C 6o 9 ] 
In the Appendix, the Author anfwers feme of the 
principal Arguments brought in favour of the con- 
trary Side. 
I. The firft is drawn from the compound Motion 
of a Body along the Diagonal of a Redangle, whofe 
Sides reprefent the fimple Motions. Here it is faid, 
that the fimple Forces are no-ways contrary to each 
other 5 that being united or added together in the 
compound Force, that compound Force will not be 
to both or either of the fimple Forces, as the Dia- 
gonal is to both or either of the Sides; but as the 
Square of the Diagonal to the Sum of the Squares of 
the Sides, or to the Square of either Side refpedively. 
He anfwers, The fimple Forces, while they ad: in 
their proper Diredions, are not contrary to each other, 
either Wholly or in Part ; but when confidered as 
contributing to the Motion of the Body in the Di- 
redion of the Diagonal, Part of the one ads contrary 
to Part of the other, and deftroys it j as is evident, if 
you refolve each fimple Force into two others, one 
ading along the Diagonal, the other in a Diredion 
perpendicular to it. And then it is to be obferved, 
that the Sum of the two former is equal to the Dia- 
gonal (while the two latter deftroy each other) : 
Which is perfedly agreeable to the old Opinion, but 
not at all to the new ; for the demonftrating of which 
this Argument is brought. 
II. The fecond Proof is taken from the equal Com- 
preffion of Four equal Springs, before the Force was 
confumed, by the fame Body moving with double 
the Velocity ; and labours at the Bottom under the 
fame Parallogifm,. 
III. The 
