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Pail Hirose you wrote:The latest issue of Journal of Astronomical History and Heritage has a review of "The World of Visual Time Signals for Mariners: Time Balls, Time Guns, Time Lights and Other Signals," edited by Roger Kinns (who wrote most of the chapters).

That sounds great, but expensive. I wonder if they cover the seemingly implausible lights at the entrance to some 'harbours of refuge' which are green when there is less, not more, than, a particular amount of water in the entrance. The idea was that you could run in with a following gale and be safely brought to a halt in the mud before you ran into anything important. I believe either Bridlington or Scarborough had them. Bill Lionheart will confirm which. DaveP