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    Re: Harrison's H1
    From: George Huxtable
    Date: 2009 May 7, 11:10 +0100

    Brad wrote-
    
    I must say the one of the more enjoyable parts of my many visits to the UK
    was seeing H1 functioning at the Royal Observatory.  Okay, I realize that
    makes me an engineering wonk, but I just couldn't take my eyes off of it.
    Wonderful instrument.  A marvel.
    
    I was confused, at first, by the odd analog hands and dials.  For example,
    the minutes dial goes from 0 to 59 and from 0 to 59 in one revolution, with
    a hand that points to both sides (and the same number).  Why would he do
    that?  I finally realized that Harrison was balancing the hands.  Rotating
    up would take more energy than rotating down.  Therefore, the clock could
    speed or slow down, if we had a hand like modern clocks.  Gravity would play
    a part.  Solution: give it two hands that point at the same number on either
    side of a dial.  Brilliant!
    
    I wish the horologist nothing but the best of luck.  Bring H1 back to life!
    
    ==================
    
    comment from George.
    
    To see the dials Brad was referring to, look at-
    
    http://www.nmm.ac.uk/collections/displayRepro.cfm?reproID=D6783%5F2#content
    
    The upper dial is seconds, on the left minutes, on the right hours, and
    below, a count of days.
    
    Brad may indeed be right, about the reasoning behind the double-pointer
    arrangement, though it would have been simple enough to counterbalance the
    pointer with a small blob, or put a balance-weight out of sight on its
    shaft. The two-minute seconds hand was an arrangement used on
    "astronomical" on-land regulator clocks with a pendulum. On such clocks, the
    longer the pendulum was, and the more slowly it swung, the greater the
    obtainable accuracy . (That wasn't the case for a balance-wheel marine
    timekeeper, as Harrison came to realise by the time he got to H4). A 4-times
    longer pendulum meant a halved tick rate, which meant that with conventional
    escape-wheel arrangement, it would take two minutes rather than one to make
    a turn. So that necessitated a seconds-dial that covered two minutes, and
    with unchanged gearing, a minute-hand that covered two hours, and then an
    hour-hand that covered 2 x 12 hours. It was sensible, then, to provide a
    double pointer, and you could read either end. That isn't so sendible for
    the hour-hand; because with such a double-pointer, you can't distinguish
    between am and pm, but Lecky, for one, and correspondence to this list, for
    another, has emphasised how convenient it would be to have such a 24 hour
    dial. However, very few chronometers do so. I have seen a picture from the
    1920s of H1 which seems to show only a single-ended pointer for its hour
    hand, which would have been handy at sea..
    
    The coil spring that's failed is one of the four, of which you can see the
    upper two, right at the top of the picture. What I should have mentioned in
    my last posting (but didn't realise it then) was that these springs, as well
    as many other components, were missing when Rupert Gould made his
    restoration (more a reconstruction) in the 1930s, and he had to make
    replacements. When he took the task over, none of these clocks was in
    working order, and they had been abandoned for many years, though after his
    attentions H1, H2, and H3 have been running ever since. H4, which unlike the
    others calls for regular oiling, has only been restarted on special
    occasions.
    
    Thanks for GregR for posting that link to the Guardian website.
    
    Jim Wilson's reference to jewelling applies only to Harrison's culminating
    effort, K4, which was on completely different lines from its predecessors.
    The others had no jewels but achieved almost frictionless motion by allowing
    the balance-shafts to rest on a pair of intersecting arcs, which could rock
    about slightly, and were counterbalanced. It's the regular movent of all
    those balance-bobs, in and out, that create the strong impression of the
    clock as a sort-of breathing animal.
    
    Apparently, it's possible to see Betts working on H1 from a gallery at the
    museum. I imagine the job will take some time.
    
    George.
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    
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