[LEAPSECS] Leap smear and Big Ben

mike cook michael.cook at sfr.fr
Sun Oct 2 01:57:55 EDT 2011

Le 02/10/2011 00:38, Tom Van Baak a écrit :

> To implement a leap second they add coin (yes, time is money).

> Each penny changes rate by about "2/5 second per day", which

> is about 5 ppm.

There is nice animated description of the clock mechanism at

> Now, I've glanced at:

> http://en.wikipedia.org/wiki/Penny_(British_pre-decimal_coin

> <http://en.wikipedia.org/wiki/Penny_%28British_pre-decimal_coin>)

> but perhaps one of our UK members can tell us the exact mass

> of a pre-decimal penny and so tell us the rate change of Big

> Ben per £ or per kg. Which will tell us how many kg-seconds

> or £-hours is takes to implement one leap second in Big Ben.

The clock was made in 1854, though not installed and started in the
tower until 1859. In those days the penny was 18,8 grams, twice that of
the 1860 and latter pennies.
So I wonder which ones are currently in use? If the penny story is true
I would have thought that pennys available at the time of testing and
installation would still be there. The halfpenny of the 1825-1860 period
was 9,3 grammes, so maybe the original weights were halfpenny's and
later swapped with 9.4g penny's.

> /tvb


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