Posted 5 years ago
I've had this ship's prism for quite some time, but honestly cannot remember the family member it came from. The smooth, hexagonal face measures 4 1/2" between opposing vertices, and 4 1/8" between opposing sides. The overall height to the tip is 4 1/2". It is quite heavy for it's size, and I'm not sure exactly how old this particular prism is.
What I found out was that for centuries, sailing ships used deck prisms to provide a safe source of natural sunlight to illuminate areas below decks. Before electricity, light below a vessel's deck was provided by candles, oil and kerosene lamps—all dangerous aboard a wooden ship. The deck prism was a clever solution: laid flush into the deck, the glass prism refracted and dispersed natural light into the space below from a small deck opening without weakening the planks or becoming a fire hazard.
In normal usage, the prism hangs below the overhead and disperses the light sideways; the top is flat and installed flush with the deck, becoming part of the deck. A plain flat glass window would just form a single bright spot below—not very useful for general illumination—hence the prismatic shape.