“This resistance offered to the moving body by the medium does not occur in the way Aristotle has established in the fourth book when he discussed the void. The velocity of a body is not inversely proportional to the density of the medium, but it is the retardation the motion is subject to by virtue of the medium, which is proportional to the density. If what Aristotle said was true, natural motion in a supposed void would not meet any resistance and it would not take time but be instantaneous. Also, the motion of the heavenly spheres, which do not traverse a medium, would occur instantaneously. We see these motions occurring with different finite velocities: the motion of the fixed stars is very slow; the daily motion is very fast. These differences in velocity are due to the fact that the movers of the spheres differ in nobility and the more noble a mover, the faster is the motion of the sphere moved by it.”