The great and disastrous conflagration of Vesuvius, which took place on
the 26th of April, 1872, was, in my opinion, the last phase of an
eruption which commenced at the end of January, 1871, an account of
which I was unwilling to write, because I was convinced that it would
not really terminate without a more or less violent explosion, such as I
had often predicted. I shall now state the reasons upon which my
prediction was founded.
When the central crater begins to heave, with slight eruptions, one may
always predict a series of slight convulsions of greater or less
duration, which are preparatory to the grand explosion, after which the
Volcano remains for the most part in repose. Thus, when I observed the
cone fissuring in November, 1868, and copious lava streams issuing from
it, and flowing over the beautiful and fertile plains of the Novelle,
through the Fossa della Vetrana, instead of announcing the beginning of
an eruption, I announced the termination of one which had been manifest
for upwards of a year by the constant flow of lava from the summit of
the cone.
From the month of November, 1868, until the end of December, 1870, the
mountain remained quiet, except that the fumaroles at the head of the
fissure showed a degree of activity by which chlorides and sulphides of
copper, sulphide of potash and other products, were engendered.
But in the beginning of 1871 the seismograph was disturbed,[1] and the
crater discharged, with a slight detonation, a few incandescent
projectiles. Then I announced that _a new eruption had commenced, which
might be of long duration, but with phases that could not possibly be
foreseen_; and on the 13th January, on the northern edge of the upper
plain of the Vesuvian cone, an aperture appeared, from which at first a
little lava issued, and then a small cone arose and threw out
incandescent projectiles, with much smoke of a reddish colour, whilst
the central crater continued to detonate more loudly and frequently. The
lava-flow continued to increase until the beginning of March, without
extending much beyond the base of the cone, although it had great
mobility. In March, this little cone appeared not only to subside, but
even partly to give way, as almost happens with eccentric cones when
their activity is at an end. Upon visiting it, I observed that four
prismatic or pillar-like masses remained standing, three of which were
formed of scoriæ which had fallen back again in a pasty condition, and
had become soldered together, the fourth consisting of a pyramidal block
of compact and lithoidal lava, which appeared to have been forced up by
impetus from the ground beneath. A little smoke issued from the small
crater, and a loud hissing from the interior was audible. By lying
along the edge, I could see a cavity of cylindrical form about ten
metres in depth, tapestried with stalactitic scoriæ covered with
sublimations of various colours. The bottom of this crater was level,
but in the centre a small cone of about two metres had formed, pointed
in such a manner that it possessed but a very narrow opening at the
apex, from which smoke issued with a hissing sound, and from which were
spurted a few very small incandescent scoriæ. This little cone increased
in size as well as activity until it filled the crater, and rose four or
five metres above the brim.[A] New and more abundant lavas appeared near
the base of this cone, and, pouring continually into the Atria del
Cavallo, rushed into the Fossa della Vetrana in the direction of the
Observatory and towards the Crocella, where they accumulated to such an
extent as to cover the hill-side for a distance of about 300 metres;
then turning below the Canteroni, they formed a hillock there without
spreading much farther. These very leucitic lavas are capable of great
extension, the pieces which are ejected forming for the most part very
fine filiform masses, which may be collected on the mountain in great
quantities, and specimens of which I presented to the Academy under the
name of _filiform lapilli_. These threads were often of a clear
yellowish colour, and, when observed under the microscope, were found to
consist of very minute crystals of leucite embedded in a homogeneous
paste. The crystals were still smaller as the diameter of the threads
was less, and never formed knots or swellings even in the most hair-like
threads. These observations led me to reject the opinion of those who
hold that crystals of leucite are pre-existent in the lava. The viscous
nature of these lavas prevented their being covered with fragmentary
scoriæ, but caused the formation at first of a skin, which, thickening,
became at last a more or less pliable shell, that, when more solidified,
allowed the still fluid part to run as in a tube formed of this solid
shell. For many months the lava descended thus from the cone and
traversed the Atria del Cavallo, always covered, appearing below the
Canteroni of a lively fluidity, until it could no longer be enveloped in
its skin, which was stretched by the addition of new lava, and finally
rent asunder to give room to the current until, owing to diminished
liquidity, it was constrained to stop. When the lava, having traversed
the covered channel it had made for itself from the top of the mountain
to below the Canteroni, made its appearance still running, it frequently
formed large bubbles on the surface, which mostly burst to give vent to
smoke, and then disappeared.
