﻿92 
  

  

  Prof. 
  W. 
  Stroud 
  on 
  a 
  Telemetrical 
  

  

  so 
  that 
  only 
  the 
  extreme 
  beams 
  are 
  used 
  to 
  form 
  the 
  image. 
  

   In 
  this 
  way 
  a 
  crude 
  range-finder 
  is 
  formed, 
  which 
  suffers 
  from 
  

   a 
  radical 
  defect, 
  arising 
  from 
  the 
  fact 
  that 
  the 
  beams 
  enter 
  the 
  

   eye 
  in 
  different 
  directions, 
  so 
  that 
  any 
  alteration 
  in 
  the 
  accom- 
  

   modation 
  of 
  the 
  eye 
  produces 
  a 
  duplication 
  of 
  the 
  image. 
  

   An 
  attempt 
  is 
  made 
  to 
  avoid 
  error 
  from 
  this 
  cause 
  by 
  

   keeping 
  the 
  eye 
  focussed 
  all 
  the 
  time 
  on 
  cross-wires 
  fixed 
  in 
  

   the 
  focal 
  plane 
  of 
  the 
  eyepiece. 
  (2) 
  The 
  short-focus 
  

   telescope 
  has 
  not 
  usually 
  base 
  enough 
  for 
  accurate 
  telemetry 
  

   (the 
  maximum 
  available 
  base 
  being 
  the 
  diameter 
  of 
  the 
  

   objective), 
  or 
  if 
  it 
  should 
  have 
  base 
  enough, 
  the 
  minimum 
  

   range 
  which 
  it 
  can 
  measure 
  is 
  too 
  great. 
  

  

  Looked 
  at 
  from 
  the 
  range-finding 
  point 
  of 
  view 
  the 
  problem 
  

   of 
  optical 
  spherometry 
  and 
  focometry 
  is 
  one 
  of 
  excessive 
  

   simplicity. 
  What 
  is 
  required 
  is 
  a 
  range-finder 
  whose^ 
  prime 
  

   reflectors 
  can 
  be 
  fixed 
  at 
  any 
  distance 
  apart 
  (to 
  furnish 
  the 
  

   adjustable 
  base) 
  and 
  at 
  any 
  angle 
  to 
  that 
  base 
  (to 
  furnish 
  the 
  

  

  adjustable 
  range) 
  . 
  

  

  Fia-. 
  1. 
  

  

  

  

  

  

  

  

  ^N 
  

  

  A' 
  

  

  \2> 
  

  

  — 
  5H 
  

  

  A 
  

   b\/b 
  

  

  / 
  N 
  

  

  

  O 
  A 
  / 
  <&/ 
  

  

  I 
  

  

  y 
  

  

  

  

  

  c 
  

  

  

  

  

  

  

  One 
  arrangement 
  is 
  shown 
  

  

  in 
  plan 
  in 
  fig. 
  1 
  and 
  in 
  

  

  perspective 
  in 
  fig. 
  2. 
  A, 
  A' 
  are 
  two 
  triangular 
  reflecting 
  

  

  