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  REPORT 
  ON 
  THERMOMETERS. 
  

  

  187 
  

  

  For 
  deep-sea 
  thermometers, 
  which 
  are 
  protected 
  against 
  water 
  press- 
  

   ure 
  by 
  a 
  double 
  glass 
  bulb, 
  and 
  which 
  are 
  therefore 
  slow, 
  and 
  require 
  

   exposure 
  to 
  a 
  constant 
  temperature 
  for 
  at 
  least 
  ten 
  minutes, 
  a 
  con- 
  

   trivance 
  is 
  used, 
  for 
  the 
  plan 
  of 
  which 
  I 
  am 
  indebted 
  to 
  Mr. 
  T. 
  Russell, 
  

   of 
  the 
  U. 
  S. 
  Signal 
  Service, 
  and 
  which 
  is 
  illustrated 
  by 
  the 
  sectional 
  

   diagram, 
  Fig. 
  2. 
  A 
  is 
  a 
  galvauized-iion 
  can 
  (in 
  this 
  case 
  a 
  3| 
  gallon 
  

  

  Fio. 
  

  

  -Comparing 
  jar 
  for 
  deep-sea 
  thermometers. 
  

  

  lard 
  can), 
  13J 
  inches 
  high 
  by 
  11 
  inches 
  wide 
  ; 
  B 
  is 
  an 
  earthenware 
  jar, 
  

   1 
  1 
  inches 
  high 
  by 
  8 
  inches 
  wide 
  ; 
  is 
  a 
  tinned 
  copper 
  pot, 
  fitting 
  pretty 
  

   closely 
  into 
  B, 
  and 
  suspended 
  by 
  a 
  flange 
  at 
  the 
  top. 
  Inside 
  of 
  C 
  is 
  a 
  

   copper 
  frame, 
  movable 
  about 
  a 
  central 
  spindle, 
  to 
  which 
  the 
  thermom- 
  

   eters 
  are 
  attached. 
  A 
  ring 
  stirrer 
  moves 
  in 
  the 
  space 
  between 
  A 
  and 
  

   B, 
  and 
  another 
  in 
  the 
  space 
  between 
  C 
  and 
  the 
  thermometer 
  frame. 
  

   When 
  the 
  temperatures 
  to 
  be 
  observed 
  are 
  below 
  that 
  of 
  the 
  air, 
  the 
  

   spaces 
  between 
  A 
  and 
  B 
  and 
  within 
  C 
  are 
  filled 
  with 
  water, 
  that 
  in 
  the 
  

   outer 
  space 
  being 
  from 
  5° 
  to 
  10° 
  colder 
  than 
  that 
  in 
  contact 
  with 
  the 
  

   thermometers. 
  It 
  is 
  advisable 
  that 
  these 
  latter 
  should 
  be 
  immersed 
  for 
  

   a 
  time 
  in 
  water 
  near 
  the 
  temperature 
  sought, 
  before 
  transferring 
  them 
  to 
  

   the 
  comparing 
  jar. 
  By 
  agitating 
  both 
  bodies 
  of 
  water 
  briskly 
  with 
  the 
  

   stirrers, 
  and 
  observing 
  the 
  standard 
  thermometer 
  (in 
  the 
  inner 
  jar) 
  from 
  

  

  