﻿Visibility 
  of 
  Radiation. 
  

  

  175 
  

  

  by 
  Adam 
  Hilger 
  of 
  London. 
  This 
  type 
  of 
  apparatus 
  has 
  

   been 
  described 
  by 
  Jones 
  *, 
  but 
  the 
  modifications 
  made 
  for 
  

   its 
  use 
  in 
  this 
  experiment 
  warrant 
  a 
  separate 
  description 
  in 
  

   this 
  paper. 
  The 
  light 
  from 
  an 
  acetylene 
  burner 
  f 
  S 
  2 
  is 
  

  

  Fig. 
  1. 
  

  

  -«°r<H 
  

  

  tgv 
  

  

  Modification 
  of 
  Nutting 
  Colorimeter. 
  

  

  focussed 
  on 
  the 
  slit 
  0! 
  by 
  the 
  lens 
  L. 
  The 
  pressure 
  of 
  the 
  

   gas 
  was 
  kept 
  constant 
  at 
  9 
  cm. 
  as 
  indicated 
  on 
  a 
  water 
  

   manometer, 
  and 
  the 
  width 
  of 
  1 
  was 
  determined 
  by 
  a 
  series 
  

   of 
  preliminary 
  experiments. 
  A 
  pair 
  of 
  nicol 
  prisms 
  N 
  con- 
  

   trolled 
  the 
  intensity 
  of 
  light 
  from 
  S 
  2 
  , 
  and 
  by 
  means 
  of 
  the 
  

   vernier 
  V 
  and 
  a 
  graduated 
  quadrant 
  attached 
  to 
  the 
  movable 
  

   nicol 
  we 
  are 
  able 
  to 
  determine 
  the 
  ratio 
  of 
  the 
  incident 
  to 
  

   the 
  transmitted 
  intensities. 
  C 
  2 
  is 
  a 
  collimating 
  lens, 
  P 
  a 
  

   constant 
  deviation 
  dispersing 
  prism 
  operated 
  by 
  a 
  screw 
  

   carrying 
  a 
  wave-length 
  drum 
  D, 
  which 
  indicates 
  directly 
  

  

  * 
  L. 
  A. 
  Jones, 
  Phys. 
  Rev. 
  iv. 
  p. 
  454 
  (1914) 
  ; 
  Trans. 
  I. 
  E. 
  S. 
  ix. 
  p. 
  687 
  

   (1914). 
  J 
  F 
  v 
  /. 
  

  

  t 
  L. 
  A. 
  Jones, 
  Trans. 
  I. 
  E. 
  S. 
  ix. 
  p. 
  716 
  (1914). 
  

  

  02 
  

  

  J« 
  

  

  