tsoever, of such a nature as to be of any _practical
value_, or any certainty beyond that which a certain amount of _mere
experience_ as to the _role commonly played_ by Vesuvius or other
Volcanoes in pretty habitual activity affords to the observer for a
lengthened period. And even this affords scarcely any guide as to what
may happen next. Monte Nuovo was thrown up in a night; Vesuvius _might_
double its volume in a night, or might sink into a hollow like that of
the Val del Bove in a not much longer time. A small _fusillade_ may go
on for months, and yet, without an hour's notice, by any premonitory
sign, may waken up to a roar and darken the air with ashes and lapilli
such as those which overwhelmed Pompeii. One eruption may blow forth
little but dust and ashes (so called), another may pour out rivers of
lava and little else.

The _main_ mischief of all eruptions is effected in two ways: by the
deposit of dust and ashes, lapilli, etc., to the injury or destruction
of fertile land, and by the streams of lava which overwhelm it, as well
as buildings, etc. But what information of any value can seismographic
observation afford as to the course that either of these may take in any
eruption? The volume of pulverulent material that may be ejected cannot
be foreseen; its distribution depends mainly upon its nature and upon
the direction and force of the wind at the time; or again, how shall
these warn us as to the course that the lava, if it appear, shall take,
when we cannot possibly foretell when, how, or by what mouth it may
issue. Even in this late eruption of 1872, with Palmieri stoutly at his
post upon the mountain, and the Observatory instruments in full
activity, they gave no forewarning of the sudden and unexpected belch
forth from the base of the cone, of that tremendous gush of liquid lava
which in a few minutes cut off from life the unhappy visitors whose
deaths he has recorded.

[2] (P. 94). It can scarcely be supposed that these small
eruptive-looking belchings forth from the lava stream, _en route_, are
truly of an eruptive nature at all, _i.e._, in any way connected with
forces seated deeply beneath the bed of the lava stream, or in any way
connected with the volcanic ducts of the cone or beneath it. They are
most probably merely the bursting upwards of large bubbles; that is, of
cavities formed in the mass of the more or less liquid lava by intestine
movements, as its mass winds and rolls along, and by the