(98) 



VBi=2l,0QA and Fi>'e,03= 32,06, 

 and with the aid of the given rehitions and the values for « and A 

 we find for each phase : ^ ) 



Qbj ^ 2,7641 

 Q ~ 3,1853* 



If now we just compare these values for the sides of the rhom- 

 bohedral elementary cells of the crystal structure with those of the 



quotients — in the two phases, they curiously enough show the 



following relation: 



Xr, 



© 



=:q' : q' = 1,32. 



Allowing for experimental errors, the agreement is all that can 

 be desired: in the first term of the equation the value is exactly: 

 1.312, in the last term: 1,328. 



In our case the quotient — may therefore be written for both 



phases in the form : C.9^ in which C is a constant independent of 

 the particular chemical nature of the phase. 

 Instead of the relation 



Qi' ' Qi^i perhaps q^^ sin «j : q^^ dn «^ = 1.305 

 is still more satisfactory. These expressions, however, represent 

 nothing else but the surface of the elementary mazes of the three 

 chief planes of the trigonal molecule structure, for these are in our 



case squares whose flat axis = a. The ciuotient — in the two 



Xc 



phases should then be directly proportional to the reticular density 

 of the main net-planes of Bravais's structures. 



A choice between this and the above conception cannot yet be 

 made, because «^ and «^ differ too little from 90''. Moreover, a further 

 investigation of other crystals will show whether we have to do 

 here with something more than a mere accidental agreement. Similar 

 investigations also with lower-symmetric conductors are at this 

 moment in process and will, I hope, be shortly the subject of further 

 communications. 



Zaandam, May 1906. 



1) For bismuth a = 87°:34' and J. = 87o40': for haematite a==85°42' and 

 A = 86°0', The angle A is the supplement of the right angle on Ihe polar axes 

 of the rhorabohedral cells and x is the Hat angle enclosed between the polar axes. 



