﻿Hutchins 
  — 
  Adjustment 
  of 
  the 
  Quartz 
  Spectrograph. 
  329 
  

  

  be 
  "slightly 
  adjustable 
  about 
  that 
  position. 
  Any 
  projecting 
  

   portions 
  of 
  the 
  plate-holder, 
  at 
  the 
  ends 
  of 
  short 
  waves, 
  that 
  

   might 
  prevent 
  the 
  oblique 
  rays 
  from 
  reaching 
  the 
  very 
  end 
  

   of 
  the 
  plate, 
  should 
  be 
  cut 
  away 
  ; 
  for, 
  with 
  a 
  focus 
  of 
  70 
  cm 
  the 
  

   spectrum 
  just 
  occupies 
  the 
  length 
  of 
  a 
  10-inch 
  plate. 
  

  

  The 
  plate 
  should 
  be 
  firmly 
  held 
  by 
  buttons 
  or 
  otherwise 
  

   and 
  bent 
  over 
  ways 
  along 
  its 
  edges 
  to 
  a 
  curve 
  whose 
  radius 
  is 
  

   four 
  times 
  the 
  focal 
  length 
  of 
  the 
  camera 
  lens 
  for 
  sodium 
  

   light. 
  

  

  Focus 
  of 
  the 
  collimator. 
  — 
  The 
  distance 
  of 
  the 
  slit 
  to 
  the 
  

   collimator 
  lens 
  should 
  be 
  87 
  per 
  cent 
  of 
  the 
  focus 
  of 
  the 
  colli- 
  

   mator 
  lens 
  for 
  sodium 
  light. 
  

  

  Adjustment 
  of 
  the 
  prism. 
  — 
  The 
  collimator 
  and 
  camera 
  lenses 
  

   should 
  come 
  close 
  up 
  to 
  the 
  prism. 
  Lay 
  off 
  on 
  a 
  sheet 
  of 
  zinc 
  

   an 
  angle 
  of 
  55°'3, 
  cut 
  out 
  and 
  file 
  the 
  edges 
  true. 
  Lay 
  one 
  

   edge 
  of 
  this 
  templet 
  across 
  the 
  front 
  of 
  collimator 
  and 
  rotate 
  

   the 
  prism 
  until 
  its 
  face 
  fits 
  the 
  other 
  edge 
  of 
  the 
  templet. 
  This 
  

   adjustment 
  causes 
  light 
  of 
  wave-length 
  about 
  2025 
  to 
  pass 
  at 
  

   minimum 
  deviation, 
  and 
  is 
  a 
  much 
  more 
  ready 
  means 
  of 
  set- 
  

   ting 
  the 
  prism 
  than 
  is 
  finding 
  the 
  minimum 
  deviation 
  by 
  suc- 
  

   cessive 
  exposures 
  and 
  rotations 
  of 
  the 
  prism, 
  while 
  at 
  the 
  same 
  

   time 
  it 
  is 
  sufficiently 
  accurate 
  for 
  all 
  purposes. 
  The 
  angle 
  of 
  

   the 
  prism 
  is 
  supposed 
  to 
  be 
  60° 
  ; 
  should 
  it 
  be 
  otherwise 
  it 
  is 
  

   merely 
  required 
  to 
  calculate, 
  in 
  any 
  case, 
  the 
  deviation 
  for 
  

   X 
  2025 
  and 
  cut 
  the 
  templet 
  accordingly. 
  

  

  Adjustment 
  of 
  the 
  camera. 
  — 
  The 
  spark 
  spectrum 
  of 
  copper 
  

   is 
  excellent 
  for 
  adjusting 
  purposes. 
  The 
  lines 
  are 
  not 
  remark- 
  

   ably 
  sharp 
  but 
  are 
  numerous 
  and 
  well 
  distributed 
  throughout 
  

   the 
  spectrum 
  from 
  the 
  red 
  to 
  X 
  1979. 
  Using 
  a 
  high-tension 
  

   transformer 
  (Woods' 
  Cail), 
  large 
  condenser, 
  Seed 
  No. 
  26 
  plate, 
  

   two 
  seconds 
  was 
  found 
  to 
  give 
  a 
  well 
  exposed 
  negative 
  from 
  

   X 
  5000 
  to 
  X 
  2150. 
  

  

  A 
  valuable 
  addition 
  to 
  the 
  apparatus 
  is 
  a 
  shutter 
  hinged 
  on 
  

   the 
  inside 
  of 
  the 
  camera, 
  and 
  movable 
  by 
  a 
  handle 
  from 
  with- 
  

   out. 
  When 
  swung 
  parallel 
  to 
  the 
  plate 
  it 
  covers 
  all 
  but 
  the 
  

   extreme 
  ultra-violet 
  end 
  of 
  the 
  spectrum 
  and 
  enables 
  giving 
  a 
  

   long 
  exposure 
  to 
  the 
  shortest 
  waves 
  without 
  over-exposing 
  the 
  

   remainder. 
  To 
  get 
  the 
  line 
  1979 
  from 
  one-half 
  to 
  one 
  minute 
  

   is 
  required. 
  

  

  The 
  camera 
  is 
  supposed 
  to 
  be 
  furnished 
  with 
  some 
  sort 
  of 
  

   focussing 
  scale, 
  and 
  further, 
  a 
  scale 
  for 
  measuring 
  the 
  plate 
  

   inclination. 
  

  

  An 
  unexposed 
  but 
  fixed 
  plate 
  being 
  placed 
  in 
  the 
  plate- 
  

   holder 
  it 
  may 
  be 
  focussed 
  at 
  the 
  visible 
  end 
  of 
  the 
  spectrum, 
  

   which 
  should 
  lie 
  at 
  the 
  extreme 
  end 
  of 
  the 
  plate. 
  The 
  best 
  

   focus 
  being 
  found, 
  draw 
  out 
  the 
  camera 
  3 
  or 
  4 
  millimeters. 
  

  

  Now 
  with 
  a 
  plate 
  in 
  the 
  camera 
  make 
  an 
  exposure 
  near 
  the 
  

   edge 
  of 
  the 
  plate, 
  move 
  the 
  camera 
  in 
  one 
  millimeter 
  at 
  a 
  time 
  

  

  