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  XXXIX. 
  The 
  Variation 
  of 
  Manganin 
  Resistances 
  ivith 
  Atmo- 
  

   spheric 
  Humidity. 
  By 
  F. 
  E. 
  Smith, 
  A.R.C.Sc. 
  (From 
  

   the 
  National 
  Physical 
  Laboratory.) 
  * 
  

  

  IN 
  the 
  issue 
  of 
  ' 
  The 
  Electrician 
  ' 
  dated 
  June 
  14th, 
  1907, 
  

   Drs. 
  Rosa 
  and 
  Babcock 
  published 
  an 
  article 
  o£ 
  great 
  

   interest 
  under 
  the 
  above 
  title. 
  A 
  long 
  series 
  of 
  measure- 
  

   ments 
  on 
  manganin 
  resistances 
  was 
  given, 
  and 
  it 
  was 
  

   shown 
  that 
  the 
  higher 
  resistances 
  exhibited 
  a 
  yearly 
  cycle 
  

   corresponding 
  to 
  the 
  variations 
  in 
  the 
  relatiTe 
  humidity 
  

   of 
  the 
  atmosphere. 
  Later 
  f, 
  Drs. 
  Jaeger 
  and 
  Lindeck 
  pub- 
  

   lished 
  results 
  proving 
  that 
  the 
  variations 
  of 
  many 
  high 
  

   resistances 
  at 
  the 
  Reich 
  sanstalt 
  were 
  quite 
  negligible 
  even 
  

   when 
  the 
  humidity 
  was 
  believed 
  to 
  have 
  appreciably 
  changed. 
  

   That 
  the 
  humidity 
  variations 
  at 
  Washington 
  were 
  not 
  very 
  

   abnormal 
  has 
  been 
  shown 
  by 
  Dr. 
  Rosa 
  J, 
  and 
  it 
  appears, 
  

   therefore, 
  that 
  some 
  shellaced 
  coils 
  remain 
  approximately 
  

   constant 
  with 
  varying 
  humidity, 
  while 
  others 
  change 
  by 
  

   considerable 
  amounts. 
  Indeed, 
  Dr. 
  Rosa 
  emphasizes 
  the 
  

   point, 
  that 
  of 
  the 
  resistances 
  examined 
  by 
  him 
  the 
  coils 
  of 
  

   nominally 
  equal 
  value 
  did 
  not 
  change 
  by 
  equal 
  amounts. 
  

  

  The 
  changes 
  in 
  resistance 
  of 
  the 
  manganin 
  standards 
  of 
  

   the 
  National 
  Physical 
  Laboratory 
  have 
  been 
  reported 
  on 
  

   from 
  time 
  to 
  time, 
  and 
  we 
  have 
  also 
  stated 
  that 
  small 
  changes 
  

   in 
  the 
  resistances 
  of 
  1 
  ohm 
  coils 
  have 
  been 
  detected 
  within 
  

   twenty-four 
  hours. 
  On 
  the 
  publication 
  of 
  the 
  paper 
  by 
  

   Drs. 
  Rosa 
  and 
  Babcock, 
  we 
  were, 
  therefore, 
  convinced 
  that 
  

   some 
  of 
  the 
  changes 
  we 
  had 
  observed 
  were 
  due 
  to 
  variations 
  in 
  

   atmospheric 
  humidity, 
  and 
  shortly 
  afterwards 
  we 
  proceeded 
  

   to 
  measure 
  the 
  effect 
  of 
  humidity 
  on 
  various 
  standard 
  coils. 
  

  

  The 
  first 
  coil 
  experimented 
  with 
  was 
  one 
  of 
  10,000 
  ohms 
  

   of 
  manganin, 
  of 
  the 
  Reichsanstalt 
  form, 
  and 
  made 
  by 
  O. 
  Wolff 
  

   of 
  Berlin. 
  It 
  was 
  placed 
  inside 
  a 
  box 
  through 
  which 
  passed 
  

   two 
  well-insulated 
  copper 
  leads 
  connected 
  to 
  mercury 
  cups, 
  

   to 
  which 
  also 
  the 
  leads 
  of 
  the 
  coil 
  were 
  connected. 
  The 
  

   metal 
  cylinder 
  surrounding 
  the 
  coil 
  was 
  removed 
  so 
  that 
  the 
  

   shellac 
  was 
  fully 
  exposed 
  to 
  the 
  atmosphere. 
  The 
  box 
  was 
  

   made 
  practically 
  air-tight 
  by 
  coating 
  it 
  on 
  the 
  outside 
  with 
  

   paraffin 
  wax, 
  and 
  the 
  humidity 
  inside 
  the 
  box 
  was 
  varied 
  by 
  

   introducing 
  a 
  large 
  quantity 
  of 
  fused 
  calcium 
  chloride, 
  or 
  by 
  

   the 
  insertion 
  of 
  water 
  contained 
  in 
  large 
  crystallizing 
  dishes. 
  

   The 
  temperature 
  could 
  be 
  varied 
  by 
  placing 
  the 
  box 
  inside 
  a 
  

   large 
  electric 
  oven, 
  but 
  it 
  was 
  not 
  allowed 
  to 
  exceed 
  35° 
  C. 
  

   Measurements 
  of 
  resistance 
  were 
  made 
  at 
  an 
  approximately 
  

   constant 
  temperature 
  of 
  17° 
  C. 
  

  

  * 
  Communicated 
  by 
  Dr. 
  R 
  T. 
  Glazebrook, 
  F.R.S. 
  

  

  t 
  ' 
  The 
  Electrician,' 
  Aug. 
  2, 
  1907. 
  % 
  ' 
  The 
  Electrician,' 
  Nov. 
  15, 
  1907. 
  

  

  