54 Transactions of the Royal Society of South Africa. 
rotation within the mass, but that those molecules, which are near the 
surface resist a rotation most forcibly. This is represented in Figs. 3a 
and 3b. 
Similar experiments were made on the effects of celluloid. Its effects 
are not so well marked as that of mica. 
"When the celluloid becomes plastic it seems to have an effect oppo- 
site to that of glass. The optic axis of the molecules is rotated in the 
same way as a weak magnetic force would act on it. The central part 
of the layer seems amorphous. 
These experiments show that different substances have different 
influences on the neighbouring molecules of liquid crystals. 
