Admiralty Lists of Visual Time Signals After 1880

Admiralty lists, first published in 1880, included time signals that ranged from time balls, discs, lights and flags to time guns, whose flash was the precise signal. Preparatory signals and procedures to be followed in case of an inaccurate signal were described. After 1911, the list was widened to include other navigation signals and issued in different parts covering specific geographical areas, each including a chapter on visual time signals. At first, signal times in Admiralty lists were specified as local (astronomical) mean time based on zero hours at noon and GMT. The latitude and longitude of the signal location were also specified. Standard times, governed by time zones, were introduced later and civil time, based on zero hours at midnight was used from 1925 onwards. Entries for St Helena, Vladivostok and China are used to demonstrate the detail of published time signal information and the chosen simplification in other chapters.