( 615 ) 



The last column contains the angle of the plane of polarisation 

 of Nic^ derived from the other columns, for the adjustment at equal 

 intensity, with this plane of polarisation wlien Nic^ crosses Nic^ 

 and JSfic,. In general the adjustment for the wavelength F was 

 less accurate than for D on account of the slighter intensity in 

 the spectrum for tiie former wavelength. The greater deviation 

 which the latter angle <p siiows for the wavelength F in table I 

 from the preceding ones, may be explained from the differetice in 

 temperature. 



The results thus obtained have been joined in table II. 



The observations of series VI ceased after the adjustments for 

 the wavelength D at ll.°24, because after this the temperature 

 fell below the critical temperature, which was determined at 11 .°1 8 ^) 

 (cf. § 3 beginning). 



The difference between the angles cp for Series V 12.°55 and 

 Series VI 12.°54, wavelength D, is owing to this that between 

 these observations a slight modification in the position of the lenses 

 jLj, Lf, has taken place. The observations mentioned here may serve 



1) Comparison of this value of the critical temperature with that of other 

 investigators indicates th at the critical temperature of the admixture (cf. § 2 

 p. 612, note 1) does not lie much higher than that of ethylene. 



42 



Proceedings Royal Acad. Amsterdam. Vol. X. 



