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  LXXXIII. 
  On 
  the 
  Measurement 
  of 
  Wave 
  Length 
  for 
  High 
  

   Frequency 
  Electrical 
  Oscillations, 
  By 
  Albert 
  Campbell, 
  

   B,A* 
  

  

  (From 
  the 
  National 
  Physical 
  Laboratory.) 
  

  

  [Plate 
  XXVIII.J 
  

  

  § 
  1. 
  Introduction. 
  

  

  IN 
  all 
  work 
  with 
  high 
  frequency 
  electrical 
  oscillations, 
  

   such 
  as 
  for 
  example 
  in 
  wave 
  telegraphy, 
  it 
  is 
  of 
  the 
  

   utmost 
  importance 
  to 
  be 
  able 
  to 
  determine 
  with 
  accuracy 
  

   the 
  wave-length 
  actually 
  employed, 
  and 
  for 
  this 
  purpose 
  

   several 
  types 
  of 
  wavemeter 
  are 
  now 
  in 
  common 
  use. 
  In 
  

   order 
  to 
  ensure 
  accuracy 
  in 
  such 
  measurements, 
  it 
  was 
  

   suggested 
  some 
  time 
  ago 
  by 
  the 
  Post 
  Office 
  Authorities 
  

   that 
  arrangements 
  should 
  be 
  made 
  for 
  the 
  calibration 
  of 
  

   wavemeters 
  at 
  the 
  National 
  Physical 
  Laboratory. 
  As 
  the 
  

   results 
  of 
  our 
  first 
  series 
  of 
  investigations 
  in 
  the 
  matter 
  

   appeared 
  to 
  be 
  of 
  general 
  interest, 
  we 
  publish 
  them 
  here 
  by 
  

   the 
  kind 
  permission 
  of 
  Major 
  O'Meara, 
  C.M.G., 
  Engineer-in- 
  

   Chief 
  to 
  the 
  Post 
  Office. 
  Our 
  experiments 
  comprised 
  the 
  

   construction 
  and 
  testing 
  of 
  a 
  standard 
  wavemeter, 
  and 
  the 
  

   verification 
  of 
  an 
  ordinary 
  commercial 
  wavemeter 
  sent 
  to 
  us 
  

   by 
  the 
  Post 
  Office. 
  I 
  shall 
  designate 
  this 
  instrument 
  (A) 
  

   and 
  our 
  standard 
  wavemeter 
  (B) 
  respectively. 
  While 
  it 
  is 
  

   unnecessary 
  here 
  to 
  go 
  into 
  the 
  history 
  of 
  the 
  subject, 
  I 
  

   should 
  like 
  to 
  give 
  one 
  or 
  two 
  references 
  to 
  earlier 
  work 
  by 
  

   other 
  observers 
  which 
  gave 
  us 
  much 
  assistance, 
  namely 
  the 
  

   experiments 
  of 
  Pierce 
  t 
  and 
  those 
  of 
  Gehrcke+. 
  

  

  While 
  our 
  work 
  was 
  in 
  progress 
  an 
  important 
  paper 
  by 
  

   Diesselhorst 
  § 
  appeared, 
  and 
  the 
  results 
  there 
  published 
  were 
  

   in 
  ample 
  confirmation 
  of 
  those 
  we 
  were 
  obtaining, 
  as 
  also 
  

   were 
  the 
  earlier 
  results 
  of 
  Pierce. 
  

  

  § 
  2. 
  Description 
  of 
  Wavemeter 
  (A). 
  

  

  Wavemeter 
  (A) 
  is 
  of 
  the 
  Donitz 
  type 
  and 
  consists 
  of 
  a 
  

   variable 
  air 
  condenser, 
  with 
  a 
  range 
  from 
  about 
  100 
  to 
  

   1070 
  mmfd. 
  (micromicrofarads), 
  a 
  thermo-junction 
  and 
  

   galvanometer, 
  and 
  a 
  series 
  of 
  coils 
  (A 
  1, 
  A 
  2, 
  .... 
  to 
  A 
  10) 
  

   of 
  self 
  inductances 
  ranging 
  from 
  0*76 
  to 
  2313 
  microhenries. 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  June 
  25, 
  1909. 
  

  

  t 
  Phys. 
  Review, 
  vol. 
  xxiv. 
  p. 
  152, 
  1907. 
  

  

  X 
  Elektrotech. 
  Zeitschr. 
  (26), 
  p. 
  697, 
  1905. 
  

  

  § 
  Jahrbuch 
  der 
  drahtlosen 
  Telegr. 
  u. 
  Teleph. 
  vol. 
  i. 
  (1908). 
  

  

  