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Hi Patrick:

Pendulum clocks could be moved by ship, but not operated on the ship.
Once on land the clock could be set using astronomical methods, which is
equivalent to finding the longitude.
A pendulum clock could be compared to astronomical events and it's rate
determined.  This rate would apply after the clock was moved to some
other location as long as the temperature was the same as when it was
calibrated.

In Harrison's time the Earth's rotation was good enough to set clocks.
Today atomic standards are much more precise than the rotation of the
earth, so we have leap seconds every now and then, but not on a
schedule, only when the atomic clocks are getting out of sync with the
Earth.

The error between the atomic clocks and the Earth is maintained at less
than 1 second now, but there is some lobbying to allow larger deltas,
maybe up to 10 seconds.  This has implications on sundials and CN.

Does this answer to your question, or is it's scope greater?

Have Fun,

Brooke Clarke, N6GCE
http://www.PRECISIONCLOCK.com
http://www.PRC68.com

Patrick Stanistreet wrote:

> Just curious but when Harrison created his chronometers
> there had to be some standard against which they were
> set.  Of course land based clocks were around but even
> those clocks had to be set against some other standard.
> I would guess that the ultimate standard at that time
> would have been astronomical. But still what exactly
> was used to arrive at accuracy of a few seconds.
> Was the land based authority setting GMT associated
> with the Almanac office?
> Assuming timing of a star one ends up with a sidereal
> clock but when did land based clocks achieve sufficient
> accuracy to time a star over 24 or more hours so as
> to differentiate between sidereal and solar time?
>
> Any book recommendations that cover this topic in detail?
>
>

   

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