Of GREATEST ATTRACTION. 237 
This propofition may be proved to be rigoroufly true, if we 
confider the inverfe ratio of the fquares of the diftances, as a 
limit to which the other ratio conftantly converges. 
Ir is a propofition alfo ufually laid down in optics, where 
the visible space fubtended by a furface, is the fame with what 
we have here called the angular space {fubtended. by it, or the 
portion of a fpherical fuperficies that would be cut off by a 
line pafling through the centre of the fphere, and revolving 
round the boundary of the figure. The centre of the {phere is 
fuppofed to coincide with the eye of the obferver, or with the 
ree of the particle attracted, and its radius is fuppofed to be 
nity. 
Tue propofitions that have been val now demonftrated con- 
cerning the attraction of a thin plate contained between paral- 
lel planes, have an immediate application to fuch inquiries 
concerning the attraction of Me as were lately made by Mr 
CAVENDISH. 
In fome of the experiments inftituted by that ingenious and 
profound philofopher, it became neceflary to determine: the at- 
traction of the fides of a wooden cafe, of the form of a parallel, 
epiped, on a body placed anywhere within it. (Philofophical 
Tranfactions, 1798, p. 523.). The attraction in the direction 
perpendicular to the fide, was what occafioned the greateft dif- 
ficulty, and Mr Cavenntsu had recourfe to two infinite feries, 
in order to determine the quantity of that attraction. The de- 
termination of ‘it, 45 ae Bea eae is eafier and 
more accurate.’ 
Let MD’ (Fig. 15.) seplunene a thin rectangular plate, A, a 
particle attracted by it, AB a perpendicular on the plane MD’, 
NBC, LBL’, two lines nce through B parallel to the fides of 
the rectangle MD’. Let AC, AL, AN, AL’, be drawn. 
Gg 2 wake THEN, 
