The two revolutions, I mean the annual revolutions of the declination and of the centre of the Earth, are not completely equal; that is the return of the declination to its original value is slightly ahead of the period of the centre. Hence it necessarily follows that the equinoxes and solstices seem to anticipate their timing, not because the sphere of the fixed stars moves to the east, but rather the equatorial circle moves to the west, being at an angle to the plane of the ecliptic in proportion to the declination of the axis of the terrestrial globe.

First of all, we must note that the universe is spherical.

Mathematics is written for mathematicians.

In the midst of all dwells the sun.

Therefore, having obtained the opportunity from these sources, I too began to consider the mobility of the earth.

Every light has its shadow, and every shadow hath a succeeding morning.

Although all the good arts serve to draw man's mind away from vices and lead it toward better things, this function can be more fully performed by this art, which also provides extraordinary intellectual pleasure.