Visitors to the U.S.S. Constitution often wonder what purpose is served by the glass tiles that are flush with Old Ironsides' deck. Before electricity, kerosene lamps and candles brought light, and the risk of fire, below deck. Glass prisms laid into the ship's deck helped reflect sunlight into the spaces below without weakening the planks. This authentic reproduction of a six-sided aqua glass prism is a conversation-starting piece of maritime history for home or office. Approximately 4'' diameter x 5''H.