﻿Method 
  of 
  Testing 
  PhotograpMe 
  Shutters, 
  783 
  

  

  the 
  total 
  duration 
  of 
  the 
  exposure 
  only, 
  the 
  general 
  arrange- 
  

   ment 
  is 
  shown 
  in 
  fig. 
  1. 
  Light 
  from 
  a 
  point 
  source 
  A 
  is 
  

  

  Fig. 
  1. 
  

  

  reflected 
  by 
  the 
  mirror 
  M 
  of 
  the 
  vibration 
  galvanometer 
  G, 
  

   through 
  the 
  shutter 
  S 
  on 
  to 
  the 
  photographic 
  plate 
  P. 
  The 
  

   mirror 
  makes 
  oscillations 
  in 
  a 
  horizontal 
  plane, 
  and 
  the 
  

   amplitude 
  is 
  such 
  that 
  the 
  vibrating 
  beam 
  nearly 
  fills 
  the 
  

   horizontal 
  diameter 
  of 
  the 
  shutter 
  aperture. 
  The 
  plate 
  falls 
  

   vertically, 
  and 
  in 
  doing 
  so 
  sets 
  off 
  the 
  shutter. 
  In 
  practice, 
  

   instead 
  of 
  a 
  point 
  source 
  of 
  light 
  a 
  Nernst 
  lamp 
  is 
  used 
  with 
  

   its 
  filament 
  vertical, 
  and 
  in 
  front 
  of 
  the 
  plate 
  is 
  placed 
  a 
  

   narrow 
  horizontal 
  slit 
  T 
  to 
  limit 
  the 
  w^idth 
  of 
  the 
  record 
  on 
  

   the 
  plate. 
  Lenses 
  Li 
  and 
  L2 
  are 
  employed 
  to 
  regulate 
  the 
  

   intensity 
  of 
  the 
  light 
  and 
  the 
  amplitude 
  of 
  the 
  vibration 
  

   recorded 
  as 
  well 
  as 
  for 
  focussing. 
  

  

  II. 
  Description 
  of 
  the 
  Special 
  Apparatus 
  employed, 
  

  

  (a) 
  Camera, 
  

   Fig. 
  2. 
  

  

  A 
  special 
  camera 
  has 
  been 
  constructed 
  to 
  hold 
  the 
  shutter 
  

   S, 
  the 
  lens 
  Lj, 
  and 
  the 
  slit 
  T 
  (fig. 
  1). 
  It 
  is 
  provided 
  with 
  

  

  