﻿238 
  

  

  Prof. 
  R. 
  W. 
  Wood 
  on 
  

  

  with 
  a 
  small 
  Cooper-Hewitt 
  mercury 
  lamp 
  (glass, 
  not 
  quartz). 
  

   The 
  bulb 
  should 
  project 
  a 
  centimetre 
  or 
  two 
  beyond 
  the 
  cap 
  

   on 
  the 
  positive 
  electrode, 
  and 
  the 
  drawn- 
  down 
  end 
  should 
  

   reach 
  not 
  quite 
  down 
  to 
  the 
  negative 
  electrode 
  bulb. 
  Two 
  

   small 
  pads 
  of 
  thick 
  asbestos 
  paper 
  should 
  be 
  placed 
  between 
  

   the 
  two 
  tubes, 
  which 
  are 
  then 
  securely 
  fastened 
  together 
  

   with 
  copper 
  wire. 
  

  

  The 
  Cooper-Hewitt 
  lamp 
  is 
  supported 
  in 
  a 
  clamp 
  fastened 
  

   close 
  to 
  the 
  negative 
  bulb, 
  just 
  beyond 
  the 
  end 
  of 
  the 
  iodine 
  

   tube, 
  as 
  shown 
  in 
  fig. 
  1. 
  

  

  Fig. 
  1. 
  

  

  A 
  cylindrical 
  reflector 
  is 
  now 
  prepared 
  by 
  cutting 
  off 
  the 
  

  

  bottom 
  of 
  a 
  beaker 
  glass 
  measuring 
  about 
  12 
  x 
  25 
  cm., 
  and 
  

  

  silvering 
  the 
  outside 
  with 
  Brashear's 
  solution. 
  This 
  can 
  be 
  

  

  done 
  with 
  a 
  minimum 
  amount 
  of 
  solution 
  by 
  rotating 
  the 
  

  

  beaker 
  slowly 
  in 
  a 
  glass 
  or 
  porcelain 
  tray, 
  tipped 
  slightly 
  on 
  

  

  its 
  longer 
  side. 
  A 
  preliminary 
  trial 
  with 
  water 
  shows 
  at 
  

  

  once 
  the 
  minimum 
  amount 
  that 
  can 
  be 
  used. 
  It 
  is 
  sufficient 
  

  

  if 
  the 
  solution 
  wets 
  one 
  side 
  of 
  the 
  beaker 
  from 
  one 
  end 
  to 
  

  

  the 
  other. 
  After 
  the 
  silvering 
  the 
  inside 
  of 
  the 
  beaker 
  is 
  

  

  cleaned 
  with 
  a 
  cloth 
  dampened 
  with 
  dilute 
  nitric 
  acid, 
  and 
  

  

  the 
  hollow 
  r 
  reflecting 
  cylinder 
  slipped 
  over 
  the 
  iodine 
  tube 
  

  

  and 
  mercury 
  lamp. 
  The 
  lamp 
  is 
  clamped 
  at 
  a 
  suitable 
  angle 
  

  

  for 
  operating, 
  say 
  5° 
  from 
  the 
  horizontal, 
  and 
  started 
  by 
  

  

  tipping 
  the 
  clamp-stand. 
  The 
  reflector 
  should 
  be 
  supported 
  

  

  so 
  that 
  the 
  tubes 
  are 
  centrally 
  placed. 
  The 
  luminous 
  iodine 
  

  

  vapour 
  is 
  viewed 
  " 
  end-on 
  " 
  through 
  the 
  bulb. 
  If 
  a 
  prism 
  of 
  

  

  about 
  8°, 
  such 
  as 
  is 
  used 
  for 
  mounting 
  Lippman 
  photographs, 
  

  

  is 
  placed 
  in 
  front 
  of 
  and 
  close 
  to 
  the 
  bulb,, 
  it 
  has 
  the 
  effect 
  

  

  of 
  bringing 
  the 
  tube 
  into 
  the 
  horizontal 
  position, 
  which 
  is 
  

  

  