"[The figure] illustrates an instrument contrived to illustrate the theory which ascribes the magnetism of the earth to electrical currents circulating around it at right angles to its axis. N S is merely a wooden axis to the globe. When a galvanic current is sent through the coil of wire about the equatorial regions, small needles placed in different situations will arrange themselves as they would in similar terrestrial latitudes. By comparing this figure with [an earlier figure], representing the globe with the included magnet, a comparison may be made between the two theories of magnetism. The small needle arranges itself similarly on both globes. With a small dipping needle the resemblance between its positions on both, and those assumed by it on the earth's surface are very striking." (from the 1842 edition of the Manual of Magnetism, pg 59). This apparatus is at St. Mary's College.
Note that other
magnetic models of the earth have been constructed.
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