C nr 3 
XVI. Of the Attraction of such Solids as are terminated by Planes ; 
and of Solids of greatest Attraction . By Thomas Knight, Esq. 
Communicated by Sir H. Davy, LL.D . Sec. R. S» 
Read March 19, 1812. 
Mathematicians, in treating of the attraction of bodies, 
have confined their attention, almost entirely, to those solids 
which are bounded by continuous curve surfaces ; and Mr. 
Playfair, if I do not mistake, is the only writer, who has 
given any example of that kind of inquiry, which is the chief 
object of the present paper. This learned mathematician has 
found expressions* for the action of a parallelopiped ; and of 
an isosceles pyramid, with a rectangular base, on a point at 
its vertex ; and observes, on occasion of the first mentioned 
problem, that what he has there done, “ gives some hopes of 
“ being able to determine generally the attraction of solids 
w bounded by any planes whatever/* 
It is this general problem, that I venture to attempt the 
solution of, in what follows : viz. any solid, regular or irregular , 
terminated by plane surfaces , being given , to find , both in quantity 
and direction , its action , on a point , given in position, either within 
or without it . 
• Ed. Trans. Vol. VI. p. 228 to 243. It is proper however to observe, that Mr. 
Playfair’s expression, at p. 242, for the action of a parallelopiped, requires to have 
its sign changed ; being, as it stands at present, negative, from the manner of cor- 
recting the fluent. 
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