134 



also crystals may be reckoned, are all facts which give the con- 

 viction that an explanation of crystallonomical phenomena, pre- 

 supposing an analogous internal structure for crystals such as those 

 dealt with in the above, will certainly be successful. 



It was precisely for this purpose that in the middle of the nine- 

 teenth century Bravais began his famous studies on space-lattices. 

 With great acumen and in a most ingenious way he really developed 

 these views gradually for the explanation of the most important 

 properties of crystalline substances; later on his methods were 

 followed with admirable success especially by French authors, for 

 the explanation of a great number of physical phenomena, and it 

 cannot be denied that Bravais' simpler and more transparent 

 ideas have been far more effectual for the development of the science 

 of crystalline matter, than those concerning the more general, but 

 incomparably more complicated regular arrangements of Sohncke, 

 Von Fedorow and Schoenflies. Another cause of this is also 

 the particular fact that up till now there had been no method avai- 

 lable which allowed in any concrete case of making a definite choice 

 between the numerous structures possible in the same crystal-class. 

 In most cases it remained therefore merely a question of personal 

 preference, which grouping of particles an observer wished to attribute 

 to the crystal-species under investigation; and it is conceivable 

 that under such conditions most crystallographers felt inclined 

 rather to adopt the simpler views of Bravais, than the much more 

 complicated doctrine of the regular arrangements in space, discussed 

 in the above 1 ). 



15. The problem of giving a rational deduction of the crys- 

 talline structure from the chemical composition of the crystal has 

 puzzled investigators ever since early times. It has been more in 

 particular the deduction of the observed symmetry which originally 

 occupied most workers in this field, and in this respect the endea- 

 vours of Groth 2 ) in 1870 are worthy to be remembered, who tried 



1) Cf. also: G. Friedel, Bull, de la Soc. Miner. 31. 326. (1907); G. W. 

 Wulff, Zeits. f. Kryst. 47. 607. (1910). 



W. J. Sollas, Proc. Royal Soc. 63. 270. (1898); 67. 493. (1900); 69. 294. 

 (1902; 80. A. 267. (1908); Brit. Assoc. Rep. (1907), p. 481. 



G. Cesaro, Bull. Acad. R. beige, (1901), p. 303; P. Groth, Zeits. f. Kryst. 

 54. 65, 498. (1914); E. Riecke, Phys. Zeits. (1900). /. 277; Ann. der Phys. 

 3. 545. (1900). 



2) P. Groth, Ber. d. d. Chem. Ges. 3. 449. (1870). 



