FLUID CRYSTALS 177 



gradually lose their doubly refractive qualities. This notwith- 

 standing, they may appear as an intermediate stage in the 

 process of crystallization of the pure oleates out of pure watery 

 solutions. 



What is the Meaning of this Phenomenon ? 



Not one of those who had worked on the myelins had even 

 incidentally touched on this question. Nevertheless the solution 

 had already been given by the physicists. To one of these, 

 Professor Schenck, working in the very next institute at Marburg, 

 we went with our inquiries and found that he had been busied 

 over this very problem for the past few years. Schenck himself, 

 it is true, had not discovered the solution; that was due to 

 Professor 0. Lehmann, 1 of the Technical High School in Carls- 

 ruhe, who two years ago had entombed his findings in a huge 

 quarto monograph of 250 pages, a superb example of everything 

 that a monograph ought not to be — verbose, diffuse, wandering, 

 abundantly polemic, wanting in anything of the nature of a 

 table of contents, let alone an index ; in short, wholly mediaeval 

 save for its profuse and admirable illustrations (which neverthe- 

 less are devoid of legend or key), and for the valuable facts that 

 can be dug out of its pages. Schenck, who had been working 

 independently along the same lines, has given to the world a 

 luminous description of the whole matter, giving clearly in a 

 few pages all the important data and conclusions gained from 

 the researches of Lehmann and himself 2 and his pupils. 



The popular impression is that a crystal is essentially a solid 

 unyielding body. It has indeed been known for long that 

 metals like lead and gold can, under pressure, be forced through 

 apertures ; the same is true of solid (or crystalline) sodium, of 

 wax, paraffin, etc. But the general impression has been that 

 change of shape in these cases is essentially brought about by 

 translation, by the minute solid crystals of these substances 

 gliding one on the other, or even — as shown by my colleague, 

 Prof. F. D. Adams, in his remarkable observations on the 

 alteration in shape of marble cubes submitted to great pressure 



1 O. Lehmann, Fliissige Kristalle sowie Plastizitat von, Kristalhn, etc., 

 Leipzig, Engelmann, 1904. 



a B. Schenck, Kristallinische FlUssigkeiten und fiussige Kristalle, Leipzig, 

 Engelmann, 1905. 



N 



