﻿602 
  

  

  Mr. 
  I. 
  Williams 
  on 
  the 
  Absolute 
  

  

  at 
  D. 
  The 
  other 
  junction 
  was 
  placed 
  in 
  the 
  cold 
  water 
  in 
  

   which 
  the 
  apparatus 
  was 
  immersed. 
  

  

  The 
  electric 
  currents 
  employed 
  to 
  heat 
  the 
  column 
  of 
  

   mercury 
  varied 
  in 
  magnitude 
  from 
  3*5 
  to 
  5 
  amperes. 
  The 
  

   readings 
  of 
  the 
  ammeter 
  were 
  calibrated 
  by 
  passing 
  the 
  

   current 
  through 
  a 
  known 
  resistance 
  and 
  comparing 
  the 
  

   potential 
  differences 
  between 
  the 
  ends 
  of 
  this 
  resistance 
  with 
  

   that 
  produced 
  by 
  ii 
  cadmium 
  cell. 
  The 
  calibration 
  numbers 
  

   obtained 
  in 
  this 
  way 
  are 
  given 
  in 
  the 
  following 
  table: 
  — 
  

  

  Ammeter 
  

  

  Readings. 
  

  

  amps. 
  

  

  Corrected 
  

  

  Readings. 
  

  

  amps. 
  

  

  3-50 
  

   4-00 
  

   4-50 
  

   5-00 
  

  

  349 
  

   396 
  

   449 
  

  

  4-98 
  

  

  The 
  potential 
  differences 
  E 
  : 
  and 
  E 
  2 
  were 
  measured 
  as 
  

   indicated 
  in 
  § 
  4 
  with 
  a 
  millivoltmeter 
  which 
  had 
  been 
  

   standardized 
  by 
  means 
  of 
  a 
  cadmium 
  cell. 
  

  

  In 
  some 
  of 
  the 
  earlier 
  experiments 
  the 
  Crompton 
  potentio- 
  

   meter 
  was 
  used 
  to 
  measure 
  the 
  currents 
  and 
  potential 
  dif- 
  

   ferences 
  directly, 
  but 
  ultimately 
  it 
  was 
  found 
  more 
  convenient 
  

   to 
  use 
  direct-reading 
  instruments 
  which 
  had 
  been 
  previously 
  

   calibrated 
  by 
  means 
  of 
  a 
  potentiometer. 
  

  

  The 
  capillary 
  tube 
  had 
  a 
  very 
  uniform 
  bore, 
  and 
  its 
  mean 
  

   internal 
  diameter 
  was 
  determined 
  by 
  means 
  of 
  a 
  mercury 
  

   thread. 
  The 
  mean 
  external 
  diameter 
  was 
  determined 
  by 
  

   means 
  of 
  a 
  screw-gauge. 
  The 
  apparatus 
  had 
  the 
  following 
  

   dimensions 
  :• 
  — 
  

  

  AB^AjB^ 
  5 
  cm. 
  

   CD 
  = 
  dD 
  = 
  2-5 
  cm. 
  

   BC 
  = 
  44-0cm. 
  

   B 
  1 
  C 
  1 
  = 
  22-0 
  cm 
  . 
  

  

  Mean 
  internal 
  diameter 
  of 
  capillary 
  = 
  '100 
  cm. 
  

   „ 
  external 
  „ 
  „ 
  ='663 
  cm. 
  

  

  § 
  6. 
  In 
  carrying 
  out 
  an 
  experiment, 
  the 
  apparatus 
  shown 
  

   in 
  fig. 
  3 
  was 
  placed 
  in 
  a 
  tank 
  through 
  which 
  a 
  rapid 
  flow 
  of 
  

   cold 
  water 
  was 
  maintained. 
  The 
  temperature 
  of 
  this 
  water 
  

   was 
  read 
  at 
  regular 
  intervals 
  by 
  means 
  of 
  a 
  standard 
  ther- 
  

   mometer 
  graduated 
  in 
  -^ 
  ° 
  0. 
  The 
  electric 
  current 
  was 
  then 
  

   put 
  on 
  and 
  the 
  regulating 
  resistance 
  adjusted 
  whenever 
  

   necessary 
  so 
  as 
  to 
  maintain 
  the 
  current 
  quite 
  constant. 
  The 
  

   rapid 
  flow 
  stirred 
  the 
  water 
  in 
  the 
  tank 
  very 
  thoroughly, 
  and 
  

   its 
  temperature 
  during 
  a 
  reading 
  did 
  not 
  vary 
  by 
  ^°. 
  

  

  