TERMINOLOGY. 



at E the acute, solid angles ; the lateral edges at H the obtuse, those 

 at G the acute, lateral edges ; the edges B are the greater, and C 

 the lesser, terminal edges. 



The axes, also, are the same as in the right rhombic Prism. 



The individuals belonging to this class will differ in the inclina- 

 tion of M on T, and in the relative lengths of the edges C,B, and H. 



Sulphate of Lime, Heulandite, Wolfram, &c. are seen in crys- 

 tals of this form. 



. 44. THE OBLIQUE RHOMBIC PRISM. 



The oblique rhombic Prism is a quadrangular prism, 

 whose bases are equal rhombs, and whose lateral faces are 

 equal oblique-angled parallelograms. 



Fig. 32 is supposed to lean in the 

 direction O, A, so that the terminal 

 plane P forms an obtuse angle with 

 the edge H. The planes M M' may 

 meet at an acute, or an obtuse angle. 

 For the convenience of description, 

 the solid angle at A will in either 

 case be called the acute solid angle, 

 that at O, the obtuse solid angle ; 

 and those at E, the lateral solid an- 

 gles. The edges B, are called the 

 acute terminal edges, and those at 

 D, the obtuse terminal edges. The 



edge H and its opposite, are the oblique edges of the prism, and G 

 and its opposite, the lateral edges of the prism* 



* It is obvious, that the bases of a rhombic Prism, whatever maybe its 

 inclination from a perpendicular, are capable of being disposed upon 

 that prism in a variety of ways. But as there are but two modes of 

 disposition observed by them, among the crystals belonging to the class 

 now under consideration, it will be sufficient to confine ourselves to their 

 particular elucidation. 



In order to ^discover the more readily their different positions, 

 there is drawn towards the middle of the two oblique rhombic Prisms 



