if Earth is in the middle of the heavens, and spherical, it doesn’t need either air or any other such physical necessity to stop it from falling; the complete uniformity, everywhere, of the heavens themselves and the equilibrium of the earth itself are sufficient to hold it up, because an object in equilibrium placed in the centre of a uniform container cannot incline any more or any less in any direction, and because it is in a uniform state it will stay where it is.