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    Re: Clockmaker John Harrison vindicated
    From: Geoffrey Kolbe
    Date: 2015 Apr 19, 17:16 +0100
    This clock was entered into the Guinness book of Records as the “most accurate mechanical clock with a pendulum swinging in free air”. For pendulum clocks, a limiting factor on their timekeeping accuracy is the changes in air pressure, which affect the period of the pendulum. The world's most accurate clocks up until the advent of quartz crystal clocks was the Shortt clock, which was a pendulum clock where the pendulum operated in a partial vacuum. Properly set up, these clocks were accurate to within a second a year. It is notable that this Burgess 'B' clock was sealed in a plastic box to "prevent tampering", but which (depending on the degree to which it was sealed) would also have isolated the pendulum against changes in air pressure - and I suspect that this has more than a little to do with the remarkable accuracy of this particular clock over 100 days.

    It should be noted that this clock is not - and was never meant to be - a marine chronometer. Rather, it was meant to be a 'regulator' clock against which the performance of marine chronometers (and other clocks) could be measured. Marine chronometers from H4 onwards had balance wheel escapements as the oscillating element rather than pendulums. Friction is the main limiting factor in watch escapements and the invention of the 'detent' escapement in the first practical sea-going chronometers minimised the friction. The 'Q' of the mechanical oscillator was thereby increased and so gave these chronometers great stability in time-keeping. My own Ulysse Nardin chronometer, made in 1920 and recently cleaned and oiled, is quite phenomenal in its timekeeping ability and I would not be surprised if it would match the Burgess 'B' clock in accuracy.

    Geoffrey Kolbe

    Dr Geoffrey Kolbe, Riccarton Farm, Newcastleton, Scotland, TD9 0SN
    Tel: 013873 76715
    Mob: 0773 8069 663

    On Sun, Apr 19, 2015 at 2:56 AM, Ed Popko <NoReply_EdPopko@fer3.com> wrote:

    Interesting reading ...

    "Clockmaker John Harrison vindicated 250 years after 'absurd' claims"
    Science column, April 18, 2015, The Guardian news service:

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