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ON THE SPACE-LATTICE OF LIQUID CEYSTALS. 
By J. Steph. van der Lingen. 
Introduction. 
During the past two years numerous experiments have shown that 
solid crystals cause interference phenomenon when Eontgen rays are 
passed through them, and that the positions of maximum interference in 
the pattern depend upon the direction of transmission of the rays through 
the crystals, that is, they are dependent on the space-lattices of the 
crystals.''' 
Liquid crystals, according to O. Lehmann, only have space-lattices 
when they are polyhedral in form, similar to solid polyhedral crystals, and 
when thin layers of the crystalline solution are placed between similar 
crystalline plates, each of which must have the same orientating effect on 
the molecules of the solution. 
In the second case the structure of the space-lattice is not necessarily 
the same as in the first case. If these solutions are placed between 
amorphous plates (glass plates) or dissimilar crystalline plates, then the 
effect of these plates on the molecules causes the solution to become 
pseudo-isotropic. In this case only the principal axis of the molecules lies 
in a fixed direction ; the secondary axes lie in all directions. 
The principal axis is the axis round which the molecules are most 
easily rotated. According to 0. Lehmann, it is perpendicular to the 
plane of the molecules, which are in all probability disc-shaped. 
When ordinary light is transmitted through such a pseudo-isotropic 
liquid crystalline layer, then it causes the same optical effects as a uniaxial 
crystal cut perpendicular to its optic axis. 
The question now arises, " Do changes in the molecules themselves 
cause the different forms of crystals of the same substance, or do aggrega- 
tions of a different order of the same unchangeable molecules cause the 
* W. Friedrich, P. Knipping, and M. Laue, Miinch. Sitzber., 1912, p. 303 ; M. Laue 
and F. Tank, Ann. d. Phys. (4), 41, 1003, 1913 ; W. H. and W. L. Bragg, Proc. Cambridge 
Phil. Soc, 17, 43, 1913 ; T. Terada, Tokyo Math. Phys. Soc, 7, 60, 1913. 
