"If it resulted in an oscillation of the earth of only a few inches there would be no likelihood of a great tidal wave. If, however, there was produced a radical depression in the bed of the ocean, the sinking of an island, or some other extraordinary disturbance, a tidal wave along the Pacific Coast would almost certainly be one of the events of this great disaster. "There are apparently three distinct weak spots in the United States, which are peculiarly subject to earthquake shocks, and we are likely sooner or later to hear from all of them in connection with the shock at San Francisco. There is one weak area along the southern Atlantic coast in the vicinity of Charleston, another is in Missouri, and the third includes the Pacific Coast from a point north of San Francisco down to and beyond San Diego." In describing the instruments at the weather bureau which make the record of earthquakes, even when the movement is so small that the ordinary person does not recognize it, Prof. Moore said: "The apparatus we have is a pen drawing a continuous line on a cylinder which revolves once every hour and is worked continuously by clockwork in an exact record of time. It moves in a straight line when there is no disturbance, and it jumps from right to left and back again when there are serious oscillations of the earth. The extent of these movements of the pen measures the grade of the oscillation. You may think it is a fantastic statement, but this seismographic pen is adjusted so delicately that it will register your step in its vicinity. "The instrument is mounted on a solid stone foundation and what it registers is the effect of your weight pressing upon the earth. It is easy to see, therefore, that the record we have obtained of this earthquake shows a few preliminary tremblings, which seem to be premonitions, for about four minutes, then a great crash which threw the pen off the cylinder and finally a period of nearly four hours, during which there were slight tremblings of the earth, this latter period marking the readjustment after the actual shock." Most of the scientists were inclined to believe that the boiling process in the interior of the earth, although it goes on continuously, is subject to periods of greater or less activity. This activity may be, however, purely local, according to the scientific theory, for otherwise there would be eruptions in all the active volcanoes of the earth at the same time, and there would be earthquakes in every one of the areas where there is liability to seismic disturbances.