Others assign the Pressure of the _Atmosphere_, to be the Cause of this Tendency towards the Center of the Earth; but unhappily they have mistaken the Cause for the Effect; it being from undoubted Principles plain, that the _Atmosphere_ has no other Pressure but what it derives from its _Gravity_; and that the Weight of the upper Parts of the _Air_, pressing on the lower Parts thereof, do so far bend the Springs of that _Elastick_ Body, as to give it a Force equal to the Weight that compress'd it, having of it self no force at all: And supposing it had, it will be very hard to explain the _Modus_, how that Pressure should occasion the Descent of a Body circumscribed by it, and pressed equally above and below, without some other Force to draw, or thrust it downwards. But to demonstrate the contrary of this Opinion, an _Experiment_ was long since shewn before the _Royal Society_, whereby it appeared, that the _Atmosphere_ was so far from being the Cause of _Gravity_, that the Effects thereof were much more vigorous, where the Pressure of the _Atmosphere_ was taken off; for a long _Glass-Receiver_ having a light Down-feather included, being evacuated of Air, the Feather, which in the Air would hardly sink, did _in vacuo_ descend with nearly the same _Velocity_, as if it had been a Stone. Some think to illustrate this Descent of Heavy Bodies, by comparing it with the Vertue of the _Loadstone_; but setting aside the difference there is in the manner of their Attractions, the _Loadstone_ drawing only in and about its Poles, and the Earth near equally in all Parts of its Surface, this Comparison avails no more than to explain _ignotum per æque ignotum_. Others assign a certain _Sympæthetical Attraction_ between the Earth and its Parts, whereby they have, as it were, a desire to be united, to be the Cause we enquire after: But this is so far from explaining the _Modus_, that it is little more, than to tell us in other Terms, that Heavy Bodies descend, because they descend. This, I say, not that I can pretend to substitute any Solution of this Important Philosophical Problem, that shall more happily explicate the Appearances of Gravity; only it may be serviceable to those with whom the Credit of great Authors sways much, and who too readily assent _in Verba Magistri_, to let them see that their Books are not always infallible: Besides, the detection of Errors is the first and surest Step towards the discovery of Truth.