Williamson Equation Clock

Discussion in 'General Clock Discussions' started by NigelW, Feb 10, 2020.

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  1. NigelW

    NigelW Registered User

    Jan 2, 2015
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    I came across this clock yesterday in the Ashmolean museum in Oxford, which was labelled as an equation clock but with no technical description. The movement was not visible. It was going and the hands on the main dial were showing Greenwich Mean Time. I looked long and hard at it and just couldn't figure out why it was an equation clock. The subsidiary dial in the arch seemed just rotate once a year.

    Researching the clock when I got home, it seems it is probably the type which raises and lowers the pendulum thus changing the rate at different times of the year. If so, the hands should have shown solar time and were incorrectly set; at this time of year the difference between solar and mean time is close to its maximum (solar is ahead of mean by about 14 and a half minutes) so rather than showing quarter to four it should have shown something closer to four o'clock.

    I don't think the museum has a specialist clock curator so perhaps the person who winds it up doesn't realise?

    452px-Clock_by_Joseph_Williamson.jpg
     
  2. zedric

    zedric Registered User

    Aug 8, 2012
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    It’s difficult to read from the photo. What day is at 6 and what day at 12?
     
  3. novicetimekeeper

    novicetimekeeper Registered User

    Jul 26, 2015
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    I can't make out the detail from the pic but I would expect the subsidiary to advise on how much time to add or subtract from a sundial reading to obtain the correct time.I don't think the clock is supposed to display the time from the sun. I have a printing block for a watch paper where you have to pick your day to do that. Doesn't this just point to the correct day for you?

    I see it has maintaining power, is it deadbeat?
     
  4. NigelW

    NigelW Registered User

    Jan 2, 2015
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    I got my first post wrong - solar time is currently lagging mean time, so the time shown should have been half past three if mean time was quarter to four.

    The subsidiary dial was just a calendar wheel as far as I could see. I wasn't paying attention to the ticks and tocks so I am not sure of the escapement type. A similar clock by Williamson came up for auction a few years ago and was clearly of the type which raises and lowers the pendulum as the year progresses - this link has a picture of the very similar dial and the one of the back of the movement shows a cam on the back of the year dial which is connected to a rise and fall mechanism.

    Fine and rare English walnut eight day longcase clock with solar equation and five pillar movement, the 12" brass arched dial signed Josephus Williamson, Londini.Inv fecet on pierced shaped foliate engraved plates to the matted centre, also inscribed on a separate silvered oval plate ‘Horce indicantur apparentes invo lutis equationibus’, also with a subsidiary seconds dial and calendar aperture enclosed with a silvered chapter ring, the arch fitted with the solar equation dial inscribed with day - Price Estimate: £7000 - £10000
     
  5. NigelW

    NigelW Registered User

    Jan 2, 2015
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