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    From: Christian Scheele
    Date: 2009 Aug 13, 22:37 +0200

    I haven't read "History of Nautical Astronomy". Before my last posting I did
    a quick search of the list on all subject matter relating to Cotter and
    discovered that an enquiry was made regarding "Elements of Navigation"  back
    in March 2003. In the foreword to "Elements" Cotter writes that it is
    intended as a work of instruction for "Officers of the Merchant's Service":
    Your idea was spot-on, no (navigators') pun intended.
    Christian Scheele
    What I've done, years ago, in collaboration with other
    > listmembers, is to point out an immense number of errors in Cotter's
    > "History of Nautical Astronomy" (1968), list attached. This is a later
    > work
    > than his "Elements of Navigation", which Christian has mentioned, and
    > which
    > I haven't read.
    > That list of errata was produced to be useful for anyone that owned tor
    > used
    > the book, to print it out and slip it within the pages.
    > In his "History", Cotter refers to the use of equal-altitude observations,
    > either side of noon, to determine the time of the apparent peak; then
    > correcting that time by an amount that takes account of the rate of change
    > of ship's latitude and of the object's declination. I wouldn't describe it
    > as "Cotter's method", Cotter was reporting, rather badly, on developments
    > made by others.
    > It's a perfectly viable way of doing the job, particularly if a wide
    > time-span is chosen, and to my mind is a more efficient use of navigator's
    > time than by trying to measure and plot many altitudes close to noon. The
    > vessel's speed and course will usually be known to sufficient accuracy to
    > allow the correction to be estimated. The problem is that in that text
    > Cotter gets much of the technical detail hopelessly wrong, and provides an
    > incorrect formula. In contrast, Jim Wilson gets it right.
    > The correction is simple to calculate, and gets complicated only if
    > there's
    > a course-change between the observations, such as a tack of a sailing
    > vessel.
    > It is, indeed, only a special case of the standard St Hilaire method of
    > crossing two position lines of a single body, ideally separated in time
    > enough to provide a decent angle of cut. To my mind, the standard St
    > Hilaire
    > plot does the job as well as any, and doesn't require the two observations
    > to be made symmetrically about the peak. Would-be navigators can get
    > seduced
    > by the simple-sounding notion of "longitude at noon", even though it has
    > to
    > be "longitude around noon"; indeed, the further from noon, the better it
    > gets.
    > 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.
    > >
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