82 Mr. Matter on the Dynamics of Earthquakes. 
shall be no reason discernible for all this, in the form, structure, or circumstances 
of the country itself where so shattered. 
And again, if, by the crossing of two partial earth waves, the crest of one wave 
fall into the hollow of the other, a negative node will be produced at their inter- 
section, so that the ground here shall not be moved, though in the midst of a 
country shattered all round it. Facts have been occasionally observed, that 
scarcely admit of any other explanation. Thus, Dolomieu states that, in the 
centre of Radicina, a small village totally levelled by the Calabrian earthquake, 
one solitary small house remained, without a sign of having been disturbed. But 
it would be tedious to follow further such corollaries from our general principle, 
many of which will occur to those familiar with the mechanics of waves. 
Having thus traced most of the direct and collateral phenomena resulting 
from the transit of the earth wave, and of the great sea wave, it remains to say 
a few words as to the aerial wave, that is to say, the sound of the original dis- 
turbing impulse, transmitted from this point to or over the land, through the air. 
The wave of sound in air, has a velocity greater than that of the great sea 
wave, but less than that of the sound wave transmitted through the sea, and also 
much less than that of the sound wave through the earth, or of the great earth 
wave of shock; hence, after the first hollow sounds, carried by the earth, which 
accompany or slightly precede the shock, and before the approach of the great 
sea wave, a continuous succession of sounds, like the rolling of distant thunder, 
will arrive, first promptly through the water of the sea, and afterwards more slowly 
through the air, and when the origin of disturbance extends over a consider- 
able line of territory, these sounds may continue even after the arrival of the 
great sea wave, which usually closes the terrible event. There can never be a 
sound wave through the air unless there be considerable fracturing of the earth’s 
crust at the centre of disturbance. Very many other modified conditions, as to 
the arrival and continuation of the aerial, aqueous, and terrestrial waves of sound, 
will at once occur to those versed in acoustics, but which need not here be 
enlarged upon. 
To recapitulate, therefore, the order of the successive phenomena, as they 
would present themselves to an observer upon the shore, we have the whole of 
the possible waves of every sort, viz., the earth sound wave and great earth wave 
or shock ; the sound wave through the sea; the sound wave through the air ; the 
