VOLCANOES. 
kindle ; in saying the world, we wish to be 
understood as meaning those who have seen 
or read of eruptions without examining the 
subject further. Of natural philosophers, 
there were many who coincided with this 
general opinion ; and others have main- 
tained the direct contrary supposition, as- 
serting, that volcanic fires are extremely 
feeble in their operations; following the 
example of Spallanzani, we shall give tlie 
substance of the arguments of each, in 
order that the reader may draw his own 
conclusion. It is evident that we must have 
recourse to the same rule for ascertaining 
the intensity of volcanic fires, which we 
make use of in measuring the effects of 
our fires when in activity on bodies im- 
mersed in them ; and we have already men- 
tioned, that Wedgwood’s pyrometer answers 
for the purpose, as nearly as the nature of 
the pursuit will permit; but tong before 
the invention of this instrument, attempts 
were made to attain the object in question, 
particularly by the academicians of Naples, 
who, at the time of the great eruption in 
the year 1737, made an experiment on the 
lava near the Torre del Greco, in a valley 
where it had accumulated ; and though it 
had ceased its motion several days, yet re- 
tained a heat equal to that of red-hot iron. 
They formed a piece of lead, weighing two 
ounces, in a conical shape, which they placed 
on the red-hot surface of the lavaj the 
metal became soft in two minutes and a 
half, and in one minute more it was com- 
pletely melted : another piece of lead, in 
every respect exactly similar, was then de- 
posited on a plate of red-hot iron, rendered 
so by burning coals beneath it, when they 
found that it required six: minutes and a 
lialf to soften, and seven and a half to li- 
quify it. Water placed on the lava, boiled 
furiously in three minutes, and on burning 
coals, one minute later. Judging from these 
tacts, the academicians concluded that lava, 
tliough exposed to the external air for some 
days, and consequently far less intensely 
heated than when first issuing from the 
crater, was much more fiery in its nature 
than red-hot iron or burning coals : but this 
conclusion is obviously incorrect ; because 
Uie plate of iron, being surrounded by aif, 
could not acquire all tlie heat which was 
applied to it ; neither was it fair to rest an 
opinion of this description upon a result 
produced by means so unequal, as a vast 
depth of ignited matter opposed to a thin 
plate of iron. 
' Prince Cassano, a meiuber «f our Royal 
Society, produced an instance of the vio- 
lent heat of tlie lava which issued from Ve- 
suvius, to that learned body, which seems 
more to the purpose than that of the Aca- 
demicians : the torrent of lava alluded to 
approached a convent of Carmelites ; every 
combustible article was immediately con- 
sumed, even before the mass came into 
contact with itq and the heat was so ex- 
cessive, that the glasses standing upon a ta- 
ble in the refectory, were instantly reduced 
to shapeless pieces of that useful material : 
this circumstance produced an experiment, 
attended with the same consequences, 
which was the fastening of a fragment of 
glass to the end of a long stick, and hold- 
ing it near the lava, when, at the close of 
four minutes, it became a mere paste. A 
fact of tlie same nature is mentioned by 
Professor Bottis, in his account of the erup- 
tion ofVesuvius, in the year 1667. Now, 
tliough this effect may be produced by sus- 
pending a piece of glass in the air of a glass 
furnace, it must be admitted, tliat this being 
in a state of full activity, and the heat excited 
to the utmost, by every human means, is 
not a just comparison with a body of lava 
far removed from the spot where it acquired 
its heat, which must, without doubt, be at 
that spot ten times greater ; hence it ap- 
pears decidedly clear, that the internal fires 
ofVesuvius far exceeds that of our glass- 
furnaces. 
Bottis seems to have been one of the first 
naturalists, who observed the rapidity with 
which the fire of Vesuvius causes fusion ; 
that gentleman mentions, in his descrip- 
tion of the eruption of July, 1779, that he 
saw a small hill, composed of porous lava 
and scoriae, inclosing an inconsiderable 
gniph, that produced a noise like that of 
oil or fat, in the act of boiling or simmering 
over a fire ; this appearance induced him 
to examine it, when he found it contained 
matter in fusion, which immediately heated 
red hot, and then melted fr.igments of lava 
or scori®, thrown into it. As Spallanzani 
acknowledges, that his efforts to melt simi- 
lar substances leqiiired half an hour, we 
must admit, that this is another proof of 
the superior heat of volcanic tires. A still 
further evidence of their extreme heat is, 
the great length of time which lavas retain 
it. In the year 1737, some labourers, were 
employed to remove the lava which had 
crossed a road, and although a month had 
elapsed from the period of the eruption, 
they were compelled to desist, as tlie heat 
softened their tdols beyond the possibility 
