A forgotten proposal for determination of the temporal variation of the magnetic declination



John Churchman, a now forgotten early American geophysicist (for a brief biographical note, see “First Congress of the United States Tackled Geophysics in 1789,” Eos, June 2, 1998, p. 257), proposed that the temporal variation of the magnetic declination could be determined from early land surveys [Churchman, 1794, 1800], He pointed out that boundary lines in the United States were drawn by the use of the magnetic compass as if there were no deviation from true north. Hence if the then current latitudes and longitudes, determined by other more accurate methods, were compared with the boundary lines as entered in these earlier surveys, then the declination at the time of those initial surveys could be easily determined. Churchman's proposal is perhaps best described in his own words [Churchman, 1800]: