Simpler Methods in Crystallography. 419 



that it must be done by inspection, with the aid of a good 

 lens, and with maps on more than one projection before one. 

 In some cases I have found three stereograms useful, a, b, 

 and c projections, and one or more gnomonograms, in addition, 

 to refer to for the all-important matter of zones. With aids 

 such as these, and with an eye trained to estimate angles 

 and a hand trained to delineate them, it is not really diffi- 

 cult to make a series of freehand drawings of face after face 

 of the crystal, and to join these one on to the other in the 

 drawing until the whole solid is, so to speak, unfolded into 

 one plane, so as to be like a crystal-net. By this means 

 the planes of symmetry can soon be made out ; and if the 

 observer have a good knowledge of the habit of the species 

 under consideration, it ought not to be long before some of 

 the leading forms of the crystal are determined by inspec- 

 tion. Then, a knowledge of the zonal relation of the faces, 

 got by a careful study of the maps, will enable him to carry 

 the determination further ; and not unfrequently this may 

 sufi&ce for making a drawing of the crystal itself. 



Here, perhaps, is an appropriate place for some observa- 

 tions I have long wished to make upon what may be termed 

 the ethics of crystal-drawing. To a man of science, interested 

 not only in a crystal as a thing of beauty in itself, but as 

 the outcome of a long series of interesting changes in the 

 past, and bearing within itself much which, if properly 

 interpreted, would serve to throw valuable light upon 

 many physical problems of great interest, one would have 

 thought it would be a point of the very first importance to 

 delineate that crystal as exactly as possible. Instead 

 of doing this, the usual practice seems to be to 

 generalise the drawing as much as possible, reducing any 

 inequalities (or " distortions ") to which the crystal may have 

 grown, and, generally, they seem to wish to represent it in 

 what people are pleased to call " ideal symmetry." Surely 

 to do this is simply to wipe out evidence which may, sooner 

 or later, lead to the discovery of important principles. Who 

 is to know, in such a case, how much light the abnormal 

 development of one set of faces, as compared with other of 

 the same form, may cast upon some otherwise obscure chapter 



