[time-nuts] Pendulums & Atomic Clocks & Gravity

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat May 26 21:57:49 EDT 2007


Tom Van Baak wrote:
> Depends on what you mean by "real clocks". The best pendulum
> clocks, made in the early 1900's, solved almost all the normal
> sources of error and instability. That left gravitational tides as
> the one of the few remaining sources of "error", down well below
> the 1 ppm level. I say error in quotes because if you call them
> gravimeters instead of clocks, they we're just doing their job
> and did it well. These were real clocks; most of the pendulum
> clocks, vintage or modern, that you see are toys.
>
> Specifically, these used aged invar rods, at very low amplitude,
> running in partial vacuum inside brass chambers. That helped
> reduce buoyancy, humidity, and barometric pressure issues.
> They were also either well temperature compensated and were
> operated deep in constant-temperature basements.
>
> Some modern attempts at world-class pendulum clocks have
> tried fused quartz instead of invar to avoid the reputation that
> fresh invar has for long-term instability. A great example is:
> http://www.precisionclocks.com/
> You should know Bill had hp cesium clocks in his home clock
> collection long before I did.
>
> Those of you really interested in the history, art, and science
> of pendulum clocks should see the following six books:
>
> Accurate Clock Pendulums by Robert J. Matthys
> Precision Pendulum Clocks, A Trilogy of Books by Derek Roberts
> My Own Right Time, by Philip Woodward
> The Science of Clocks & Watches, by Arthur L. Rawlings
>
> /tvb
> http://www.LeapSecond.com
>   
Tom

Even fused silica is unstable (see attachment).
Single crystal materials should be significantly better.
Ageing Invar doesn't do much for its dimensional instability.

Bruce
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