120 Mr. William Phillips on the Oxyd of Uranium, 



Fourth Modification. 



This modification, like the preceding, consists in a decrease on 

 each solid angle of the primitive prism by an isosceles triangular 

 plane, but which, instead of being placed, as in that modification, 

 more on the lateral edges than on the terminal faces, inclines more 

 on the terminal faces than on the lateral edges. On the crystal 

 represented by fig. 42, the planes of this modification are per- 

 fectly brilliant. 



Fifth Modification. 



By this modification the terminal edges of the primitive prism 

 are replaced by trapezoidal planes tending to form an octohedron, 

 fig. 46. The succeeding figure shews the planes of this, in com- 

 bination with those of the second modification, or the acute 

 octohedron. The crystals described by figs. 46 and 47 are nu- 

 merous, brilliant, and well defined : they rarely exhibit any lateral 

 striae, but are so minute as to render it impossible even to approx- 

 imate the real admeasurement of the angles formed by the meet- 

 ing of any two of their planes. An attentive examination induces 

 the belief of their being somewhat more obtuse than the regular 

 octohedron ; and they are so delineated. 



