TABLE OF THE MODIFICATIONS OF THE PRIMITIVE CRYSTAL OF BARDIGLIONE.
According to the determination of it by Abbé Haüy
Number of the modifi- cations |
Figure of the Crystal | Angle of Incidence between the two planes, and the sides of the primitive crystal. | Angle of incidence of the new plane with each other above those of the prism on which the cleavage is least easy | Nature of the retrogradations | ||
On those on which the cleavage is most easy | On the others | On the sides of the prism, on which the cleavage is most easy | On the others, considered as auxiliary. | |||
Retrogradations along the longitudinal edges of the primitive crystal. | ||||||
1st | Primitive crystal with plane of substitution on its edge. | 135°,8′ | 134°,52′ | 89°,16′ | Retrogradation by 5 rows in breadth, and 6 laminæ in a height. | Retrogradation by 6 rows in breadth, and 5 laminæ in height. |
2d | 108°,50′ | 161°,10′ | 125°,36′ | Retrogradation by 2 rows in breadth, and 7 laminæ in height | Retrogradation by 7 rows in breadth, and 2 laminæ in height | |
3d | 115°,32′ | 154°,28′ | 125°,36′ | Retrogradation by 2 rows in breadth, and 5 laminæ in height | Retrogradation by 5 rows in breadth, and 2 laminæ in height | |
4th | 128°,31′ | 141°,29′ | 102°,58′ | Retrogradation by 2 rows in breadth, and 3 laminæ in height | Retrogradation by 3 rows in breadth, and 2 laminæ 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 laminæ in height | Retrogradation by 2 rows in breadth, and 5 laminæ in height |
As the determination of the primitive crystal of bardiglione offers some difficulties, with respect to which I have felt myself obliged to differ from the Abbé Haüy, 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 calculations of the same modifications as in the preceding table, but on the supposition that the bases of the primitive prism of this substance are rectangular,