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    Re: Mid XIX century Nav
    From: Frank Reed CT
    Date: 2005 Nov 16, 22:47 EST

    Alex, you wrote:
    "Meridian observations
    (with a meridian circle or  teodolite)
    need a firm base. But what about time
    sights?"
    
    Time  sights ashore can be done with an artificial horizon so that yields
    about ten  times better accuracy for a skilled observer than a time sight taken
    with a sea  horizon. Of course, a time sight will tell your you chronometer's
    error only if  you know the longitude of your observing sight. By the date in
    question, the  longitude of Nagasaki was reasonably well known, assuming you
    trust your  tables.
    
    If we don't trust the tabulated longitude, you have other options  for
    determining longitude ashore like moon culminations that are generally more
    accurate than lunars. These depend on a careful determination of true  azimuth.
    
    -FER
    42.0N 87.7W, or 41.4N  72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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