In October, 1871, near the edge of the central crater, another small
crater was formed by falling in, which, after a few days, gave vent to
smoke and several jets of lava. The principal cone frequently opened in
some point of the slope to give egress to small currents of lava, which
quickly ceased. But towards the end of October the detonations
increased, the smoke from the central crater issued more densely and
mixed with ashes, and the seismograph and accompanying apparatus were
disturbed: for all these reasons, I said in one of my bulletins, _we
have either reached a new phase or the end of the eruption_, not knowing
whether the new phase would be the last. On the 3rd and 4th November
copious and splendid lava streams coursed down the principal cone on its
western side, but were soon exhausted. The cone of 1871 appeared again
at rest, and partly even fell in, but did not cease to emit smoke and to
show fire in the interior.
In the beginning of January, 1872, the little cone again became active,
the crater of the preceding October resumed strength, with frequent
bellowings and projectiles, and soon after lavas of the same kind as
before reappeared. The cone of 1871, formed again by the lava ejected,
became so full that the lava poured from its summit in the most singular
and enchanting manner. So far only an eccentric or ephemeral cone had
risen close to the central crater, which, after exhaustion, regained
vigour and discharged lava from the apex instead of the base, as usually
happens.
In the month of February matters were somewhat moderated; but in March,
with the full moon, the cone opened on the north-west side--the cleavage
being manifest by a line of fumaroles--and a lava stream issued from the
lowest part without any noise and with very little smoke, and poured
down into the Atria del Cavallo as far as the precipices of Monte di
Somma. This lava ceased flowing after a week, but the fumaroles pointed
out the cleft of the cone; and between the small re-made cone, which had
risen to the height of 35 metres, and the central crater, a new crater
of small dimensions and interrupted activity opened.
On the 23rd April (another full moon) the Observatory instruments became
agitated, the activity of the craters increased, and on the evening of
the 24th splendid lavas descended the cone in various directions,
attracting on the same night the visits of a great many strangers. All
these lava streams were nearly exhausted on the morning of the 25th;
only one remained, which issued from the base of the cone, not far from
the spot whence that of the preceding month had issued. Numbers of
visitors, attracted by the splendour of the lava streams of the
preceding night, which they supposed still continued, soon arrived, but,
finding them exhausted, were for the most part conducted by their guides
to see the one still flowing. It was almost inaccessible, and to reach
it one had to walk over the rough inequalities of the scoriæ. It took me
two hours to get there from the Observatory, when I visited it that
morning, and therefore I endeavoured to dissuade those who wished to
visit it at night from the attempt, but set out myself from the
Observatory at 7 p.m., leaving my only assistant there. The instruments
were agitated. After midnight the Observatory was closed, and my
assistant retired to rest. Late and unlucky visitors passed unobserved
with an escort of inexperienced guides; at half-past 3 o'clock in the
morning of the 26th they were in the Atria del Cavallo, when the
Vesuvian cone became rent in a north-westerly direction, the fissure
commencing at the little cone which disappeared, and extending to the
Atria del Cavallo, whence a copious torrent of lava issued. Two large
craters formed at the summit of the mountain, discharging numerous
incandescent projectiles with white ashes, and glittering with particles
of mica, which frequently recurred.
