X

60 Sir I s a a c N e w t o n’s Book I.

way, it must move in the arch of a circle. Let it receive suchan impulse, as shall cause it to move in the arch A C ; and letthis impulse be os such strength, that the body may be car-ried from A as far as D, before its motion is overcome by itsweight: I fay here, that the body forthwith returning fromD, shall come again into the point A with the same velocity,as that wherewith it began to move.

2.4. I t will be proper in this place to observe concerningthe power os gravity, that its force upon any body does notat all depend upon the shape of the body ; but that it conti-nues constantly the same without any variation in the lamebody, whatever change be made in the figure of the body: andif the body be divided into any number of pieces, all thosepieces shall weigh just the same, as they did, when unitedtogether in one body : and is the body be of a uniform con-texture, the weight of each piece will be proportional to itsbulk. This has given reason to conclude, that the power osgravity acts upon bodies in proportion to the quantity of mat-ter in them. Whence it should follow, that all bodies mustfall from equal heights in the same space of time. And aswe evidently fee the contrary in feathers and such like sub-stances, which fall very slowly in comparison os more solidbodies; it is reasonable to suppose, that some other cause con-curs to make so manifest a difference. This cause has been-found by particular experiments to be the air. The experi-ments for this purpose are made thus. They set up a verytall hollow glass; within which near the top they lodge a fea-ther and some very ponderous body, usually a piece of gold,

this