8o 



constant, bcing= AD 2 ~ A C 2 . Taking any four points in a 

 straight line parallel to the dotted lines AB and CD, viz., EFG 

 and H, EF has a constant ratio to AB, and EG has a constant 

 ratio to CD; wherefore EF, EG is constant ; also EF, FH is 

 constant. Thus by fixing equal links to E and F, according to 

 the proof in the proposition, the link attached to E being sta- 

 tionary and that attached to F moving from the centre K, G 

 will always traverse in a straight line perpendicular to EK, or, 

 the link attached to F being made stationary, H will traverse, 

 as in the negative cell, in a line perpendicular to FK. 



