answers the purpose with clearness and brevity, we owe to our celebrated seismologist Mercalli.
<1 We believe it to be better, for the better understanding of the isoseismographic tables, to reproduce
Mercalli’s Seismic Scale here:
1. Instrumental shock, that is only observed by seismic instruments.
2. Very slight, felt only by some persons under conditions of perfect quiet, especiality in the upper floors of houses, and
by very nervous and sensitive persons.
3. Slight, felt by several persons but few relatively to the number of inhabitants of a given village or town; said to be scarcely
felt, without any apprehension,-and, in general without knowing that it was an earthquake, except after hearing that others
felt the phenomenon too.
4. Noticeable or mediocre, not generally felt; noticed by many persons in houses, but by few on the ground floor, without
causing fear, but with trembling of fixtures, of glasses, creaking of floors, etc., slight swaying of suspended objects.
5. Strong, generally noticed in houses, but by few in the streets; awakening sleepers, frightening some, banging of doors,
ringing of bells, considerable swaying of suspended objects, stopping of clocks.
6. Very Strong, felt by everyone in the houses, and by many with fear and flight into the open, falling of objects in the
houses, fall of plastering with some slight damage to buildings of little strength.
7. Exceedingly strong, felt with general fear and flight from houses, also noticeable in the streets; ringing of church bells;
fall of chimney pots and tiles; damage to numerous buildings, but in general slight.
8. Ruinous, felt with great fear, partial ruin of some houses and general damage of others, in some cases considerable; without
victims or only with some personal accident in isolated cases.
9. Disastrous, with total ruin to some houses, grave damages in many others, such as to render them uninhabitable; human
victims not very numerous, but distributed in various places among inhabited houses.
10. Very disastrous, with ruin of many buildings and many human victims, crevices in the ground, changes in the; mountfll
In judging of the intensity of the shocks by their effects, it is necessary to take into consideration the
complex of damages and ruins, rather than of some isolated fact, which often has for its cause some particular
conditions of some building rather than the intensity of the shock; and more especially one ought to
notice if the population, at the moment of the earthquake, were in the houses or in the streets, or gathered
together in churches Or theatres.
<1 And this, in short, is the most simple and most generally used way, for determining according to numerous
informations, the epicentre of an earthquake; by joining together with a line all the villages, which according
to information received, have suffered the same characteristic damages, the said isoseismographic lines are
obtained. Herwith are published those traced by the learned D.r Martinelli of the Royal Central Office of
Meteorology and Geodynamics, according to the supply of abundant material collected in that institute. It
must be understood that the said isoseismographic lines are provisory, as is natural, given the brevity of the
time, but I can assure you that up to now the scientific scrupulousness of him who traced them being well
known, even if they had to be modified in some points, according to fresh news which might yet be made,
the variations would be of very slight importance and would have none other than a purely scientific interest.
Cfl From this seismographic map therefore, the reader can obtain a lucid idea of the extent of the zone most
severely damaged, and so too, of all the other zones of relatively minor intensity.
C]j And now I beg a word to explain the meaning of numerous scientific diagrams as well.
C| It is now well known that even where an earthquake ceases to be felt directly by man, yet it does not
seem to exist but continues to transmit itself through the earth for immense _ distances.
<1 From the central point, a great number of undulations proceed in rays of varied nature and different speeds.
At the point of the disaster they are naturally mixed up together, but then, little by little as they move
away from the centre, and in virtue of their different velocity they separate and thus arrive at the distant
seismographic apparatuses in groups at a good distance one from the other; each one having a velocity of
propagation determined and known, we can easily calculate the distance at which the earthquake took place.
4J Whoever reads this book will find here various diagrams or rather seismograms of different appearance,