Of GREATEST ATTRACTION. 231 



In the fame manner, 



L tan (48 ° + /3) = 0.0455626 -f .0002540 /3, 

 andL.coverf. (48° + /3) ~ 9.4096883 — .0003292 /3 



L3 = 0.4771213 



Sum r^ 9.9323722 — .0000752 /3 

 Subtract Log arc (48 ° -f- P) = 9. 9231186 + .0001506 (2 



Remainder — .0092536 — .0002258 /3 = o„ 



Whence, (B = ^^ = 41' nearly. 

 2258 



A second approximation will give a correction— — 2o // , 



2 

 fo that <p = arc . 48 ° . 40' - ; and fince lin <p rz fin jj 2 , fin 73 — 



V fin <p, fo that ^ — 76 °. 30', and 2 37, or the whole angle of the 

 pyramid cs 153 °. 



An ifofecles pyramid, therefore, with a fquare bafe, will at- 

 tract a particle at its vertex with greateft force, when the in- 

 clination of the oppofite planes to one another is an angle of 



I53°- 



XX. 



To return to the attraction of the parallelepiped, it may be 

 remarked, that the theorem concerning this attraction already 

 inveftigated, § xviii. though it applies only to the cafe when 

 the parallelepiped is indefinitely thin, leads, neverthelefs, to fome 

 very general conclufions. It was fhewn, that the attraction 

 which the folid EL (Fig. n.) exerts on the particle A, in the di- 

 rection AB, is n . <p, <p being an arch, fuch that fin <p — fin BAG 

 X fin B AL = fin z . fin E > and, therefore, if B be the centre of 



a 



