[LEAPSECS] Adjusting Big Ben video (was Re: Of stepping motors and leap seconds)

Warner Losh imp at bsdimp.com
Sat Feb 9 18:00:17 EST 2019

How do they keep big Ben in sync these days? Eg, who decides it is running
fast or slow? In the past I've been told they steered to Greenwich
observatory who would shoot a cannon off and drop a red ball to announce
the time to London... on my recent trip to Greenwich observatory I
discovered they no longer fire off the cannon, etc.


On Sat, Feb 9, 2019, 5:50 PM Peter Vince <petervince1952 at gmail.com wrote:

> Sorry Tom, that BBC news item is ten years old, and it looks like the
> video has been removed.  There are a number of videos on Youtube which talk
> about adding or removing old pennies from the pendulum to correct it.  See,
> for example:
> https://www.youtube.com/watch?v=_Elffjsjbio
> An eight-minute video extracted from the Discovery channel's "Blowing Up
> History" series, entitled:  The Mechanical Genius of Big Ben
>      Regards,
>            Peter
> On Fri, 8 Feb 2019 at 13:29, Tom Van Baak <tvb at leapsecond.com> wrote:
>> There's a wonderful BBC video showing how Big Ben is adjusted for leap
>> seconds:
>> "Leap second: Slowing down Big Ben" [1]
>> http://news.bbc.co.uk/2/hi/science/nature/7792436.stm
>> In this case they do not literally move the massive weight up or down,
>> but instead, by adding tiny weights (usually penny coins) they change the
>> effective center of gravity of the bob, which is all that matters. This is
>> an unexpected application of the saying that "time is money".
>> /tvb
>> [1] If someone (UK only?) can capture this short video as mp4 I'd
>> appreciate it.
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