﻿the 
  Electromotive 
  Force 
  of 
  Clark 
  Cells 
  with 
  Temperature. 
  287 
  

  

  the 
  water-bath 
  directly. 
  E 
  is 
  an 
  escape-tube, 
  which 
  serves 
  

   to 
  carry 
  off 
  some 
  of 
  the 
  heat 
  of 
  the 
  jet 
  ; 
  G 
  is 
  a 
  little 
  by-pass, 
  

  

  Fig-. 
  1. 
  

  

  burning 
  at 
  the 
  mouth 
  of 
  the 
  tube 
  E, 
  and 
  serves 
  to 
  relight 
  

   the 
  main 
  jet 
  when 
  extinguished. 
  M 
  is 
  an 
  electromagnet 
  ; 
  

   H, 
  its 
  armature, 
  is 
  pivoted 
  at 
  S 
  and 
  weighted 
  at 
  P, 
  and 
  carries 
  

   a 
  platinum 
  wire 
  Q 
  which 
  dips 
  into 
  the 
  mercury 
  cup 
  Q 
  f 
  . 
  

  

  When 
  the 
  temperature 
  of 
  the 
  water-bath 
  has 
  reached 
  a 
  

   certain 
  arbitrary 
  value, 
  the 
  mercury 
  -index 
  electrically 
  con- 
  

   nects/! 
  and 
  / 
  2 
  , 
  completing 
  the 
  circuit 
  of 
  the 
  electromagnet 
  M 
  

   and 
  the 
  battery 
  Z. 
  The 
  electromagnet 
  being 
  thus 
  excited, 
  

   attracts 
  its 
  armature 
  H, 
  which 
  compresses 
  the 
  indiarubber 
  

   tube 
  T 
  that 
  feeds 
  the 
  main 
  gas-jet 
  J, 
  between 
  the 
  brass 
  

   piece 
  N 
  and 
  the 
  adjustable 
  wooden 
  block 
  W, 
  and 
  so 
  extin- 
  

   guishes 
  the 
  light. 
  The 
  water-bath 
  now 
  cools 
  slowly 
  till 
  its 
  

   temperature 
  has 
  fallen 
  below 
  the 
  fixed 
  value, 
  and 
  the 
  contact 
  

   is 
  broken 
  at/ 
  2 
  by 
  the 
  falling 
  of 
  the 
  mercury-index. 
  When 
  

   this 
  happens, 
  the 
  armature 
  of 
  the 
  electromagnet 
  is 
  released 
  

   and 
  pulled 
  up 
  at 
  once 
  by 
  the 
  weight 
  P, 
  the 
  gas 
  coming 
  on 
  

   again 
  at 
  the 
  jet 
  J 
  ; 
  some 
  of 
  the 
  gas 
  passing 
  up 
  the 
  tube 
  E 
  

   is 
  ignited 
  at 
  the 
  top 
  by 
  the 
  by-pass 
  G, 
  and 
  then 
  striking 
  

   back, 
  lights 
  the 
  main 
  jet 
  J, 
  restarting 
  the 
  heating, 
  and 
  the 
  

   cycle 
  is 
  repeated. 
  

  

  As 
  it 
  requires 
  a 
  less 
  current 
  to 
  hold 
  the 
  armature 
  down 
  

   than 
  it 
  takes 
  originally 
  to 
  attract 
  it, 
  the 
  current 
  circuit 
  of 
  

   the 
  magnet 
  is 
  so 
  arranged 
  that 
  when 
  the 
  armature 
  is 
  

   attracted 
  it 
  breaks 
  the 
  direct-current 
  circuit 
  at 
  the 
  mercury 
  

   cup 
  Q', 
  and 
  inserts 
  into 
  the 
  circuit 
  a 
  resistance 
  of 
  50 
  ohms, 
  

   thus 
  economizing 
  the 
  energy. 
  

  

  The 
  temperature 
  at 
  which 
  the 
  cut-off 
  acts 
  can 
  be 
  adjusted 
  

   several 
  degrees 
  by 
  altering 
  the 
  distance 
  which 
  the 
  wire 
  f 
  2 
  

   projects 
  down 
  the 
  tube 
  L. 
  

  

  By 
  carefully 
  adjusting 
  the 
  size 
  of 
  the 
  jet, 
  the 
  by-pass, 
  and 
  

   the 
  height 
  of 
  the 
  block 
  N 
  7 
  , 
  we 
  could 
  keep 
  the 
  temperature 
  of 
  

  

  X2 
  

  

  