SOME RECENT PROGRESS IN CHEMICAL 

 AND STRUCTURAL CRYSTALLOGRAPHY 



By A. E. H. TUTTON, M.A., D.Sc. (Oxon.), F.R.S. 



In no branch of science has the refining influence of sceptical 

 criticism been more active than in crystallography. Time after 

 time in the history of the subject has a theory, founded on a 

 keen estimation of the probabilities rather than on rigid and 

 then unattainable proofs, been generally rejected, and only now 

 are we beginning to obtain evidence of a truly unassailable 

 character which places the oldest of these theories on a firm 

 basis of fact. In the year 1669, Nicolaus Steno observed that 

 the angles between the corresponding faces of different specimens 

 of rock crystal were equal, and within ten years subsequently 

 Guglielmini established to his own satisfaction that the con- 

 stancy of the interfacial angles of the crystals of the same 

 substance was a general law of nature. Yet for a hundred years 

 afterwards the idea was rejected as absurd, the great variation 

 in the relative development of faces, which causes such remark- 

 able difference in the exterior appearance of crystals, causing its 

 rejection even by such great minds as those of Boyle (1690) and 

 Werner (1770), in the absence of adequately precise means of 

 measurement. The invention of the contact goniometer, about 

 the year 1780, by Carangeot, assistant to Rome de l'lsle, at 

 length, however, compelled its acceptance as a fact, within the 

 limits of accuracy of that instrument. 



In another couple of years the important work of the Abbe 

 Haiiy, Professor of the Humanities at the University of Paris, 

 was made known to the French Academy, and published in 1784 

 in a volume entitled Essai dune Theorie sur la Structure des 

 Crystaux. Haiiy may truly be called the father of crystallography, 

 for he showed that all the varieties of crystalline forms could 

 be referred to a few simple types of symmetry ; he enunciated 

 the laws of symmetry, proved that all the apparently different 

 forms of the same substance are based on one of these simple 



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