The Sun.
London, England, 1859-06-29 00:00:00

EARTHQUAKES.

The theory of those appalling convulsions which
in a few seconds may spread desolation over the
most populous and fertile districts is still among
philosophers a subject of patient, but hitherto un-
successful investigation. the success of which must
depend on the accumulation of accurate evidence,
combined with geological and meteorological ob-
servations. Hence scientific descriptions of earth-
quakes of recent occurrence are peculiarly useful;
and the following facts, gleaned from an account of
those which took place in Tuscany in April last,
by Professors Campani and Toscani, of the Uni-
versity of Siena, will, we think, be read with in-
terest. The town of Siena, which has always been
subject to such visitation, is about 320 metres above
the level of the sea, and situated on a soil of ter-
tiary formation, known as sub appenine among geo-
logists, and consisting above of a thick stratum of
yellow sand degenerating into sandstone, and here
and there interspersed with calcareous pudding-
stone ; below, of a clayey and bluish marl rich in
fossils, and extending to a great depth. This for-
mation exists with little variety all round the town ;
whence it appears that, notwithstanding the pre-
valence of earthquakes on or near that spot, there
is no volcanic formation there. There are, how-
ever, other tokens of internal terrestrial activity in
the neighbourhood; such as hot mineral springs of
great medicinal power, and in the tunnel of Mon-
tarioso, not a mile from the town, a natural jet of in-
flammable protocarhuretted hydrogen gas. Having
thus given an idea of the geological structure of
the country, the authors proceed to state that last
winter was in those parts remarkably dry, and the
commencement of spring both dry and cold. Dur-
ing March the barometer was exposed to frequent
oscillations, a circumstance which, as our readers
may remember, exactly coincides with M. Prost's
observations communicated on the 20th of Sep-
tember, 1855, to the Academy of Sciences. In
the present case, a circumstance which seems to
bear some analogy to M. Prost's curious observa-
tions on the oscillations of the pendulum for many
days before an earthquake
,opcurs,w4s,,cpmmuni-
cated the Academy of Sciences on 'September 20i
1858. In the present case, the barometrical oscilla-
tions were accompanied with clouds, which after-
wards resolved themselves into heavy fall of snow,
especially on the North-eastern Apennines. From
the 4th to the 7th of April there were heavy fogs,
the barometer maintaining itself rather about the
average height for Siena, until the Bth, when it
began to fall slowly and gradually, reaching 13
millimetres below the average on the 11th at noon,
the eventful day when the shocks commeiced. From
the 3d to the 11th the wind had regularly veered
from N.E. to N., and thence to W., and W.S.W.,
when it degenerated into a calm. There was rain
on the 10th, especially during the night, the rain-
gauge measuring about twelve millimetres ; slight
showers on the 11th yielded three millimetres
more. On that day, at 25 minutes past 9 p.m.,
the first slight shock occurred, which, in the course
of the next twenty-two hours, was followed by no
less than thirty-four others, the most violent oc-
curring at 3 min. past 2 and 28 min. past 4 a.m. on
the 12th. The former only lasted three seconds,
but was more intense than the latter, which lasted
eight seconds, and consisted of a violent undulation
with three distinct shakes. Of the thirty-four
shocks mentioned five nearly equalled the latter;
the remaining twenty-seven were of average inten-
sity. Each of the heavy shocks was followed by a
long rumbling noise; nor could the ground be said
to be perfectly still even during the intervals.
Shocks continued to be felt until the 19th, the total
number registered amounting to fifty-two. During
the whole of this period the sky was variable, alter-
nately cloudy and fair; the air was close, and there
was some rain occasionally. Almost in every in-
stance there was a calm at the time of a shock. ; in
the intervals there was either a breeze or a violent
wind blowing S.W. or W.S.W. Professors Cam-
pani and Toscani were enabled to take most accurate
observations of the winds, since they had at their
command the late Professor Pianigiani's anemome-
trograpli, incomparably the most perfect instrument
of the kind in Europe. It consists of a vertical cylin-
der, about a foot in diameter and two in height, which
is made to descend the same space regularly in the
course of 24 hours by means of clockwork. A
vane, freely revolving above the roof, according to
the impulse of the wind, communicates its motion
to a pencil, which marks strokes of a correspond-
ing length on a graduated paper rolled round the
cylinder, and which may be exchanged for another
when full. These papers collected in a file, form
the completest catalogue of the variations of the
wind that can possibly•be imagined; the altitude
denoting the time of day, and the adiplitude, mea-
sured by degrees, indicating both the intensity and
the extremes of each variation. The authors of
the pamphlet before us conclude their interesting
account by stating the curious fact, that the space
within which the shocks were felt was confined
within an eclipse, the transverse axis of which
passed through Siena, or nearly so, from E.S.E. to
W.N.W., and forming a total length of 28 miles,
a eSeo,
that ex a e tic!.
the centre being about two miles from the town.
The minor axis appears to have been little more
limitedt ha n fourt o
places ce s was
theyi lying thisg but phenomenonashort
distance outside of it were t u terly unconscious of
the shocks which convulsed the soilat the •
of a mile or two.—Galignani.