l3l 
"A 
DISCOURSE 
Concernimg GRAVITY, and its PropertieSy 
wherein the Defcent of Hea vy Bodies, and the Motion 
of Proje£l:s ^ briefly^ but fully handled : Together with 
the Solution of a Problem of great Z)fe in GUN- 
NERY. By E.H ALLE Y. 
T^TA T U R E amidft the great variety of Prohlems where- 
in with She exercifes the Wits of Philofophical men, 
karcc affords any one wherein the EfFe£t is more vifible, and 
the Caufe more concealed than in thofe of the Thoenomem of 
Gravity. Before we can go alone, we muft learn to defend 
our lelves frorrl the^violen^Ge of its Impulfe, by not trufting 
xhQ Center oiGravj^ty oSoVit Bodies beyond our reach; and 
yet the Aeuteft Philofbphers, arid the fiibtileft Enquirers into 
the Original of this Motion, have been fo far from fatisfying 
their Readers, that they themfclves feem little to have un- 
derftood the Confequcnces of their own Hjpothefes. 
Des Cartes his Notion, I muft needs confefs to be to me 
Incomprehenfible , while he will have the Particles of his 
CeleBid matter \ by being reflected on the Surface of the 
Eartbj and fb alcending therefrom, to drive down into their 
places thofe TerreFirial Bodies they find above them : This is 
as near as I can gather the feope of the 20, 21, 22, and 23 
SeBions of the laft Book of his l?rincipA Fhilofofhi^ ; yet nei- 
ther he, nor any of his Followers can fhew how a Body fuf- 
pended in libcro athere , fliall be carried downwards by a 
A conti« 
