move equal Jp^ces in equal timesy were it not defle(2:cd Aov/rx- 
wards by the force of Gr47y/>7. Let G B be the Horizjsntd 
Une^ and G C a PerfendicuUr thereto. Then the line G R F 
being divided into equal parts, anfwering to equal jp^ices of 
timcj \Qt the def cents of the Project he laid down in lines pa- 
rallel to GC, proportioned as the fquares of the lines GS, GR, 
GL, GF, or as the fquares of the times^ from S to T, from R to 
V, from L to X, and from FtoB, and draw the lines TH, 
VE>,XY, BCpa{dleltoGF; I fay the Points T,V, X,B, are 
Points in the CVi^^ defcribed by the Project y and that that 
Curve is a Parabola. By the {kcond Axiom they are Points in 
the Curve ; and the parts of the defcent GH, GD, GY, GC,= 
to ST, RV, LX, FB, being as the (quares of the times (oj the 
fecond Prop.) that is, as the fqutires of tlie Ordinates^ HT, DU, 
YX,BC, equal to GSjGR, GL, GF, the jj^^f^j meafured in 
thoft times ; and there being no other Curve but the Parabola^ 
whole parts of the Diameter are as the fyt^ares of the Ordi-- 
it follows that the C/^ri/f defcribed by a Proje^, can 
be no other than z Parahla : And faying, as RU the defcent 
in any tirne^ to GR or UD the dire5l motion in the lame time^ 
fb is U D, to a third proportional ; that third will be the 
line called by all Writers of Conicks^ the Parameter of the Pa- 
raiola io the Diameter GC^ which is alwaies^ the iam€in Pr<?- 
jetfs Q2i^ with, tht^km^ Velocity: And th.Q Velocity being de* 
fined by the number oi feet moved in a fecond of time ^ the 
Parameter w'l^i be found by dividing the fcjuare of the Velocity^ 
by 1 6 feet i inch:, the fall of a in the fame time. 
Lemma, 
T^ht Sine of the double of any Arch^ is equal to twice tlie 
^Sine ot that Arch into its Co-fine^ divided by Radim \ and the 
Verf ed fine of ihQ double, of any Arch is equal to the fquAre of 
the Sine thereof divided by Radit^. 
Let the ^r^:^ BC (infg.i.) be double the ^r^:^ BF, and A 
the Center J draw the Radii AB, AF, AC, and the Chord 
BDC, 
