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    Re: 7 ways to determine longitude
    From: Frank Reed CT
    Date: 2003 Dec 24, 16:12 EST
    Dan wrote:
    "I have just started to read an old book called "Spherical and Nautical
    Astronomy", a two volume set by William Chauvenet who was a professor
    at Washington University in St. Louis.  My copy was printed in 1903 but
    it appears that it is just a reprint of an 1863 edition."

    Yes, that's the "Chauvenet" that you may have seen in a couple of subject lines on the list. It's a classic.

    "Chapter 7 is "Finding Longitude by Astronomical Observation" where it
    lists seven different methods, which are:
      1st method - by portable chronometers
      2nd method - by signals
      3rd method - by the electric telegraph
      4th method - by moon culminations
      5th method - by azimuths of the moon, or transits of the moon
                   and a star over the same vertical circle
      6th method - by altitudes of the moon
      7th method - by lunar distances"

    One little thing to keep in mind is that Chauvenet was an astronomer who was writing for other astronomers. Most of the methods were meant to be used by astronomers at fixed positions on land. The only method significant for ocean navigation is "by lunar distances". His method was probably only used rarely at sea because it came along so late and perhaps because so many other methods were already in place. His analysis of the Earth's oblateness (polar flattening) is clever, and his approach can be applied to other methods of clearing lunars without much modification.

    Frank E. Reed
    [X] Mystic, Connecticut
    [ ] Chicago, Illinois
       
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