﻿1875.] 
  

  

  Exact 
  Rectilinear 
  Motion 
  by 
  Linkwork. 
  

  

  571 
  

  

  to 
  B 
  A 
  in 
  opposite 
  directions 
  ; 
  and 
  the 
  linkwork 
  is 
  one 
  of 
  those 
  given 
  by 
  

   me 
  in 
  the 
  * 
  Messenger.' 
  

  

  Fig. 
  6. 
  

  

  § 
  7. 
  This 
  case 
  does 
  not 
  strictly 
  come 
  under 
  the 
  same 
  head 
  as 
  those 
  

   coming 
  before, 
  but 
  is 
  an 
  exceptional 
  one. 
  

  

  Fig. 
  7. 
  

  

  Since 
  P 
  and 
  F 
  in 
  § 
  5 
  lie 
  vertically 
  the 
  one 
  over 
  the 
  other, 
  it 
  is 
  clear 
  

   that 
  if 
  the 
  links 
  PO=FB, 
  P'0=PB 
  be 
  added, 
  O 
  lies 
  on 
  the 
  straight 
  

   line 
  O 
  B 
  perpendicular 
  to 
  A 
  B, 
  and 
  thus 
  O 
  B 
  is 
  the 
  locus 
  of 
  O. 
  

  

  II. 
  § 
  8. 
  Make 
  k 
  = 
  - 
  in 
  the 
  fundamental 
  linkage, 
  so 
  that 
  B 
  and 
  D' 
  

  

  coincide. 
  

  

  Fix 
  A 
  B, 
  add 
  the 
  bars 
  R 
  P 
  O, 
  R 
  P' 
  O', 
  making 
  

  

  ep=po=fd; 
  

  

  EP'=P' 
  0'=PB, 
  

  

  