( 531 ) 



Fig. 2. 

 the elements of the two tetrahedra 



Jt — a 



a. 



14 i 



a' u = £ jt — a t4 , 

 A 31 — a' = a. 



'34 ' 



(( 



23 ' 



l 12 » 



4',. = A 



«'is = h 3 * — «is ; 



A J + ^43 = k a , 



14 "48 ) 1- C ( 2 JT 



^'43 + «13 = k ^ > 



«U 4" «t4 = 2 * » 



«24 + A 2 = è * 1 



A' lt = A u , i. e. A' lt + (è » — ,1 41 ) = 4 * , 

 .4' 41 -f ,1 14 = i * »), i. e. (* * - A'„) + (i* - A lt ) 





\n 



* l 4 2 2 *'' Ct 2 3 ' 



A'=z A.. . 



4. So if we regard instead of a ls . a, 4 , .4 14 , A 4i and a„ their 

 complements as elements of the tetrahedron, then the elements of the 



l ) In giving the proof' of this we must remember that A' t A' s and A, A.< lie on 

 a sphere and therefore cut each other in a point P, just as A\A' 2 and 4 A, cut 

 each other in a point Q. 



36* 



