Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/254

				Measurements.
Substances	Primitive Crystal.		Reference to Plate 12	According to Haüy	According to Bournon	By the Reflecting Goniometer
Cyanite	An oblique prism of which the plane P is very nearly a rhomb	$\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}$	Fig. 7. M on T	106° 6′		106° 15′
	Haüy		M or T on the adjacent plane, over the edge A			73° 45′
Corundum	A slightly acute rhomboid.	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	Fig. 3. P on P	86° 38′	86°	86° 4′
	Haüy & Bournon		P on P'	93° 32′	94°	93° 56′
Sulphate of Strontian	A right prism with rhombic bases.	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	Fig. 2. M on M	104° 48′		104°
	Haüy		M on the adjacent plane, over the edge A	75° 12′		76°
Carbonate of Lead	An octoheron, of which the common base of the pyramid is rectangular	$\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}$	Fig. 2. M on the opposed plane over the apex	70° 30′		71° 40′
	Haüy		M on M			108° 20′
			P on its opposed plane over the apex	62° 56′		62° 42′
			P on P			117° 18′
	A rectangular tetrahedral prism with square bases. Bournon.
Sulphate of Lead	A rectangular octohedron. Haüy.	$\left.{\begin{matrix}\ \ \end{matrix}}\right\}$	Fig.2 P' on P' P on P	72° 28′ 109° 18′
	A right tetrahedral rhomboidal prism with rhombic bases. Bournon.	$\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}$	Fig. 11. P on P		101° 30′
			P on the adjacent plane over the edge a		78° 30′
	A right prism with rhombic bases. W.P.		Fig. 13. P' on P'			76° 18′
			P on the adjacent plane over the edge a			103° 42′

Oxide of Tine

Pl. 12. Fig. 1.

The crystals of this substance admit of cleavage parallel with all the sides of the common prism, and of its diagonals, as well as the faces of the primitive octohedron, which is obtuse. The first is