or percuflion, is that which ( at that point y is at right an- 
gles to that Tangent. 
41. If the Prbjedion ( at ^ 27. ) be not infinitely con- 
tinued, but terminate (fuppofe) at A", fo that the laft 
term in the firft Cokimn or Series ereSt be a ; and confe- 
quently in the fecond, a ; in the third, m m &c. ( each 
SeWes having one term fewer than that before it ;)thenf'for 
the l^me reaibns as at ^ 22. ) the Aggregates of the feve- 
ral Columns ( or ered Series j will be ^ ^ . ^ — 
} \ and fbforth, ti\\( the multiple of ^ becoming 
^ I ) the progreflion expire. 
42, Now all the abatements here, a, ma,?nmay &c* 
are the fame with the terms of the firft Column taken 
backward. For a is the laft, m a the next before it ; and 
foof the reft. 
4 J. And the. Aggregate of all the Numerators is fo 
many times i as is the number of terms ( fuppofe ) want- 
ing the firft Column ; that is ^ — ^ — or ^^"^ ' ; & 
this'again divided by the common denominator t;^, becomes 
^ therefore ^ jg> is the line of 
n ' ' ^ 
defcent by its own Gravity. 
44. If therefore this be added to a projecting force down- 
ward in a perpendicular ; or fubdufted from fuch projeft- 
ing force upward ; that is, to or from-——/: The Dc? 
fcent in the firft cafe will b e ^ f + ^ j and 
the Afcent in the other cafe ^ / — ^izJ-i-?^. And 
in this latter cafe, when the ablative part becomes equal 
to the pofitive part, the Afcent is at the higheft : and 
M m thence^ 
