﻿666 
  Dr. 
  F. 
  C. 
  Brown 
  on 
  the 
  Kinetic 
  E7iergy 
  of 
  the 
  

  

  determination 
  is 
  R 
  = 
  2'9xl0^ 
  which 
  is 
  for 
  silver, 
  and 
  the 
  

   highest 
  value 
  is 
  given 
  for 
  iron, 
  which 
  is 
  R 
  = 
  5'2 
  x 
  10^. 
  The 
  

   mean 
  of 
  all 
  the 
  experimental 
  values 
  is 
  R 
  = 
  3*8 
  X 
  10^. 
  This 
  last 
  

   fact 
  is 
  not 
  inconsistent 
  with 
  the 
  view 
  that 
  all 
  the 
  variations 
  

   between 
  the 
  experimental 
  and 
  theoretical 
  values 
  are 
  due 
  to 
  

   experimental 
  errors. 
  These 
  errors 
  may 
  be 
  largely 
  due 
  to 
  

   the 
  inherent 
  structure 
  of 
  the 
  thermionic 
  radiator, 
  such, 
  for 
  

   example, 
  as 
  might 
  obtain 
  in 
  a 
  very 
  irregular 
  crystalline 
  

   surface. 
  Considering 
  the 
  close 
  agreement 
  between 
  the 
  

   mean 
  experimental 
  value 
  and 
  the 
  theoretical 
  value 
  of 
  R, 
  and 
  

   that 
  the 
  disagreement 
  is 
  not 
  very 
  bad 
  in 
  any 
  instance, 
  we^ 
  

   may 
  state 
  the 
  following 
  law 
  to 
  be 
  true 
  as 
  a 
  first 
  approximation 
  : 
  

   The 
  mean 
  kinetic 
  energy 
  of 
  the 
  positive 
  thermions 
  emitted 
  

   from 
  hot 
  bodies 
  is 
  independent 
  of 
  the 
  material 
  from 
  which 
  

   the 
  thermions 
  radiate 
  and 
  varies 
  directly 
  as 
  its 
  absolute 
  

   temperature. 
  

  

  By 
  referring 
  to 
  the 
  summary 
  it 
  is 
  noted 
  that 
  the 
  varia^ 
  

   tion 
  in 
  the 
  values 
  of 
  R 
  for 
  any 
  one 
  material 
  is 
  decidedly 
  

   less 
  than 
  the 
  variation 
  in 
  the 
  values 
  when 
  different 
  materials 
  

   are 
  considered. 
  For 
  example, 
  the 
  mean 
  variation 
  of 
  the 
  

   values 
  of 
  R 
  for 
  each 
  radiator 
  separately 
  is 
  5 
  per 
  cent, 
  

   from 
  the 
  mean 
  value 
  obtained, 
  while 
  the 
  mean 
  variation 
  of 
  

   the 
  values 
  of 
  R 
  for 
  all 
  the 
  radiators 
  together 
  is 
  about 
  16 
  per 
  

   cent, 
  from 
  the 
  value 
  3*8 
  x 
  10'^ 
  From 
  these 
  facts 
  we 
  may 
  

   obviously 
  make 
  two 
  deductions. 
  First, 
  the 
  errors 
  in 
  the 
  

   temperature 
  determinations 
  cannot 
  be 
  great 
  enough 
  to- 
  

   explain 
  all 
  the 
  variations 
  in 
  the 
  values 
  of 
  R. 
  Second, 
  there 
  

   is 
  no 
  such 
  change 
  in 
  the 
  material 
  with 
  the 
  time 
  of 
  heating 
  

   or 
  the 
  intensity 
  of 
  heating 
  as 
  would 
  warrant 
  the 
  variations 
  

   obtained. 
  Changes 
  in 
  the 
  form 
  or 
  the 
  size 
  of 
  the 
  metallic 
  

   crystals 
  would 
  be 
  included 
  in 
  this. 
  Of 
  course 
  these 
  state- 
  

   ments 
  would 
  not 
  necessarily 
  be 
  true 
  outside 
  the 
  limits 
  of 
  

   temperature 
  and 
  time 
  prevailing 
  in 
  the 
  experiments. 
  

  

  We 
  must 
  look 
  elsewhere 
  then 
  for 
  an 
  explanation 
  of 
  the 
  

   variation 
  of 
  our 
  values 
  of 
  R. 
  If 
  the 
  temperature 
  were 
  not 
  

   uniform 
  over 
  the 
  surface, 
  the 
  conditions 
  would 
  be 
  such 
  as 
  

   the 
  theory 
  does 
  not 
  provide 
  for. 
  But 
  as 
  the 
  area 
  of 
  the 
  

   thermionic 
  radiator 
  was 
  only 
  3 
  mm.^, 
  and 
  set 
  up 
  as 
  it 
  was,. 
  

   there 
  should 
  have 
  been 
  very 
  little 
  difference 
  of 
  temperature 
  

   at 
  any 
  instant. 
  To 
  the 
  eye 
  the 
  surface 
  appeared 
  to 
  be 
  at 
  

   the 
  same 
  temperature 
  all 
  over. 
  Such 
  errors 
  as 
  would 
  arise 
  

   from 
  the 
  edge 
  of 
  the 
  disk 
  being 
  at 
  slightly 
  lower 
  temperature 
  

   than 
  the 
  middle 
  would 
  tend 
  to 
  give 
  relatively 
  too 
  many 
  ions 
  

   with 
  small 
  kinetic 
  energy. 
  The 
  author 
  is 
  quite 
  certain 
  that 
  

   the 
  errors 
  arising 
  from 
  unequal 
  distribution 
  of 
  temperature 
  

   would 
  not 
  be 
  sufficient 
  to 
  explain 
  the 
  variations 
  obtained. 
  

  

  