Page:The fairy tales of science.djvu/334

288 the crust. The generally received notion is that, assuming the radius of the earth to measure 4000 miles in round numbers, and dividing it into ten equal parts of 400 miles each, the density of the materials severally constituting the ten divisions increases in an arithmetical progression by about 1·5 for each part, which, taking the density of the first annular space of 400 miles at 2·7, gives for the second 4·2, for the third 5·7, and so on, the density of the central portion being about 16·2.

In Cordier’s purely thermometrical theory as to the nature and mode of action of the great elevating force that has at successive periods raised and broken the earth’s crust, lifting up various igneous or plutonic rocks, and forcing them into the cracks and fissures, the central nucleus of the earth is considered in the light of an immense sea of molten mineral matter. As the solid crust continues to contract as its temperature decreases in a greater ratio than the central mass, and the velocity of rotation increases as the diameter of the globe shortens, a tendency will necessarily be induced to additional divergence from the spherical form, and the fluid matter within will accordingly press against the contracting crust, and thus produce volcanic eruptions.

M. Cordier has calculated that a contraction of $1⁄12350$ of an inch in the mean radius of the earth would be sufficient to force out the matter of a volcanic eruption. And a most wise arrangement