﻿250 
  Mr. 
  L. 
  Vegard 
  : 
  Researches 
  upon 
  

  

  The 
  Manometer. 
  

  

  4. 
  For 
  measuring 
  the 
  pressure 
  I 
  used 
  the 
  usual 
  way 
  of 
  

   compressing 
  air 
  in 
  a 
  glass 
  capillary. 
  The 
  length 
  of 
  the 
  

   manometer 
  was 
  about 
  135 
  cm., 
  exterior 
  diam. 
  7'5 
  mm., 
  and 
  

   the 
  average 
  inner 
  diameter 
  0*472 
  mm. 
  It 
  was 
  given 
  the 
  

   form 
  shown 
  in 
  fig. 
  3 
  (PL 
  VIII.) 
  . 
  In 
  this 
  form 
  the 
  manometer 
  

   could 
  be 
  made 
  long 
  without 
  being 
  inconvenient, 
  and 
  the 
  

   temperature 
  accurately 
  determined 
  as 
  the 
  column 
  of 
  air 
  in 
  

   the 
  vertical 
  part 
  of 
  it 
  could 
  be 
  put 
  into 
  a 
  thermostat. 
  With 
  

   this 
  form 
  the 
  vertical 
  part 
  must 
  have 
  a 
  small 
  diameter 
  : 
  it 
  

   ought 
  not 
  to 
  surpass 
  0*6 
  mm. 
  

  

  The 
  manometer 
  joined 
  on 
  to 
  a 
  U-shaped 
  capillary 
  with 
  an 
  

   inner 
  diameter 
  1*01 
  mm., 
  that 
  was 
  filled 
  with 
  mercury, 
  and 
  

   thus 
  the 
  mercury 
  level 
  in 
  the 
  U 
  tube 
  had 
  only 
  to 
  move 
  a 
  

   relatively 
  short 
  distance 
  to 
  fill 
  the 
  whole 
  manometer 
  with 
  

   mercury. 
  

  

  As 
  the 
  exactitude 
  of 
  the 
  results 
  greatly 
  depends 
  upon 
  the 
  

   manometer, 
  I 
  shall 
  give 
  a 
  more 
  minute 
  description 
  of 
  its 
  

   construction. 
  

  

  The 
  capillary 
  itself 
  was 
  graduated, 
  the 
  distance 
  between 
  

   each 
  mark 
  being 
  0'5 
  cm. 
  The 
  marks 
  were 
  cut 
  in 
  wax 
  by 
  

   means 
  of 
  a 
  cutting-machine 
  marking 
  with 
  an 
  accuracy 
  of 
  

   about 
  1/50 
  of 
  a 
  mm., 
  and 
  the 
  marks 
  etched 
  to 
  the 
  glass. 
  

   The 
  manometer 
  was 
  then 
  given 
  its 
  final 
  form, 
  cleaned 
  and 
  

   calibrated 
  . 
  

  

  The 
  calibration 
  was 
  carried 
  out 
  in 
  the 
  following 
  manner. 
  

   The 
  manometer-tube 
  was 
  placed 
  horizontally 
  on 
  a 
  table. 
  By 
  

   means 
  of 
  a 
  rubber 
  tubing 
  put 
  on 
  one 
  end, 
  the 
  column 
  of 
  

   mercury 
  could 
  be 
  given 
  the 
  position 
  desired. 
  The 
  ends 
  of 
  

   the 
  mercury 
  column 
  were 
  measured 
  relatively 
  to 
  the 
  nearest 
  

   marks 
  on 
  the 
  manometer 
  by 
  means 
  of 
  a 
  microscope 
  with 
  

   a 
  vertical 
  filament 
  movable 
  along 
  a 
  horizontal 
  steel 
  rod 
  

   and 
  furnished 
  with 
  a 
  micrometer-screw. 
  By 
  these 
  means 
  I 
  

   was 
  able 
  to 
  measure 
  with 
  an 
  accuracy 
  of 
  about 
  1/50 
  mm. 
  

  

  For 
  each 
  position 
  the 
  mercury 
  column 
  was 
  pushed 
  forward 
  

   as 
  nearly 
  as 
  possible 
  its 
  own 
  length. 
  In 
  the 
  calculation, 
  the 
  

   length 
  from 
  the 
  end 
  of 
  one 
  position 
  to 
  the 
  beginning 
  of 
  the 
  

   next 
  was 
  considered 
  to 
  have 
  the 
  average 
  diameter 
  of 
  the 
  

   neighbouring 
  position. 
  The 
  end 
  where 
  the 
  volume 
  of 
  air 
  

   was 
  to 
  be 
  measured 
  was 
  calibrated 
  with 
  a 
  smaller 
  mercury 
  

   column. 
  

  

  The 
  calibration 
  finished, 
  the 
  U-tube 
  was 
  put 
  on 
  at 
  the 
  

   point 
  h. 
  The 
  capillary 
  was 
  well 
  cleaned 
  and 
  a 
  current 
  

   of 
  air 
  drawn 
  through 
  it, 
  the 
  air 
  being 
  dried 
  by 
  passing- 
  

   through 
  a 
  solution 
  of 
  NaOH 
  and 
  over 
  dry 
  CaCl 
  2 
  . 
  Without 
  

   disturbing 
  the 
  connexion 
  to 
  the 
  drying 
  apparatus 
  the 
  IJ-tube 
  

  

  