58 ESSAYS anp OBSERVATIONS 
motion, we muft neceffarily admit, firft, that 
gravity is exerted by repeated impulfes ; and 
next, that thefe impulfes, continually turn- 
ing ftronger, form an increafing feries, hold- 
ing an exa& proportion with the growing ve- 
locity, of which thefe impulfes are the caufe. 
AnD this leads us readily to conceive the 
‘operation of gravity in the afcent and defcent 
of bodies. A ftone, in its perpendicular mo- 
tion, is carried upwards by its ws énfita coun- 
ter-acted by gravity : in its return, it is carried 
down by gtavity without any counter-action. 
At firtt view, the afcent will be confidered 
‘as.the operation of two powers acting in op- 
pofite directions ; the effect of which com- 
monly is, to produce an equable motion with 
the difference of the forces. And, were the 
action of gravity one uniform action, like 
that of the ws zn/fita; fuch would truly be 
the effet: but, as gravity is exerted by re- 
peated impulfes, a different effect muft fol- 
low. The very firft impulfe of gravity takes 
off from the force of the vis infita; what 
remains is leflened by the fecond impulfe ; 
and fo on, till the urs zufita, gradually de- 
creafing by the repeated counter-actions of 
gravity, be annihilated altogether. In the 
return 
