﻿172 
  Holhorn 
  and 
  Day 
  — 
  Gas 
  Thermometer 
  at 
  

  

  The 
  left 
  side 
  of 
  the 
  equation 
  is 
  a 
  constant 
  quantity 
  for 
  each 
  

   filling 
  if 
  the 
  zero 
  point 
  remains 
  constant. 
  

  

  For 
  the 
  various 
  bulbs 
  used 
  the 
  values 
  of 
  To 
  and 
  v^ 
  are 
  quite 
  

   different 
  ; 
  the 
  value 
  in 
  each 
  case 
  is 
  therefore 
  especially 
  stated, 
  

   and 
  the 
  percentage 
  of 
  effect 
  which 
  the 
  "unheated 
  space" 
  has 
  

   on 
  the 
  resulting 
  t. 
  

  

  2. 
  Electrical 
  Measurement. 
  

  

  The 
  measurement 
  of 
  the 
  electromotive 
  force 
  of 
  the 
  thermo- 
  

   elements 
  was 
  made 
  by 
  the 
  " 
  compensation 
  " 
  method. 
  Cad- 
  

   mium 
  cells 
  served 
  as 
  standards 
  of 
  potential-difference. 
  

  

  The 
  cold 
  junctions 
  of 
  the 
  thermo-elements 
  were 
  contained 
  in 
  

   glass 
  tubes 
  surrounded 
  by 
  melting 
  ice. 
  

  

  A 
  Siemens 
  and 
  Halske 
  voltmeter 
  w^as 
  of 
  great 
  service 
  in 
  the 
  

   regulation 
  of 
  the 
  temperature 
  of 
  the 
  oven. 
  

  

  &' 
  

  

  S. 
  Experiments 
  loith 
  glass 
  bulb. 
  

  

  A 
  bulb 
  of 
  Jena 
  glass 
  ^NTo. 
  59^" 
  was 
  used 
  for 
  the 
  measurements 
  

   between 
  200° 
  and 
  500°. 
  The 
  gas 
  was 
  hydrogen, 
  chosen 
  chiefly 
  

   in 
  order 
  to 
  see 
  whether 
  this 
  gas, 
  whose 
  expansion 
  is 
  made 
  the 
  

   basis 
  of 
  modern 
  thermometry, 
  can 
  be 
  advantageously 
  used 
  in 
  

   practice 
  above 
  200°. 
  

  

  In 
  these 
  lower 
  temperatures 
  the 
  thermo-elements 
  do 
  not 
  

   form 
  a 
  good 
  basis 
  of 
  comparison 
  for 
  the 
  air 
  thermometer; 
  it 
  is, 
  

   however, 
  perfectly 
  possible 
  to 
  detect 
  any 
  change 
  which 
  the 
  gas 
  

   may 
  have 
  undergone 
  during 
  the 
  heating 
  through 
  changes 
  in 
  

   the 
  ice 
  point 
  or 
  coefficient 
  of 
  expansion. 
  

  

  Dimensions 
  of 
  Bulb. 
  — 
  The 
  glass 
  bulb 
  had 
  the 
  form 
  of 
  a 
  

   cylinder 
  with 
  rounded 
  ends, 
  16^"' 
  long 
  and 
  S-S"""" 
  outside 
  diam- 
  

   eter. 
  The 
  stem 
  was 
  40*0^"' 
  long, 
  O'TS"""' 
  in 
  inside 
  diameter, 
  

   and 
  bent 
  to 
  a 
  right 
  angle 
  nearly 
  in 
  the 
  middle. 
  

  

  The 
  volume 
  as 
  measured 
  at 
  the 
  beginning 
  was 
  IGG'SS""', 
  

   and 
  at 
  the 
  end 
  16()*43'^'^'", 
  the 
  determination 
  being 
  made 
  by 
  

   filling 
  with 
  distilled 
  water 
  and 
  weighing. 
  The 
  bulb 
  had 
  

   already 
  been 
  seasoned 
  by 
  repeated 
  heatings 
  to 
  500° 
  before 
  the 
  

   first 
  determination 
  was 
  made. 
  

  

  TJnheated 
  Space. 
  — 
  The 
  temperature 
  of 
  the 
  stem, 
  as 
  well 
  as 
  

   of 
  the 
  platinum 
  manometer 
  capillary, 
  was 
  determined 
  by 
  mer- 
  

   cury 
  thermometers 
  placed 
  at 
  intervals 
  close 
  by 
  and 
  from 
  whose 
  

   readings 
  an 
  integral 
  temperature 
  of 
  the 
  unheated 
  space, 
  in 
  this 
  

   case 
  amounting 
  to 
  2-701'^*^'", 
  was 
  obtained. 
  This 
  value 
  is 
  the 
  

   result 
  of 
  a 
  volumetric 
  determination 
  nuide 
  at 
  the 
  beginning 
  

   of 
  the 
  experiments. 
  A 
  determination 
  by 
  weighing 
  with 
  water 
  

   at 
  the 
  close 
  gave 
  2-668"°\ 
  

  

  