﻿336 
  

  

  Dr. 
  J, 
  R. 
  Milne 
  on 
  a 
  Device 
  to 
  prevent 
  Backlash 
  

  

  It 
  is 
  seen 
  from 
  this 
  that 
  as 
  the 
  temperature 
  o£ 
  the 
  air 
  

   increases, 
  the 
  less 
  readily 
  do 
  the 
  ions 
  recombine, 
  and 
  that 
  

   the 
  change, 
  with 
  temperature, 
  of 
  the 
  coefficient 
  of 
  recombi- 
  

   nation 
  is 
  represented 
  by 
  a 
  compound 
  curve, 
  the 
  point 
  of 
  

   inflexion 
  of 
  which 
  is 
  at 
  about 
  250° 
  absolute 
  temperature. 
  

  

  Fig. 
  2. 
  

  

  

  

  

  

  1 
  

  

  

  .^^ 
  

  

  

  

  "«--^aj 
  

  

  ^< 
  

  

  N^^-^ 
  

  

  

  

  

  

  

  

  

  

  "~" 
  

  

  

  • 
  fg. 
  

  

  c40 
  290 
  5A0 
  

  

  i^Bl 
  OL 
  L 
  T£ 
  77" 
  VPlff/; 
  TUffS 
  

  

  The 
  writer 
  intends 
  to 
  continue 
  this 
  investigation, 
  using 
  

   higher 
  temperatures 
  and 
  also 
  different 
  gases. 
  

  

  In 
  conclusion 
  I 
  wish 
  to 
  express 
  my 
  sincere 
  thanks 
  to 
  

   Prof. 
  Thomson 
  for 
  suggesting 
  this 
  problem 
  and 
  for 
  his 
  kind 
  

   interest 
  during 
  this 
  research. 
  

  

  June 
  2, 
  1909. 
  

  

  XL. 
  A 
  Device 
  to 
  prevent 
  Backlash 
  in 
  the 
  Toothed 
  Wheels 
  

   and 
  Rack-and-Pinion 
  Gears 
  of 
  Scieritific 
  Instruments. 
  By 
  

   James 
  Robert 
  Milne, 
  D.Sc, 
  Assistant 
  to 
  the 
  Professor 
  of 
  

   Natural 
  Philosophy 
  in 
  the 
  University 
  of 
  Edinburgh 
  * 
  . 
  

  

  MANY 
  scientific 
  instruments 
  have 
  either 
  toothed 
  wheels 
  

   or 
  a 
  rack-and-pinion 
  as 
  a 
  part 
  of 
  their 
  mechanism. 
  

   When 
  a 
  measured 
  motion 
  has 
  to 
  be 
  transmitted 
  by 
  these 
  parts, 
  

   it 
  is 
  essential 
  that 
  there 
  should 
  be 
  no 
  backlash 
  ; 
  and 
  even 
  if 
  

   these 
  parts 
  are 
  only 
  used 
  for 
  making 
  an 
  adjustment, 
  they 
  

   should 
  have 
  as 
  little 
  backlash 
  as 
  possible. 
  

  

  The 
  usual 
  way 
  of 
  overcoming 
  backlash 
  is 
  to 
  fit 
  the 
  teeth 
  of 
  

   the 
  wheels 
  very 
  closely 
  to 
  one 
  another. 
  This 
  can 
  only 
  be 
  

   accomplished 
  by 
  very 
  skilled 
  workmanship 
  ; 
  and 
  however 
  

   accurately 
  the 
  teeth 
  fit 
  at 
  first, 
  in 
  course 
  of 
  time 
  they 
  begin 
  

   to 
  wear, 
  and 
  develop 
  backlash. 
  Moreover, 
  closely 
  fitted 
  

   teeth 
  work 
  with 
  a 
  certain 
  amount 
  of 
  stiffness, 
  which 
  is 
  fre- 
  

   quently 
  a 
  drawback. 
  

  

  * 
  Communicated 
  by 
  Dr. 
  C. 
  G. 
  Knott. 
  

  

  