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    Re: Old stone walls record the changing location of magnetic north
    From: Lu Abel
    Date: 2019 Mar 12, 21:35 +0000
    What I find strange is that the author found magnetic declination (or, as mariners call it, variation) to be around 7 degrees.  When I left New England for the Left Coast about 25 years ago, Variation was about 15 degrees.   So that says the magnetic north pole slipped southward before doing its about face and heading for Siberia as recently discussed.  Or maybe it headed significantly westward, which would also increase the value of Variation.

    Regardless, an interesting article -- on my 3-1/2 acres in Massachusetts, I had a stone fence built by a Shaker colony running through my lot and in all the time living (and sailing) in New England, I never thought of checking the orientation of the fence...

    Lu Abel

    On Tuesday, March 12, 2019, 1:33:07 PM PDT, Frank Reed <NoReply_FrankReed@fer3.com> wrote:

    I didn't see the link to the original article in the short "conversation" piece and missed the key point here. The claim is not that there are boundaries which were laid down to match magnetic directions but rather that the boundaries, haphazard as they are and with origins in many different orientation schemes, were recorded by surveyors with magnetic bearings. Then the stone walls provide lasting ground evidence that can be seen in aerial LIDAR surveys and referred back to those old orientations. Fair enough and not at all controversial.

    Of course we also have magnetic survey data on the town boundaries themselves which still exist in their original positions. So what does any of this analysis of LIDAR surveys yield? More detail at a level that does not impact the magnetic models? We already have this data.

    Frank Reed

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