﻿Manganin 
  Resistances 
  with 
  Atmospheric 
  Humidity. 
  453 
  

  

  the 
  probable 
  increase 
  in 
  resistance 
  when 
  a 
  coil 
  is 
  taken 
  from 
  

   a 
  dry 
  to 
  a 
  saturated 
  atmosphere 
  at 
  17° 
  C. 
  is 
  given 
  in 
  the 
  last 
  

   column. 
  

  

  Here 
  we 
  have 
  positive 
  evidence 
  of 
  changes 
  in 
  standards 
  

   of 
  the 
  best 
  construction 
  ; 
  and 
  the 
  fact 
  that 
  the 
  coil 
  made 
  by 
  

   0. 
  Wolff 
  is 
  affected 
  by 
  varying 
  humidity 
  to 
  a 
  less 
  extent 
  

   than 
  the 
  coils 
  made 
  by 
  Mr. 
  Melsom 
  points 
  either 
  to 
  a 
  

   difference 
  in 
  the 
  shellac 
  varnishes 
  employed, 
  or 
  to 
  an 
  effect 
  

   due 
  to 
  the 
  ageing 
  of 
  the 
  varnish, 
  or 
  both. 
  The 
  changes 
  

   recorded 
  in 
  Table 
  I. 
  are 
  comparable 
  with 
  those 
  given 
  by 
  

   Drs. 
  Rosa 
  and 
  Babcock. 
  

  

  It 
  is 
  of 
  interest 
  to 
  compare 
  the 
  changes 
  in 
  resistance 
  from 
  

   Jan. 
  1906 
  to 
  Jan. 
  1908, 
  of 
  one 
  of 
  these 
  coils 
  with 
  the 
  

   humidity 
  change 
  given 
  in 
  Table 
  I. 
  For 
  this 
  purpose 
  the 
  

  

  Curve 
  showing 
  variation 
  in 
  10 
  ohm 
  manganin 
  resistance 
  L. 
  19. 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  \ 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  5 
  //v 
  

  

  oooo 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  1 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  (0 
  

  

  

  

  > 
  

  

  

  <0 
  

   

   X 
  

  

  3 
  

  

  

  

  

  5 
  

  

  

  

  ■5 
  

  

  

  

  § 
  

   * 
  

   3 
  

  

  coil 
  L. 
  19 
  is 
  chosen 
  because 
  it 
  has 
  been 
  kept 
  under 
  very 
  

   close 
  observation. 
  In 
  comparing 
  the 
  changes 
  it 
  is 
  necessary 
  

   to 
  bear 
  in 
  mind 
  that 
  during 
  the 
  period 
  1906-8 
  the 
  coil 
  L. 
  19 
  

   was 
  kept 
  in 
  oil, 
  and 
  hence 
  the 
  variations 
  of 
  atmospheric 
  

   humidity 
  would 
  have 
  an 
  appreciably 
  less 
  effect 
  on 
  the 
  shellac, 
  

   and 
  hence 
  on 
  the 
  resistance, 
  than 
  when 
  the 
  coil 
  was 
  exposed 
  

   to 
  the 
  air. 
  The 
  observations 
  on 
  L. 
  19 
  for 
  1906-8 
  are 
  sum- 
  

   marized 
  in 
  the 
  form 
  of 
  a 
  curve, 
  from 
  which 
  it 
  will 
  be 
  seen 
  

   that 
  the 
  resistance 
  has 
  gradually 
  increased 
  since 
  Jan. 
  1906 
  

   by 
  about 
  8 
  parts 
  in 
  100,000 
  ; 
  that 
  maxima 
  occur 
  about 
  July 
  

   each 
  year, 
  and 
  that 
  it 
  is 
  improbable 
  that 
  the 
  change 
  in 
  

   resistance 
  due 
  to 
  humidity 
  variations 
  has 
  exceeded 
  2 
  parts 
  

   in 
  100,000, 
  or 
  one-twentieth 
  of 
  the 
  change 
  recorded 
  for 
  the 
  

   same 
  coil 
  in 
  Table 
  I. 
  Observations 
  on 
  other 
  manganin 
  

   coils, 
  immersed 
  in 
  oil, 
  indicate 
  maximum 
  changes 
  in 
  their 
  

   resistances, 
  due 
  to 
  variations 
  in 
  atmospheric 
  humidity, 
  of 
  the 
  

   order 
  of 
  1 
  part 
  in 
  100,000. 
  

  

  Of 
  air-cooled 
  manganin 
  coils 
  coated 
  with 
  shellac, 
  a 
  number 
  

   in 
  boxes, 
  by 
  R. 
  W. 
  Paul 
  and 
  by 
  O. 
  Wolff, 
  have 
  been 
  measured 
  

  

  