FINE DOWN OF QUARTZ.
Sir David Brewster having broken in two a crystal of quartz of a smoky colour, found both surfaces of the fracture absolutely black; and the blackness appeared at first sight to be owing to a thin film of opaque matter which had insinuated itself into the crevice. This opinion, however, was untenable, as every part of the surface was black, and the two halves of the crystals could not have stuck together had the crevice extended across the whole section. Upon further examination Sir David found that the surface was perfectly transparent by transmitted light, and that the blackness of the surfaces arose from their being entirely composed of a fine down of quartz, or of short and slender filaments, whose diameter was so exceedingly small that they were incapable of reflecting a single ray of the strongest light; and they could not exceed the one third of the millionth part of an inch. This curious specimen is in the cabinet of her grace the Duchess of Gordon.