The emergence of time light signals for rating of marine chronometers

Abstract

Precise visual time signals for marine chronometer rating began with a shuttered oil lamp in about 1823, but dropping time balls became the favoured visual signal for chronometer calibration. Electric time light signals became practicable in the twentieth century and replaced or complemented time balls as principal signals at various locations from 1909 onwards, with the first known implementations in Mozambique, China and Argentina. They were listed by the British Admiralty for 46 locations worldwide between 1911 and 1947. Not all existed together. There were 29 listed locations in Europe but none in the British Isles or North America. Their locations and types are described in this article, with specific details of signals outside Europe. They existed in extraordinary variety, ranging from coloured lights that replaced time balls in New Zealand to steady or flashing white lights at many other locations. All used the moment of extinction as the time signal.