Lines and centre

Meaning

Lines drawn from a circle's circumference to its centre establish the direction called downward in the author's spherical cosmology. Moving away from that centre necessarily counts as rising.

II.2.16 uses the geometric image to explain why earth, already at the lowest place, cannot fall farther. Equal settlement around the centre gives the globe its stable roundness. The argument is not that a line possesses weight, but that the image fixes the relation of centre and circumference used in the physical inference. Book III later invokes indivisible points and a central source of universal life; neither passage should be mistaken for modern mathematical analysis or a demonstrated account of planetary motion.

The English preserves “cannot be drawn out again without rising,” the negative that gives the comparison its force. Superficie d'un cercle means the circle's boundary or circumference in this context, not an added three-dimensional surface.