425 
Fig. 7 gives the curve (abscissae in kilovolts) which has a similar 
form as the preceding one. 
K(n 4) | : » 
Sp. 
Sese MEE Slee ee Ee Ee EESTE Pe 
| Nr 3 
Fig. 7. 
It was remarkable, that the double refraction of this modification 
is sometimes several times greater than that of the a-form. This 
may be caused by differences in density and difference in specific 
double refraction. 
5. Dispersion in the electric double’ refraction. This oceurs by 
no means always and if it does distinctly for the 3-modification. 
It may be observed by the coloured edges of the black band of the 
bead, but for a more accurate investigation special decomposition 
was required. For this purpose an arrangement was used, much 
similar to that which Prof. ZerMAN used formerly for his measurements 
of the Kerr-effeet in liquid air’). ‘ 
In the telescope of the spectroscope an ocular micrometer had 
been fixed and by means of this the position of the black band 
could be read for the different colours. Some results have been 
given below. 
Tension  Zero- Place | Place Displacement Displacement 
in volts | position; red | blue | red blue 
500, | vbs |, 8 4° 21/, | 11/2 
Baia he 49) oh: 3 4 | 13), 3), 
1) ZEEMAN, these Proceedings XIV, p. 650. 
