VOLCANOES. 
inclined id different angles in different 
places : “ on the west the inclination is gen- 
tle ; on the north the steepness increases ; 
and from tliis point to the south-east the 
descent becomes more sudden, till, where 
the observer stood, they were almost per- 
pendicular. The funnel-shape, however, 
still prevails, as in every other instance, 
and the surface was extremely rugged, and 
strewed with concretions of an orange co- 
lour, which proved to be the muriate of 
ammonia; and it is very probable that the 
numerous stripes of yellow on the nearly 
horizontal plane at the bottom may be the 
same substance. “ In this plain, from the 
place where I stood, a circular aperture 
was visible, apparently about five poles in 
diameter, from which issued the larger co- 
lumn of smoke, which I had seen before I 
arrived at the snmmit of iEtna. I shall not 
mention several streams of smoke which 
arose like thin clouds fl ora the same bot- 
tom, and different places in the sides. The 
principal column, which at its origin might 
be about twenty feet in diameter, ascended 
rapidly in a perpendicular direction while 
it was within the crater ; but when it had 
risen above the edges inclined towards tlje 
west, from the action of a light wind ; and 
when it had risen higher, dilated into an ex- 
tended but thin volume. This smoke was 
white, and being impelled to the side op- 
posite to that on which I was, did not pre- 
vent my seeing within the aperture; in 
which I can affirm, I very distinctly per- 
ceived a liquid ignited matter, whidi conti- 
nually undulated, boiled, and rose and fell, 
without spreading over the bottom. This 
certainly was the melted lava, which had 
arisen to that aperture from the bottom of 
the jEtnean gulph.” 
Being favourably situated for observing 
the effects of external violence on the liquid 
matter within the aperture, the abbe rolled 
large fragments of lava down the side, which 
entering the opening, produced a sound re- 
sembling the sudden immersion of a heavy 
substance in a thick tenacious paste. In 
performing this experiment, the effect was 
multiplied by the stones loosening others in 
their passage, some of which fell on the 
plane ; those, rebounding, even when very 
large, caused a sound extremely different 
from the others that struck the liquid lava : 
this circumstance proves, that, though the 
bottom may be a comparatively thin cover- 
ing of the gulph, it is capable of great re- 
sistance, We shall proceed with a short 
notice of 
Volcanoes in the moon. As the moon 
has on its surface mountains and valleys in 
common with the earth, some modern as- 
tronomers have discovered a still greater 
similarity, viz. that some of these are really 
volcanoes, emitting fire as those on earth 
do. An appearance of this kind was dis- 
covered some years ago by Don Ulloa in 
an eclipse of the sun. It was a sniail bright 
spot, like a star, near the margin of the 
moon, and which he at that time supposed 
to have been a hole, with tlie sun’s light 
shining through it. Succeeding observa- 
tions, liowever, have induced astionomers 
to attribute, appearances of this kind to the 
eruption of volcanic fire; and Dr. Herschel 
has particularly observed several eruptions 
of the lunar volcanoes, the last of which he 
gives an account of in the Philosophical 
Transactions for 1787. “ April 19, 10'* 
36”, sidereal time. I perceive (says he) 
tliree volcanoes in different places of the 
dark part of the new moon. Two of them 
are either already nearly extinct, or other- 
wise in a state of going to break out ; which 
perhaps may be decided next lunation. The 
third shows an actual eruption of fire, or 
luminous matter. I measured the distance 
of the crater from the northern limb of the 
moon, and found it S' 57.3" : its light is 
much brighter than the nucleus of the co- 
met which M. Mechain discovered at Paris 
the lOth of this month. 
“ April 20, 10** 2” sidereal time. Tlie 
volcano burns with greater violence than 
last night. Its diameter cannot be less 
than 3" by comparing it with that of the 
Georgian planet : as Jupiter was near at 
hand, I turned the telescope to his third 
satellite, and estimated the diameter of the 
burning part of the volcano to be equal to 
at least twice that of the satellite : whence 
we may compute that the shining or burn- 
ing matter must be above three miles in 
diameter. It is of an irregular round figure, 
and very sharply defined pn the edges. The 
other two volcanoes are much further to- 
wards the centre of the moon, and resemble 
large, pretty faint nebulae, that are gradually 
much brighter in the middle ; but no well- 
defined luminous spot can be discerned in 
them. These three spots are plainly to be 
distinguished from the rest of the nrarks 
upon the moon; for the reflection of the 
sun’s rays from the earth is, in its present 
situation, sufficiently bright, with a ten feet 
reflector, to show the moon’s spots, even 
the darkest of them ; nor did I perceive 
any similar phenomena last lunation, though 
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