Caption

19th-century lightship. Historical artwork of a lightship using a lamp on top of a mast to guide other ships (seen in background). Lightships are ships anchored in place to act as a lighthouse. They can be used to warn ships away from rocks and reefs where it is not possible to build a lighthouse, and are also used to mark shipping routes where a buoy is not suitable. The first lighthouse was anchored at the mouth of the River Thames, England, in 1732. From around 1892, oil lamps were replaced by electric lights. The globe at the top of the mast made the ship visible during the day. Artwork from A Travers l'Electricite (G. Dary, Paris, 1900).