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    Re: Dip-meter again
    From: Frank Reed
    Date: 2013 Apr 12, 10:49 -0700

    Gary, you wrote:
    " I realized that I could get an accurate measurement of the width of the channel by using Google Earth and that I could measure the angle below the horizon to the waterline on the opposite breakwater and with this information calculate my accurate height of eye."

    If I've understood your description correctly, essentially you're using "dip short" to get height of eye. And yes, this works exceptionally well in cases like this where you can figure out the exact linear distance to some feature with a clearly defined waterline.

    Next, suppose you have several objects with clearly defined waterlines at exactly known distances between you and the horizon (ideally, these would be at regular intervals, e.g. a mile apart). If you measure the angles from their waterlines to the horizon, it should be possible to solve for height of eye AND the terrestrial refraction constant k (the rotation of a light ray in minutes of arc per nautical mile). And if you return to the same site under different weather conditions, you should find that the angles change as k changes. Visually, the more distant objects would appear to group together or spread apart vertically as the refraction changes. I'm still hoping someone will make a great time-lapse video of this showing the refracted view of objects towards the horizon breathing in and out during the course of a day.


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