5 ms·

200 years ago, how would you validate his claim? You would have to have a more accurate time reference, and I'm not sure exactly what that would be.

by leecb 11y ago

ColinWright 11y ago
Harrison measured the accuracy of his clocks by observing eclipses of stars by chimneys. We know that for a given star such eclipses happen every 86164.09056 seconds. For those who might be wondering why it's not every 24 hours, or 86400 seconds, look up "Sidereal Day"[0][1][2]. [0] https://www.google.co.uk/search?q=sidereal+day https://www.google.co.uk/search?q=sidereal+day [1] http://simple.wikipedia.org/wiki/Sidereal_day http://simple.wikipedia.org/wiki/Sidereal_day [2] http://en.wikipedia.org/wiki/Sidereal_time http://en.wikipedia.org/wiki/Sidereal_time
- dllu 11y 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 11y ago
    This 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 11y ago
      > The Harrison clocks had no pendulums. The clock referred to in the article does have a pendulum.
      - magicalist 11y ago
        Oh, 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 11y 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 11y ago
    Eyeballing 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?
mpweiher 11y ago
As long as you're at a fixed location, how about a sundial?
- lostlogin 11y ago
  To the second? I'm not a sundial expert but have seen a few and those that I have seen have been vaguely useful for telling which hour it is. Maybe even which half hour. I assume you could just lengthen the vertical to get a longer and more accurate shadow. But it's still a bit hard to see this being a reference. Edit: here is a link to some accuracy measurement. I have no idea what the record is, but these ones were getting down to 30 seconds ish. http://www.sage.unsw.edu.au/currentstudents/ug/projects/o%27brien/o%27brien.htm http://www.sage.unsw.edu.au/currentstudents/ug/projects/o%27...
pcl 11y ago
That part is easy: you just compare it to local solar noon. Earth's rotation is considerably more accurate than this clock's target. For more info about the number of seconds in a solar day, see this awesome Wikipedia page: http://en.wikipedia.org/wiki/Leap_second http://en.wikipedia.org/wiki/Leap_second
- stromgo 11y ago
  For more info about the number of seconds in a solar day, I would rather recommend the table at http://en.wikipedia.org/wiki/Solar_time#Apparent_solar_time http://en.wikipedia.org/wiki/Solar_time#Apparent_solar_time . The Leap_second article discusses a much smaller variation (~2 ms) on top of the big cyclic variation (~20 s).
jacobolus 11y ago
The most obvious way would probably be to build two of them and see how accurate they were against each-other. Alternately, you could use astronomical angle measurements. You can get quite accurate measure if you don’t move around. (The reason determining time was difficult on ships is that you need to know precisely where the ship is to figure out the time from the stars, or precisely what time it is to figure out position.)
deleted 11y ago
[deleted]
zkhalique 11y ago
You could simply build 10 of them and test them against each other. Even though statistical significance hadn't been discovered yet, I'm sure someone could have worked out the math.

200 years ago, how would you validate his claim? You would have to have a more accurate time reference, and I'm not sure exactly what that would be.

by leecb 11y ago

200 years ago, how would you validate his claim? You would have to have a more accurate time reference, and I'm not sure exactly what that would be.

ColinWright 11y ago

Harrison measured the accuracy of his clocks by observing eclipses of stars by chimneys. We know that for a given star such eclipses happen every 86164.09056 seconds. For those who might be wondering why it's not every 24 hours, or 86400 seconds, look up "Sidereal Day"[0][1][2]. [0] https://www.google.co.uk/search?q=sidereal+day https://www.google.co.uk/search?q=sidereal+day [1] http://simple.wikipedia.org/wiki/Sidereal_day http://simple.wikipedia.org/wiki/Sidereal_day [2] http://en.wikipedia.org/wiki/Sidereal_time http://en.wikipedia.org/wiki/Sidereal_time

dllu 11y 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 11y ago
  This 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 11y ago
    > The Harrison clocks had no pendulums. The clock referred to in the article does have a pendulum.
    - magicalist 11y ago
      Oh, 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 11y 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 11y ago
  Eyeballing 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?

mpweiher 11y ago

As long as you're at a fixed location, how about a sundial?

lostlogin 11y ago
To the second? I'm not a sundial expert but have seen a few and those that I have seen have been vaguely useful for telling which hour it is. Maybe even which half hour. I assume you could just lengthen the vertical to get a longer and more accurate shadow. But it's still a bit hard to see this being a reference. Edit: here is a link to some accuracy measurement. I have no idea what the record is, but these ones were getting down to 30 seconds ish. http://www.sage.unsw.edu.au/currentstudents/ug/projects/o%27brien/o%27brien.htm http://www.sage.unsw.edu.au/currentstudents/ug/projects/o%27...

pcl 11y ago

That part is easy: you just compare it to local solar noon. Earth's rotation is considerably more accurate than this clock's target. For more info about the number of seconds in a solar day, see this awesome Wikipedia page: http://en.wikipedia.org/wiki/Leap_second http://en.wikipedia.org/wiki/Leap_second

stromgo 11y ago
For more info about the number of seconds in a solar day, I would rather recommend the table at http://en.wikipedia.org/wiki/Solar_time#Apparent_solar_time http://en.wikipedia.org/wiki/Solar_time#Apparent_solar_time . The Leap_second article discusses a much smaller variation (~2 ms) on top of the big cyclic variation (~20 s).

jacobolus 11y ago

The most obvious way would probably be to build two of them and see how accurate they were against each-other. Alternately, you could use astronomical angle measurements. You can get quite accurate measure if you don’t move around. (The reason determining time was difficult on ships is that you need to know precisely where the ship is to figure out the time from the stars, or precisely what time it is to figure out position.)

deleted 11y ago

[deleted]

zkhalique 11y ago

You could simply build 10 of them and test them against each other. Even though statistical significance hadn't been discovered yet, I'm sure someone could have worked out the math.