as are terminated by Planes , &c. 303 
If we choose to express this by the lines and angles of the 
figure (so), it is 
A = 4 x pu x arc, opu — 4 x ps x arc, bps -f^xbsxL^ 
Prop. B. 
Let the section of the prism be an isosceles triangle ; the 
attracted point p being in the line psm (fig. 21), which passes 
through the vertex s to the middle of the base r'p'. 
Draw rm parallel to the base, and put r = tang, rsm ; call 
ps, u ; sm, x; then rm = rx ; and we have for the attraction 
of the infinite solid 
A = 4 Jx arc (tang. = = 4 * arc ( tan g- = ~ 
—7—7 P - — if we put & — —7—.. Make, moreover x + * 
1 r z a. z ’ 1 i-fr* ’ 1 
i +r 
= z, x = z — a, x = z, and it becomes 
which fluent is 
— 7^7* { ru ^~ J • v/z a -j- — u arc ( tang. 
*(ruz — ruaS) k 
k 1 r 2 « a ’ 
£)}• 
we have then at length 
A = 4a: arc (tang. = ;{r«L s/ (x + *)• + rV — « 
arc (tang. = j -f cor. 
Cor. If the position of the attracting solid be reversed, as in 
fig. 22, call ps, u, and the attraction will be given by the same 
formula; only the fluent (if it begin at the point) must now 
R r 2 
