26'i PHILOSOPHICAL TRANSACTIONS. j^ANNO l685-6. 



Philosophiae; yet neither he, nor any of his followers, can show how a body 

 suspended in libero aethere shall be carried downwards by a continual impulse 

 tending upwards. 



Vossius and others assert the cause of the descent of heavy bodies, to be 

 the diurnal rotation of the earth upon its axis ; not considering that, according 

 to the doctrine of motion, all bodies moved in a circle, recede from the centre 

 of their motion; by which an effect contrary to gravity would follow, and all 

 loose bodies would be thrown into the air in a tangent to the parallel of latitude 

 without the intervention of some other principle to keep them fast, such as 

 that of gravity. Besides, the effect of this principle is found throughout the 

 whole surface of the globe nearly equal ; and certain experiments seem to argue 

 it rather less near the equator, than towards the poles ; which could not be the 

 case, if the diurnal rotation of the earth on its axis were the cause of gravity ; 

 for where the motion is swiftest, there the effect would be most considerable. 



Others assign the pressure of the atmosphere, as the cause of this tendency 

 towards the centre of the earth ; but unhappily they have mistaken the effect 

 for the cause, it being plain from undoubted principles, 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, do so far bend the springs 

 of that elastic body, as to give it a force equal to the weight that compressed 

 it, having of itself 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 push it downwards. But to demonstrate the contrary of this 

 opinion, an experiment was long since shown before the Royal Society, by which 

 it appeared, that the atmosphere was so far from being the cause of gravity, 

 that its effects are much more vigorous where the pressure of the atmosphere is 

 removed; 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 a stone. 



Some think to illustrate this descent of heavy bodies, by comparing it with 

 the virtue of the loadstone. But, setting aside the difference in the manner 

 of their attractions, the loadstone attracting only in and about its poles, but 

 the earth almost equally in all parts of its surface, this comparison avails no 

 more than to explain unknown things by another equally so. 



Others assign as the cause, a certain sympathetical attraction between the 

 earth and its parts; whereby they have, as it were, a desire to be united.. But 

 this is so far from explaining the modus, that it is little more than telling us in 

 other terms, that heavy bodies descend, because they descend. 



