BOWS METHOD OF DRAWING DIAGRAMS IN GRAPHICAL STATICS. 495 



Peaucellier's linkage consists of the four equal pieces forming the jointed 

 rhombus PQRS together with two equal arms OS and OR. 



Fig 1 



When these arms are longer than the sides of the rhombus the linkage 

 is said to be positive ; when they are shorter the linkage is said to be negative. 



When Peancellier's linkage is employed as a machine it is acted on by 

 three forces, applied respectively at the fulcrum 0, and the two tracing poles 

 (J and S. 



