Note 45 — Chapter VIII

The application which the Dr. makes of this structure of the earth is this: that the concave sides of the spheres are made up of magnetic matter; that they revolve about their diurnal axes in about twenty-four hours; that the outer sphere moves either a little faster or a little slower than the internal ball; that the magnetic pole, both of the external shell and included globe, are distant from the poles of rotation; and that the variation arises from a change of the relative distances of the external and internal poles in consequence of the difference of their revolutions. [See life of Dr. Halley.]

In Rees' Cyclopedia, under the article 'ring,' is the following sentence; by which it appears that Kepler first suggested the earth to be composed of concentric crusts. "Kepler, in his Epitom. Astron. Copern. (as after him Dr. Halley, in his enquiry into the causes of the variation of the needle, Phil. Trans. No. 195.) supposes our earth may be composed of several crusts or shells, one within another, and concentric to each other. If this be the case, it is possible the ring of Saturn may be the fragment or remaining ruin of his former exterior shell, the rest of which is broken or fallen down upon the body of the planet."