System of three mirrors (two movable above, one stable down) on a wrought-iron bracket used for discreet domestic surveillance of the front door/alleyway/surrounds. One of Ben Franklin's inventions, native to Philadelphia, where homes with the original glass are much sought-after. Copies of these are still available, and warmly recommended -- cheaper than a closed-circuit system, and won't break down in a power failure -- Colonial Geek Chic!