﻿400 
  C. 
  Barus 
  — 
  Diffusion 
  of 
  Air 
  through 
  Water. 
  

  

  since 
  at 
  constant 
  H, 
  it 
  is 
  merely 
  the 
  rate 
  at 
  which 
  A 
  varies 
  

   with 
  t, 
  the 
  temperature 
  of 
  the 
  air 
  in 
  the 
  float. 
  

  

  This 
  is 
  the 
  method 
  which 
  I 
  have 
  adopted. 
  It 
  depends 
  for 
  

   its 
  success 
  chiefly 
  on 
  the 
  determination 
  of 
  t, 
  so 
  that 
  slow 
  work, 
  

   avoiding 
  the 
  thermal 
  effects 
  of 
  adiabatic 
  expansion, 
  is 
  presup- 
  

   posed. 
  After 
  standardizing 
  the 
  vessel 
  it 
  -is 
  to 
  be 
  put 
  away 
  to 
  

   be 
  examined 
  in 
  the 
  lapse 
  of 
  years. 
  

  

  The 
  following 
  data 
  were 
  obtained 
  in 
  the 
  standardization 
  in 
  

   question 
  : 
  

  

  A. 
  B. 
  H, 
  computed, 
  

  

  cm. 
  0° 
  C. 
  

  

  985-4 
  5-27 
  77*02 
  

  

  •26 
  

  

  T, 
  observed. 
  

  

  h: 
  

  

  t. 
  

  

  cm. 
  0° 
  C. 
  

  

  cm. 
  

  

  0° 
  C. 
  

  

  77*25 
  

  

  — 
  76-83 
  

  

  17-2 
  

  

  •27 
  

  

  -67-45 
  

  

  19-6 
  

  

  •28 
  

  

  — 
  57-45 
  

  

  21-5 
  

  

  •24 
  

  

  -49-75 
  

  

  22-8 
  

  

  •21 
  

  

  — 
  43-60 
  

  

  24-1 
  

  

  •21 
  

  

  — 
  37*95 
  

  

  25-0 
  

  

  •21 
  

  

  — 
  32-27 
  

  

  26-2 
  

  

  •21 
  

  

  — 
  24-94 
  

  

  27'6 
  

  

  X 
  

  

  •26 
  

   •20 
  

   •25 
  

   •18 
  

   •23 
  

   •24 
  

  

  The 
  errors 
  encountered 
  in 
  this 
  work 
  are 
  shown 
  by 
  the 
  com- 
  

   parison 
  made 
  of 
  II. 
  The 
  first 
  datum 
  observed 
  is 
  wrong 
  for 
  

   some 
  special 
  reason, 
  probably 
  the 
  column 
  h 
  parted. 
  The 
  

   remainder 
  show 
  a 
  fair 
  order 
  of 
  agreement, 
  remembering 
  that 
  

   with 
  a 
  glass 
  float, 
  at 
  a 
  temperature 
  different 
  from 
  that 
  of 
  the 
  

   atmosphere, 
  it 
  is 
  impossible 
  to 
  get 
  the 
  temperature 
  of 
  the 
  air 
  

   in 
  the 
  float 
  accurately 
  by 
  mere 
  waiting. 
  

  

  3. 
  In 
  spite 
  of 
  the 
  unfavorable 
  conditions 
  of 
  experiment, 
  it 
  

   is 
  interesting 
  to 
  note 
  that 
  the 
  arrangement 
  given 
  is 
  a 
  water 
  

   barometer, 
  which 
  instead 
  of 
  being 
  upwards 
  of 
  30 
  feet 
  long, 
  con- 
  

   sists 
  of 
  two 
  ordinary 
  vessels. 
  I 
  have 
  not 
  thought 
  it 
  worth 
  

   while 
  to 
  look 
  up 
  the 
  literature 
  of 
  barometry, 
  but 
  it 
  is 
  hardly 
  

   probable 
  that 
  a 
  device 
  like 
  the 
  above 
  has 
  been 
  left 
  untried. 
  I 
  

   will 
  merely 
  remark 
  that 
  if 
  a 
  barometer 
  is 
  made 
  in 
  this 
  way, 
  

   the 
  metallic 
  float 
  should 
  either 
  be 
  annular 
  so 
  as 
  to 
  encircle 
  the 
  

   thermometer, 
  T, 
  when 
  observations 
  are 
  made, 
  or 
  the 
  thermom- 
  

   eter 
  should 
  be 
  an 
  integral 
  part 
  of 
  the 
  float. 
  In 
  the 
  above 
  ves- 
  

   sel, 
  for 
  instance, 
  a 
  temperature 
  error 
  of 
  1° 
  C. 
  corresponds 
  to 
  

   •39 
  cm 
  of 
  mercury, 
  so 
  that 
  the 
  temperature 
  reading 
  must 
  be 
  

   vouched 
  for 
  to 
  about 
  *025 
  C, 
  if 
  the 
  barometer 
  is 
  to 
  be 
  correct 
  

   to 
  1/10 
  millimeter. 
  A 
  table 
  of 
  double 
  entry, 
  or 
  a 
  chart, 
  would 
  

   then 
  give 
  H 
  for 
  the 
  arguments 
  h 
  and 
  t 
  as 
  shown. 
  

  

  Brown 
  University, 
  Providence, 
  R. 
  I. 
  

  

  