Theory of CryJlaUifation. 389 



2. Elongated Oriental (Jig. 72.). 

 De l'lfle Cryjlallograpbie, torn. ii. p. 21^. A. 



GeomeL charaEl. Refpe£tive inclinations of the triangles 

 IAS, IBS, 139 54/. Angles of the triangle I A S, 

 A = 22° 54', I or S = 78 48'. 



This form is the effea of a decrement by a Ample range of 

 fmall quadrangular prifms on all the edges of the bafes of the 

 nucleus. Let q d (Jig. 67.) be the fuperior bafe, undi- 

 vided into fmall triangles, which reprefent the analogous 

 bafes of fo man} moleculae. The edges of the laminae of 

 fuperpofkion will correfpond fucceffively to the hexagons 

 Jjilmnr, eku xy v, &c. ; from which it evidently follows, 

 that the fubtra&ions take place, as I have faid, by ranges of 

 fmall parallelopipedons or quadrangular prifms, compofed 

 .each of two triangular prifms. 



3. Minor Oriental. 



Gcomet. cbaratl. Dodecaedron formed of two right pyra- 

 mids lefs elongated than thofe of the preceding variety. The 

 triangles which correfpond to IAS, IBS,, are inclined to 

 each other 122 36'. In each of thefe triangles the angle of 

 the fummit is 31 , and each of the angles at the bafe is 



74° 3°'- 



The law from which this variety remits differs from that 



which produces the preceding, as it determines a mixed 



decrement by three ranges in breadth and two ranges in 



height. 



4. Enncagonal Oriental (jig. 73-)> 



Geotnet. cbaratl. Inclination of each fmall triangle, fuch 

 as cqi to" the adjacent bafe aciplbged, 122 18 . 



It is the elongated oriental the fummits of which are 

 replaced by two faces, parallel to the bafes of the nucleus, 

 with the addition of fix fmall ilbfceles triangles cqi, Ibf, 

 •v z vi, See. the three fuperior of which are alternate in po- 

 rtion with the three inferior. Thefe triangles rcfult from a; 

 decrement by three ranges of fmall quadrangular prifms on 

 C c 3 the 