A cloud of smoke enveloped these unfortunates, who were under a hail of
burning projectiles and close to the lava torrent. Some were buried
beneath it[B] and disappeared for ever; two dead bodies were picked up,
and eleven grievously injured, one of whom died close to the
Observatory. He alone revealed his name, Antonio Giannone. I learned
afterwards that he was a fine young fellow, and Assistant-Professor in
one of the Universities.
Assistant-Professors Signor Franco, who is a priest, and Signor
Francesco Cozzolino, a priest also, entrusted with the festive mass for
the Observatory, hastened to assist the dying. On my own return thither,
the sad spectacle of the dead and dying awaited me; the former were
conveyed, through the assistance of the municipal officer of Resina, to
the Cemetery, and the latter to the Hospital. But we must leave this
scene of grief and sorrow, and return to the eruption.
The fissure of the cone on the north-west side was large and deep, and
extended into the Atria del Cavallo, about 300 metres. No mouth opened
along the cleft of the cone itself; all the lava issued from that part
which extended into the Atria. From previous experience I should have
expected to have seen the formation of adventitious cones along the
widest part of the fissure, which is never that most elevated, and these
discharging from their summits æriform matter frequently mixed with
projectiles, and from their base lava; but on this occasion no cone
appeared at the widest part of the fissure, but a long hillock was
formed like a little chain of mountains, one point of which was elevated
about fifty metres above the plain beneath, and bearing no resemblance
to a cone.
Another fissure opened in the cone on the south side, which did not
extend to the base, and lava issued from this and flowed in the
direction of the Camaldoli. Streams of less importance furrowed the cone
in other directions, but the largest quantity of lava proceeded from the
fissure in the Atria del Cavallo, below the hillock or miniature chain
of collines just described. This lava stream was for some time
restrained within the Atria del Cavallo, among the holes and
inequalities of the lavas of 1871, but these being filled up and
overcome, it divided into two branches--the smaller one flowing through
a hollow which separated the lavas of 1867 from those of 1871, and made
its way over the lavas of 1858, threatening Resina, but stopped as soon
as it reached the first cultivated ground; the larger branch
precipitated itself into the Fossa della Vetrana, occupying the whole
width, about 800 metres; and traversing the entire length of 1,300
metres in three hours. It dashed into the Fossa di Faraone; here it
again divided into two streams, one overlying the lava of 1868, on the
Plain of the Novelle, partially covering the cultivated ground and
country-houses; the other flowing on through the Fossa di Faraglione,
over the lava of 1855, reached the villages of Massa and St. Sebastiano,
covering a portion of the houses, and thence continued its course
through the bed of a foss or trench which, contrary to my advice, had
been excavated after the eruption of 1855, in the expectation of
diverting the course of that lava. I did not fail to observe that the
rains which previously descended through these steep channels, would in
future be kept back to filtrate through the scoriæ, without ever
reaching the new channel.
The lava of this eruption, meeting with this said excavation, flowed
into it, instead of pursuing its road over the lava of 1855, and thus
invaded highly cultivated ground and towns of considerable value,
extending to the very walls of a country-house belonging to the
celebrated painter, Luca Giordano. This lava stream, having surmounted
the obstacles which the heaps of scoriæ in the Atria del Cavallo
presented to it, ran with great velocity (notwithstanding its being
greatly widened out in the Fossa del Vetrano), so that between 10 a.m.
and 11 p.m. it traversed about five kilometres of road, occupying a
surface of five to six square kilometres. If it had not greatly
slackened after midnight, from the failure of supply at its source, in
twenty-four hours more, by occupying Ponticelli, it would have reached
Naples, and flowed into the sea.
Although I had often visited the two villages of Massa and St.
Sebastiano, previously greatly injured by the lava of 1855, yet I could
not well estimate, upon now seeing them again, the number of houses
which had disappeared. Massa seemed to me diminished by about one-third,
and St. Sebastiano by somewhat less than a fourth. But the way of escape
was open to the inhabitants of Massa; whilst a great river of lava
occupying the road leading to St. Giorgio a Cremano would have hindered
the flight of the inhabitants of St. Sebastiano, if they had been
dilatory. The lava stream now separating the two villages is little less
than a kilometre in width, and is about six metres in height.
