C 4*1 ] 
By Art . 8. we have a P p—AV uxadt‘, there- 
fore, by Prob. V. the inftantaneous preceffion will be 
A r r J , PR .rr J , C P © 1 
A V u xflij/x — — , or AV u* a a t x - , the tn- 
Pp *P D 
angles P pr, P D s, being fimilar, fince the three 
fides of the one are perpendicular to the three fides of 
the other. Putting, therefore, inftead of P D , P s, 
and d t , their values above found, we ffiall have the 
• n . rr a rr a & P V aa UU 
lnltantaneous preceiiion = A v u x — - x — — • 
aV 2 7 r rr 
z=. Ab* — x 
uu du 
2 7 T ^ aa — «« 
rr 
But 
uu d u 
' f — = 
J V aa — uu 
rr 
U V aa — uu- f- jdti'J aa — z/zq or limply = 
rr 
rr 
uu d u 
fv aa — uu 
rr 
when u = — , as it happens when the fun is in the fol- 
r 
Bice s , and then J d u V aa — uu, which is the area 
rr 
of a quadrant of a circle whofe radius is will be 
a 7r a 
2 r 2 r 
aa-jr 
4 rr 
Therefore the preceffion, whilft the fun is paffing 
_ . . . T aa 7 r 
from Y to £p, is A b x — x 
2 7r 4?*r 
Ff f 2 
A , P aa 
A bx - x - T 
2 4 rr 
and 
» 
