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    Mid XIX century Nav
    From: Bruce Stark
    Date: 2005 Nov 19, 20:23 EST
    Alex,

    I've been gone several weeks, but have read your post in the archives.

    The 1804 Moore lists three places on Kuisin Island. "Nangasaki" is given as 32d, 52' N; 130d, 42' E.

    The 1848 Norie lists eighteen places on Kiusiu Island. "Nangasaki City" is given as 32d, 45' N; 129d, 52' E.

    The two navigation manuals spell "Nangasaki" the same, but have different spellings for the island.

    After a long voyage it was standard practice to turn the chronometers over to an instrument maker to have their rates checked by pendulum clock. That a chronometer gave the correct longitude of the landfall wasn't a sure sign its rate hadn't changed. Several rate changes might have averaged out over the Voyage.

    If a long voyage didn't end at a port where there was an instrument maker the navigator could rate the chronometers himself, either by equal altitudes observations or a series of time sights. With an artificial horizon he could get local time to a fraction of a second this way. A week or so later he'd do it again, which would give him the chronometers' rates of gain or loss.

    Any navigation manual of that era will have an explanation of how to use equal altitudes to rate a chronometer, and a way of calculating the "equation of equal altitudes" to allow for the sun's change of declination between the morning and afternoon observations.

    I think the main reason the Russian navigators wanted to land was so they could use their artificial horizons. As you know, the sea horizon is too variable for such precise work.

    Bruce
       
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