On the night of the 26th April, the Observatory lay between two torrents
of fire, which emitted an insufferable heat. The glass in the
window-frames, especially on the Vetrana side, was hot and cracking, and
a smell of scorching was perceptible in the rooms. The cone, besides
being furrowed by the lava streams just described, was traversed by
several others, which appeared and disappeared. It seemed completely
perforated, and the lava oozed as it were through its whole surface. I
cannot better express this phenomenon, than by saying that _Vesuvius
sweated fire_. In the day-time, the cone appeared momentarily covered
with white steam jets (fumaroles), which looked like flakes of cotton
against the dark mountain-side, appearing and disappearing at brief
intervals.
Simultaneously with the grand fissure of the cone, two large craters
opened at the summit, discharging with a dreadful noise, audible at a
great distance, an immense cloud of smoke and ashes with bombs and
flakes, rising to the height of 1300 metres[C] above the brim of lava
(_sull' orlo de essi_). The white ashes, before described, although they
did not fall beyond the Crocella, were carried by the wind as far as
Cosenza, from whence they were sent to me by Dr. Conti. These ejections
were followed by dark sand, with lapilli and small fragments of scoriæ
of the same colour. The smoke, driven up with violence, assumed the
usual aspect of a pine tree, of so sad a colour that it reminded us of
the shadowy elm of Virgil's dreams ("_ulmus opaca ingens_"). From the
trunk and branches of the pine-tree cloud fell a rain of incandescent
material, which frequently covered all the cone. The lapilli and the
ashes were carried to greater distances.
The victims of the morning of the 26th, the torrents of fire which
threatened Resina, Bosco and Torre Annunziata, and which devastated the
fertile country of the Novelle, of Massa, St. Sebastiano and Cercola,
the two partially buried villages, the continual and threatening
growlings of the craters, caused such terror that numbers fled from
their dwellings near the mountain into Naples, and several in Naples
went to Rome or to other places. Very many delayed from the knowledge
that I was in the Observatory, and held themselves in readiness for
flight whenever I should abandon it.
The rapidity with which the vast torrent of fire assailed the houses
(_i.e._, in these villages), and the great heat which spread to a
distance, scarcely allowed the fugitives to carry away any of their
belongings; many were completely destitute. The authorities vied with
each other in zealous efforts to relieve the distress, and the
municipality of Naples sheltered and fed the wretched beings for many
days.
The igneous period of the eruption was short, for on the morning of the
27th the lava stream, bearing down upon Resina, having covered a few
cultivated fields, stopped; the lava descending from the summit of the
mountain towards the Camaldoli also stopped; and the great lava torrent,
which passed the shoulders of the Observatory through the Fossa della
Vetrana, lowered the level of its surface below those of its two sides,
which appeared like two parallel ramparts above it.
If these streams had continued on the 27th, flowing in the same manner
as they did on the night of the 26th, they would have reached the sea,
bringing destruction to the very walls of Naples.
But before leaving the subject of these lavas I must narrate an
important fact to which I was witness, and which was thrice repeated,
near the banks of the great river of fire that ran close to the
Observatory. At three several points, and at different times, I observed
great balls of black smoke issue from the lava, driven up with continued
violence, as if from a crater; through the smoke I frequently observed
numerous projectiles thrown up into the air, but I could not say whether
with noise or in silence, for the noise of the central crater was
deafening. Each of these little eruptions, which I may call _external
eruptions_, lasted from fifteen to twenty minutes. The first took place
at the most elevated point of the Fossa della Vetrana, on the right bank
of the torrent; the second, under the hill of Apicella, where the lava
divided into the two branches, before described; and the third near to
the Observatory on the left bank of the lava stream. These singular
explosions terminated without leaving little cones or craters, the lava
in its impetuosity carrying every trace away. These eruptions were seen
from Naples, and the Observatory was justly believed to be in danger.
