L 78 ] 
if T falls direcflly upon S, no area can then be de- 
fcribed by the right line connecting T and S ; blit 
yet, this is certainly one of the cafes whereby S and T 
may poflibly aCt upon each other. 
So in three bodies, S, T, and P j if P moves in the 
fame plane with S and T, no folid can then be de- 
fcribed by the plane whofe right lined Tides are the 
lines connecting P to T and S ; but yet, this muft be 
one of the cafes whereby S, T, and P, may poflibly 
aCl upon each other. 
XIII. A 
