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    Scrap paper with time sights c.1870
    From: Frank Reed
    Date: 2013 Feb 20, 15:41 -0800

    Many years ago, I bought an old copy of Bowditch. In the back there were some scraps of paper with some calculations in almost illegibly small script. Here are scans of the front and back of one piece. The paper is about five inches tall on the long dimension.

    The calculations are time sights, worked in the common fashion (none of that Martelli nonsense!). You can see what's happening at each step. The observed altitude is at the upper left of each block. It's corrected by some minutes (a net correction for SD, dip, and refraction), and then that's added to latitude and polar distance (90+/-Dec). Then divide the angle by two. Look up four logarithms, add those, etc. So you can pull out some interesting information without a whole lot of effort. There is separate information that the observations were in the North Atlantic on a voyage either to or from Boston. Where was the vessel? You can read out its latitude. What was the date? Summer? Winter? Can we determine anything else? Can you draw any conclusions about the scarcity of paper in this era?? ;)


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