Count de Bournon on BardtgUone. 



387 



Tx\BLE OF THE MODIFICATIONS OF THE PRiMITIVE CRYSTAL 

 OF BARDIGLIONE, 



According to the determination of it by the Abbe Haiiij. 



Primitive Crystal. A rectangular tctrahcdral prism, the terminal faces of which are rectangles, 

 the sides of which are in the ratio of 16 to 13.4, and the height of which is unknown. 



Number 

 of the 

 modifi- 

 cations. 



Fig-ure of the 

 crystal. 



AHgles of incidence between the 

 new planes, and the sides of the 

 primitive crystal. 



Angle of inci- 

 dence of the new 

 planes with each 

 other above those 

 of the prism on 

 which the clea- 

 vage is least easy. 



Nature of the retrogradations. 1 



On the sides of 

 the prism, on 

 which the clea- 

 vage is most easy. 



On the others, 



considered as 



at iiliary. 



On those on 

 which the clea- 

 vage is most easy. 



On the others. 



Retrogradat 



ons along the edges of the prim 



itive crystal. 





1st. 



.5 

 1 



1 



•a 



. . 135-, 8' . . 



^. . 134°, 52'. 5 



. . 89% 16'. . 



Retrogradation 

 by 5 rows in 

 breadth, and 6 

 'aminas in height. 



Retrogradation 

 by 6 rows in 

 breadth, and 5 

 lamins in height. 



2d. 



. . 108", 50'. . 



. . 161% 10'. . 



. . 142% 20'. . 



Retrogradation 

 by 2 rows in 

 breadth, and 7 

 laminae in height. 



Retrogradation 

 by 7 rows in 

 hreadth, and 2 

 laminae in height. 



3d. 



. . 115', 32'. . 



. . 154% 28' . . 



. . 125% 36' . . 



Retrogradation 

 by 2 rows in 

 breadth, and 5 

 laminx in height. 



Retrogradation 

 by 5 rows in 

 breadth, and 2 

 lamina; in height. 



4th. 



. . 128% 31'. . 



. . 141% 29' . . 



, . 102% 58' . . 



Retrogradation 

 by 2 rows in 

 breadth, and 3 



Retrogradation 

 by 3 rows in 

 breadth, and 2 

 lamina in height. 



5th. 



. . 140*, 4'. . 



. . 129% 56*. . 



. . 79% 52' . . 



Retrogradation 

 by a single row. 



Retrogradation 

 by a single row. 



6th. 



. . 161°, 29'. . 



. . 108% 31'. . 



. . 37% 2'. . 



Retrogradation 

 by 5 rows in 

 breadth, and 2 

 laminae in height. 



Retrogradation 

 by 2 rows in 

 breadth, and 5 

 lamina; in height. 



As the determination of the primitive crystal of bardigHone offers some 

 difficulties, with respect to which I have felt myself obliged to differ from 

 the Abbe Haiiy, whose decisions are of great weight in this science; and 

 as it is very possible that I may be mistaken, I have given above, the calcu- 

 lations of the same modifications as in the preceding table, but on the suppo- 

 sition that the bases of the primitive prism of this substance are rectangular, 



3 c2 



