The Astronomer Royal, the Hydrographer and the time ball: collaborations in time signalling 1850–1910

This paper examines the relationship between the Admiralty and the Royal Observatory, Greenwich, by studying the roles of the Hydrographer and the Astronomer Royal as they worked together on the problem of communicating accurate time to ships. The collaboration between the Astronomer Royal and the Hydrographer directed the development of time balls and other visual signals throughout their period of use in Britain and its colonies. This paper focuses on the time ball and clock developed by the Astronomer Royal William Christie and the Hydrographer William Wharton as a key example of significant and productive collaboration between the two institutions. The paper also highlights the importance of the telegraph system to visual time signals. The ability to drop a time ball at a distance from an observatory created significant opportunities to improve the time signal service to mariners and stimulated further innovation in this field.