As Humboldt had moved south along the Andes from Bogotá to Quito, coming closer to the Equator, he had measured how the earth’s magnetic field decreased. To his surprise, even after they had crossed the Equator near Quito the intensity of the magnetic field had continued to drop, until they reached the barren Cajamarca Plateau in Peru which was more than 7 degrees and about 500 miles south of the geographic Equator. It was only here that the dip of the needle turned from north to south: Humboldt had discovered the magnetic equator.
