Whatever falls through water or thin air, the rate Of speed at which it falls must be related to its weight, Because the substance of water and the nature of thin air Do not resist all objects equally, but give way faster To heavier objects, overcome, while on the other hand Empty void cannot at any part or time withstand Any object, but it must continually heed Its nature and give way, so all things fall at equal speed, Even though of differing weights, through the still void.
He's still arguing that heavy objects would fall faster when dropped anywhere on Earth, though, specifically bringing up air resistance as the reason. His argument is that they would fall at the same rate in a vacuum.