638 RESISTANCE TO VOLCANIC ACTION. 
and flowed rapidly towards Paterno; but the inhabitants of 
that place, not caring to sacrifice their own town to save Cata- 
nia, rushed out in arms and put a stop to the operation.”* In 
the eruption of Vesuvius in 1794, the viceroy saved from im- 
pending destruction the town of Portici, and the valuable col- 
lection of antiquities then deposited there but since removed to 
Naples, by employing several thousand men to dig a ditch 
above the town, by which the lava current was carried off in 
another direction. 
posed surface, which bury and conceal the fluid mass. The stream rolls on 
under the coating, and between the wails of scorie, and it was the lateral crust 
which was broken through by the workmen mentioned in the text. 
The distance to which lava flows, before its surface begins to solidify, de- 
pends on its volume, its composition, its temperature and that of the air, the 
force with which it is ejected, and the inclination of the declivity over which it 
runs. In most cases it is difficult to approach the current at points where it is 
still entirely fluid, and hence opportunities of observing it in that condition are 
not very frequent. In the eruption of February, 1850, on the east side of 
Vesuvius, I went quite up to one of the outlets. The lava shot out of the 
orifice upwards with great velocity, like the water from a fountain, in a stream 
eight or ten feet in diameter, throwing up occasionally volcanic bombs three or 
four feet in diameter, which exploded at the height of eight or ten yards, but 
it immediately spread out on the declivity down whichit flowed, to the width 
of several yards. It continued red-hot in broad daylight, and without a par- 
ticle of scorize on its surface, for a course of at least one hundred yards. At 
this distance, the suffocating, sulphurous vapors became so dense that I could 
follow the current no farther. The undulations of the surface were like those 
of a brook swollen by rain. I estimated the height of the waves at five or 
six inches by a breadth of eighteen or twenty. To the eye, the fluidity of the 
lava seemed as perfect as that of water, but masses of cold lava weighing ten 
or fifteen pounds floated upon it like cork. 
The heat emitted by lava currents seems extremely small when we consider 
the temperature required to fuse such materials and the great length of time 
they take in cooling. I saw at Nicolosi ancient oil-jars, holding a hundred 
gallons or more, which had been dug out from under a stream of old lava 
above that town. They had been very slightly covered with volcanic ashes 
before the lava flowed over them, but the lead with which holes in them had 
been plugged was not melted. The current that buried Mompiliere in 1669 
was thirty-five feet thick, but marble statues, in a church over which the lava 
formed an arch, were found uncalcined and uninjured in 1704. See ScROPE, 
Volcanoes, chap. vi. § 6. 
* T’eERRARA, Descrizione dell? Etna, p. 108. 
+ LANDGRELE, Naturgeschichte der Vuikane, ii., p. 82. 
