In the days before electricity, light below a vessel's deck was limited to candles, oil and kerosene lamps. A clever solution for the light problem was a deck prism. Laid flush into the deck, the prism point drew light down below the decks. Used alone this prism, an exact reproduction of those used on old sailing ships, is a fascinating artifact: used with a base, it is a practical night light as well. Prism size 4" wide x 4¾" high.