420 Proceedings of the Royal Physical Society. 



in the history of the crystal ? Who is to say that we may 

 not some day be able to trace in such features the history of 

 changes of temperature, or of pressure, in the solutions, or 

 the record of some variations, perhaps only slight, in the com- 

 position of the solutions, giving rise thereby to important 

 variations in the surface-tensions between those solutions 

 and the growing crystal ? Again, how are we to know how 

 much of the characteristics of an individual crystal may be 

 due to solution along one set of planes, or to alternate solu- 

 tion and deposition ? There are many other possibilities of 

 this same kind which will immediately occur to anyone inter- 

 ested in crystal-genesis. It seems to me that to draw crystals 

 in " ideal symmetry " instead of as they actually are, is tanta- 

 mount to deliberate wiping out of the history of the crystal, 

 and ignoring evidence which may some day be of considerable 

 value. In the case of text-book figures, some excuse may be 

 found for this mode of working, because a student needs to 

 have the broader features kept before his eyes, and that in a 

 more or less idealised form. But when a writer has to deal 

 with a particular specimen, formed, perhaps, under very 

 special conditions, regarding which it is desirable to obtain 

 all the knowledge we can, this perversion of the facts seems 

 to me most reprehensible. I wonder what would be thought 

 of a palaeontologist who, in figuring, say, a particular speci- 

 men of a fossil fish, were to add on fins here, or scales there, 

 to make his specimen look more complete than it actually 

 was ? His reputation would soon be lost. Notwithstanding 

 this, one would think, self-evident principle, author after 

 author continues the practice. As examples of what a 

 drawing should be, I should like to instance Mligge's 

 drawings of Greenockite, — Jahh. /. Min., ii. 18 (1882), 

 which anyone who knows the habit of actual crystals of 

 this mineral must at once recognise as faithful portraits. 

 Some day we may know ivhy most Greenockites are built 

 up of irregular oscillatory combinations. But the figures 

 usually given do not afford us even as much as a hint that 

 the crystals are generally of this kind. 



Let us have portraits of the crystals, with nothing added, 

 nothing essential omitted, and with no attempt at idealisa- 



