How could the Darkness limit the Light?

And if those illustrations of the Sun and Shadow which [P. 98, l. 8.] they bring forward do belong to things ; if (they are) Earths, because they are dense bodies, they touched one another and were limited by one another . . . how is it (the Light) [L. 20.] limited by the Darkness, seeing that the Light scatters the Darkness and rends it asunder and (enters) into its Domain, and . . . also its nature . . .? [L. 28.]