752 Mr. button’s Calculations to afcertain 
being km = gp ; alfo fl is the coiiae of fan to the fame 
radius : confequently c-p : fl = d : c. But the triangles 
lfa, pgh are equiangular, and therefore gp ; fl=gb : af. 
G II 
Confequently gh : Af = d: c; or ~ x c ~ d. This equa- 
tion is accurately true when gh is the chord of the arc; 
and as the fmall arc differs infen Ably from its chord, the 
fame equation is fuffidently near the truth when gi-i is 
the arc itfelf. Subftituting now d inftead of the quantity 
— x c in the theorem above, it will become BExds for 
the meafure of the attraction of the. pillar whole bafe is 
bd in the direction an. Which is as eafy and Ample an 
expreffion for the attraction of a Angle pillar as can well 
be defired or expeCled. 
But to make the application of this theorem ftill more 
eafy to the great number of fmall pillars concerned in 
this buAnefs, let us fuppofe be and d to be conftant or in- 
variable quantities, and then it is evident that we fliall 
have nothing more to do but to colled all the s ' s or Anes 
of elevation of all the pillars into one fum, and then 
multiply that fum by the conftant quantity be xd, bf 
which there will be produced the meafure of the attrac- 
tion of all the pillars, or of the whole part of the ground 
on one Ade of we. Now be will be made to become 
conftant, by making the circles equi-diftant from one 
another, 
