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    Re: Sadler
    From: George Huxtable
    Date: 2008 Dec 3, 16:08 -0000

    Thanks to dw for pointing to this account of Donald Sadler's long period at
    the Nautical Almanac Ofiice, in the UK, from 1930 to 1972; much of the time
    as Superintendent.
    One thing that struck me was the rarity, in that office, of anyone with a
    direct practical interest, or any personal experience, in navigation. I
    would have thought that having a grizzled old retired seadog on-hand might
    have been rather useful, when choosing the bast layout for tables. I wonder
    whether that was the case, also, with their counterparts in the US.
    I found quite a lot to interest me in his account, though it doesn't contain
    much technical content.
    One passage, from page 112, may be of some interest, however, in which he
    "We also conducted observations with a sextant and theodolite in order to
    investigate the dependence of dip of the sea horizon on various factors. The
    programme was to observe the dip, accurately by theodolite, from fixed
    locations on the seashore (or cliffs as appropriate) using the height of the
    tide to give varying heights above sea-level. The cooperation of Trinity
    House enabled air and water temperatures to be taken by the staff on the
    Royal Sovereign lightship, which was approximately on the horizon.
    Unfortunately we had not allowed for the tidal 'wave' which affects the dip
    near the shore as the sea surface is not an equipotential near the shore. I
    was never able to find anyone able to provide an adequate theory of the
    shape (curvature) of the tidal wave and so it did not prove possible to
    reduce the observations. These were made very largely by Scott, with the
    assistance of Harragan, Taylor and several of the girls. We got various
    results, but we did not publish them. "
    Why should the sea surface not be an equipotential near the shore? Is he
    talking about gravitational effects from the adjacent land-mass? Or about
    the effects of tidal inertia? Or what? Are these effects, whatever they are
    due to, likely to be big enough to affect dip observations?
    contact George Huxtable, now 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.
    ----- Original Message -----
    From: "dw" 
    To: "NavList" 
    Sent: Tuesday, December 02, 2008 9:52 PM
    Subject: [NavList 6646] Sadler
    | If you haven't seen this, it's worth a look.  An interesting first
    | person account of 42 years of work at the almanc office:
    | http://www.hmnao.com/nao/history/dhs_gaw/index.html
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