[time-nuts] Absolute time accuracy pre-Cesium?

[John Ackermann. N8UR]

All -- thanks much for all the great references!  I am giving the preso this afternoon (to a bunch of university space science students) so this will be a big help.  And it looks like there's a lot of great reading for when I have time to breathe.

Thanks again.
John

On Mar 25, 2019, 10:03 PM, at 10:03 PM, Ben Bradley <ben.pi.bradley at gmail.com> wrote:
>For independent standards (not quite what you asked) I recall from
>"The Science of Clocks and Watches" (a book with much technical info
>if you're interested in these mechanical devices) that the most
>accurate mechanical/pendulum clock was the Shortt Clock that used a
>pendulum in a vacuum chamber for its standard. Mechanical clocks were
>replaced by more stable electronic quartz crystal oscillators, and
>then finally by atomic clocks.
>
>Perhaps closer to your question: I recall in my readings about
>clockmaker John Harrison (likely either in "The Quest for Longitude"
>or Dava Sobel's "Longitude") that he would look from the edge of his
>window at a particular star each night and note (while counting the
>ticks he heard from his clock) the exact moment it would disappear
>behind a nearby chimney, and knowing the Earth's rotation takes four
>minutes and some (I forget) seconds off from a day, he used this to
>calibrate and test the precision and accuracy of his long clocks. It
>was suggested he could get within less than second with this method.
>This was around age 21, so the year would be about 1714. Looking
>online for PZT (photographic zenith tube), I didn't find much about
>it, but it was surely first made a couple centuries after this.
>
>The Sobel book (all about how Harrison won the Longitude prize) is
>more a popular book and less technical, but "Quest" has many
>mostly-technical articles, mostly about Harrison, as well as beautiful
>photos of his clocks. One or two of the articles is by the man who
>made (or made the parts for it, the story is complicated) the
>one-second-in-100-days "Clock B" pendulum clock, built from Harrison's
>writings and claims of just that accuracy in the book he wrote shortly
>before his death.
>
>On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR <jra at febo.com>
>wrote:
>>
>> Does anyone have a pointer to information about the absolute time
>> accuracy (not stability) that was available via PZT or other
>techniques
>> prior to the Cesium definition?  I'm doing a presentation and want to
>> show the evolution of accuracy.  My Google-fu has failed me in
>finding
>> anything pre-Atomic.
>>
>> Thanks!
>> John
>>
>>
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