﻿174 
  Mr. 
  Prentice 
  Reeves 
  on 
  the 
  

  

  light, 
  after 
  reflexion, 
  is 
  propagated 
  with 
  the 
  velocity 
  c 
  + 
  v, 
  

   where 
  v 
  is 
  the 
  component 
  of 
  the 
  velocity 
  of 
  the 
  image 
  in 
  the 
  

   direction 
  of 
  the 
  reflected 
  ray. 
  

  

  To 
  complete 
  these 
  researches 
  I 
  intend, 
  as 
  I 
  have 
  said 
  

   above, 
  to 
  investigate 
  further 
  with 
  the 
  same 
  interferential 
  

   arrangements, 
  the 
  velocity 
  of 
  propagation 
  of 
  light 
  from 
  a 
  

   source 
  set 
  in 
  motion 
  artificially 
  ; 
  but 
  of 
  these, 
  and 
  of 
  the 
  

   general 
  conclusions 
  to 
  be 
  drawn 
  from 
  these 
  investigations, 
  I 
  

   reserve 
  mention 
  for 
  a 
  future 
  occasion. 
  

  

  XIX 
  . 
  The 
  Visibility 
  of 
  Radiation. 
  

   By 
  Pkentice 
  Reeves 
  *. 
  

  

  THE 
  theory 
  of 
  this 
  subject 
  has 
  been 
  given 
  previously 
  by 
  

   Nutting 
  f 
  and 
  Ives 
  J, 
  and 
  in 
  those 
  papers 
  may 
  be 
  

   found 
  a 
  thorough 
  treatment 
  of 
  the 
  early 
  literature. 
  In 
  

   this 
  paper 
  the 
  writer 
  wishes 
  to 
  present 
  further 
  data 
  obtained 
  

   by 
  a 
  method 
  similar 
  to 
  that 
  employed 
  by 
  the 
  above 
  writers 
  

   but 
  using 
  a 
  different 
  apparatus. 
  The 
  writer 
  has 
  data 
  from 
  

   thirteen 
  subjects, 
  five 
  of 
  whom 
  were 
  also 
  used 
  as 
  observers 
  

   by 
  Nutting 
  in 
  his 
  list 
  of 
  twenty-one 
  subjects. 
  The 
  values 
  

   for 
  the 
  spectral 
  energy 
  distribution 
  of 
  acetylene 
  were 
  those 
  

   offered 
  by 
  Nutting, 
  and 
  were 
  obtained 
  by 
  weighting 
  the 
  data 
  

   accessible 
  up 
  to 
  that 
  time 
  as 
  well 
  as 
  his 
  own 
  results 
  in 
  this 
  

   laboratory. 
  By 
  using 
  these 
  values 
  the 
  writer 
  was 
  able 
  to 
  

   directly 
  compare 
  results 
  with 
  those 
  of 
  the 
  other 
  writers, 
  and 
  

   by 
  using 
  the 
  values 
  offered 
  by 
  Coblentz 
  § 
  and 
  revised 
  by 
  

   Coblentz 
  and 
  Emerson 
  ||, 
  we 
  can 
  see 
  the 
  effect 
  of 
  various 
  

   values 
  for 
  the 
  spectral 
  energy 
  distribution 
  of 
  acetylene. 
  

   The 
  variations 
  in 
  the 
  acetylene 
  values 
  are 
  probably 
  due 
  to 
  

   the 
  different 
  kinds 
  of 
  burners 
  used, 
  as 
  Coblentz 
  has 
  shown 
  

   that 
  the 
  spectral 
  energy 
  distribution 
  in 
  the 
  longer 
  wave- 
  

   lengths 
  is 
  affected 
  by 
  the 
  thickness 
  of 
  the 
  radiating 
  layer 
  of 
  

   incandescent 
  particles 
  in 
  the 
  flame. 
  

  

  The 
  apparatus 
  represented 
  in 
  fig. 
  1 
  is 
  a 
  modification 
  of 
  

   the 
  Nutting 
  monochromatic 
  colorimeter^! 
  as 
  manufactured 
  

  

  * 
  Communicated 
  by 
  Dr. 
  C. 
  E. 
  Kennett 
  Mees, 
  being 
  communication 
  

   No. 
  55 
  from 
  the 
  Research 
  Laboratory 
  of 
  the 
  Eastman 
  Kodak 
  Company. 
  

  

  t 
  P. 
  G. 
  Nutting, 
  Phil. 
  Mag. 
  xxix. 
  p. 
  301 
  (1915) 
  ; 
  Trans. 
  Ilium. 
  Eng. 
  

   Soc. 
  ix. 
  p. 
  633 
  (1914). 
  

  

  X 
  H. 
  E. 
  Ives, 
  Phil. 
  Mag. 
  xxiv. 
  p. 
  149 
  (1912). 
  

  

  § 
  W. 
  W. 
  Coblentz, 
  Bull. 
  Bur. 
  Stds. 
  vii. 
  p. 
  243 
  (1911) 
  ; 
  reprinted, 
  ix. 
  

   p. 
  109 
  (1912). 
  

  

  || 
  W. 
  W. 
  Coblentz 
  and 
  W. 
  B. 
  Emerson, 
  Bull. 
  Bur. 
  Stds. 
  xiii. 
  p. 
  1 
  

   (1916). 
  

  

  f 
  P. 
  G. 
  Nutting, 
  Bull. 
  Bur. 
  Stds. 
  ix. 
  p. 
  1 
  (1913) 
  ; 
  Zsch.f. 
  Instrument- 
  

   enkund., 
  xxxiii. 
  p. 
  20 
  (1913). 
  

  

  