“This chart,” said the speaker, “presents to you the structural conception of Professors Jeans and Sollas, of the form of the earth. It is the shape more or less familiar to you, commonly known as a pear-shaped earth, the tip carrying the Sahara Desert on its bulging top, and its broader and inferior extremity holding the disturbed Pacific basin. “Now it makes a very practical difference what the shape of the earth is, because the shape affects the stability, has an important influence upon the fluctuating strains under its surface. Observe that the chart has developed, upon two circles of instability, these lines of weakness,” and the lecturer swept his pointer over the contrasted belts, one around Africa, and the other inflicting the west coast of North America with its ominous intersection. The pointer paused on the latter circle, stopping near the position of San Francisco. “You recall,” the speaker continued, “the terrifying affliction of this great city in 1906, and the pall of discouragement and gloom which it cast over the region in which the city naturally held the sway of mercantile supremacy. Now it was shown by Prof. H. H. Turner, the English astronomer, that San Francisco lies on one of the two great earthquake rings, which surround the end of the pear, as in this chart, like wrinkles produced by the crowding down of the protuberances under the force of gravitation. And, according to this view, such rings, marking lines of weakness and yielding in the rocks would not exist, if the earth was, in its shape, what we most usually assume to be its figure, an oblate spheroid, with the present north and south poles at the ends of its axis of rotation, to which axis of rotation the rest of the earth was symmetrically disposed. “The existence of these earthquake and volcanic rings was known before the pear theory had been defined, but then of course their relation with any peculiar form of the earth was not understood. The ring surrounding the Pacific, or butt end of the pear includes a large part of the shores of the Pacific Ocean, running from Alaska down to the western coast of South America, then across to the East Indies, and back, around the other side, through Japan. The other ring is somewhat smaller in diameter, including the earthquake regions of West Africa and the Atlantic Islands. Now the point of interest is this, as Garrett P. Serviss has significantly said, ‘If the pear hypothesis is accepted, and the two great earthquake rings are found to be definitely connected with the strains to which the planet is subjected in its effort to attain a state of equilibrium, under the forces of its own gravitation and rotation, which tend to compel it into spheroidal shape, then we have a perfectly rational explanation of the existence of certain places where earthquakes are sure to occur more or less frequently, and of other places, like eastern America, where they are very rare and never of maximum violence.’