﻿High 
  Temper 
  atures. 
  169 
  

  

  The 
  raaDometer 
  consists 
  of 
  two 
  upright 
  tubes, 
  A 
  and 
  B, 
  

   which 
  dip 
  into 
  a 
  closed 
  iron 
  reservoir, 
  R, 
  from 
  which 
  mercury 
  

   may 
  be 
  drawn 
  off 
  through 
  the 
  steel 
  cock, 
  D, 
  and 
  let 
  in 
  from 
  a 
  

   storage 
  reservoir, 
  G, 
  at 
  the 
  top, 
  by 
  way 
  of 
  the 
  tube, 
  C, 
  and 
  a 
  

   second 
  steel 
  cock, 
  E. 
  Small 
  changes 
  in 
  the 
  height 
  of 
  the 
  mer- 
  

   cury 
  column 
  such 
  as 
  were 
  necessary 
  in 
  the 
  final 
  adjustment 
  for 
  

   reading 
  may 
  be 
  effected 
  by 
  means 
  of 
  the 
  powerfal 
  screw, 
  S, 
  

   working 
  upon 
  a 
  thin 
  sheet-steel 
  plate 
  which 
  forms 
  the 
  bottom 
  

   of 
  the 
  reservoir. 
  

  

  The 
  shorter 
  tube 
  is 
  80^"^ 
  long 
  up 
  to 
  the 
  metallic 
  point 
  where 
  

   the 
  adjustment 
  to 
  constant 
  volume 
  is' 
  made, 
  for 
  m 
  order 
  to 
  

   avoid 
  pressures 
  much 
  too 
  great 
  for 
  the 
  strength 
  of 
  the 
  bulb 
  at 
  

   high 
  temperatures, 
  the 
  pressure 
  at 
  0° 
  must 
  be 
  chosen 
  small. 
  

  

  The 
  adjustment 
  to 
  constant 
  volume 
  was 
  made 
  in 
  the 
  older 
  

   instrument 
  at 
  the 
  end 
  of 
  the 
  platinum 
  capillary 
  which 
  consti- 
  

   tuted 
  the 
  connection 
  between 
  the 
  manometer 
  and 
  the 
  bulb, 
  

   and 
  which 
  was 
  melted 
  directly 
  into 
  the 
  top 
  of 
  the 
  shorter 
  tube 
  

   (corresponding 
  to 
  A). 
  This 
  arrangement, 
  which 
  we 
  at 
  first 
  

   retained, 
  left 
  the 
  " 
  unheated 
  space 
  " 
  unnecessarily 
  large, 
  which 
  

   for 
  our 
  purpose 
  was 
  a 
  decided 
  disadvantage. 
  The 
  influence 
  

   of 
  this 
  " 
  unheated 
  space 
  " 
  (the 
  space 
  between 
  the 
  surface 
  of 
  

   the 
  mercury 
  in 
  the 
  manometer 
  and 
  the 
  bulb, 
  filled 
  with 
  gas 
  

   like 
  the 
  bulb 
  but 
  not 
  heated 
  with 
  it) 
  upon 
  the 
  resulting 
  tem- 
  

   perature 
  increases 
  much 
  more 
  rapidly 
  than 
  the 
  temperature 
  

   itself. 
  We 
  have 
  consequently 
  since 
  then 
  adopted 
  the 
  arrange- 
  

   ment 
  of 
  Chappuis"^ 
  and 
  closed 
  the 
  short 
  tube 
  (A) 
  by 
  a 
  care- 
  

   fully 
  fitted 
  metallic 
  cap 
  with 
  polished 
  under 
  surface. 
  This 
  cap 
  

   was 
  fastened 
  upon 
  the 
  tube 
  with 
  sealing 
  wax 
  and 
  carried 
  near 
  

   the 
  middle, 
  where 
  the 
  capillary 
  tube 
  opened 
  into 
  the 
  glass 
  

   tube, 
  a 
  metallic 
  point 
  04™''' 
  long 
  to 
  which 
  the 
  mercury 
  column 
  

   is 
  brought 
  at 
  each 
  reading. 
  In 
  this 
  way 
  the 
  space 
  above 
  the 
  

   meniscus 
  was 
  reduced 
  from 
  2^^^™ 
  to 
  O'^'^""^ 
  in 
  a 
  tube 
  of 
  S*^"" 
  

   diameter. 
  The 
  metal 
  point, 
  intentionally 
  rounded 
  off 
  in 
  order 
  

   to 
  allow 
  of 
  more 
  accurate 
  setting, 
  was 
  made 
  of 
  nickel, 
  as 
  was 
  

   also 
  the 
  entire 
  cap, 
  in 
  order 
  that 
  it 
  might 
  not 
  become 
  amalga- 
  

   mated 
  by 
  contact 
  with 
  the 
  mercury. 
  

  

  On 
  the 
  upper 
  side 
  this 
  cap 
  was 
  hollow 
  and 
  was 
  originally 
  

   intended 
  to 
  contain 
  mercury 
  ; 
  at 
  the 
  last, 
  however, 
  we 
  preferred 
  

   to 
  fit 
  into 
  the 
  space 
  a 
  massive 
  block 
  of 
  copper 
  bored 
  with 
  a 
  

   cylindrical 
  hole 
  to 
  admit 
  the 
  bulb 
  of 
  a 
  mercury 
  thermometer. 
  

   In 
  this 
  way 
  the 
  temperature 
  of 
  the 
  space 
  above 
  the 
  mercury 
  

   column 
  (A) 
  is 
  more 
  accurately 
  determined 
  than 
  if 
  the 
  ther- 
  

   mometer 
  were 
  hung 
  at 
  the 
  side. 
  

  

  We 
  had, 
  to 
  be 
  sure, 
  in 
  the 
  old 
  instrument 
  a 
  thermo-element 
  

   within 
  this 
  space 
  itself, 
  the 
  wires 
  being 
  passed 
  in 
  through 
  the 
  

  

  *Cliappuis, 
  Trav. 
  et 
  Mem. 
  du 
  Bureau 
  internat., 
  vi, 
  28, 
  1888, 
  

  

  