[2.4] From this it follows that the heart of the earth must be quite large; however, it cannot be determined with an exact measure for the reason that this heart of the earth, depending on the necessity, is soon enlarged by a significant amount, soon reduced again by a significant amount. But so on the average at least the space for this center of gravity may be assumed to be a hundred miles in diameter; but may extend further to two hundred miles, and in contrast, diminish to fifty miles.

[2.5] But what does this so-called heart of the earth consist of?