I
know, however, that other celebrated chemists (Heinrich Rose and Wohler) do
not admit this as absolutely certain. If out of two carefully-purified
masses of cobalt totally free from nickel, one appears altogether
non-magnetic (in a state of equilibrium), I think it probable that the other
owes its magnetic property to a want of purity; and this opinion coincides
with Faraday's view.
According to the experiments of the
p 180
first-mentioned of these great physicists, water, ice, glass, and carbon
affect the vibrations of the needle entirely in the same manner as mercury
in the rotation experiments.*
[footnote] *Arago, in the 'Annales de Chimie', t. xxxii., p. 214; Brewster,
'Treaties on Magnetism', 1837, p. 111; Baumgartner, in the 'Zeitschrift fur
Phys. und Mathem.', bd. ii., s. 419.
Almost all substances show themselves to be, in a certain degree, magnetic
when they are conductors, that is to say, when a current of electricity is
passing through them.
Although the knowledge of the attracting power of native iron magnets or
loadstones appears to be of very ancient date among the nations of the West,
there is strong historical evidence in proof of the striking fact that the
knowledge of the directive power of a magnetic needle and of its relation to
terrestrial magnetism was peculiar to the Chinese, a people living in the
extremest eastern portions of Asia.
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