“Hull Guildhall's Time Ball set to rise and fall once again”. BBC News. BBC. 19 October 2018閲覧。 “The ball is one of just a few nationally and is the only maritime timepiece on a municipal building. It dates back to 1918 and is the highest in the UK.”[リンク切れ]
“Time ball”. Greenwich2000. Greenwich Mean Time (2019年). 12 December 2019閲覧。
harvard.edu
ui.adsabs.harvard.edu
Kinns, Roger (2017). “The Principal Time Balls of New Zealand”. Journal of Astronomical History and Heritage20 (1): 69–94. Bibcode: 2017JAHH...20...69K.
“The HE TIME BALL ON GDAŃSK NOWY PORT LIGHTHOUSE”. The Lighthouse Gdańsk Nowy Port. 2022年3月26日閲覧。 “From 1901, when Guglielmo Marconi sent the first radio signal across the Atlantic from the Poldhu Lighthouse in Cornwall to the Signal Hill Lighthouse in Newfoundland, great changes took place in navigation. Time signals began to reach ships on all the oceans of the world by means of radio. By the early twentieth century the time ball had become an anachronism. In Gdańsk a radio station started in 1921 and one of its basic functions was to transmit an accurate time signal each noon. It was probably because of this that after the gale which wrecked it in 1929 there was no need to repair the Gdańsk time ball.”
