828 



8, we miisl find at tlie one side of curve D' the ourves A' and 

 F' and at the otlier wide the curves B' , (" and E' . Therefore 

 curve D' must be situated, as it is drawn in eacii of these figures. 

 Consequently also b^- this the place of curve B' is defined. 



We should have been able to deduce the same also from (18). 



In each of the y-*, 7-diagrams, when starting in a definite direction 

 from />, the succession of the curves is: B' D' A' F' E' C' . In order 

 to understand the meaning of this succession, we shall bear in mind 

 the following. The points BM, and A of the solids, are particular 

 points, each defined in a particular wa}'. BD is viz. the side in 

 which terminate the tetrahedrons, of which we imagined each octo- 

 hedrou to be built up. On this side the point B occupies again a 

 special place, as we ha^e assumed that the line AF intersects the 

 triangle BCE. Also the point A is a particular point, as the line 

 AF intersects the triangle BCE. 



When we compare the succession of the curves in the P,7-diagrams 

 with the succession of the anglepoiuls of the solids then we go in 

 these solids fii'st along the sides from B towards D and afterwards 

 towards A. Starting from A we go along a diagonal, consequently 

 towards F; starting from F we go along the other diagonal, conse- 

 quently towards E (figs. '6, 5 and 7) or, when no other diagonal 

 starts from F (fig, 1) we go along a side towards the point, which 

 is situated on the other side of the triangle ABD, consequently 

 also towards E. At last we go, starting from E along a diagonal, 

 consequently towards C. 



When we summarize the results obtained above, the following is 

 apparent : 



1. There exist four types of P, T-diagrams. The six phases form 

 the anglepoiuts of 



a. a symmetrical octohedron (fig. 1); then in the P,T-diagram 

 the six curves form three twocurvical bundles (fig. 2); 



b. an asymmetrical octohedron (fig. 3) ; then in the P, T-diagram the 

 six curves form one twoeurxical and four onecurvical bundles (fig. 4); 



V. a monoconcave octohedron (fig. 5); then in the P, P-diagram 

 the six curves form one threecurvical, one twocurvical and one 

 onecurvical bundle (fig. 6) ; 



d. a biconcave octohedron (fig. 7); then in the P, P-diagram the 

 six curves form one fourcurvical and two onecurvical bundles (fig. 8). 



2. The four types are in accordance with one another in that 

 respect that the curves succeed one another in a same definite 

 succession. 'To be continued). 



