428 Corresjjondence — Mr. T. W. Banly. 



ON A NEW METHOD OF WRITING CRYSTALLOGRAPHIG 

 FORMULiE. 



Sir, — All mineralogists, or at any rate all whose hard lot it is to 

 be commencing the study of mineralogy, must cordially agree with 

 Mr, Eutley that it " would doubtless be productive of much satis- 

 faction if a universal system of crystallographic notation could be 

 adopted." There is no doubt that the many difficulties with which 

 mineralogy unnecessarily bristles are largely due to confusion, re- 

 sulting from the conflicts of rival methods of classification and 

 nomenclature, and of different systems of crystallography. I have 

 carefully compared the new method unfolded by Mr. Eutley in the 

 Geol. Mag. for July (p. 299) with the principal systems now in 

 vogue, and as it does not seem to have merits so pre-eminent as to 

 insure its sweeping all others from the field, it is doubtful whether 

 its partial acceptance will not place one more obstacle in the 

 student's path. 



The system of crystallography originated, I believe, by Dr. 

 Whewell, perfected by Professor Miller, and accepted by Professor 

 Haidinger, contrasts more favourably even than that of Naumann, 

 with Mr. Eutley's new method ; and I am surprised that no reference 

 is made to it by the author. T question much whether the concise 

 hieroglyphs of Mr. Eutley will be found so easy to imitate as the 

 more accustomed symbols of Naumann, or the plain indices of 

 Miller ; — both these have the immense advantage of being already 

 familiar to mathematicians, and without some mathematical skill, 

 extended acquaintance with crystallography is well nigh hopeless. 

 The introduction of this new method, too, involves the replacement 

 of certain known symbols by others hitherto used with different 

 meanings, as well as the alteration in value of some that are re- 

 tained. Thus the substitution of a dot for the usually accepted sign 

 of infinity is a loss rather than a gain : a dot, in manuscript, 

 generally causes perplexity, which the close neighbourhood of small 

 vertical and horizontal strokes will, in the new method, much intensify. 



In the calculations that occur in the more advanced parts of 

 crystallography, the inferiority of the " new method " to that of 

 Professor Miller becomes more and more apparent. We do not 

 suppose that Mr. Eutley intends to limit the application of his 

 system to the mere beginning of crystallographic science ; — to as- 

 sume this would be at once to pronounce the system unprofitable. 

 Professor Miller's indices are perfectly adapted for employment in 

 mathematical investigations, and practical numerical results are at 

 once obtained by simple substitution at the end of such process. 

 But if Mr. Eutley's " prolonged vertical cross " and " curved line " 

 take the place of the " conventional distances m and n," numbers 

 must be substituted for them throughout the calculations, the labour 

 of which is thereby greatly increased ; for these difficult signs 

 would undergo a process of natural deterioration in the mazes of 

 hastily, perhaps carelessly, written mathematical analysis, and 

 would, certainly, be illegible at the end of it. 



Downing College, Cambridge. T. W. Danbt, M.A. 



