282 NOTES TO BOOK XV. 



by projecting upon one face of the crystal all the other 

 faces. This invention appears to be more curious than 

 useful. 



The Handbuck der Optik, von F. W. G. Radicke, Ber- 

 lin, 1839, contains a chapter on the optical properties of 

 crystals. The author's chief authority is Sir D. Brewster, 

 as might be expected. 



Dr. Karl Naumann, who is spoken of in Chap. ix. of 

 this Book, as the author of the best of the Mixed Systems 

 of Classification, published also Grundriss der Krystallo- 

 graphie. Leipzig, 1826. In this and other works he mo- 

 difies the notation of Mohs in a very advantageous manner. 



Professor Dana, in his System of Mineralogy, New 

 Haven (U. S.), 1837, follows Naumann for the most part, 

 both in crystallography and in mineral classification. In 

 the latter part of the subject, he has made the attempt, 

 which in all cases is a source of confusion and of failure, 

 to introduce a whole system of new names of the members 

 of his classification. 



In the Philosophy of the Inductive Sciences, B. vm. C. iii., 

 I have treated of the Application of the Natural-history 

 Method of Classification to Mineralogy, and have spoken 

 of the Systems of this kind which have been proposed. I 

 have there especially discussed the system proposed in the 

 treatise of M. Necker, Le Regne Mineral ramene aux Me- 

 thodes d'Histoire Naturelle. (Paris, 1835.) More recently 

 have been published M. Beudant^s Cours elementaire d^His- 

 toire Naturelle Mineralogie. (Paris, 1841) ; and M. A. 

 Dufresnoy's Traite de Mineralogie. (Paris, 1845). Both 

 these works are so far governed by mere chemical views that 

 they lapse into the inconveniences and defects which are 

 avoided in the best systems of German mineralogists. 



