Edmund Halley's isogonic chart of 1701 showing lines of equal magnetic declination. This was the earliest chart of this nature and one of the earliest geophysical thematic maps.
Image ID: cgs02147, NOAA's Historic Coast & Geodetic Survey (C&GS) Collection Photo Date: 1701 Category: Coast and Geodetic Survey/Geophysics Geomagnetism/ • High Resolution Photo Available
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