Fuchs gives an example of the movement of a seismic centre in the case of the Calabrian earthquake. The first shock commenced near Oppiedo, the second shock commenced four or five miles farther to the north, and the third shock had its origin five or six miles still farther, near to Girifalco. CHAPTER XIII. DISTRIBUTION OF EARTHQUAKES IN TIME (_continued_). _Seismic energy in relation to geological time._—If we admit that seismic energy is only a form of volcanic energy, it must also be admitted that any cause tending to produce a general decrease in the amount of the latter will also produce an alteration in the amount of the former. The nebular hypothesis of Laplace tells us that the solar system is the result of the whirling of a heated gaseous mass, which as it cooled continually contracted and consequently whirls the faster. With this hypothesis before us, we understand why all the planets and their satellites have a similarity in the directions of their movements, why they revolve nearly in the same plane, in orbits nearly circular, why some have a flattened figure and are surrounded by rings or belts, why the exterior planets should have a greater velocity of rotation, a greater number of satellites, and a less density as compared with the interior planets, the similarity of the elements in meteoric stones, the sun, the stars, and those found upon our earth, and lastly why there should be an increase in temperature as we descend into our earth.[92] This increase in temperature as we descend into the earth as deduced from many observations appears to be about 1° F. for every fifty or sixty feet of descent.