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.brad...@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 <j...@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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