  

  

  out, 
  as 
  it 
  was 
  very 
  small 
  when 
  condensers 
  2 
  and 
  3 
  microfarads 
  

   were 
  used. 
  

  

  