DIAGRAMS. 



657 



the polygonal areas inclosed by the links of the frame, and also in each of 

 the divisions of surrounding space as separated by the lines of action of the 

 external forces. 



When one link of the frame crosses another, the point of apparent 

 intersection of the links is treated as if it were a real joint, and the stresses 

 of each of the intersecting links are represented twice in the diagram of 

 stress, as the opposite sides of the parallelogram which corresponds to the 

 point of intersection. 



M 



FIG. 1. Diagram of Configuration. 



F 



Fio. 2. Diagram of Stress. 



This method is followed in the lettering of the diagram of configuration 

 (fig. 1), and the diagram of stress (fig. 2) of the linkwork which Professor 

 Sylvester has called a quadruplane. 



In fig. 1 the real joints are distinguished from the places where one link 

 appears to cross another by the little circles 0, P, Q, R, S, T, V. 



The four links RSTV form a " contraparallelogram " in which RS=TV and 

 RV=ST. 



The triangles ROS, RPV, TQS are similar to each other. A fourth triangle 

 (TNV), not drawn in the figure, would complete the quadruplane. The four 



VOL. II. 83 



