"There is an instrument called the seismograph, which records the vibratory movements of the earth, and also locates the distances at which the shocks are from the observer, but there is nothing to indicate what the extent and probable dangers are."
"Is it true that the interior of the earth is in a liquid state?"
"Such has been the theory for many years; but it is now believed to be a solid—a body with a density five and a half times greater than water."
"If that is the case, why is it that the molten metal flows out of the volcanoes?"
"There may be fissures in the earth, or portions less dense than others which, by the general disarrangements of the adjacent parts, and by the enormous pressure exerted by the force of gravity, are contracted, and the movement causes such friction and intense heat as to liquefy the rock. In doing so a large amount of gas is evolved, the movement of which causes the disturbance of the earth's crust, which manifests itself to us in the form of earthquakes. At the same time the confined gases seek an outlet, which they find at the weakest part, and the volcanoes spout forth the lava, flame, and gases. There is an undoubted connection between earthquakes and volcanic eruptions. Earthquakes usually precede volcanic action. This internal combustion is going on at all times, and is only more violent at some period than at others. The lava in the Crater of Stromboli has been in a liquid state for more than two thousand years."
"Before we left home I saw in a paper that some scientist described the kind of rock and other matter which was seven miles down in the earth."
"Was anyone ever down as far as that?"
"No; a little over a mile is as far as man has actually penetrated the earth."
"Then, I should like to know how geologists can tell with any certainty what the rock is like several miles down?"
"That is known just as positively as though a hole had been dug down that distance."