proving that we can with farre more expeditious Velocity move a Hand or a Board to and again in one than in the other[29]: nevertheless, we never could finde any Body, that did not ascend much more swiftly in the water than in the Air. Yea of Bodies which we see continually to ascend in the Water, there is none that having arrived to the confines of the Air, do not wholly lose their Motion[30]; even the Air it self, which rising with great Celerity through the Water, being once come to its Region it loseth all [23] Of Natation, Lib. 1. Prop. 7. [24] Of Natation, Lib. 1. Prop. 4. [25] _Plato_ denyeth Positive Levity. [26] The Authors defence of the doctrine of _Plato_ and the _Ancients_, who absolutely deny Levity: [27] According to _Plato_ there is no Principle of the Motion, of descent in Naturall Bodies, save that to the Centre. [28] No cause of the motion of Ascent, save the Impulse of the _Medium_, exceeding the Moveable in Gravitie. [29] Bodies ascend much swifter in the Water, than in the Air. [30] All Bodies ascending through Water, lose their Motion, comming to the confines of the Air. [Sidenote: The lighter Bodies ascend more swiftly through Water.] And, howbeit, Experience shewes, that the Bodies, successively less grave, do most expeditiously ascend in water, it cannot be doubted, but that the Ignean Exhalations do ascend more swiftly through the water, than doth the Air: which Air is seen by Experience to ascend more swiftly through the Water, than the Fiery Exhalations through the Air[31]: Therefore, we must of necessity conclude, that the said Exhalations do much more expeditiously ascend through the Water, than through the Air; and that, consequently, they are moved by the Impulse of the Ambient _Medium_, and not by an intrinsick Principle that is in them, of avoiding the Centre of the Earth; to which other grave Bodies tend. [31] Fiery Exhalations ascend thorow the Water more swiftly than doth the Air; & the Air ascends more swiftly thorow the Water, than Fire thorow the Air. [Sidenote: _T_he Authors confutation of the Peripateticks Causes of Natation & Submersion.]