823 



"bundle of curves", then we may express the results in the following 

 way : when the six phases form the anglepoints of a symmetrical 

 octahedron, then the six monovariant curves form in the P.T'-diagram 

 three "twocurvical" bundles. 



Now we should yet also have to consider the bivariant regions; 

 as, however, the reader can easily draw them in each of the P,T- 

 diagrams, we shall omit this. Later we shall, however, refer to an 

 example. 



Type II. In fig. 3 the six piiases form the anglepoints of an 

 asymmetrical octohedron. We may considei' this solid as to be 

 composed of three tetrahedrons, which terminate in the side BD. 



In order to define the position of the curves with respect to curve 

 F' , we consider the hexahedron CADBE, hence we find: 



C' E' I F' I A' B' D' (5) 



In order to find the position of the curves with res[)ect to cui've 

 E' , we consider the hexaiicdron AllDCF; hence we deduce; 



Fig. 3 



B' C' D' I E' I A' F' (6) 



Now we draw in a P, 7'-diagram (fig. 4) the curves E' and F' 

 and we take in this case E' at the left of F' . For this reason (5) 

 and (6) have been written also in such a way that herein E' is 

 situated at the left of F' . 



It follows from (5) and (H) tiiat II' and D' are situated both at 

 the right of F' and at the left of A"; consequently, as is also drawn 



53 



Proceedings Royal Acad. Amsterdam. Vol. XVIII. 