One has been clearly photographed, the one which was the best seen from
Naples, being the nearest and the least darkened by the smoke of the
lava. (Plate 4.) Is this the first time that the phenomenon has been
remarked? I believe that it is at least the first time it has been
authenticated. The authority of Julius Schmidt, quoted by Scrope, has no
weight with me, for I was also a witness of what happened at Vesuvius in
1855; and, although these cones were in the midst of the lava in the
Atria del Cavallo, they originated, according to the opinion of
everyone, from the fissure from which the other and much larger cones
proceeded. The same phenomenon was observed in the Atria del Cavallo in
1858, when I caused two of the little cones to be brought to the
Observatory; but these also might belong to the fissure along which the
other cones were arranged. The same may be said of the little craters
observed, after they had been exhausted, by Professor Scacchi in 1850.
But the discharging mouths now observed in the Fossa della Vetrana,
which existed for twenty minutes and then disappeared, and which were
not at all in a continuous line, and could not be supposed to correspond
with any fissure beneath, constitute a circumstance which, if not new,
is evident for the first time, and cause the recognition of a power in
the lava itself to form eruptive fumaroles.[2]
The igneous period of the eruption having terminated on the evening of
the 27th, the ashes, lapilli, and projectiles became a little more
abundant, whilst the roaring noises of the craters apparently became
greater. The pine-tree cloud was of a darker colour, and was furrowed by
continual lightning, visible by daylight from the Observatory. Many
writers on the subject of Vesuvius affirm that the flashes which appear
through the smoke cloud were lightning unaccompanied with thunder, but
they studied the phenomena from Naples, or some place more or less
distant from the crater, where the report of the thunder was inaudible,
or could not be distinguished from the bellowing and detonation of the
mountain. The fact is that these flashes were constantly followed by
thunder, after an interval of about seven seconds.[D] When the flash was
very short, a simple noise like the report of a gun was heard, but if it
were long, a protracted sound like that from torn paper ensued.
On the 28th the ashes and lapilli, continuing to fall abundantly,
darkened the air, yet without diminishing the terrible noise; at Resina,
Portici, St. Giorgio a Cremano, Naples, etc., terror was universal.
On the 29th, with a strong wind blowing from the east, scoriæ of such a
size fell at the Observatory, that the glass of the windows unprotected
by external blinds was broken. The noise from the crater continued, but
the projectiles rose to a less height, indicating a diminution in the
dynamic power of the eruption. Towards midnight the noise of the craters
was no longer continuous, and recurred with less force and for shorter
intervals. Almost at the same hour a tempest burst over the Campania
with loud thunder and a little rain. The grass, the seeds, the vine
tendrils, the leaves and tops of the trees dried up immediately, and the
country was changed from spring to winter. The storm, although repeated
on the following days, passed away by degrees, and thus the floods,
which I strongly feared, did not occur. Almost always after great
eruptions of Vesuvius, storms of heavy rain have followed, and the
ground being covered with ashes, the water could not filtrate through
into the soil, but descended in muddy torrents over the adjacent
country, occasioning as much damage as the fire itself.
On the 30th, the detonations were very few, and the smoke issued only at
intervals, and by the 1st May the eruption was completely over.
When the smoke had cleared off the figure of the cone was seen to be
changed. (_Vide_ Plate 5a.)
The ground was perpetually disturbed whilst the Volcano raged, so that
the Observatory oscillated continually. Some shocks were felt not only
in the adjacent territory, but at a greater distance, at Montovi and
elsewhere. The oscillations at the Observatory were chiefly undulatory,
from N.E. to S.W. They were observed for some days after the termination
of the eruption, but not continuously, although they maintained some
intensity.
