5, p. 231); the
latter, observed by Erman at 19 degrees 59' S. lat., and 37 degrees 24' W.
long. from Paris, 320 miles eastward from the Brazilian coast of Espiritu
Santo (Erman, 'Phys. Beob.', 1841, s. 570), at a point where the inclination
is only 7 degrees 55'. The actual ratio of the two intensities is therefore
as 1 to 2.906. It was long believed that the greatest intensity of the
magnetic force was only two and a half times as great as the weakest
exhibited on the Earth's surface. (Sabine, 'Report on Magnetic Intensity',
p. 82.)
If the intensity near the magnetic south pole
p 188
be expressed by 2.052 (the unit still employed being the intensity which I
discovered on the magnetic equator in Northern Peru), Sabine found it was
only 1.624 at the magnetic north pole near Melville Island (70 degrees 27'
north lat.), while it is 1.803 at New York, in the United States, which has
almost the same latitude as Naples.
The brilliant discoveries of Oersted, Arago, and Faraday have established a
more intimate connection between the electric tension of the atmosphere and
the magnetic tension of our terrestrial globe. While Oestred has discovered
that electricity excites magnetism in the neighborhood of the conducting
body, Faraday's experiments have elicited electric currents from the
liberated magnetism.
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