LIGHT FROM QUARTZ.
Among natural phenomena (says Sir David Brewster) illustrative of the colours of thin plates, we find none more remarkable than one exhibited by the fracture of a large crystal of quartz of a smoky colour, and about two and a quarter inches in diameter. The surface of fracture, in place of being a face or cleavage, or irregularly conchoidal, as we have sometimes seen it, was filamentous, like a surface of velvet, and consisted of short fibres, so small as to be incapable of reflecting light. Their size could not have been greater than the third of the millionth part of an inch, or one-fourth of the thinnest part of the soap-bubble when it exhibits the black spot where it bursts.