1315 
In this integral the function #'(rj7) is zero without the sphere of 
action, therefore this integral has only to be extended to this region. *) 
Thus the abnormal character, stated by KAMERLINGH ONNES and 
Krrsom, cannot be explained by a function of disturbance as a con- 
sequence of the accidental deviations. 
Physics. — “Contributions tosthe research of liquid crystals.” By 
Dr. W. J. H. Morr. and Prof. L. S. ORNSTEIN. (Communicated 
by Prof. W. H. Juttus). 
(Communicated in the meeting of October 28, 1916). 
1. The extinction of para-azoxyanisol in the magnetic field. 
Vorer has devoted a circumstantial report to the liquid crystals 
in the Physikalische Zeitschrift XVII 1916. In this report he points 
specially to the fact that a great uncertainty still exists on the 
influence exercised by a magnetic field on the extinction. For this 
reason we further examined the extinction. 
We will provisionally explain our method in this communication, 
and mention some of the results attained, and add a few remarks 
on a possible explanation of these results. 
§ 1. Method of observation. 
The extinetion was measured with the aid of the galvanometer 
and the thermopile described by one of us formerly.’) These sensitive 
instruments have the great advantage of indicating quickly within 
two seconds, and so they enable us to follow the changes in the 
‚ liquid erystals proceeding slowly, but nevertheless so quickly that 
they must necessarily escape the observer’s attention. 
These very changes however are of great interest in order to under- 
stand the phenomena under consideration. 
The substance is heated in a small electric oven, consisting of a 
strip of copper AA coiled at the two ends with resistance wire. 
By regulating the current sent through these coils each desired 
1) According to the explicit calculation of g, executed by one of us, the solid 
character is denoted by 7—1 e—kr, where k = 0 for the critical point. Comp. ZERNIKE, 
The clustering tendency of the molecules in the critical state and the extinc- 
tion of light caused thereby. These Proc. XVIII p. 1520. 
2) W. J. H. Mott. Proc. Kon. Acad. v. Wetensch. May and Nov. 1913. Mrs. Kipp 
and Sons were so kind as to put the apparatus at our disposal. 
84 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
