( 302 ) 



The fact that d^ is almost the same I'oi' all ^^ases v.irh small 

 coefficients of' magnetisation seems favourable to Mascart's formula 

 which leads to a formula for interpolation of the form (I) ; coeffi- 

 cient ;' in this form is related in a simple way to (/j, and is acc(U"- 

 diug to Joubin's investigation ^) in a high degree dependent on the 

 coefficient of magnetisation. 



If we express the rotatory constants in circular measure instead 

 of minutes, we obtain the following coefficients 



UVO,,=.^+^^ 



1 + 



(h 



(I) 



10.1" 6/ ^ -^ + -^ 



/2 A* 





A3 



1 4- 



(11) 



For practical use the following table may serve, which gives the 

 magnetic rotatory constants for diffeient wave-lengths, expressed in 

 minutes and multiplied by 10''. 



Wienek) this result may easily be explained without assuming a negative rotatory 

 constant. It is not improbable that Quincke's result may be accounted for in a 

 similar way. 



') According to a formula for iuterpohition (11) with two terms, which is not 

 mentioned in this paper. 



2) Quincke's constants relative to air. Toplee and Hennig. Wied. .\nn. 34, p. 790 

 (18SÜ). 



') JouBiN. These Paris 1SS8, p. 24. Ann. de Ch. et de Ph. (6) 10, p. ÏS (1SS9). 