If we refer to January, 1871, we shall find that that eruption was
preceded by several earthquakes, among which were those of the months of
October, November and December, in the previous year, that wrought such
destruction in Calabria, and especially in the province of Cosenza; if
we consider that as only the last phase, we shall find that it was
preceded by great shocks of earthquake that devastated some regions of
Greece.[3]
The great quantity of lapilli which fell buried the scoriæ with which
the Vesuvius cone was covered, so that it became somewhat more difficult
to ascend to the summit, and much less difficult to descend. Having
reached the top of the mountain, I found a large crater divided into two
parts by what seemed a cyclopean wall. The two abysses had vertical
sides, and revealed the internal structure of the cone. Their vertical
depth was 250 metres; and beyond that I observed a sort of tunnel
perforated in the rock, with a covering arch raised above the bottom of
the eastern abyss about 12 metres, judging by the eye. The interior
walls of the crater showed neither the usual stalactitic scoriæ nor
sublimations, nor fumaroles, but alternate beds of scoriæ and of compact
lava. The fumaroles and sublimations abounded, only about the brims of
the craters. Hydrochloric and sulphuric acid and sometimes sulphuretted
hydrogen affected respiration, and the temperature rose sometimes to 150
degrees. Various fissures about the brim of the double crater indicated
prolongations downwards, which allowed me to descend with a rope, in
order to examine the interior of the tunnel to which I have just
alluded. The highest brim of the crater was fissured for a distance of
80 metres, and the greatest depth of fissure was at that place.
By measurement with the barometer, we ascertained approximately (for
only one barometer was used) that the height of the Vesuvian cone was
somewhat diminished.
Not only the Vesuvian cone, but the whole adjacent country appeared
white for many days, as if covered with snow, when exposed to sunlight.
This was due to the sea-salt contained in the ashes with which the
surface was strewn.
A great quantity of coleoptera assembled on the flat roof of the
Observatory, where the ashes and lapilli were heaped up two decimetres
in height. I found the same species on the cone, where many insects were
observed on other occasions, such as the _Cuccinella septempunctata_;
the crysomela populi, etc., were wanting. This phenomenon of the
extraordinary concourse of insects on the top of Vesuvius, in order to
die in some of the fumaroles, especially noted previous to and after
great eruptions, is a circumstance for which I cannot account.[4] The
whole of the lava emitted in this eruption occupies a surface of about
five square kilometres; allowing an average thickness of four metres, we
obtain a mass of twenty millions of cubic metres. About three-fifths of
this lava did no injury, being deposited upon other pre-existing lava.
However, the lava in the Novelle, which was deposited upon the lava of
1858, covered quarries of the best stone which had been worked at the
time, covered many paths that had been cleared, and buried the new
Church of St. Michele, with some houses that surrounded it, which had
been rebuilt on the site of the former church, which was covered by the
lava of 1868. The destruction of land in occupation, of buildings and of
crops, exceeded three million francs in value. Many proposals for
relieving the sufferers have been received. Wishing to aid in this
benevolent work, I gave a public lecture, admission for each person
being one franc; and this lecture, from notes badly taken, was printed
by private speculation, and I was compelled to repudiate the report of
it through the public papers.
The evolutions of carbonic acid (_mofette_), which usually appear at the
end of great Vesuvian eruptions at low-situated spots or hollows, with
very rare exceptions, were observed on this occasion a few days after
the eruption had completely ceased. They appeared in the direction of
Resina. I found the most elevated at Tironi, and the most numerous
between La Favorita and the Bosco Reale di Portici.
The water in wells was on this occasion neither deficient nor scarce
previous to the eruption, but was very acid after the appearance of the
carbonic acid evolutions in those neighbourhoods in which they
abounded. Having stated that the disastrous conflagration of the 26th
April ought, in my opinion, to be regarded as the last phase of a long
period of eruption, which commenced at the beginning of 1871, I consider
it right to discuss the question at somewhat greater length.
