Thus she [one of the moons of Mars] has a disc, always on this assumption be it remembered, equal to about a quarter of our moon's; and being illuminated by the sun, like the other moon, with a light varying from one-half to one-third that which he pours on the earth, it follows that the light she reflects to Martians, or would reflect to them if there were any such beings, varies from one-eighth to one-twelfth of that which we receive from the full moon.