﻿Device 
  for 
  evaluating 
  Formulce 
  and 
  solving 
  Equations. 
  303 
  

  

  permissible 
  this 
  is 
  not 
  necessary. 
  To 
  illustrate 
  this 
  point, 
  

   and 
  also 
  the 
  method 
  of 
  using 
  the 
  device 
  in 
  this 
  case^ 
  let 
  us 
  

   consider 
  the 
  numerical 
  equation 
  

  

  .i-3-5-7^ 
  + 
  0-12.y 
  + 
  8-6-0-04i'-2 
  + 
  l-3.?j-s=0. 
  

   Fig. 
  8. 
  

  

  Putting 
  X 
  equal 
  to 
  unity 
  we 
  see 
  that 
  the 
  term 
  0*04 
  can 
  be 
  

   neglected 
  compared 
  with 
  5.7, 
  only 
  five 
  slide 
  resistances 
  

   therefore 
  are 
  required. 
  We 
  connect 
  A3B3 
  with 
  P2, 
  A0B2 
  

   with 
  Qo, 
  AjBi 
  with 
  P3 
  and 
  make 
  the 
  reading 
  on 
  it 
  1*2, 
  AB 
  

   with 
  P2 
  and 
  A"'B'^^ 
  with 
  Po. 
  The 
  finger 
  on 
  the 
  slide 
  A'^'B'" 
  

   gets 
  to 
  the 
  end 
  A'" 
  of 
  its 
  scale 
  first. 
  We 
  then 
  disconnect 
  it 
  

   from 
  Pa 
  and 
  connect 
  it 
  with 
  P3. 
  We 
  also 
  alter 
  the 
  reading 
  

  

  