XIII.—On the Decomposition and Dispersion of Light within Solid and Fluid Bodies

Abstract

Hauy, and other mineralogists, observed the two colours which are visible in several varieties of fluor-spar. He regarded the two tints as complementary, and explained them, as he did every other analogous phenomenon, by a reference to the colours of thin plates. In describing a species of dichroism noticed by Dr Prout in the purpurates of ammonia and potash, Sir John Herschel ascribes the green reflected lights “to some peculiar conformation of the green surfaces producing what may be best termed a superficial colour, or one analogous to the colour of thin plates, and striated or dotted surfaces.” And he adds—“A remarkable example of such superficial colour, differing from the transmitted tints, is met with in the green fluor of Alston Moor, which, on its surfaces, whether natural or artificial, exhibits, in certain lights, a deep blue tint, not to be removed by any polishing.”