There seems to be no reason to believe the earthquake shock in San Francisco had any direct connection with the eruption of Vesuvius. That eruption had been recorded from day to day on the delicate instruments established by the weather bureau at the lofty station on Mount Weather, high up in the Virginia hills. This eruption of Vesuvius did not disturb the seismograph even at the period of great activity, but apparently Vesuvius and Mount Weather were like the lofty poles of two wireless telegraph stations, and between them there passed electrical magnetic waves encircling the earth. The records made at Mount Weather were of the most distinct character, but they showed disturbances in the air of a magnetic type and did not indicate any earthquake. In explaining the San Francisco trembling, C. W. Hays, the director of geology in the geological survey, explained that earthquakes are, according to modern scientific theory, caused by subterranean land slides, the result of a readjustment as between the solid and the molten parts of the earth's interior. "The earth," he said, "is in a condition of unstable equilibrium so far as its insides are concerned. The outer crust is solid, but after you get down sixty or seventy miles the rocks are nearly in a fluid condition owing to great pressure upon them. They flow to adjust themselves to changed conditions, but as the crust cools it condenses, hardens, and cracks, and occasionally the tremendous energy inside is manifested on the surface. "When the semi-fluid rocks in the interior change their position there is a readjustment of the surface like the breaking up of ice in a river, and the grinding causes the earthquake shocks which are familiar in various parts of the world. The earthquake at San Francisco was probably local, although the center of the disturbance may have been thousands of miles away from that city." Prof. Willis L. Moore, the chief of the weather bureau, in talking of the records of the earthquake in his department, said: "We have a perfect record of this earthquake, although we are thousands of miles away from the actual tremor itself. There were premonitory tremblings, which began at 8:19 and continued until 8:23 or thereabout. Then there was severe shock which threw the pen off the cylinder. "According to our observations here there was a to and fro motion of the earth in the vicinity of Washington amounting to about four-tenths of an inch at the time of its greatest oscillation. These movements kept up in a constantly decreasing ratio until nearly half an hour after noon. "San Francisco may have been a long way away from the real earthquake and merely have been within the radius of severe action so as to produce disastrous results. It is quite likely, in fact, that the greatest disturbance may have taken place beneath the bed of the Pacific Ocean.