Magneto-optic Phenomenon. 

 Table I. 



261 



9. 



eo- 



3'. 



'*J&- 



e. 



e o- 



3'. 



«o/3'. 





Cobalt 



§=93C 



>. 





Steel. 



§=930. 





29° 



-109 



894 



-•0121 



31° 



-10-7 



983 



-•0109 



98 



-110 



894 



-•0123 



101 



-10-8 



979 



-•0111 



167 



-11-2 



894 



-•0126 



147 



-10-7 



964 



-•0111 



220 



-11-2 



897 



-•0125 





Nickel 



§=820 







Iron. 



§=930. 





27° 



-49 



472 



-•0103 



27° 



-13-0 



1528 



-•0085 



99 



-54 



452 



-•0118 



78 



-12-3 



1524 



-•0080 



162 



-52 



426 



-•0123 



120 



-12-1 



1523 



-•0080 



245 



-4-8 



330 



- -0146 



164 



-136 



1517 



-0090* 



282 



-3-2 



198 



-•0163 



increases! : the self-demagnetizing action thereby decreases 

 at higher temperatures, so that the distribution approaches to 

 uniformity, and the values of 5 ar *d j' tend to become equal. 

 It follows that even if e /3 be constant, e /3 / will none the 

 less increase with 0, and this is what the numbers for nickel 

 actually do. Experiment therefore does not contradict the 

 highly probable assumption that K is practically constant for 

 nickel as well as for the other metals. At temperatures above 

 280° no more data could be obtained with sufficient accuracy. 

 But on further heating I observed a rapid decrease of both 

 rotation and magnetization until both vanished for tempera- 

 tures above 335°, only to reappear simultaneously on cooling. 

 This qualitative experiment affords a convincing instance of 

 the close relation between both quantities. The result of this 

 paragraph may be thus expressed : — 



III. The variation of the constant K with temperature is 

 practically zero ; it is certainly less' than a few per cent, per 

 100°, and therefore much below that of the electric resistance 



* It is quite possible that a thin colourless film of oxide begins to 

 cover iron about 164°, which would explain the larger rotation here given ; 

 the temperature corresponding to a pale yellow is stated to be about 220° 

 on heating for a short time. See Loewenherz, Zeitschr. f. Instrum. Kunde, 

 ix. p. 316 (1889). For cobalt, and especially for nickel, these temperatures 

 happen to lie much higher. 



t It may not be superfluous to remark that from the values of 3'' given, 

 nothing more than a qualitative conclusion may be drawn as to the 

 thermomagnetic behaviour of the metals ; for the self-demagnetizing 

 action of the rather short ovoids tends to diminish any temperature- 

 variations of their magnetization. For quantitative determinations in 

 thermomagnetism the metals have to be used in forms fulfilling the con- 

 dition of perfect or approximate endlessness. 



