﻿360 
  Prof. 
  Richardson 
  and 
  Mr. 
  Brown 
  on 
  the 
  Kinetic 
  

  

  desired 
  potential. 
  In 
  this 
  way 
  the 
  rate 
  o£ 
  charging 
  of 
  the 
  

   upper 
  plate 
  could 
  be 
  determined 
  both 
  with 
  the 
  two 
  plates 
  

   initially 
  at 
  the 
  same 
  potential 
  and 
  with 
  any 
  desired 
  difference 
  

   of 
  potential 
  between 
  them. 
  The 
  charging 
  quadrants 
  could 
  

   also 
  be 
  connected 
  to 
  a 
  subdivided 
  standard 
  condenser 
  not 
  

   shown 
  in 
  the 
  diagram. 
  

  

  The 
  platinum 
  strip 
  was 
  heated 
  by 
  a 
  current 
  furnished 
  by 
  

   the 
  battery 
  B 
  and 
  regulated 
  by 
  two 
  sliding 
  rheostats 
  in 
  

   parallel 
  (shown 
  as 
  one 
  in 
  the 
  diagram) 
  at 
  r 
  2 
  . 
  One 
  of 
  these 
  

   had 
  a 
  much 
  higher 
  resistance 
  than 
  the 
  other, 
  and 
  served 
  as 
  

   a 
  fine 
  adjustment. 
  The 
  temperature 
  was 
  determined 
  from 
  

   the 
  resistance, 
  which 
  was 
  measured 
  by 
  the 
  Wheatstonc's 
  

   bridge 
  arrangement, 
  of 
  which 
  H, 
  R 
  a 
  , 
  Rj, 
  and 
  R 
  formed 
  the 
  

   four 
  arms. 
  This 
  is 
  the 
  method 
  previously 
  used 
  by 
  Richardson. 
  

   The 
  essential 
  conditions 
  that 
  R 
  and 
  R 
  b 
  should 
  both 
  be 
  large 
  

   compared 
  with 
  R 
  a 
  and 
  H, 
  and 
  that 
  R 
  a 
  should 
  carry 
  the 
  

   current 
  without 
  heating, 
  were 
  satisfied. 
  

  

  It 
  is 
  important 
  that 
  the 
  middle 
  point 
  of 
  the 
  exposed 
  

   portion 
  of 
  the 
  hot 
  strip 
  should 
  be 
  at 
  zero 
  potential. 
  If 
  a 
  

   fine 
  wire 
  was 
  welded 
  to 
  the 
  middle 
  portion 
  of 
  H 
  and 
  soldered 
  

   to 
  the 
  lower 
  plate 
  it 
  was 
  found 
  that 
  this 
  gave 
  rise 
  to 
  local 
  

   variations 
  in 
  the 
  heating, 
  and 
  also 
  that 
  any 
  slight 
  displace- 
  

   ment 
  of 
  the 
  strip 
  during 
  the 
  experiments 
  put 
  it 
  out 
  of 
  

   adjustment. 
  These 
  difficulties 
  were 
  overcome 
  by 
  shunting 
  

   the 
  whole 
  TVheatstone's 
  bridge 
  circuit 
  with 
  a 
  high 
  resistance 
  

   r 
  l9 
  any 
  point 
  of 
  which 
  could 
  be 
  connected 
  to 
  earth. 
  By 
  trial 
  

   a 
  point 
  in 
  i\ 
  was 
  found 
  so 
  that 
  when 
  it 
  was 
  connected 
  to 
  

   earth 
  the 
  initial 
  rate 
  of 
  leak 
  to 
  the 
  upper 
  plate 
  was 
  unchanged 
  

   on 
  reversing 
  the 
  main 
  heating 
  current. 
  The 
  condition 
  for 
  

   this 
  is 
  evidently 
  that 
  the 
  centre 
  of 
  the 
  hot 
  strip 
  should 
  be 
  at 
  

   zero 
  potential. 
  By 
  simply 
  reversing 
  the 
  main 
  current 
  from 
  

   time 
  to 
  time 
  this 
  adjustment 
  could 
  be 
  tested 
  and 
  a 
  readjust- 
  

   ment 
  made, 
  if 
  it 
  were 
  required 
  during 
  the 
  course 
  of 
  the 
  

   experiments. 
  The 
  lower 
  plate 
  was 
  permanently 
  connected 
  

   to 
  earth. 
  

  

  A 
  section 
  through 
  the 
  platinum 
  strip, 
  showing 
  the 
  plates 
  

   and 
  arrangement 
  of 
  apparatus 
  in 
  their 
  immediate 
  neighbour- 
  

   hood, 
  is 
  shown 
  in 
  fig. 
  2. 
  The 
  detailed 
  construction 
  of 
  the 
  

   plates 
  will 
  be 
  described 
  later. 
  The 
  lower 
  plate 
  consisted 
  of 
  

   two 
  sections 
  screwed 
  together. 
  The 
  platinum 
  strip 
  was 
  held 
  

   between 
  them 
  and 
  insulated 
  from 
  them 
  by 
  strips 
  of 
  mica. 
  

   The 
  thickness 
  of 
  the 
  platinum 
  strip 
  was 
  *0018 
  cm. 
  Its 
  

   other 
  dimensions 
  were 
  '2 
  x 
  *5 
  cm. 
  Its 
  ends 
  were 
  welded 
  to 
  

   heavier 
  platinum 
  leads 
  which 
  dipped 
  into 
  glass 
  mercury-cups 
  

   sealed 
  into 
  the 
  heavy 
  brass 
  base-plate 
  B. 
  These 
  served 
  to 
  

   intioduce 
  the 
  heating 
  current. 
  The 
  resistance 
  of 
  the 
  portion 
  

  

  