Nature, amidst the great Variety of _Problems_, wherewith She exercises the Wits of Philosophical Men, scarce affords any one wherein the Effect is more visible, and the Cause more concealed, than in those of the _Phænomena_ of _Gravity_. Before we can go alone, we must learn to defend our selves from the Violence of its Impulse, by not trusting the _Center_ of _Gravity_ of our Bodies beyond our reach; and yet the acutest Philosophers, and the subtilest Enquirers into the Original of this Motion, have been so far from satisfying their Readers, that they themselves seem little to have understood the Consequences of their own _Hypotheses_. _Des Cartes_ his Notion, I must needs confess to be to me incomprehensible, while he will have the Particles of his _Cœlestial Matter_, by being reflected on the Surface of the _Earth_, and so ascending therefrom, to drive down into their Places those _Terrestrial Bodies_ they find above them: This is, as near as I can gather, the Scope of the 20, 21, 22, and 23 _Sections_ of the last Book of his _Principia Philosophiæ_; yet neither he, nor any of his Followers, can shew how a Body suspended in _Libero Æthere_, shall be carried downwards by a continual Impulse tending upwards, and acting upon all its Parts equally: And besides the Obscurity wherewith he expresses himself, particularly, _Sect. 23._ does sufficiently argue according to his own Rules, the confused _Idea_ he had of the thing he wrote. Others, and among them Dr. _Vossius_, assert the Cause of the _Descent_ of _heavy Bodies_, to be the _Diurnal Rotation_ of the _Earth_ upon its _Axis_, without considering, that according to the Doctrine of Motion fortified with Demonstration, all Bodies moved _in Circulo_, would recede from the Center of their Motion; whereby the contrary to _Gravity_ would follow, and all loose Bodies would be cast into the Air in a _Tangent_ to the _Parallel_ of _Latitude_, without the intervention of some other Principle to keep them fast, such as is that of _Gravity_. Besides, the Effect of this Principle is throughout the whole Surface of the Globe found nearly equal; and certain Experiments have proved it rather less near the _Æquinoctial_, than towards the _Poles_; which could not be by any means, if the _Diurnal Rotation_ of the _Earth_ upon its _Axis_ were the Cause of _Gravity_; for where the Motion was swiftest, the Effect would be most considerable.