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>>What is a timeball tower ?
10 mai 2010
Last March, we saw a timeball tower in Deal when we had a walk along the seafront from Walmer Castle to the town of Deal also famous for its castle.
Deal Timeball Tower
A time ball is a large painted wooden or metal ball that drops at a predetermined time, mainly to help the sailors check their marine chronometers from their boats off shore. The ships would wait in front of Deal Timeball tower until 13:00 to see the timeball fall and the sailors could make sure they had the right time before they left England for a long trip.
They needed to know what the time was in Greenwich wherever they were on the Earth. This helped them calculate their longitude (on which meridian they were). They calculated the difference between Greenwich Mean Time and the local time. 1 hour difference made an angle of 360° divided by the difference in time.
Time balls are usually dropped at 1 pm . They were raised half way about 5 minutes earlier to alert the ships, then with 2-3 minutes to go they were raised the whole way. The time was recorded when the ball began descending, not when it reached the bottom.
Greenwich Timeball Tower next to the Royal Observatory
Time ball stations set their clocks according to the positions of the sun and stars they observed. Originally they either had to be situated next to an observatory, or they had to keep a very accurate clock at the station which was set manually to observatory time. But the problem was to get the perfect time.
two other timeball towers
The use of the electric telegraph* (from around 1850)allowed time balls to be located further from their source of Mean Time (Greenwich Mean Time).
With the commencement of radio time signals (in Britain from 1924), time-balls gradually became obsolete (old-fashioned and then useless) and many were demolished in the 1920s.
*A telegraph is a device for transmitting and receiving messages over long distances,The word telegraph alone now generally refers to an electrical telegraph. An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages.
Thibault and Alinoé