Determination of Diallage. 129 



name *. Modern mineralogy itself can scarcely be said to go be- 

 yond that period. Smaragdite was joined to Felspar by ROME' DE 

 I/ISLE, and to Schorl by DE BORN. On account of the difference in 

 the perfection of its lamina?, HAUY gave it the name of Diallage f , 

 and thus introduced it into the mineralogical systems. When 

 HAUY was publishing the first edition of his Traite, he was not yet 

 acquainted with those substances which in the second he calls Dial- 

 lage metattoide ; but he exhibits among his Diallage, under the 

 very same denomination, the varieties of Hypersthene (prismatoi- 

 dal Schiller-spar), which he afterwards established as a par- 

 ticular species. WERNER ^ does not acknowledge Diallage as 

 a particular species, but considers it as a variety of granular Acti- 

 nolite. Very little, at that period, had yet been prepared for a 

 more accurate examination of the natural properties of minerals, 

 and in determining new varieties, any principle upon which it was 

 possible to rely, was almost entirely wanting. Destitute of 

 the means now afforded to the mineralogist, WERNER has, in the 

 present instance, displayed that remarkable acuteness, by which 

 he often discovered the close natural-historical relation of certain 

 minerals of a very different aspect, whilst, on the other hand, he 

 pointed out a difference between substances, very much resem- 

 bling each other, which it required a long period of time to de- 

 monstrate by examining their properties with the greatest accu- 

 racy. But even WERNER has often been deceived, by founding 

 his determinations upon mere ocular inspection ; and we shall be 

 the more disposed to abandon so deceitful a method of obser- 

 vation, the more we are able to ascertain those properties of mi- 



* Voyages dans les Alpes, t. v. 1318. 

 f Traite, t. iii. p. 125. 



{ HOFFMANN, " Handbuch der Mineralogie,'" continued by BHEITHAUPT, 

 Th. ii. 2. s. 800. 



VOI X. P. I. R 



