Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1Humboldt, Alexander von
History
Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1
Humboldt, Alexander von
Astronomy; Cosmography; Physical geography; Science -- History
[footnote] *From the observations hitherto collected, it appears that the
maximum of intensity for the whole surface of the Earth is 2.052, and the
minimum 0.706. Both phenomena occur in the southern hemisphere; the former
in 73 degrees 47' S. lat., and 169 degrees 30'E. long. from Paris, near
Mount Crozier, west-northwest of the south magnetic pole, at a place where
Captain James Ross found the inclination of the needle to be 87 degrees 11'
(Sabine, 'Contributions to Terrestrial Magnetism', 1843, No. 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. Magnetism is one of the manifold forms under which
electricity reveals itself. The ancient vague presentiment of the identity
of electric and magnetic attraction has been verified in our own times.
"When electrum (amber)," says Pliny, in the spirit of the Ionic natural
philosophy of Thales,* is 'animated' by friction and heat, it will attract
bark and dry leaves precisely as the loadstone attracts iron."
[footnote] *Of amber (succinum, glessum) Pliny observes (xxxvii., 3),
"Genera ejus plura. Attritu digitorum accepta caloris anima trahunt in se
paleas ac folia arida quae levia sunt, ac ut magnes lapis ferri ramenta
quoque." (Plato, 'in Timaeo', p. 80. Martin, 'Etude sur le Timee', t. ii.,
p. 343-346. Strabo, xv., p. 703, Casaub,; Clemens Alex., 'Strom.', ii., p.
370, where, singularly enough, a difference is made between [Greek words])
When Thales, in Aristot., 'de Anima', 1, 2, and Hippias, in Diog. Laert.,
i., 24, describe the magnet and amber as possessing a soul, they refer only
to a moving principle.
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