146 
no effect; this was irregular and moreover parallel to the magnetic plane. 
In the present work, as in the case of pyrrhotine, a mirror was 
obtained by grinding, normal to the above. It gave a small positive 
rotation of some tenths of a minute. 
Amorphous iron sulphide (FeS). This substance, which is not ferro- 
magnetic, was also investigated by pu Bors l.c. in 1889. The same 
mirror now also gave a negative result. Should a rotation exist, it 
must be smaller than 0,3’. 
Cerium-iron. The dispersion in the case of pyrophorous cerium- 
iron of umknown composition exhibited nothing exceptional. The 
rotation increased a little on passing from violet to red. The material 
was not quite saturated. 
TABLE Ai: 
ay) 0) Cerium-iron (nearly saturated) 
N A(ue) | OQ(mm) =(min.) tos 
25 435 — 33,9 — 5,09’ 0,05'= 1 % 
20 466 — 36,7 — 5,50 0,04 = 075, 
20 503 — 39,8 — 5,97 0020 
20 530 — 41,5 — 6,22 GOO 
20 567 | — 42,7 — 6,41 001 = 6:2,,; 
20 615 — 43,5 — 6,52 00203 
25 675 —440 | —6,60 0,03 = 0,4,, 
TAA B I EZ, 
= (A) Tron (unsaturated) WEISS 
N i4(ee) | Q(mm) =(min.) + 0: 
xe ae 0430 — 126,4 | — 18,96' 0,10’ = 0,5 Oo 
8 20 483 — 131,0 | — 1965 0,05 = 0,25, 
20 530 — 136,6 | — 20,47 0,03 =0)15;, 
20 567 — 141,7 | — 21,25 0,02 = 0,09 , 
20 615 — 1495 | — 22,42 0,02 = 0,09 , 
20 675 -- 164,6 | — 24,70 0/03 = 0:12); 
