| Description | Grover writes that 'there are several circumstances which tend to show, that the magnetic poles or portices, towards which the magnetic currents incline, do circulate in proper orbits about the poles of the Earth in the two hemispheres'. He suggests that variations of the northern needle over the past 250 years indicate a transit of this 'moving vortex' across the North Pole towards the 'western tropic'. He presents various observations on the variation of the compass.
Includes three figures in the text relating to the Earth's magnetic field and magnetic poles. Preceded by a covering letter.
Subject: Magnetism |