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

[Brooke Clarke]

Hi John:

One of the papers from 1968 mentioned "continental drift" could be detected if two stations were at the same latitude, 
i.e. looking at the same set of stars.
That was also the case for the Latitude Observatories which were all at 39:08.  While they were setup with Zenith 
Telescopes optimized to measure the angle between plumb and a star near the Zenith, near the end some PZTs were tried 
and worked about the same.
https://prc68.com/I/UkiahObs.shtml

The observatory here in Ukiah, CA at first used a sidereal pendulum clock, but at the end it was using a Heathkit GC-100 
clock.  It was a big deal and so showed up in the local newspaper.
https://prc68.com/I/HeathkitGC1000.shtml

-- 
Have Fun,

Brooke Clarke
https://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------
> 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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