Pigeons standing on the hands

Glitches in clock performance always occur around hh:40 to hh:50 (when the minute hand is horizontal and rising) , and always in daylight hours. The pigeons are present on the dial in large numbers especially when the sun is shining - a warm south-facing place to sit [link] . A quick calculation: suppose a pigeon weighing 0.5kg is sitting on the minute hand at a distance of 0.5m from the pivot, and so rising at about 1mm/sec. It requires 5mW of power to lift it (force*velocity). Then the 80kg _going_ weight falling 9m in 7 days generates 12mW of power (again force*velocity). So a power balance suggests that a couple of pigeons can easily stop the clock.

Here are some links to some recent clear pigeon events: 16 September 2010, 5 March 2010, 9 Jan 2010, 29 Dec 2009 and 8 Dec 2009
Many more can be found by following links on the COMMENTS page.


Pigeons standing on the hands - photo courtesy Ian Galloway, 13 Dec 2009.