﻿474 
  Profs. 
  Cooke 
  and 
  Richardson 
  on 
  Absorption 
  of 
  

  

  current 
  the 
  galvanometer 
  did 
  not 
  always 
  indicate 
  an 
  increase 
  

   in 
  resistance 
  corresponding 
  to 
  a 
  recovery 
  from 
  the 
  cumulative 
  

   decrease 
  brought 
  about 
  by 
  the 
  previous 
  thermionic 
  emission, 
  

   although 
  in 
  most 
  cases 
  such 
  a 
  recovery 
  was 
  undoubtedly 
  

   indicated. 
  Attempts 
  were 
  made 
  to 
  detect 
  the 
  cooling 
  effect 
  

   sought 
  by 
  trying 
  to 
  detect 
  a 
  sudden 
  initial 
  decrease 
  of 
  

   resistance 
  of 
  the 
  wire 
  caused 
  by 
  turning 
  on 
  the 
  thermionic 
  

   current 
  in 
  addition 
  to 
  the 
  cumulative 
  effect 
  just 
  described, 
  

   but 
  without 
  success. 
  Our 
  conclusion 
  with 
  regard 
  to 
  lime- 
  

   coated 
  platinum 
  wires 
  is 
  that 
  if 
  the 
  effect 
  sought 
  is 
  present 
  

   it 
  is 
  masked 
  by 
  the 
  larger 
  cumulative 
  effect. 
  No 
  attempts 
  

   were 
  made 
  to 
  examine 
  this 
  cumulative 
  effect 
  in 
  great 
  detail, 
  

   but 
  it 
  is 
  perhaps 
  worth 
  mentioning 
  that 
  the 
  data 
  obtained 
  in 
  

   the 
  course 
  of 
  this 
  investigation 
  would 
  be 
  satisfactorily 
  ex- 
  

   plained 
  on 
  the 
  assumption 
  that 
  this 
  effect 
  is 
  due 
  to 
  an 
  

   increase 
  in 
  the 
  radiating 
  power 
  of 
  the 
  surface 
  of 
  the 
  lime 
  

   brought 
  about 
  by 
  electrolytic 
  effects 
  in 
  the 
  lime 
  occasioned 
  

   by 
  the 
  passage 
  through 
  it 
  of 
  the 
  thermionic 
  current. 
  

  

  Experiments 
  ivith 
  Tungsten 
  Wires. 
  

  

  The 
  behaviour 
  of 
  this 
  material 
  resembles 
  that 
  of 
  the 
  osmium 
  

   filaments 
  already 
  investigated 
  and 
  is 
  quite 
  different 
  from 
  the 
  

   lime-coated 
  wires. 
  The 
  change 
  of 
  resistance 
  due 
  to 
  turning 
  

   the 
  thermionic 
  current 
  on 
  or 
  off 
  is 
  complete 
  in 
  a 
  few 
  seconds, 
  

   and 
  the 
  cooling 
  effect 
  when 
  the 
  current 
  is 
  turned 
  on 
  is 
  equal 
  

   to 
  the 
  heating 
  effect 
  when 
  the 
  current 
  is 
  turned 
  off. 
  

  

  The 
  ductile 
  tungsten 
  wire 
  used 
  was 
  3*3 
  cm. 
  long 
  and 
  

   0*00375 
  cm. 
  in 
  diameter. 
  It 
  was 
  kindly 
  presented 
  to 
  us 
  by 
  

   Dr. 
  W. 
  11. 
  Whitney, 
  of 
  the 
  General 
  Electric 
  Co. 
  After 
  

   being 
  welded 
  electrically 
  in 
  hydrogen 
  to 
  stout 
  german-silver 
  

   leads, 
  it 
  was 
  sealed 
  into 
  a 
  glass 
  tube 
  so 
  as 
  to 
  pass 
  axially 
  

   down 
  a 
  cylindrical 
  electrode 
  of 
  copper 
  foil 
  3*5 
  cm. 
  in 
  

   diameter. 
  The 
  ends 
  of 
  the 
  latter 
  were 
  boxed 
  in 
  by 
  sheets 
  of 
  

   the 
  foil 
  with 
  a 
  small 
  hole 
  in 
  the 
  centre, 
  so 
  that 
  the 
  electrode 
  

   practically 
  enclosed 
  the 
  hot 
  wire. 
  The 
  tube 
  was 
  exhausted 
  

   and 
  heated 
  for 
  several 
  hours 
  in 
  a 
  vacuum 
  furnace 
  at 
  a 
  

   temperature 
  of 
  550°-570° 
  C. 
  With 
  the 
  tube 
  at 
  250°-300° 
  C. 
  

   the 
  wire 
  was 
  glowed 
  out 
  at 
  above 
  2500° 
  K. 
  in 
  a 
  liquid 
  air 
  

   and 
  charcoal 
  vacuum 
  until 
  the 
  evolution 
  of 
  gas 
  was 
  not 
  more 
  

   than 
  10~ 
  3 
  c.c. 
  x 
  mm. 
  of 
  mercury 
  in 
  5 
  minutes. 
  It 
  was 
  then 
  

   sealed 
  oft' 
  for 
  use. 
  The 
  measurements 
  were 
  carried 
  out 
  

   exactly 
  as 
  described 
  in 
  the 
  previous 
  paper. 
  Some 
  of 
  the 
  

   experimental 
  data 
  are 
  given, 
  using 
  our 
  former 
  notation, 
  in 
  

   the 
  following 
  table 
  : 
  — 
  

  

  

  