Magneto-optic Phenomenon. 



259 





Polar, e . 



Inclined. 



Equat. 



0° 

 -16'5 

 -16'5 



39°-4 

 -12'-6 

 -12' -8 



50° -5 

 - 9'-7 

 -10'5 



77°-2 



- 4'-6 



- 3'-7 



90° 

 

 



Rotat. observ. e 



Rotat. caleul. e cos a 



ments having been difficult to construct, many sources of error 

 occurred ; considering these, the observed and calculated 

 values of € sufficiently agree. 



II. This leads to the Cosine Law 



e = e cos (3,9?). 



It must still be remarked that the plane parallel to the 

 mirror's normal and to the direction of magnetization may 

 be called a "magnetic principal plane." In the above 

 experiments this principal plane and the plane of polarization 

 of the incident light were both horizontal. Experiments with 

 a cobalt mirror, obliquely magnetized, proved that the same 

 rotation is obtained whether one plane is perpendicular or 

 parallel to the other. The effect is therefore independent 

 of the azimuth of incidence. Equally good extinction was 

 observed with inclined magnetization as on polar reflexion. 



§ 12. Normal residual magnetization. — In order to obtain 

 this an elongated ovoid (2a = 18 ; 25 = 1*2 ; n = 1/15) of glass- 

 hard. English cast steel, tempered at 100°, had to be used. 

 This, on the other hand, offered the disadvantage that the end 

 was considerably disfigured by grinding on a mirror. The 

 magnetic distribution must therefore differ considerably from 

 a uniform one. I succeeded in obtaining a residual rotation 

 in the shape of a change of the analyser's zero on impressing 

 reversed residual magnetizations ; it could be measured as a 

 mean of 30 observations. The influence of magnetic history 

 was each time eliminated after the manner of Gaugain, 

 Auerbach, Maxim, Ewing, and others, by gradually diminish^ 

 ing reversals. Results follow : — 



Residual 











200 



3'. 



e . 



yy. 



180 

 250 

 570 



-0'-6 



-0'-8 



-2'-8 



-•0033 

 -0032 

 -0049 



Residual 



Temporary 





