ve electricity. Now, as the ashes separate from the positively
electrified smoke in order to approach the ground, which is negatively
electrified, it follows that they must manifest negative electricity
upon touching the ground, leaving the positive electricity in the smoke
above. For this reason, the electric tension of the smoke is increased
by the descent of the ashes and lapilli, so that discharges between the
upper and lower part of the pine-tree cloud, or the surface of the
crater, are rendered possible. Hence it follows that the flashes of
lightning of Vesuvius play through the smoke, and with difficulty strike
bodies upon the earth; and from this circumstance our ancestors believed
the thunderbolts of Vesuvius to be harmless. However, if the smoke were
very great, and driven by the force of the wind to some distance from
the crater, with an abundant fall of ashes, it would be possible to have
lightning flashes proceed from the smoke to the earth. I possess some
documents which relate that, in 1631, thunderbolts fell upon the Church
of Santa Maria del Arco, and other places on the coast of Sorrento.

After upwards of twenty years' study and observation of meteoric
electricity, I am enabled to prove that atmospheric electricity is never
manifested without rain, hail or snow, and that manifestations of light
are always accompanied by thunder--manifestations of light (_lampi_),
thunder and rain being most closely connected. We may have rain without
manifestations of light, but never the latter without rain or hail. I
cannot here repeat what I have demonstrated in other memoirs; I can only
say that the lightnings of Vesuvius, erroneously believed to be not
accompanied by thunder, are really not accompanied by rain, but are
induced by the descent of ashes and lapilli.[6]

GENERAL CONCLUSIONS.

We may conclude from what I have stated:

1. That by the assiduous study of the central crater, and the
indications afforded by the "Apparatus of Variations" and the
"Electro-Magnetic Seismograph," we can obtain precursory signals of
eruptions; and that the other premonitory signs pointed out by our
ancestors, such as the drying up of wells, either only happen
occasionally or are mere coincidences, such as those of the coincidence
of a dry or a rainy season, the prevalence of certain winds, etc.[F]

2. That the fumaroles of the lavas are communications between the
external surface of the lava, hardened and more or le