682 Dr. A. E. H. Tutton [March 14, 



stances, expect that some of the properties of a crystal, dependent on 

 the space-lattice formation on lines of definite symmetry, such as 

 the optical property of double refraction and polarization of light, 

 would be developed and exhibited, while the production of exterior 

 plane faces would l)e either only partial, with rounded edges and the 

 exhibition of plasticity and viscosity, or would not be achieved at all, 

 the objects produced being still fluid. One cause of such a condition 

 of partial success at crystallization might well be that the substance 

 was composed of a large number of atoms arranged in a long chain, 

 such as the well known " long chain compounds " of organic chemistry, 

 which would offer considerable resistance to marshalling. The author 

 believes that herein lies the explanation of the remarkable " liquid 

 crystals " which Professor Lehmann has made the subject of bis 

 particular study, many of which are of just such long-chain character. 

 By the kindness of Professor Lehmann, who has sent over speci- 

 mens of some of the most characteristic of his substances for the 

 special purpose of this lecture, and of Mr. Poser, of Messrs. Zeiss, 

 who construct an admirably convenient form of heating microscope 

 and projection arrangement for demonstrating the formation of 

 liquid crystals and their l)ehaviour in polarized light, it is possible 

 to exhibit some of the typical phenomena of these interesting objects 

 on the screen. The substances in question are chiefly such as form 

 two or more polymorphous forms, each stable within a limited range 

 of temperature, and the liquid crystals are usually the second phase 

 observed on allowing the truly liquid heated sul)stance to cool ; the 

 liquid crystal phase is produced at a definite temperature during the 

 cooling, and persists during a definite interval of temperature during 

 the continued cooling. It either exhibits distinct attempts at the 

 formation of pyramidal or prismatic crystals, more or less rounded 

 at their edges, as in the case of ammonium oleate shown on 

 the screen (Fig. 4), or manifests itself as doubly refractive and 

 brilliantly polarizing drops or streams, such as the drops of para- 

 azoxyanisol, which are set rotating independently by the addition of 

 a little colophon ium, as demonstrated in brilliant polarization colours 

 on the screen ; it then suddenly passes with further cooling into the 

 final solid phase, often with the production of brilliantly coloured 

 acicular crystals, as in the case of para-azoxyphenetol exhibited on 

 the screen, or of l^eautif ul star-like or flower-like apparitions, radiating 

 from innumerable centres all over the field, as in the exceedingly 

 beautiful case of cholesteryl acetate. The view here put forth is 

 apparently in agreement with that of Lehmann himself, as most 

 recently expressed both in letters to the lecturer and in a memoir of 

 July 27, 1912, to the Heidelberg Akademie der Wissenschaften, in 

 which he says that in all probability : " Die Rundung der Formen 

 hange zusammen mit der Plastizitiit der Stoffe und habe ihren (irund 

 in unzureichender molekularer Richtkraft, welche wohl geniigt, ein 

 Raumgitter herzustellen, nicht aber regelmiissige Treppenstufen, wie 



