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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Harrison's H1
From: George Huxtable
Date: 2009 May 7, 11:10 +0100
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@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---