During the day of the 24th of October there
was a constant change of position, but after midnight, when the Aurora began
perceptibly to decline in brightness, the disturbance entirely ceased. The
changes of position of the horizontal-force magnet were as large and as
frequent as those of the declination magnet, but the vertical-force magnet
was at no time so much affected as the other two instruments. See 'On the
Aurora Borealis, as it was seen on Sunday evening, October 24th, 1847, at
Blackheath,' by James Glaisher, Esq., of the Royal Observatory, Greenwich,
in the 'London, Edinburgh, and Dublin Philos. Mag and Journal of Science for
Nov.', 1847, by John H. Morgan, Esq. We must not omit to mention that
magnetic disturbance is now registered by a 'photographic' process: the
self-registering photographic apparatus used for this purpose in the
Observatory at Greenwich was designed by Mr. Brooke, and another ingenious
instrument of this kind has been invented by Mr. F. Ronalds, of the Richmond
Observatory.] -- Tr.
When this disturbance attains a great degree of intensity, the equilibrium
of the distribution is restored by a discharge attended by a development of
light "The Aurora* itself is, therefore, not to be regarded as an externally
manifested cause of this disturbance, but rather as a result of telluric
activity, manifested on the one side by the appearance of the light, and on
the other by the vibrations of the magnetic needle.
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