138 
Physics. — “The magieto-optic Kurr-effect in ferromagnetic com- 
pounds and metals.” II]. By Pierre Martin of Geneva. (Com- 
munication from the Bosscua-Laboratory). (Communicated by 
Prof. H. pu Bors). 
The purpose of the following work was the extension of the 
investigations of LortA*) on the magneto-optical properties of the 
newly obtained ferromagnetic compounds and alloys. I limited myself 
to the determination of the dispersion of different manganese and 
iron compounds, and to a repetition of the measurements for the 
case of the three chief metals. The literature has been fully discussed 
by Lorra so that it is not necessary to introduce it here; his experi- 
mental arrangement has been again adopted, for a description of 
which I may therefore refer to his publication. The direct vision 
monochromator, with high illuminating power, was subjected to a 
new calibration. Throughout, pole end-pieces (V) with rectangular 
bore were used, the profile of which (2,5>< 4mm.) was nearly 
always exceeded by the size of the mirrors: the latter were irregu- 
larly shaped and fixed by means of plaster of Paris. 
As a simple relation between the optical constants and the disper- 
sion curve was sought for in vain by Loria, I have not on this 
occasion determined the former. In general, for my specimens the 
extinction was good and consequently the ellipticity only very slight; 
considering the very small rotations in most cases, its determination 
appeared as yet scarcely possible of execution although certainly to 
be desired. 
MATERIALS INVESTIGATED. 
Manganese compounds. “Mn 65,5n 35” = Mn,Sn, and “Mn 35, 
Sb 65” = Mn Sb nearly, were very kindly given to me for investigation 
by Prof. Tammann. The relations between the amounts of the metals 
combined together correspond, according to Honpa, to the most | 
ferromagnetic compound or alloy respectively *). Besides these, I 
investigated a specimen of MnSb and MnB from Prof. WEDEKIND 
and also Mn Bi from Dr. Hueert. The metal manganese was found 
inactive by Lorta. 
Iron compounds. A piece of a carbon alloy consisting substantially 
of cementite (Fe,C) was kindly prepared for me by Dr. Hivpert. 
For normal pyrrhotine (Fe, S,) I am indebted to Prof. P. Weiss of 
Zürich. In addition to these compact magnetic pyrite and amorphous 
1) Sranistaw Loria. These Proceedings Vol. 12, p. 835 and Vol. 14, p. 970. 
4) Koraro Honpa. Ann. der Phys. 32, p. 1003, 1910. 
