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    Bowditch 1926
    From: Chuck Taylor
    Date: 1996 Sep 03, 11:43 EDT

    Over this past weekend I was browsing in a used book store in Port
    Townsend, WA (USA) and was lucky enough to find a copy of the 1926
    edition of Bowditch. I couldn't resist. A few comments about the way
    things apparently were 70 years ago:
    1. The sextant described was of the clamp-screw vernier type, calibrated
    to 10 seconds of arc. There was only passing reference to the "new"
    micrometer drum sextants being introduced in the U.S. Navy.
    2. Altitudes were measured in degrees, minutes, and seconds and the
    computations were carried out accordingly (rather than in degrees,
    minutes, and tenths of minutes).
    3. The organization by chapter says a lot about the way navigation was
    practiced then. There are successive chapters on Chronometer Error (Time
    Sights), Latitude, Longitude, Azimuths (compass checking), and Sumner
    Lines. The altitude-intercept method of St. Hilaire is mentioned in a
    subsection of the chapter on Sumner Lines. Apparently finding your
    latitude and finding your longitude were viewed as separate, discrete
    processes. The positioning of chapters would suggest that lines of
    position were regarded as somewhat less important.
    4. Sight reduction relied on tables of trigonometric functions and
    logarithms. The basic Law of Cosines was arranged in several different
    forms to facilitate different methods involving the usual trigonometric
    functions (sines, cosines, etc.) plus haversines. All the necessary
    tables, including logarithms of the trigonometric functions, are
    provided. The only operations required besides table lookup are
    addition, subtraction, and division by 2. The tables, like most tables
    today, are to 5 decimal places. (I wonder how long that has been going
    5. At least one table was calibrated for courses given in points. There
    was an equivalent table for courses in degrees.
    6. The section on chronometer error mentions "recent" advances which
    allow chronometers to be calibrated by telegraph. They had a system
    where a signal was sent first one way, then the other, to account for
    signal lag. It also mentioned "time balls" (like Times Square on New
    Years' Eve) as being common.
    7. The original price was $2.25.
    8. It mentioned that prior to 1926, almanacs were set up to measure days
    from noon to noon, not midnight to midnight.
    I hope this is of interest to at least someone else on this list! :-)
    Chuck Taylor
    Everett, WA, USA
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