"It can not be
doubted," he observes in his masterly 'Theorie des Phenomenes
Electro-dynamiques', 1826, p. 199, "that electro-magnetic currents exist in
the interior of the globe, and that these currents are the cause of its
temperature. They arise from the action of a central metallic nucleus,
composed of the metals discovered by Sir Humphrey Davy, acting on the
surrounding oxydized layer."
[footnote] **The remarkable connection between the curvature of the
magnetic lines and that of my isothermal lines was first detected by Sir
David Brewster. See the 'Transactions of the Royal Society of Edinburgh',
vol. ix., 1821, p. 318, and 'Treatise on Magnetism', 1837, p. 42, 44, 47,
and 268. This distinguished physicist admist two cold poles (poles of
maximum cold) in the northern hemisphere, an American one near Cape Walker
(73 degrees lat., 100 degrees W. long.), and an Asiatic one (73 degrees
lat., 80 degrees E. long.); whence arise, according to him, two hot and two
cold meridians, i.e., meridians of greatest heat and cold. Even in the
sixteenth century, Acosts ('Historia Natural de las Indias', 1589, lib. i.,
cap. 17), grounding his opinion on the observations of a very experienced
Portuguese pilot, taught that there were four lines without declination.
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