_ already quite cooled on the surface. 
2 NATURE 
| Noo. 71 872 
the principal stream on the left into Fosso Vetrana, and 
the small part on the right, upon the slopes of the Piano. 
The lava does not scoop out but only rolls along the 
ground, the eroded ravines which furrow the sides of the 
mountain becoming necessarily their natural channels. 
Thus the successive currents have followed very nearly 
the same channel, being superimposed on each other 
through a great part of their course. When the lava 
streams are of considerable depth, they often pass over 
small inequalities of ground, and leap to right and left 
when they strike against any considerable obstacle. 
A good carriage road leads from Resina as far as the 
Observatory, across the cultivated slopes which are 
covered with houses. At less than a kilometre from the 
Observatory, the road traverses the lava of 1858, which 
has covered up the old route, and through which it has 
become necessary to reopen the way. Almost imme- 
diately after having passed the lava, the Observatory is 
reached, where Prof. Palmieri sojourned during the ter- 
rible days of the last eruption. This building, situated at 
a height of 600 metres, is a substantial freestone struc- 
ture of two stories, surrounded by beautiful terraces 
which overlook the lava field on all sides, and the edges 
of which are enclosed by a handsome railing not much in 
keeping with the desolate aspect of the place. M. Pal- 
mieri has been compelled, from the want of trained 
assistants, to set up registering apparatus, and can obtain 
certain connected observations only during the time of 
his occasional stay at the Observatory. But for this cir- 
cumstance, the last eruption would probably have been 
foreseen for some time.* 
From the Observatory, the summit of Mount Vesuvius 
can be reached in two hours. The road skirts the im- 
mense fields of black lava which stretch between Monte 
Canteroni and the foot of Vesuvius, and which have been 
formed by the recent eruptions as they escaped from Atrio 
del Cavallo. The lava of April 26 M. de Saussure found 
There would not 
appear to be a greater amount of incandescence at the 
‘bottom of any crevasse, although the matter certainly 
preserves its heat under the superficial stratum, as was 
attested by the great number of fumaroles encoun- 
tered almost everywhere, These emanations escaped for 
the most part from little kilns, or swollen crevasses, 
which communicate by clefts with the deeper lava. Around 
some of these fires there prevailed a strong odour of 
hydrochloric acid, while other vents did not emit anything 
but steam or warm air. These are, indeed, the successive 
phases which mark these emanations of lava until they 
reach complete coolness. 
At first, the whole surface of the lava-streams seems to 
exhale steam and hydrochloric acid, and the atmosphere 
is filled with a disagreeable odour which makes breathing 
uncomfortable, But very quickly the exhalations are 
localised around the little centres of fire, whose activity 
continues for many months, and emanations from which 
are gradually modified. Thus, as seen from Naples at the 
time of the visit, the whole of the lava appeared to be 
smoking, and it was possible clearly to distinguish the tracks 
of the whitish vapours which appeared to wander over the 
surface ; but close at hand there was nothing to be seen but 
the fumaroles, between each of which there is plenty of 
* See description ot the Observatory, NaTuRE, vol. vi. p. 145. 
space. The gas and the hot vapours which the lava emits 
are charged with numerous substances, and become the 
source of mineral deposits which fill the tourist with 
wonder, One of the most curious phenomena observed — 
is the power of burning lava fo retain an enormous 
quantity of water and salt, which it does not allow to 
escape until it begins to cool. The formation of salt is 
shown generally over the whole stretch of lava emitted in 
1872. Soon after the surface cools it is covered with a 
light crust of salt, which forms in similar flowery patterns 
on the beds of cinders that cover the plains, the cinders 
themselves emitting everywhere hydrochloric acid. The 
first showers caused this deposit rapidly to disappear, 
and there remained on the 12th of May only scanty 
traces, except on the lower surface of the blocks, where — 
the rain had not the power to dissolve it. But the salt 
continued to be deposited in the vents, from which were 
detached beautiful crystals and graceful concretions ; 
it continued also to be formed upon the great deposits 
of cinders on the cone of Vesuvius, and, even on May 19, 
the summit of the mountain, as seen from the Ob- 
servatory, appeared from this cause as if sprinkled with 
snow. 
Next to salt, the substance which is formed in greatest 
abundance upon the lava is chloride of iron, which 
assumes the most varied tints according to its sur- 
roundings, but is in general of a beautiful yellow, 
often orange, and is easily mistaken for sulphur. A 
multitude of other substances are deposited around the 
smoke-vents, besides those which have been named. 
These are for the most part metallic compounds, espe- 
cially chlorides, and more rarely sulphur compounds. 
There are chlorides of copper and lead, hematite and 
magnetic iron ore, gypsum, &c. The peroxide of iron, 
in particular, plays an important part in the life of these 
fumaroles ; it appears to be formed by the decomposi- 
tion of chloride of iron ; the protuberances of the scorize 
are often covered with the substance, which gives them 
the richest and-most brilliant variegated appearance. 
The origin of these many substances has considerably 
occupied the attention of chemists, and has not yet been 
satisfactorily explained ; but the form of the concretions, 
as much as the accumulation of substance, apparently 
foreign to laya, indicate that theyareformedby sublimation. — 
When the summit of the cone was approached, fine ashes 
were found scattered about the transverse rents that are 
apt'to be taken for ruptures caused by the concussions 
accompanying the’ eruptions. 
rather have formed radiating or longitudinal rents, while 
these are perhaps only the effect of the settlement of - 
the cinders which naturally tend to act in the direction of 
But violent fissures would — 
~* 
4 
the greatest slope,’and to give rise to fissures analogous to. . 
those which are observed in the centre of the Alps. It is 
to this same phenomenon that must be attributed the 
step-like structure, traces of which are met with on the 
external face of the summit of the mountain, and which is 
probably owing to the fact that the lower edge of the 
rents must be elevated by the settlement, while the upper 
edge remains unaffected, or is itself lowered in supplying _ 
the matter which afterwards fills the rents. On the 
outside face of the cone, these steps are scarcely more 
than three or four inches in height, but on the margin of 
the internal face of the south-west side of the crater are — 
