('Relat. Hist.', liv. iv., chap. 10.) The Turin physicist, Vassalli Eaudi,
observed Volta's electrometer to be strongly agitated during the protracted
earthquake of Pignerol, which lasted from the 2d of April to the 17th of
May, 1808; 'Journal de Physique', t. lxvii., p. 291. But these indications
presented by clouds, by modifications of atmospheric electricity, or by
calms, can not be regarded as 'generally' or 'necessarily' connected with
earthquakes, since in Quito, Peru, and Chili, as well as in Canada and
Italy, many earthquakes are observed along with the purest and clearest
skies, and with the freshest land and sea breezes. But if no meteorological
phenomenon indicates the coming earthquake either on the morning of the
shock or a few days previously, the influence of certain periods of the year
(the vernal and autumnal equinoxes), the commencement of the rainy season in
the tropics after long drought, and the change of the monsoons (according to
general belief), can not be overlooked, even though the genetic connection
of meteorological processes with those going on in the interior of our globe
is still enveloped in obscurity. Numerical inquiries on the distribution of
earthquakes throughout the course of the year, such as those of Von Hoff,
Peter Merian, and Friedrich Hoffmann, bear testimony to their frequency at
the periods of equinoxes.
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