VOLCANOES. 
of using them. Sir William Hamilton also 
found it very great, and, dropping some 
pieces of wood into the fissures of a mass, 
situated four miles from the volcano, they 
immediately took fire ; but Spallanzani il- 
lustrated this fact more decidedly, by pass- 
ing a body of lava near the upper crater of 
Aitiia, visibly red hot, even in full day-light, 
which had flowed from the mountain eleven 
months before. 
It is supposed, that the volcanic fires of 
Iceland are very active and powerful, 
which is inferred from the incompetency 
of the blow-pipe to fuse the glass issuing 
from them. Vallisueri, describing a new 
volcanic islapd, which rose from the sea in 
the year 1707, near Santorine, asserts, that 
the sea in its vicinity became so violently 
heated, that vast numbers of fish perished, 
and were actually boiled; and it is well 
known, that the same cause melted the 
pitch in the seams of ships’ bottoms, and 
occasioned their leaking : this modern fact 
is corroborated on the authority of Strabo, 
who declares, that the sea was observed to 
boil for four days, between Thera and The- 
rasia. The complete fluidity of lava is 
another convincing proof of the excessive 
heat prevailing in the centre, of volcanoes. 
M. Bottis produces two instances, derived 
from Vesuvius in 1771 and 1776, which de- 
monstrate that this fiery mass assumes a 
state of liquidity almost equal to water: the 
Professor mentions four hills to have arisen 
suddenly in the first case near the aperture 
whence the larva proceeded, and from 
three of those in the shape of cones, issued 
streams of tlie melted matter, exactly re- 
sembling fountains of water. During the 
eruptions of the latter year, fresh lava, rush- 
ing from the crater, fell upon that of I77i, 
and rebounding from it into the air, there 
congealed in various figures capriciously 
ramified, and terminating in thin sharp 
points like needles. A circumstance ob- 
served by Sir William Hamilton, Count de 
Wilzeck, Cardinal Herzan, and the Arch- 
duke Maximilian of Austria, in the year 
1775, seems to establish the fact, that the 
fluidity of the lava has been such at times, 
as to separate into portions, which, bein® 
thrown up from the crater, fell again near 
it, in a state so soft, that a guide who assist- 
ed in conducting these illustrious visitors, 
perceiving a fragment, passed his stick 
through it, and presented it thus to the 
Prince, who ordered both to be deposited 
in his private museum ; this, however, sel- 
dom occurs, at least the indefatigable Spal- 
lanzani never discovered these fragments 
flattened or indented, as if they had fallen 
on some hard substance when in the con- 
sistence of paste. 
With respect to the rapidity of its mo- 
tion, this must greatly depend upon the 
quantity ejected, as well as the intensity of 
its heat : when an opportunity happens for 
attentive observation, the lava has been 
known to rise suddenly to the summit of 
the crater, and as suddenly overflowing its 
boundaries, rush down in various rivulets of 
fire; indeed Bottis compares it to “ a li- 
quor which boils in a vessel, and rises and 
overflows the edges of that vessel from the 
violence of the heat.” The lava from Vesu- 
vius, issuing in 1751, flowed over the space 
of twenty-eight palms in one minute ; in 
1754, it proceeded in two branches, at the 
rate of thirty feet in forty-five seconds, and 
afterwards uniting at thirty-three feet in 
fifty seconds : to these facts may be added 
the testimony of Sir William Hamilton, who 
thought its velocity in 1765, equal to that 
of the Severn, at the passage near Bristol. 
It may, however, be necessary to observe, 
that the fluidity of the matter does not al- 
ways alone occasion its motion, which may 
be accelerated by a great descent, or the 
violent pressure of fresh lava constantly is- 
suing from the~source, particularly as lavas 
are known to harden when actually mov- 
ing, so as to produce a sound when struck, 
and to bear stones thrown on their surface ■ 
but to place this fact beyond a doubt. Sir 
William Hamilton informs us, that himself 
and others, following the example of Mr. 
Jamineau, British Consul at Naples, ac- 
tually crossed a moving mass above fifty 
feet in breadth ; yet even thus circum- 
stanced, those dreadful rivers of fire have 
been known to reach the sea eighteen, 
twenty, and even thirty miles from their 
commencement. 
atguiuciiis uacu to esraoiisu an idea 
that fires excited and maintained by hu- 
man means, exceed those of volcanic origin 
in force, lie in a very small compass indeed; 
they are derived from observing, that some 
furnaces “ vitrify lavas more decidedly than 
volcanoes, and melt schorls which re- 
main perfect in the former.” Dolomieu 
places this supposition in a clear point of 
view, in a memoir published by him of ba- 
saltes. “I shall again repeat,” observes 
this celebrated French naturalist, “what 
cannot be too frequently inculcated, that 
lavas are not vitrifications their fluidity is 
similar to that of metals reduced to fusion ; 
