﻿Variable 
  Frequency 
  Alternating 
  Currents. 
  

  

  487 
  

  

  exactly 
  similar 
  to 
  that 
  obtained 
  with 
  the 
  single 
  action 
  circuit, 
  

   but 
  with 
  about 
  double 
  the 
  amplitude. 
  

  

  When 
  the 
  secondaries 
  are 
  joined 
  up 
  so 
  that 
  the 
  break 
  

   oscillations 
  oppose 
  each 
  other, 
  whilst 
  the 
  make 
  oscillations 
  

  

  Fie. 
  11. 
  — 
  Double 
  Action 
  Circuit 
  with 
  Two 
  Transformers. 
  

  

  assist, 
  the 
  result, 
  i£ 
  these 
  oscillations 
  are 
  equal 
  in 
  frequency 
  

   but 
  unequal 
  in 
  amplitude, 
  is 
  to 
  give 
  a 
  continuous 
  and 
  more 
  

   or 
  less 
  uniform 
  wave. 
  

  

  The 
  first 
  wave 
  in 
  fig. 
  13 
  (PL 
  XVIII.) 
  shows 
  the 
  effect 
  of 
  

   opposing 
  two 
  850-^- 
  oscillations, 
  and 
  the 
  second 
  the 
  effect 
  with 
  

   two 
  490^- 
  oscillations. 
  The 
  continuous 
  waves 
  resulting 
  are 
  

   850-^ 
  and 
  490-^ 
  respectively. 
  

  

  The 
  regularity 
  of 
  the 
  continuous 
  wave 
  can 
  be 
  best 
  modified 
  

   by 
  slightly 
  varying 
  one 
  of 
  the 
  inductances, 
  which 
  have 
  air 
  

   cores 
  by 
  inserting 
  in 
  the 
  cores 
  one 
  or 
  tw 
  T 
  o 
  strands 
  of 
  fine 
  iron 
  

   wire. 
  

  

  It 
  is 
  obvious 
  since 
  the 
  output 
  depends 
  on 
  the 
  difference 
  

   between 
  the 
  two 
  circuits 
  that 
  it 
  will 
  not 
  be 
  large. 
  To 
  in- 
  

   crease 
  the 
  output, 
  different 
  inductances 
  for 
  each 
  of 
  the 
  two 
  

   circuits 
  can 
  be 
  used, 
  and 
  the 
  capacities 
  adjusted 
  so 
  as 
  to 
  get 
  

   the 
  same 
  frequency 
  in 
  each 
  circuit. 
  

  

  It 
  is 
  of 
  course 
  impossible 
  to 
  obtain 
  a 
  pure 
  sine 
  wave 
  by 
  

   this 
  method, 
  and 
  the 
  extent 
  of 
  the 
  impurity 
  has 
  not 
  yet 
  

   been 
  examined 
  analytically. 
  Some 
  tests 
  have, 
  however, 
  been 
  

   made 
  by 
  using 
  these 
  waves 
  for 
  measurement 
  purposes. 
  These 
  

   are 
  given 
  further 
  on. 
  

  

  