[time-nuts] What is the BEST crystal?

[Bruce Griffiths]

IIRC Tolansky obtained some interferograms illustrating the surface deflections of these acoustic resonators.
I'll unearth my copy of Tolansky's book on optical interferometry and check.

Bruce
> On 01 March 2020 at 13:41 "John Moran, Scawby Design" <john at scawbydesign.co.uk> wrote:
> 
> 
> Wow, that provoked an interesting discussion!
> 
> Thanks for all the information and references to further information - it should keep me quiet for a while.
> 
> Interestingly 50mm diameter was about the diameter of the crystals used by the British Post Office in the early days for generating a master oscillator. It wasn't ground into a plano-convex lens but as a ring and was about 10mm thick. Like the old WW2 crystals the electrodes weren't plated but just contact rings. I have no idea what frequency they were ... by the time that I realised they were scrapping all this kit it was gone and I only managed to salvage two GPO Type 36 master 1S pendulums from a dumpster!
> 
> Thanks again for all the feedback.
> 
> John
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