[LEAPSECS] early efforts at uniform frequency

[Steve Allen]

By the time of the 1950 meeting on Astronomical Constants held at
Observatoire de Paris under the auspices of the CNRS the quartz clock
engineers at Greenwich had some ocillators which were more stable than
earth rotation.  They still had a tendency for some of them to go
rogue and stop being more stable, but with a large enough ensemble
those could be identified and excluded.

Using those quartz clocks made it possible to get a good measure of
the seasonal variation of earth rotation.  The BIH published the first
expression for Delta T_S (what would become known as UT2-UT1) at the
end of 1951.  From 1952 through 1955 the UK radio broadcasts
controlled by Greenwich were already applying that correction (as well
as the UT1 correction they had started applying around 1947) to give
a quasi-uniform time that they called Provisional Uniform Time (PUT).
Before 1955 the USNO was also using such corrections in its radio
broadcasts, and in 1955 their time scale was named N3c.

The BIH published several subsequent expressions for the seasonal
variation both before and after the IAU directed that all radio
broadcasts should do that.  The final version of UT2-UT1 was
first used during 1962, by which point the time signal broadcasts
were already regulated by cesium.

Plots of the seasonal variation expressions are here

https://www.ucolick.org/~sla/leapsecs/seasonal.html

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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