Various, Popular Science Monthly (1894)
“ It is ordinarily looked upon as only fit to be trodden under foot of man, and very little credit is given its reflecting power. Paving stones appear of a rather somber color when held in the hand, and ordinary blue flagstone is similar. Hence it is surprising to learn that dry flagging, when illuminated by sunlight, is about the equal of the highly prized sky as a reflector of light. ”
