3 ms·
At that level of accuracy, however, you will find that the rotation of the Earth itself doesn't keep time that well. The Shortt-Synchronome clock [0] was the m
by dllu 12y ago
At that level of accuracy, however, you will find that the rotation of the Earth itself doesn't keep time that well.
The Shortt-Synchronome clock [0] was the most accurate pendulum clock, known to have an error of less than 1 second per year. It was used in 1926 to detect tiny seasonal changes in the Earth's rotation rate. An evaluation of the clock in 1984 revealed it was even more accurate than thought --- it was in fact accurate to within 1 second per 12 years, the discrepancy being due to "the slight changes in gravity due to tidal distortions in the solid Earth caused by the gravity of the Sun and Moon."
Harrison's claim of 1 second error in 100 days is clearly in the same order of magnitude as the Shortt-Synchronome's known error rate of 1 second per year in 1926, and thus would have been also affected by the tiny seasonal changes in the Earth's rotation rate.
[0] https://en.wikipedia.org/wiki/Shortt-Synchronome_clock https://en.wikipedia.org/wiki/Shortt-Synchronome_clock
- magicalist 12y agoThis is why we talk about mean time and still have to account for discrepancies as leap seconds. That's not an issue with the clocks, just the earth. However, the situations are actually pretty different. If you look into the study of the Shortt-Synchronome clock, you'll see it's actually talking about the gravitational effects of the sun and moon on pendulums. The Harrison clocks had no pendulums. The Shortt-Synchronome is still a pretty amazing clock, though.
- ColinWright 12y ago> The Harrison clocks had no pendulums. The clock referred to in the article does have a pendulum.
- magicalist 12y agoOh, I see, I thought they were asking how you would validate his claim of the "revolutionary clock"(s) he was famous for in the first place.
- dmurray 12y ago> At that level of accuracy, however, you will find that the rotation of the Earth itself doesn't keep time that well. If the main purpose of the clock was to measure longitude by observing the position of the stars, "only as accurate as the Earth's rotation is consistent" is as good as you could possibly need.
- abecedarius 12y agoEyeballing the figure at http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_day#Observations http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_d... it looks like you could expect stellar time to be off proper time by not more than around 0.1 seconds in 100 days, since the width of the band of fluctuations is around 1 ms. (I'd say 0.01 seconds since in a random walk the error grows with the square root of time, not linearly.) Maybe this fluctuation graph has subtracted out seasonal variation?