Dichroism

Dichroism (Gr. dis, 'twice,' chroma, 'a colour') is a term chiefly used in Crystallography to designate the property which many doubly-refracting crystals possess of exhibiting different colours when viewed in different directions. It, or the allied term Dichromatism, has also been applied to those fluids which appear of different colours when viewed by reflected and refracted light; when seen in thick or thin layers, &c. For example, venous blood, or any blood impregnated with carbonic acid, hydrogen, or nitrogen, appears, when seen in moderately thin layers, to be of a purple colour; while in extremely thin layers it appears green.—For Dichroite, see CORDIERITE.