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    Re: Measuring Dip in the 18th Century
    From: Frank Reed
    Date: 2014 Jan 1, 11:24 -0800

    Brad, you wrote:
    "1) that the solstice altitudes of the sun were observed with a quadrant."

    And you made some comments about horizons and bodies of water and tides...

    And you concluded:
    "The assertion that a quadrant is only good to 10 arc minutes can be readily disposed of."

    Oy... Brad, I haven't actually looked at the original reference, but I am prepared to bet many bars of gold (each individually quite small, but there are MANY of them), that the quadrant here refers to an astronomical instrument which would have been found in an early observatory, also known as a "mural quadrant". Here's an article: http://en.wikipedia.org/wiki/Mural_instrument. This is one of the sneaky tricks of astronomical and navigational history: you have to learn the vocabulary that they used at the time to describe their observations and instruments. Otherwise you can be woefully misled!

    -FER
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