so great a depth as is the case in the
channels of the rivers. Sir Isaac Newton
has even ascertained that a red-hot metal
ball, of only two inches diameter, will take
about an hour to become thoroughly cool,
and the same philosopher has laid it down
as an axiom that the time required for cooling
a body of this sort is in the same
proportion as the squares of its diameter;
therefore, although this rule may not be
perfectly applicable to the burning lava,
which is so loose and porous, yet some
idea may be formed what an immense
space of time will be requisite for cooling
the new and dreadful streams of lava in
the district of Skaptefield. The well-known
Sicilian author, Massa, informs us, that
in many places, in Catania, he has found the
lava hot even eight years after the great
eruption of iEtna, in 1669; and that the
new mountain, which, during the eruption
of 1766, arose in the middle district or
temperate zone of iEtna, was still inwardly
burning in the year 177®> four years after.
Nay, farther, that the lava which flowed
thence in 1766, retained a great degree of
heat in the year 177°> in places where it
was deep, and particularly where it had filled
up ravines to the depth of two hundred * feet.
Now, if the heat was so great in Sicily,
at the expiration of four years, where the lava
was not more than two hundred feet in thickness,
can it be matter of surprise if the
new branches of the volcanic torrent in Iceland,
which in the channels of the rivers
lay twice or thrice as deep, should still
remain very hot at the expiration of only
one year?
This may therefore be considered as a
sufficient proof that the continuance of the
heat in the lava is not to be reg©arded as a
certain symptom of the continuance of fire.
For my own part, I am thoroughly convinced
that the whole was already extinct
at the time of my travelling in the district
of Skaptefield, which was in the month of
July of last year; for, with regard to the
number of pillars of smoke seen to arise, I
consider them in reality as nothing more
than vapors, produced by the vast quantity
of water arising from the impeded rivulets,
* See Brydone’s 9th Letter.