﻿Balance 
  as 
  a 
  Seusifiir 
  Barometer* 
  137 
  

  

  In 
  the 
  micro-barograph, 
  which 
  is 
  given 
  later 
  (fig. 
  1), 
  

  

  where 
  S 
  is 
  the 
  scale-reading 
  in 
  the 
  telescope. 
  This 
  ratio 
  was 
  

   the 
  mean 
  o£ 
  several 
  obtaineil 
  by 
  moving 
  the 
  rider 
  a 
  knoAvn 
  

   distance 
  and 
  noting 
  the 
  deflexion 
  in 
  the 
  telescope, 
  taking 
  

   into 
  account 
  the 
  rate 
  at 
  which 
  S 
  was 
  altering 
  at 
  the 
  time. 
  

   The 
  quantity 
  (V— 
  r) 
  differed 
  by 
  less 
  than 
  1 
  c.c. 
  from 
  7 
  GO 
  c.c, 
  

   so 
  that 
  

  

  ^^^ 
  = 
  — 
  273D"-^^+A^^' 
  

  

  With 
  the 
  temperature 
  and 
  pressure 
  variations 
  acting 
  

   together 
  the 
  whole 
  scale 
  would 
  often 
  pass 
  across 
  the 
  field 
  of 
  

   the 
  telescope 
  in 
  less 
  than 
  half 
  an 
  hour, 
  and 
  it 
  had 
  to 
  be 
  

   brought 
  into 
  view 
  again 
  by 
  moving 
  the 
  rider 
  in 
  the 
  required 
  

   direction 
  by 
  means 
  of 
  the 
  micrometer-screws. 
  Observations 
  

   of 
  S 
  and 
  A 
  were 
  taken 
  alternately 
  every 
  thirty 
  seconds, 
  and 
  

   the 
  barograph 
  was 
  obtained 
  by 
  plotting 
  the 
  terms 
  on 
  the 
  right 
  

   of 
  the 
  above 
  equation 
  and 
  adding. 
  

  

  The 
  barographs 
  showed 
  many 
  oscillations 
  in 
  pressure 
  of 
  

   the 
  order 
  of 
  '02 
  mm., 
  the 
  period 
  of 
  oscillation 
  being 
  from 
  

   ten 
  to 
  fifteen 
  minutes, 
  a 
  period 
  quite 
  difierent 
  from 
  that 
  of 
  

   the 
  balance. 
  The 
  question 
  arose 
  whether 
  these 
  oscillations 
  

   were 
  real 
  oscillations 
  of 
  pressure, 
  or 
  whether 
  they 
  were 
  

   caused 
  by 
  oscillations 
  in 
  temperature 
  not 
  shown 
  on 
  the 
  

   mercury 
  thermometer 
  suspended 
  in 
  the 
  balance 
  in 
  con- 
  

   sequence 
  of 
  the 
  capacity 
  for 
  heat 
  of 
  its 
  bulb. 
  

  

  To 
  decide 
  this 
  question 
  twelve 
  thermojunctions 
  were 
  made 
  

   with 
  fine 
  wires 
  of 
  copper 
  and 
  constantan, 
  each 
  wire 
  being 
  

   about 
  six 
  centimetres 
  long. 
  Six 
  of 
  these 
  junctions 
  were 
  

   embedded 
  in 
  wax 
  and 
  placed 
  in 
  a 
  box 
  of 
  brass 
  filings, 
  while 
  

   the 
  other 
  six 
  were 
  left 
  exposed 
  to 
  the 
  air. 
  The 
  covered 
  

   junctions 
  having 
  their 
  capacity 
  for 
  heat 
  made 
  very 
  large 
  by 
  

   the 
  surrounding 
  brass 
  filings, 
  would 
  " 
  lag 
  ■" 
  behind 
  the 
  

   exposed 
  junctions 
  and 
  would 
  not 
  be 
  affected 
  by 
  small 
  oscilla- 
  

   tions 
  in 
  temperature. 
  The 
  ends 
  of 
  this 
  thermopile 
  were 
  

   connected 
  to 
  a 
  low 
  resistance 
  galvanometer. 
  One 
  division 
  

   on 
  the 
  scale 
  was 
  approximately 
  equal 
  to 
  a 
  difference 
  of 
  

   •009° 
  C. 
  between 
  the 
  exposed 
  and 
  covered 
  junctions. 
  When 
  

   the 
  thermopile 
  was 
  exposed 
  in 
  the 
  room 
  the 
  scale-reading 
  

   oscillated 
  aimlessly 
  to 
  and 
  fro, 
  but 
  when 
  placed 
  inside 
  the 
  

   balance 
  no 
  oscillations 
  could 
  be 
  detected. 
  The 
  spot 
  of 
  light 
  

   travelled 
  slowly 
  and 
  uniforndy 
  in 
  one 
  direction, 
  showing 
  

  

  