as are terminated by Planes , &c. 
*75 
t= — 2 nar 
\L (x + V a* + x') — X+ - L ( — * -f 
i V ' ‘ ' r l t /x L + a* “ 
+ ft?) 1 ; 80 t,iat 
I x 1 4- 
A = 2??x arc (tang. = — v' 1 4" “7 ~ ^ ) — (n — 2)7rx-|-corr. 
— 2 nr — = L(i| y 7X7- + *•) + f 7===== + 
^i + r v k ‘+f 7 t W-j-rt 1 8 
}* 
This is the attraction of a polygonal parabolic spike, on a par- 
ticle at the point. When the polygon becomes a circle. 
Arc (tang. = p s/ i + ^ ■ r ) 
L { 
2 V 
+ v/7+^l=L 7+ « 
*, and 
, , _ , * , , , whence it 
Vx z -\-a. z r x + a r ^a z -\-X z 
will easily appear that, in the case under consideration, 
A = 27? I x — «L (ur -j - s/ )} + corr. 
We may conceive the plane uvv'u', fig. 15, instead of a regu- 
lar polygon to be a rectangle, moving along the line pm, as 
in the former case, with its centre in that line ; and, with the 
middle points r and r' of its sides, touching curves pr, pr' either 
of the same or different kinds. 
The section of the generated solid, or groin, perpendicular 
to its axis, will have its action on the point p (if we put x = pm, 
and b and b' for the sides of the rectangle) expressed by 
w 
and if we multiply this by x, and put for b and b' their values, 
given by the equations of the curves pr, pr', the fluent will be 
the attraction of the generated solid. 
