xii., 1843, Sem. ii., p. 725 and 827.) Among the
numerous examples that have been recently observed, of perturbations
occurring simultaneously and extending over wide portions of the Earth's
surface, and which are collected in Sabine's important work ('Observ. on
Days of unusual Magnetic Disturbance', 1843), one of the most remarkable is
that of the 25th of September, 1841, which was observed at Toronto in
Canada, at the Cape of Good Hope, at Prague, and partially in Van Diemen's
Land. The English Sunday, on which it is deemed sinful, after midnight on
Saturday, to register an observation, and to follow out the great phenomena
of creation in their perfect development, interrupted the observations in
Van Diemen's Land, where in consequence of the difference of the longitude,
the magnetic storm fell on the Sunday. ('Observ.', p. xiv., 78, 85, and 87.)
In the former case, the simultaneous manifestation of the storm may serve,
within certain limitations, like Jupiter's satellites, fire-signals, and
well-observed falls of shooting stars, for the geographical determination of
degrees of longitude. We here recognize with astonishment that the
perturbations of two small magnetic needles, even if suspended at great
depths below the surface, can measure the distances apart at which they are
placed, teaching us, for instance, how far Kasan is situated east of
Gottingen or of the banks of the Seine.
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