﻿Transmission 
  of 
  Radiant 
  Heat 
  by 
  Gases. 
  31 
  

  

  paths 
  : 
  now 
  in 
  the 
  former 
  case 
  if 
  the 
  two 
  beams 
  travel 
  D 
  

   between 
  separating 
  and 
  meeting, 
  and 
  meet 
  again 
  at 
  an 
  angle 
  

   2a, 
  then 
  the 
  linear 
  separation 
  of 
  corresponding 
  points 
  may 
  be 
  

   taken 
  as 
  2aD, 
  which 
  amounts 
  to 
  the 
  same 
  as 
  our 
  2ccp, 
  and 
  hence 
  

   the 
  conditions 
  are 
  such 
  as 
  favour 
  the 
  degree 
  of 
  sensitiveness 
  

   expected 
  by 
  Michelson 
  and 
  Morley; 
  while 
  in 
  their 
  own 
  experi- 
  

   ment, 
  as 
  each 
  of 
  the 
  separated 
  beams 
  is 
  reflected 
  fifteen 
  times 
  

   in 
  its 
  own 
  independent 
  path 
  there 
  is 
  opportunity 
  for 
  a 
  con- 
  

   siderable 
  lateral 
  shift 
  of 
  the 
  one 
  beam 
  relative 
  to 
  the 
  other 
  

   w 
  T 
  hen 
  they 
  meet, 
  although 
  both 
  are 
  adjusted 
  as 
  nearly 
  to 
  

   parallelism 
  as 
  is 
  necessary, 
  that 
  is 
  to 
  say 
  that 
  c 
  is 
  independent 
  

   of 
  2ctp, 
  and 
  the 
  sensitiveness 
  of 
  the 
  system 
  of 
  fringes 
  is 
  

   unknown, 
  but 
  in 
  all 
  probability 
  small 
  compared 
  to 
  that 
  

   expected. 
  In 
  their 
  celebrated 
  repetition 
  of 
  Fizeau's 
  great 
  

   experiment 
  on 
  the 
  effect 
  of 
  running 
  water 
  on 
  the 
  aether 
  

   Michelson 
  and 
  Morley 
  got 
  their 
  well-known 
  positive 
  result, 
  

   but 
  in 
  this 
  case 
  the 
  divided 
  beams 
  were 
  sent 
  in 
  opposite 
  

   directions 
  round 
  the 
  same 
  path, 
  so 
  that 
  the 
  optical 
  arrange- 
  

   ment 
  had 
  the 
  sensitiveness 
  expected. 
  It 
  is 
  the 
  use 
  of 
  multiple 
  

   reflexion 
  along 
  different 
  paths 
  in 
  the 
  experiment 
  on 
  the 
  

   relative 
  motion 
  of 
  earth 
  and 
  aether 
  that 
  introduces 
  the 
  possi- 
  

   bility 
  of 
  comparatively 
  large 
  lateral 
  shift. 
  

  

  If 
  the 
  argument 
  in 
  this 
  paper 
  is 
  correct 
  it 
  ought 
  to 
  be 
  

   possible 
  by 
  careful 
  adjustment 
  for 
  the 
  requisite 
  smallness 
  of 
  

   c, 
  or 
  for 
  getting 
  the 
  absolute 
  central 
  band 
  into 
  the 
  field 
  

   of 
  view, 
  to 
  give 
  the 
  Michelson 
  and 
  Morley 
  apparatus 
  the 
  

   sensitiveness 
  desired 
  for 
  measurement 
  of 
  the 
  relative 
  motion 
  

   of 
  earth 
  and 
  aether 
  ; 
  and 
  in 
  any 
  case 
  an 
  experimental 
  examina- 
  

   tion 
  of 
  the 
  effect 
  of 
  lateral 
  shift 
  seems 
  desirable. 
  

  

  Melbourne, 
  Sept. 
  1897. 
  

  

  III. 
  The 
  Transmission 
  of 
  Radiant 
  Heat 
  by 
  Gases 
  at 
  Varying 
  

   Pressures. 
  By 
  Charles 
  F. 
  Brush 
  *. 
  

  

  [[Plates 
  I. 
  to 
  X.] 
  

  

  BEFORE 
  describing 
  my 
  own 
  investigations 
  on 
  the 
  trans- 
  

   mission 
  of 
  heat 
  by 
  gases, 
  I 
  shall 
  refer 
  briefly 
  to 
  the 
  

   classical 
  work 
  of 
  a 
  somewhat 
  similar 
  nature 
  by 
  MM. 
  Dulong 
  

   and 
  Petit 
  early 
  in 
  the 
  present 
  century. 
  Their 
  memoir 
  

   entitled 
  " 
  Researches 
  on 
  the 
  Measure 
  of 
  Temperatures, 
  and 
  

   on 
  the 
  Laws 
  of 
  the 
  Communication 
  of 
  Heat," 
  gained 
  the 
  

   prize 
  voted 
  by 
  the 
  Academy 
  of 
  Sciences 
  in 
  1818. 
  A 
  trans- 
  

   lation 
  of 
  this 
  important 
  paper 
  may 
  be 
  found 
  in 
  the 
  ' 
  Annals 
  

   of 
  Philosophy,' 
  for 
  February, 
  March, 
  April, 
  and 
  May, 
  1811). 
  

  

  * 
  Communicated 
  by 
  the 
  Author, 
  having 
  heen 
  read 
  before 
  the 
  American 
  

   Association 
  for 
  the 
  Advancement 
  of 
  Science, 
  August 
  10, 
  1897. 
  

  

  