In the days before electricity, light below a vessel's deck was provided by canles, oil and kerosene lamps. All dangerous aboard a wooden ship. A clever solution for the lighting problem was the deck prism. Laid flush into the deck, small conical prisms drew light down below decks without weakening the deck planks. This solid, poured-glass prism is an exact replica of a prism taken from the Charles W. Morgan, a 19th century New England whaling ship.