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

[Mark Spencer]

Hi:   I have a some what related question.

I'm just curious how far back in time do the current time scales extend ?   (Ie.   When was the first "second hack / synchronization"  that can be related to our current time.)

Thanks in advance for any answers.

Mark Spencer

mark at alignedsolutions.com
604 762 4099

> On Mar 26, 2019, at 2:58 AM, 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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