Not only from twenty years' personal observations, but from the
attentive study of accounts of previous eruptions, I have found that
when the central crater awakens with small eruptions after a certain
time of previous repose, these almost always have a long duration, and,
after various phases of increase and decrease, terminate in a great
eccentric eruption, that is to say, with the production of an aperture
from which a copious lava stream issues. The eruptions of 1858, 1861,
1868 and 1872, furnish the most recent examples of what I affirm. I
might cite many others of earlier date, but I shall content myself with
recording the greatest conflagration of this century, that of October,
1822.
Before the erection of the Vesuvian Observatory, it was impossible to
obtain a consecutive account of all the phases which the Volcano
presented; but we generally obtained the description of the more
splendid phases of the eruption which arrested the attention of
everyone. Hence, notices of the small phenomena which preceded a great
eruption are frequently wanting. We cannot always ascertain whether the
fumaroles of the craters became active and at what periods, what was
their temperature and what the diverse nature of their emanations, etc.:
whether and when any change in the crater with slight eruptive
manifestations occurred; discharges which sometimes commenced in the
bottom of a crater becoming active, and so are invisible at Naples.
But it may be asked whether the inverse proposition be equally true,
that is, whether all the great eruptions of our Volcano were preceded by
small fiery manifestations of long duration? There have undoubtedly been
great eruptions not preceded by small central eruptions, but these also
had their period of preparation or precursory signs. After the great
eruption of 1850, Vesuvius remained in apparent repose until the end of
May, 1855, when there was an eccentric eruption and a great flow of lava
lasting twenty-seven days. But for a year before the fumaroles on the
top of the mountain had acquired great activity, their temperature
increased, and hydrochloric and sulphuric acid became more abundant, and
generated the usual coloured products on the adjacent scoriæ. Finally,
in the month of January, a crater was formed by falling in of the
ground, and although it did not discharge fire, yet it poured forth
dense smoke. This was the beginning of the fissure manifested four
months afterwards.
Ignazio Sorrentino, who spent a long life in the study of Vesuvius, and
frequently ascended it, considered the increase of those yellow
products--which are chiefly chlorides of iron, but were, at that time,
mistaken for sulphur--as the sign of an approaching eruption.
The only grave objection that can be alleged is that of the memorable
eruption of 1631, which surprised the neighbouring population so
suddenly that many perished miserably, surrounded or covered with lava.
But that terrible conflagration occurred after centuries of repose, so
that trees had grown in the interior of the crater. No one suspected the
possibility of danger. It took place, too, at the end of autumn, when
the cone is usually covered with clouds, and, therefore, no one had an
opportunity of observing any precursory phenomena.
When the Observatory was established, I was able--in the first instance,
at my own expense, and afterwards with some slight assistance from
Government--to undertake studies more assiduous than any previously
made. I had two instruments adjusted to indicate the internal efforts of
the Volcano, viz., M. Lamond's apparatus of variations, which, by means
of finely-balanced needles and methods of amplification proposed by
Gauss, indicates the slightest trepidation of the ground, and my own
electro-magnetic seismograph, a self-registering instrument of exquisite
delicacy. These instruments, when attentively observed, give the most
valuable information with respect to the activity of the adjacent
Volcano.
If the very slightest eruption occurs, these instruments manifest slight
perturbation, increasing with the activity of the mountain. When the
Volcano attains a certain degree of activity, and the instruments are
proportionately disturbed, it is impossible to foresee a new phase of
increase without constantly watching the changes in the intensity of the
perturbations; and to effect this it is requisite to have upon the spot
a staff of assistants sufficiently numerous, scientific and intelligent.
If, therefore, on the night preceding the 26th of April the instruments
had been properly watched, they would have undoubtedly indicated the
great increase in the activity of the Volcano. The perturbations on the
23rd were steadily increasing, and on the evening of the 25th they were
much stronger than on the 24th, but on the morning of the 26th they had
become extraordinarily strong; they must, therefore, have increased
considerably during the night.