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 >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > >_______________________________________________ >time-nuts mailing list -- time-nuts@lists.febo.com >To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.