829 



In any case, I was aUlc using a polished surface lo measure with 

 tolerable precision an cxceodingiy minute rotation, (f <^ 0,2'). This 

 increases somewhat toward the blue and seems to weaken at the 

 end toward the red. The form of the curve is, of course, very 

 uncertain. (Tab. 9). 



-fO^) 



TABLE 9. 



Martite (saturated) 



Twin Peaks 



The smallness of the rotation did not permit a determination of 

 the temperature curve. 



Ferriferrite {Fe, 0, . 2Fe., 0„ haematite, hexagonal, from Elba, ^, = 

 645°). The same as above holds for the natural specular ore '). 

 From an excellent crystal a mirror was cut parallel to the principal 

 axis. LoRiA was able for this direction to give only an upper limit 

 for the rotation, 0',2. In view of the positive results with martite it 

 seemed that the rotation with liaematite could perhaps also be 

 measured. This proved to be the case, the rotations lying in the 

 neighbourhood of the above limiting value and being likewise positive. 

 The increase toward the violet appears to be less marked than with 

 martite, but little weight can be attached to the exact form of the 

 curve. (Table 10). 



A beautifully retlecting mirror cut parallel to the base gave, in 

 agreement with Loria's result, absolutely no rotation. The base is, 

 therefore, a "ferromagnetic plane". It was out of the question to 

 determine the temperature curve. 



1) T. KuNZ. (Neues Jalirb. f. Mineral, etc. p. 86 1907) deleimined for simple 

 norm-il haematite 5,, = 645° ; the optical constants were measured by G. 

 FöRSTERLTNG, loc. cit. Beil. 25, p. 344, 1907. 



