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    Re: Lunars - Finding Bermuda in 1807
    From: Ken Muldrew
    Date: 2007 May 14, 10:16 -0600

    On 12 May 2007 at 21:32, NavList@HistoricalAtlas.net wrote:
    > "As the night approached, the sky became beautifully clear, and shortly
    > after sunset I got my sextant to work. Before the twilight was ended, and
    > the horizon too faint to admit of the altitudes being taken with accuracy,
    > I had observed four or five sets of lunars.
    What do you suppose he means by "four or five sets of lunars"? The almanac
    would only have 2 stars for a given date. I don't suppose he would
    calculate the distances to other stars without mentioning the fact. Would
    a "set" consist of an altitude, a lunar distance, and the other altitude
    in succession (possibly with only a single observation of each)?
    Frank also mentioned, in reply to George, that he agreed that the
    altitudes for the later lunars would not have been calculated without
    noting the fact. This brings up the curious difference between those who
    navigated on land, and those who navigated at sea during this period,
    despite their training (and their textbooks) being essentially the same.
    The land navigators always calculated their altitudes. Even when taking
    lunars using the sun, where the time sight is from a solar altitude, they
    calculate the sun's altitude at the moment of the lunar. They take a time
    sight with every lunar, so there is no question of there being any
    difficulty associated with measuring the altitudes. They often take
    meridian altitudes of stars for latitude, so they seem comfortable enough
    sitting about in the middle of the night looking into their artificial
    horizon. The fur trade navigators were always far enough North to allow
    altitudes with an ordinary sextant. It is something of a mystery.
    If Alex is reading this, I wonder if he can comment on Wale's practice
    during Cook's voyage. Did he measure altitudes for lunars at sea and
    calculate them for lunars on land? Wales was Philip Turnor's instructor
    (or at least Master at the mathematical school where Turnor was taught),
    and Turnor (and his students David Thompson and Peter Fidler) was
    dedicated to calculating altitudes for land-based lunars.
    Ken Muldrew.
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