﻿452 
  

  

  Mr. 
  F. 
  E. 
  Smith 
  on 
  the 
  Variation 
  of 
  

  

  The 
  first 
  coil 
  experimented 
  with 
  exhibited, 
  therefore, 
  no 
  

   appreciable 
  change 
  in 
  resistance 
  with 
  change 
  in 
  humidity. 
  

  

  Our 
  next 
  experiments 
  were 
  made 
  with 
  five 
  other 
  standard 
  

   coils 
  and 
  some 
  resistance-coils 
  in 
  boxes, 
  but 
  before 
  giving 
  

   the 
  results 
  obtained 
  with 
  them, 
  it 
  may 
  be 
  of 
  interest 
  to 
  give 
  

   an 
  idea 
  of 
  the 
  amount 
  of 
  moisture 
  absorbed 
  by 
  the 
  shellac 
  

   coating 
  a 
  resistance-coil. 
  

  

  Mr.^Melsom, 
  who 
  has 
  constructed 
  very 
  many 
  standard 
  

   coils, 
  shellaced 
  a 
  metal 
  cylinder 
  of 
  the 
  same 
  size 
  as 
  those 
  

   used 
  in 
  the 
  winding 
  of 
  standard 
  coils 
  of 
  the 
  Reichsanstalt 
  

   pattern, 
  and 
  afterwards 
  he 
  baked 
  it 
  and 
  treated 
  it 
  in 
  the 
  

   same 
  way 
  as 
  standard 
  coils 
  are 
  treated. 
  After 
  remaining 
  

   for 
  10 
  days 
  in 
  a 
  desiccator 
  containing 
  phosphoric 
  anhydride, 
  

   this 
  shellaced 
  cylinder 
  weighed 
  51*2614 
  grams, 
  and 
  after 
  

   being 
  hermetically 
  sealed 
  for 
  10 
  days 
  in 
  a 
  beaker 
  containing 
  

   a 
  little 
  water 
  at 
  17°*0 
  C. 
  its 
  weight 
  was 
  51*2816 
  grams 
  ; 
  an 
  

   increase 
  of 
  0*02 
  gram. 
  It 
  appears 
  that, 
  after 
  calibration, 
  

   such 
  a 
  cylinder 
  might 
  be 
  used 
  as 
  an 
  hygrometer. 
  

  

  The 
  other 
  standard 
  coils 
  examined 
  are 
  five 
  in 
  number. 
  One 
  

   of 
  these, 
  No. 
  2449, 
  is 
  by 
  0. 
  Wolff, 
  Berlin 
  ; 
  and 
  the 
  re- 
  

   maining 
  four 
  were 
  made 
  by 
  Mr. 
  Melsom 
  in 
  accordance 
  with 
  

   the 
  Reichsanstalt 
  specification. 
  In 
  Table 
  I. 
  the 
  results 
  are 
  

  

  Table 
  I. 
  

  

  Coil. 
  

  

  Nominal 
  

   Value. 
  

  

  Atmosphere 
  dried 
  with 
  ' 
  

   P 
  2 
  5 
  for 
  

  

  Atmosphere 
  saturated 
  with 
  

   water 
  for 
  

  

  Change. 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  days 
  

  

  4 
  

  

  days 
  

  

  5 
  

   days 
  

  

  6 
  

  

  days 
  

  

  10 
  

  

  days 
  

  

  2 
  

  

  days 
  

  

  + 
  2 
  

  

  4 
  

   days 
  

  

  ~~ 
  

  

  + 
  3 
  

  

  6 
  

  

  days 
  

  

  4- 
  6 
  

  

  10 
  

   days 
  

  

  4-18 
  

  

  18 
  

  

  days 
  

  

  4-23 
  

  

  24 
  

  

  days 
  

  

  +23 
  

  

  

  L. 
  19... 
  

  

  ohms 
  

   10 
  

  

  -15 
  

  

  -16 
  

  

  -18 
  

  

  -« 
  

  

  -is' 
  

  

  +41 
  

  

  L.143... 
  

  

  10 
  

  

  - 
  1 
  

  

  - 
  2 
  

  

  _ 
  

  

  - 
  4 
  

  

  - 
  3 
  

  

  4-23 
  

  

  +36 
  

  

  4-38 
  

  

  4-38 
  

  

  4-36 
  

  

  +37 
  

  

  + 
  40 
  

  

  L.140... 
  

  

  100 
  

  

  - 
  9 
  

  

  -13 
  

  

  -17 
  

  

  -14 
  

  

  -16 
  

  

  4-20 
  

  

  +25 
  

  

  4-38 
  

  

  4-40 
  

  

  4-48 
  

  

  +48 
  

  

  +64 
  

  

  L.139... 
  

  

  1000 
  

  

  - 
  3 
  

  

  

  

  - 
  2 
  

  

  - 
  1 
  

  

  _ 
  2 
  

  

  4-16 
  

  

  '+17 
  

  

  4-30 
  

  

  4-35 
  

  

  + 
  35 
  

  

  +37 
  

  

  + 
  39 
  

  

  2449 
  ... 
  

  

  1000 
  

  

  — 
  2 
  

  

  _ 
  2 
  

  

  - 
  4 
  

  

  1 
  

  

  - 
  2 
  

  

  - 
  s 
  

  

  4- 
  6 
  

  

  + 
  8 
  

  

  + 
  8 
  

  

  + 
  9 
  

  

  + 
  11 
  

  

  + 
  11 
  

  

  + 
  14 
  

  

  recorded. 
  The 
  value 
  of 
  the 
  resistance 
  in 
  air 
  having 
  a 
  relative 
  

   humidity 
  of 
  about 
  60 
  per 
  cent, 
  at 
  17° 
  C. 
  is 
  taken 
  in 
  each 
  

   case 
  as 
  the 
  unit, 
  and 
  the 
  variations 
  from 
  this 
  value, 
  when 
  

   the 
  coils 
  were 
  placed 
  in 
  atmospheres 
  approximately 
  dry 
  and 
  

   approximately 
  saturated, 
  are 
  given 
  in 
  parts 
  in 
  100,000. 
  The 
  

   time 
  during 
  which 
  a 
  coil 
  was 
  exposed 
  to 
  the 
  action 
  of 
  a 
  

   particular 
  atmosphere 
  is 
  indicated 
  at 
  the 
  head 
  of 
  a 
  column, 
  and 
  

  

  

  