being constant, the velocities of transit in the wave-paths will be increased directly as those distances, viz., from the seismic vertical, to each station, and from mean focal point to same, neglecting the time between the focal point and surface, as common to all distances.
The actual distances along the wave-paths, the mean focal depth being 5¾ geographical miles are as follow:
| Geographical miles. | |
| Mean focal point, to Monte Peloso | 38·8 |
| „„Salerno | 35·0 |
| „„Melfi | 27·2 |
| „„Barielle | 24·9 |
| „„Atella | 21·5 |
from which the transit period in the direct path of the wave, may be easily computed.
The greatest velocity we obtained was that for Monte Peloso = 989·4 feet per second on the surface. The velocity for this range, in the direct path of the wave would be, therefore, 1038·5 feet per second; and as the transit velocity for absolutely homogeneous rock of the character of Apennine limestones and murgies, deduced from the of the elastic modulus, cannot be taken lower than from 3500 to 5000 feet per second (see 'First Report on Earthquakes, Brit. Assoc. Reports, 1850, sec. 23'), we find that from three-fourths to four-fifths of the full velocity of transit is absorbed or destroyed, by the continual loss of vis vivâ, due to the changes of molecular condition, and the discontinuity of the formations passed through.[1]
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- ↑ A still greater difference, between the theoretic maximum and the actual transit velocity, due to absorption by heterogeneity, has since been experimentally proved by myself, in the old quartz and slate rocks of North Wales. (See 'Phil. Trans., 1861-62.')-R.M.
