Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/399

TABLE OF THE MODIFICATIONS OF THE PRIMITIVE CRYSTAL OF BARDIGLIONE.

According to the determination of it by Abbé Haüy

Primitive Crystal. A rectangular tetrahedral prism, the terminal faces of which are rectangles, the sides of which are in the ratio 16 to 13,4, and the height of which is yet unknown.

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,