Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/407

342 But 5·33 X 4000 feet, is 21,320 feet, and Chimboraço is 21,100 feet in height. Or, taking the lower height of Vesuvius, (and truer one, for the 400 or 500 feet next the summit, is only a tottering and variable crest of dust, relatively to the remainder of the mass,) then 5·33 x 3500 = 18,555 feet, which is the height, of a number of the next rank of Andean volcanoes.

and Pasto and Tunguragua from 13,000 to 16,000 feet;—an interesting result, viewed in whatever aspect.

No direct connection holds, between the velocity of the wave of shock, and the average areas of seismic convulsion, either at the same or in distant regions; for the area depends, not only upon the intensity of the wave, but upon the depth of the mean focal point, in each shock; and this may, and no doubt does, vary much, for even the same region at different times. Hence we find one city only, like Coquimbo in 1820, or but a few clustered near each other, as in the Melfi shock of 1851, may be destroyed, with great violence, i.e., by a wave of high velocity, and yet the whole area of disturbance be very small.

Were the depth of focus always the same, then the area of seismic disturbance, for like formations and configuration of surface, would be a measure proportionate to the total earthquake effort expended in each case, and would also be some function of the velocity of the wave.

We may generally infer from this, that earthquakes like that of Lisbon, which have a very great area of sensible