﻿(556 
  Dr. 
  F. 
  C. 
  Brown 
  on 
  tlie 
  Kinetic 
  Energy 
  of 
  the 
  

  

  attention 
  was 
  given 
  to 
  adjusting 
  the 
  vacuum 
  to 
  any 
  par- 
  

   ticular 
  degree, 
  except 
  when 
  working 
  with 
  bodies 
  that 
  

   oxidized 
  readily. 
  

  

  Air 
  was 
  the 
  only 
  gas 
  let 
  into 
  the 
  vacuum 
  system 
  previous 
  

   to 
  taking 
  observations. 
  The 
  amount 
  of 
  absorbed 
  gas 
  given 
  

   out 
  by 
  the 
  different 
  thermionic 
  radiators 
  varied 
  considerably. 
  

   As 
  this 
  was 
  only 
  secondary 
  to 
  the 
  investigation, 
  the 
  amounts 
  

   of 
  gas 
  were 
  not 
  observed 
  carefully. 
  However, 
  it 
  was 
  noted 
  

   that 
  silver 
  and 
  tantalum 
  especially 
  gave 
  out 
  much 
  less 
  gas 
  

   than 
  platinum 
  or 
  palladium. 
  

  

  In 
  carrying 
  out 
  the 
  experiments 
  a 
  potential 
  was 
  applied 
  to 
  

   the 
  upper 
  disk, 
  and 
  the 
  electrometer 
  was 
  allowed 
  to 
  charge 
  

   up 
  until 
  there 
  was 
  a 
  readable 
  deflexion. 
  The 
  deflexion 
  was 
  

  

  noted 
  and 
  the 
  current 
  was 
  taken 
  as 
  z 
  = 
  -r— 
  . 
  In 
  case 
  AV 
  

  

  A^ 
  

  

  covered 
  several 
  divisions 
  it 
  was 
  necessary 
  to 
  make 
  a 
  small 
  

   correction, 
  in 
  order 
  to 
  allow 
  for 
  the 
  variation 
  in 
  the 
  potential 
  

   that 
  the 
  ions 
  went 
  against. 
  Often 
  there 
  was 
  a 
  difference 
  in 
  

   the 
  magnitude 
  of 
  the 
  thermionic 
  current 
  with 
  the 
  heating 
  

   current 
  direct 
  and 
  the 
  heating 
  current 
  reversed. 
  Pre- 
  

   sumably, 
  this 
  was 
  because 
  the 
  thermionic 
  radiator 
  was 
  not 
  

   at 
  zero 
  potential, 
  but 
  slightly 
  above 
  zero 
  in 
  one 
  instance 
  and 
  

   below 
  in 
  the 
  other. 
  However, 
  it 
  is 
  evident 
  that 
  the 
  ther- 
  

   mionic 
  current 
  for 
  zero 
  potential 
  should 
  be 
  between 
  the 
  

   values 
  found 
  with 
  the 
  heating 
  current 
  direct 
  and 
  the 
  heating 
  

   current 
  reversed, 
  and 
  if 
  the 
  difference 
  is 
  not 
  too 
  large, 
  the 
  

   mean 
  value 
  cannot 
  be 
  far 
  from 
  the 
  one 
  desired. 
  

  

  Gold, 
  

  

  The 
  gold 
  used 
  was 
  in 
  the 
  form 
  of 
  a 
  disk 
  of 
  about 
  3 
  mm.^ 
  

   area 
  and 
  0*005 
  cm. 
  thickness. 
  It 
  was 
  welded 
  to 
  the 
  top 
  of 
  a 
  

   platinum-wire 
  loop. 
  The 
  contact 
  between 
  the 
  platinum 
  and 
  

   the 
  gold 
  probably 
  extended 
  over 
  a 
  length 
  of 
  0*5 
  mm. 
  If 
  

   there 
  was 
  any 
  fall 
  of 
  potential 
  over 
  the 
  radiating 
  surface 
  of 
  

   the 
  gold, 
  it 
  was 
  certainly 
  less 
  than 
  0*01 
  volt. 
  

  

  In 
  this 
  particular 
  experiment 
  there 
  was 
  a 
  natural 
  charging 
  

   up 
  of 
  the 
  electrometer 
  amounting 
  to 
  1*5 
  mm. 
  in 
  30 
  seconds, 
  

   when 
  the 
  heating 
  current 
  was 
  oft'. 
  This 
  was 
  not 
  noticeable 
  

   after 
  completing 
  this 
  one 
  set 
  of 
  observations. 
  The 
  correction 
  

   for 
  this 
  is 
  made 
  in 
  the 
  accompanying 
  table. 
  

  

  The 
  temperature 
  was 
  first 
  measured 
  by 
  the 
  optical 
  method 
  

   previously 
  mentioned. 
  It 
  was 
  afterwards 
  checked 
  by 
  

   measuring 
  the 
  resistance 
  of 
  the 
  platinum-wire 
  loop. 
  The 
  

   resistance 
  at 
  which 
  the 
  gold 
  disk 
  melted 
  (1064° 
  C.) 
  was 
  

   taken 
  as 
  a 
  fiducial 
  point. 
  The 
  table 
  shows 
  two 
  sets 
  of 
  

   observations. 
  For 
  the 
  lower 
  temperature 
  the 
  optical 
  method 
  

  

  