VOLCANOES. 
was azotic, gas, from the degree 1.64 to 
1.38, with respect to what came last. On 
cooling, tiie residue broke the retort by its 
excessive inflation. 
Without entering into an examination of 
the diflerence of opinion existing between 
these philosophers, we shall give an extract 
from the works of Spallanzani, that fully 
illustrates this part of our subject ; “ I shall,” 
he observes, “ now proceed to enquire what 
part this aeriform vapour acts in the erup- 
tions of volcanoes. Where it exists in the 
depths of a volcanic crater, abundantly 
mixed with a liquid lava violently urged by 
subterranean conflagrations, I can easily 
conceive, that by its energetic force it may 
raise the lava to the top of the crater, and 
compel it to flow over the sides and form a 
current. Art can imitate this grand ope- 
ration of nature on an infinitely less scale. 
I placed in a glass furnace a cylindric cru- 
cible, one foot high, add two inches and a 
half in breadth, which I filled half full with 
one of those volcanic products which most 
inflate and boil in the fire. After some 
hours, I observed that the liquid matter 
began slowly to rise, and afterwards to rise 
higher, until it at last overflowed the edges 
of the crucible, forming small streams dow'n 
its sides, which, when they reached the 
plane on which the crucible stood, gave 
origin to small currents, if that plane was 
at all inclined. When I put more of the 
same product into the crucible, the currents 
became larger. If the plane was then taken 
from the siirtace, and tlie small currents, 
thus produced, examined, they were found 
full of minute bubbles, as was likewise the 
matter which remained in the crucible. 
This curious experiment I made with seve- 
ral glasses and volcanic enamels, as also 
with a variety of cellular lavas, and always 
with the same success.” 
Judging from the result of the above 
trial, it cannot be doubted that a similar 
elastic vapour, collecting in vast quantities 
under the surface of the earth, must, upon 
meeting with resistance in its passage, pro- 
duce loud noises resembling thunder, and 
local tremblings of the surrounding earth, 
besides forcing" its way upwards through 
super-incumbent lava : other experiments, 
made by Spallanzani, however, seem to 
prove that it must be another cause which 
expels the fiery matter with violence out of 
craters, as the matrasses he used broke 
without noise, and without ejecting or scat- 
tering the substance, and particularly, as 
the escape of gases has been frequently as- 
certained by the hissing sounds attending 
eruptions ; unfortunately, though those va- 
pours offer themselves to examination, it 
would be impossible to collect any part of 
them without exposing the life of the expe- 
rimentalist to almost certain destruction, 
we must therefore admit their existence,, *; 
and conjecture must supply the rest. 
It will be recollected that all volcanoe.s, 
at present in a state of activity, are sur- 
rounded by, or situated very' near, the sea, 
hence it appears clear, that the agency of 
that body is extremely powerful in promot- 
ing the violence of their eruptions, by rush- 
ing at uncertain intervals, and from un- 
known causes, through the caverns of the 
earth, upon the ever-enduring fires there 
existing ; and this supposition is supported 
by the fact which has been repeatedly ob- 
served of the sudden retiring of the sea im- 
mediately preceding a violent explosion 
from a crater, the certain consequence of 
a rapid diminution of water on the shore. 
Little need be urged to prove the imme- 
diate and vehement separation that takes 
place upon the collision of fire and water, 
and of the force of steam thus produced ; 
one instance however may be safely cited, 
which will place this supposed colli.sion in 
a true light, and is extracted from the 
fourth volume of the “ Memoirs of the Aca- 
demy at Bologna.” A bell of enormous di- 
mensions had been ordered to be cast, at 
Modena, and preparations of the usual de- 
scription were made under a spacious por- 
tico. After the metal had been completely 
melted, it was led into the mould, situated 
at a small depth under the pavement, 
through a small channel ; the burning fluid 
had no, sooner entered the mould than a 
dreadful explosion took place, which re- 
sembled in eveiy particular the horrid ef- 
fects of springing a mine ; a deep hole was 
sunk in the earth, the metal, the mould, 
and every material of the portico above ■ 
it, were scatterred in the air, and several 
persons were killed and severely wounded ; 
if such were the immediate consequences 
of a trifling degree of moisture remaining 
in the sand which composed the mould, it 
may be naturally inferred, that a body of 
water, meeting with subterraneous fires, 
is capable of producing eruptions and earth- 
quakes. It seems however extremely pro- 
bable from experiments, that this effect 
principally arises from the insinuation of 
water under or below the surface of the 
sides of those fires, as it has been ascer- 
tained that water thrown upon fire evapo- 
