Friday, March 15, 2019

Old stone walls record the changing location of magnetic north

via Norman Muller:

http://theconversation.com/old-stone-walls-record-the-changing-location-of-magnetic-north-112827
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4 comments :

pwax said...

I was hoping the author would be exploring the record within a single stone wall of the rocks being moved and subject to different magnetic directions over the wall's lifetime.

8:56 AM
James Gage said...

NOAA has a computer model that can determine magnetic declination in 10 years intervals from 1750 to present for any given longitude / latitude. It is extremely useful for laying our old boundaries from deeds an surveys in GIS software. (i.e. changing the magnetic bearings to true north bearings)

https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#ushistoric

2:59 PM
Tim MacSweeney said...

There's a lot more to a row of stones that how it's been recorded for the last 300 years. "What if it begins with something that resembles a snake's head??"

9:37 AM
Curtiss Hoffman said...

There are two serious problems with this account. First, the author simply assumes (as do many professional archaeologists) that Native Americans never built stone walls, either before or after European contact, a proposition that can now be considered disconfirmed. Thus, as Tim points out, a wall which appears on a 300-year old map may be much older than that.

Second, there is a peculiar statement to the effect that magnetic declination changes by about 1 degree per decade in New England. This seems extreme - maybe he meant 1 minute? In any event, compare this figure with his calculation that the declination changed by 6.6 degrees over the past 250 years! DOES NOT COMPUTE!!!

11:21 AM

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