Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/396

Rh mile, and a transit velocity = 755·6 feet per second; differing from the last by only 32·4 feet per second. This strongly corroborates the exactness of both, as the two towns, Atella and Barielle, are both in the same right line with the origin, and only about 3 geographical miles apart, so that the wave-path for both, traversed the same formations.

Collecting our results, we have the transit velocities respectively from—

and omitting the second, 658·2 (Vietri to Melfi), which is from the same elements as the first, we obtain a general mean velocity of surface transit in all directions, of 787·97 feet per second.

Such a general mean, however, cannot exist in nature, as it must vary, in different directions round the seismic vertical, with differences in continuity and elasticity, &c., of the formations. In fact, looking at the seismic map A, it may be said that, as in a map of marine cotidal lines, the tides are highest, where the cotidal lines are seen to be most crowded, so, here, the transit velocity is seen to be greatest, in those directions in which the coseismal lines are spread out furthest, from the origin.

Partial means having regard to the formation, therefore,