[ 2a I ] 



Then (39 and 40 Prop. i. Lib. Prirt.) 1 -ex J'lv 



" ~ 2 



X 



z 



may exprefs the fquare of the velocity at any point P ... (i Cor. 

 I Prop. I Lib.) 



icxa^-i::^' '7z:,-^-^^x^'~=^=?r'=^^=^'^M^' 



i^e z -T-' I — e z 2 

 Whence — — — cz'— .^-x 



z 



2 + 2 6 



Confequently — — — — — c 



X 2 -4- 2 e^ x^ 



X 2 2 ^ -t -^i: X 



TT7 



2 



2 . 



«' > 2 X — x' — c X' X 2 '+ 2 ei — *' 

 pi~ I— <?'—<: XI— f>i' 



And .-. A = .. "i^. = 



\j p- —I 



2 X X^ C at' X 2 + 2 <?' .X' \ 



Thi fluent of this quantity may be approximated by help of 

 an ellipfe, the greateft and leaft focal diftances of which are 

 i-j-tf and I — e, and a the angle included between the greateft 



E e diftance 



