rhomboids of the carbonate of lime, the bitter-spar, and the brown-spar, which had previously been considered to be alike, and conceiving them to be erroneously quoted, as in fact they were, I submitted to the reflecting goniometer some cleavages of the two former, not having a portion of the latter adapted to its use. I afterwards called on my friend Arthur Aikin, Esq. who shewed me an account of the exact admeasurements obtained by Dr. Wollaston, and had the satisfaction of convincing him that those obtained by me perfectly coincided therewith.
I possess thirty-eight varieties of crystals of quartz, resulting from the combinations of eleven modifications on the primitive rhomboid; and of the sulphate of barytes I have one hundred and thirteen varieties, the result of eighteen modifications of the primitive crystal; the former are principally foreign, the latter chiefly from the north of England.
