18 thoughts on “Timekeeping”

  1. Counting and definition?

    Probably not the same second we use today, but one as close to a whole 24*60*60 per day as was practicable given the materials and ability to work with them.

    (IE, Huygens wasn’t matching a notional Perfect Second as defined by, say, atomic oscillation.

    He was presumably counting (with mechanical or human help) the number of oscillations in a day (or perhaps an astronomically verifiable portion of a day, e.g. a noon-sextant observation or something), and calling the correct number of them “a second”.)

    1. Yeah, but it must have been pretty darned tiring and boring to sit for an entire day and count all of the swings of a stupid pendulum!

        1. From further down in the comments:

          “What I told about sitting there and counting swings was intended as a joke and now people are taking it seriously.”

          OK, one person took it seriously.

  2. Interestingly enough I came across this topic just this morning.
    http://www.math.wichita.edu/history/men/galileo.html

    In 1582, while praying in a chapel, Galileo observed a lamplighter lighting the chandeliers. The lamplighter would pull the lamps nearer him with a rod, and after lighting them, let them swing until they hung in place. Timing the swings against his own heartbeat, Galileo discovered the law of pendulum. No matter how wide an arc the lamps made, the time it took to complete a cycle, swinging from one side to the other was the same, even as the size of the arc decreased.

    Since most human resting heart rates are between 72 and 84 beats per minute the Galileo calibration gives you a start, then adjust length in order to get a one or two circle completion from gearing attached to an escapement mechanism driven by the pendulum for one day. I suspect we got two cycle (720deg/day) 12 hour clocks because it’s far easier to construct the gearing for that with less mechanical resistance using the technology available. Of course using the length of a day for a reference meant you should wait for an astronomical equinox if you want the best accuracy and certainly avoid the solstices. This would have been well understood by Huygen et al.

    Of course who knew ‘g’ would vary…. The damned colonials…
    https://www.forbes.com/sites/startswithabang/2018/09/21/the-physics-of-why-timekeeping-first-failed-in-the-americas/#12ac30b17c74

      1. Hm, I thought you were subtly prepping us for setting our pendulums on Sept. 23rd. On my cuckoo clock it’s where you put the leaf…

  3. Well, the hourglass was invented in the 8th century. He could have loaded one with 1/60 of the “sand” and used that as a first pass to establish the time for one minute, and then adjust the length of the pendulum until it swings 60 times in that period. But this begs the question: how did the people who invented the hourglass know the precise length of an hour? From a sundial?

    1. What I told about sitting there and counting swings was intended as a joke and now people are taking it seriously.

      What you do is build a pendulum clock, and you do a rough adjustment of the pendulum length, easily accomplished by a set screw attaching the pendulum weight to the pendulum rod. This rough adjustment can be made to get the clock to at least get the length of sunrise-to-sunrise about right according to Sigivald’s post, were the number of pendulum swings in tirelessly and without error counted by a clock mechanism driven by the pendulum.

      Later on, you can use a precise astronomical observation, corrected for all the known factors, including the elliptical orbit of the earth — see analemma https://en.wikipedia.org/wiki/Analemma, which must have been known by Huygens who knew about Kepler and then Newton, a contemporary?

      Think of this as a 17th century phase lock loop oscillator system, where you use a sundial for “capture” followed by corrected astronomical observations for “lock.”

  4. “This is an interesting history, but it makes me wonder how Huygens knew how long a second was to adjust the pendulum length.”

    Well, if I had been Huygens, I probably would have just used the stopwatch feature on my iPhone to do the job. Was that so difficult?

  5. According to Wiki:

    “The “Babylonian mile” was a measure of distance equal to about 11.3 km (or about seven modern miles). This measurement for distances eventually was converted to a “time-mile” used for measuring the travel of the Sun, therefore, representing time.”

    So they knew the circumference of the earth and they created the time-mile. By Huygens time the concept would be firmly in place. And we use the Babylonian math today for time.

    According to another web site , a second was defined as:

    The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. MSD was derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. Another intuitive understanding is that it is about the time between beats of a human heart.

    You did have noon to noon observations since antiquity. You could “measure” the time for that any way you liked and then start dividing.

    I would think that it could quickly become clear that seconds and minutes were useful.

    You knew the circumference of the earth after the Greeks. You knew how fast someone at the equator was traveling – i.e. feet per day – because you defind a day from noon to noon. You could select chunks of time for convenient definitions. Like an hour – 24 of them in one day looks handy. They

    Another thing I read on the web which sounds plausible is:

    “Originally, one second was defined as the time taken by simple pendulum of length of one meter in going from one extreme position to the other extreme position.”

    So after Galileo, using the 1 meter yardstick (using unit values of measures is a common choice in making definitions)

    All kinds of ways to arrive at “seconds”

  6. Solar second. If I remember my old style geometry, you can do all sorts of sub-divisions accurately. Use that to make a sundial large enough, maybe one part in a 1000 accuracy.

    1. Sun dial? You use an instrument such as a “transit telescope” that are still used at places such as the Naval Observatory.

  7. Solar second. If I remember my old style geometry, you can do all sorts of sub-divisions accurately. Use that to make a sundial large enough, maybe one part in a 1000 accuracy.

    Or maybe lunar occultation of a planet or star? Or time for the sun to cross the horizon? They did all kinds of amazing astronomy was done with nothing more than a couple sticks.

    1. They had telescopes by that time.

      As for amazing astronomy, Tycho Brahe made his pre-telescopic planetary measurements with “a couple sticks”, but it was the highest quality set of sticks up to that time because Tyco was a “stickler” for precision.

      Chased out of Denmark to Prague, his assistant Johannes Kepler inherited his observations and discovered the planets to follow elliptical orbits by studying the motion of Mars, a planet with a high orbital eccentricity

  8. The article is a bit too simple. The largest component to the local acceleration of gravity is latitude. There is more than enough difference between Northern and Southern Europe for this to be known and accounted for. The other component comes from the density of the geology underlying a location. The crust under most of the Eastern U.S. is pretty dense and thick while the Netherlands is on top of alluvial deposits that are somewhat less dense.

    The celestial stop watch in use then and until the 20th century was the moons of Jupiter. Their various transits and occlusions were well documented. Refining these were the most important application of accurate time keeping. This, in turn, made it possible to determine longitude. The problem being that it was practically impossible to make the observations from a ship.

  9. Star transits were historically the gold standard for uniform time. A transit telescope (and a table of right ascensions) was the classic instrument for reading the time, but even something as simple as watching a star blink out against a distant chimney-post would do in a pinch.

    Solar time was available too, and the correction to uniform time was well known (even in antiquity), but the quality of the reading is not quite as good.

    At sea, with no stable platform, you have to rely on lunar distances (observed distance between the sun or a star and the lunar limb).

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