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    Re: Latitude by Talcott-Horrebow Method
    From: Geoffrey Kolbe
    Date: 2018 Nov 3, 23:53 -0700

    William Porter wrote:

    "To resolve 0.1" you'd need a 40" telescope (versatile thing, the """...). 0.1' seems a bit more likely."

    Well, you don't actually need 0.1 arc second resolution to achieve 0.1 arc second precision in measurement. The so-called vernier accuity of the human eye, for example, is about ten times better than it actual resolving power. A good example is reading a vernier caliper. At a range of three feet it is possible to determine the setting of a vernier caliper to 0.001", so the 'vernier accuity' is about 0.1 arc minutes where the resolving power of the human eye is around 1.0 arc minutes.

    It was possible to obtain 0.1 arc second precision on star sightings using the Danjon 'prismatic astrolabe', which was a step up from the class one theodolites I mentioned in an earlier post, even though their objective lens was more like 4 inches than 40 inches in diameter.

    Geoffrey Kolbe

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