﻿Measurement 
  by 
  Alternating 
  Currents. 
  69 
  

  

  Thus 
  we 
  need 
  not 
  search 
  for 
  methods 
  of 
  directly 
  comparing 
  

   mutual 
  inductances 
  with 
  each 
  other, 
  although 
  I 
  have 
  given 
  

   two 
  of 
  these, 
  but 
  we 
  can 
  content 
  ourselves 
  with 
  measuring 
  

   self-inductances 
  and 
  capacities. 
  Fortunately 
  most 
  of 
  the 
  

   methods 
  are 
  specially 
  adapted 
  to 
  the 
  latter, 
  the 
  ratio 
  of 
  self- 
  

   inductance 
  to 
  capacity 
  being 
  capable 
  of 
  being 
  determined 
  

   with 
  great 
  exactness 
  by 
  many 
  methods. 
  

  

  In 
  the 
  use 
  of 
  condensers 
  I 
  have 
  met 
  with 
  great 
  difficulty 
  

   from 
  the 
  presence 
  of 
  electric 
  absorption. 
  I 
  have 
  found 
  that 
  

   this 
  can 
  be 
  represented 
  by 
  a 
  resistance 
  placed 
  in 
  the 
  circuit 
  

   of 
  the 
  condenser, 
  which 
  resistance 
  is 
  a 
  function 
  of 
  current 
  

   period. 
  

  

  I 
  have 
  developed 
  Maxwell's 
  theory 
  of 
  electric 
  absorption 
  

   in 
  this 
  manner. 
  Correcting 
  his 
  equations 
  for 
  a 
  small 
  error, 
  

   I 
  have 
  developed 
  the 
  resistance 
  and 
  capacity 
  of 
  a 
  condenser 
  

   as 
  follows 
  : 
  

  

  Let 
  a 
  condenser 
  be 
  made 
  of 
  strata 
  of 
  thicknesses 
  a 
  l9 
  a 
  2 
  , 
  &c, 
  

   and 
  specific 
  inductive 
  capacities 
  k 
  ly 
  k 
  2 
  , 
  &c, 
  and 
  resistances 
  

   Pi) 
  P2? 
  & 
  c 
  « 
  Then 
  we 
  have 
  

  

  1 
  _ 
  A 
  — 
  ^ 
  2 
  4- 
  ^ 
  

  

  — 
  A 
  — 
  2 
  -I- 
  4 
  _ 
  Xr 
  n 
  

  

  where 
  

  

  &c. 
  

  

  B 
  -^{^ 
  +&c 
  -} 
  

  

  &c. 
  

  

  Mr. 
  Penniman 
  has 
  experimented 
  in 
  the 
  Johns 
  Hopkins 
  

   University 
  laboratory 
  with 
  condensers 
  by 
  method 
  25 
  and 
  

   found 
  some 
  interesting 
  results. 
  With 
  a 
  mica 
  standard 
  con- 
  

   denser 
  of 
  I 
  microfarad 
  he 
  was 
  not 
  able 
  to 
  detect 
  any 
  electric 
  

  

  