verse proposition be equally true,
that is, whether all the great eruptions of our Volcano were preceded by
small fiery manifestations of long duration? There have undoubtedly been
great eruptions not preceded by small central eruptions, but these also
had their period of preparation or precursory signs. After the great
eruption of 1850, Vesuvius remained in apparent repose until the end of
May, 1855, when there was an eccentric eruption and a great flow of lava
lasting twenty-seven days. But for a year before the fumaroles on the
top of the mountain had acquired great activity, their temperature
increased, and hydrochloric and sulphuric acid became more abundant, and
generated the usual coloured products on the adjacent scoriae. Finally,
in the month of January, a crater was formed by falling in of the
ground, and although it did not discharge fire, yet it poured forth
dense smoke. This was the beginning of the fissure manifested four
months afterwards.

Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and
frequently ascended it, considered the increase of those yellow
products--which are chiefly chlorides of iron, but were, at that time,
mistaken for sulphur--as the sign of an approaching eruption.

The only grave objection that can be alleged is that of the memorable
eruption of 1631, which surprised the neighbouring population so
suddenly that many perished miserably, surrounded or covered with lava.
But that terrible conflagration occurred after centuries of repose, so
that trees had grown in the interior of the crater. No one suspected the
possibility of danger. It took place, too, at the end of autumn, when
the cone is usually covered with clouds, and, therefore, no one had an
opportunity of observing any precursory phenomena.

When the Observatory was established, I was able--in the first instance,
at my own expense, and afterwards with some slight assistance from
Government--to undertake studies more assiduous than any previously
made. I had two instruments adjusted to indicate the internal efforts of
the Volcano, viz., M. Lamond's apparatus of variations, which, by means
of finely-balanced needles and methods of amplification proposed by
Gauss, indicates the slightest trepidation of the ground, and my own
electro-magnetic seismograph, a self-registering instrument of exquisite
delicacy. These instruments, when attentively observed, give the most
valuable information with respect to the act