THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



NOVEMBER 1849. 



XLI. On the Notation of Crystals. 

 By Edward J, Chapman, Esq.* 



IT may be fairly assumed that an efficient system of crystal- 

 lographic notation should comprise the following essential 

 points, — simplicity, brevity, and capability of being verbally 

 expressed. It should be sufficiently simple as to be retained 

 and applied with the slightest possible effort of the memory, 

 and sufficiently brief as to admit of being placed upon the 

 usual drawings of crystals. The symbols, moreover, of which 

 it is composed, should be so constituted as to be readily con- 

 vertible into ordinary language. 



There can be but one opinion as to the necessity of the first 

 of these conditions, even if the utility of the two latter be 

 questioned. It is, however, very desirable, especially for those 

 who are studying the science, that the second condition should 

 also be fulfilled ; for, by the arbitrary and irregular lettering 

 of crystals, much trouble and chance of misconception is ob- 

 viously occasioned to the student — sometimes one, and some- 

 times another letter, being employed to designate the same 

 kind of plane ; and that, frequently, within the compass of a 

 few pages. The importance, furthermore, of the third con- 

 dition is so great, that the little attention which seems hitherto 

 to have been paid to it is much to be wondered at. In ad- 

 dressing a class, amongst numerous other instances, it is ab- 

 solutely essential that the notation should be a verbal one. 



Of all the systems at present in use, that of Levy and Du- 

 frenoy can alone be said to embody the above desiderata; but 

 its merit in this respect is, on the other hand, marred by the 

 following objections, which form a serious drawback to its 

 adoption. In the first place, totally different planes in the 

 same crystallographic group are frequently denoted by a 



* Communicated by the Author. 

 Phil. Mag. S. 3. Vol. 35. No. 237. Nov. 1849. Y 



