On the Revolutions of the Heavenly Spheres

BY THE SAME amount Completing the thought from the previous page: as one moves North or South, the celestial poles change altitude proportionally. as in no other shape but the spherical. Whence it is manifest that the Earth is also enclosed between poles and is, for this reason, a globe. Add also that the inhabitants of the East do not perceive evening eclipses of the Sun and Moon, nor do those living in the West perceive morning ones; while those in between see the former later and the latter earlier. Copernicus is arguing that if the Earth were flat, everyone would see an eclipse at the same time. The time difference proves the Earth's curvature from East to West.

That the waters also rest upon this same shape is perceived by sailors; for land which is not visible from the ship itself is often sighted from the top of the mast. Conversely, if something shining is placed on the top of the mast, as the ship moves away from land, it seems to descend little by little to those remaining on the shore, until finally it is hidden as if setting. It is also certain that waters, flowing by their nature, always seek lower places, just as the earth does, and do not push further from the shore than the convexity of the shore allows. Wherefore, the land is necessarily that much higher wherever it rises out of the Ocean.

How the earth with the water forms a single globe. Chapter III.

[An ornate initial letter H, decorated with a face]
Hence the surrounding Ocean, pouring out its seas everywhere, fills the deeper descents of the Earth. Therefore it was necessary that there be less water than land, lest the water swallow the whole earth—since both strive toward the same center by their weight—but rather that it might leave some parts of the earth for the safety of living creatures, and so many islands scattered here and there. For what else is the continent itself, the orb of lands, but an island larger than the others?

Nor should we listen to certain of the Peripatetics Followers of Aristotle’s philosophy. who declared that the whole volume of water is ten times larger than the whole earth. They base this conjecture on the idea that in the transformation of the elements, one part of earth creates ten parts of water when it dissolves. They say the earth projects to some extent in such a way that it is not balanced everywhere according to gravity, being full of caves, and that the center of gravity is one thing, while the center of magnitude The geometric center. is another.

But they are deceived by ignorance of the art of Geometry. They do not realize that water cannot even be seven times greater without the entire earth being submerged, unless the earth moved away from the center of gravity and gave place to the waters as being heavier than itself. For the volumes of spheres are to one another in the triplicate ratio The ratio of the cubes; for example, if a diameter is doubled, the volume increases eightfold. of their diameters. If therefore the earth were [composed of] seven parts of water...