LIQUID CRYSTALS. 127 



without loss of orientation in the particles. In other words, 

 in answer to the question- with which we started, it is 

 suggested both that crystals may be liquid, and that liquids 

 may be crystalline. 



It is scarcely necessary here to follow the author through 

 the remainder of his inquiry ; let it be sufficient to mention 

 that the three sorts of liquid crystals behave like isomor- 

 phous substances and mix together in all proportions ; that 

 they always separate as pure drops from the liquid into 

 which they can be converted by heating, and do not 

 possess the power of dissolving substances which are soluble 

 in the latter. 



It will now be clear that Lehmann's definition of a 

 crystal is no longer the current one. The regular arrange- 

 ment of its particles into a homogeneous anisotropic solid is 

 not an essential but an accident which may occur under 

 certain favourable conditions. 



The essential characteristic of a crystal is, according to 

 his view, the power of growing in a supersaturated solution 

 which is possessed by all crystals but not by colloids. 

 Some liquids also may be crystalline, others may be colloids, 

 the majority are probably the latter. 



If I may venture on a word of criticism I would urge 

 that here we are concerned partly with a question of words. 

 It will be wise to retain the names crystal and crystalline in 

 their old significations, rather than to extend them so as to 

 include the birefringent liquids whose existence has been 

 established by Lehmann. It may be that these remarkable 

 drops are examples of liquid matter in which particles while 

 free to move are compelled to preserve the same orienta- 

 tion, and differ in this respect from ordinary liquids. But 

 whether this peculiarity of structure, whatever may be its 

 nature, is really analogous to that of solid crystals is a 

 question in which it will be better not to commit our- 

 selves to an answer by applying the same name to both 

 until more is known about the structure both of liquids 

 and solids. 



