276 ATTRACTION. SPIN :i:n AI. 



Let C be the centre of the shell, 3/any particle of it, /' the 



attracted particle. Let <7J/=r, PM = y, CP = c, = tlie 

 an.^lc PCM, < = the angle which tlic plane PCM make* with 

 tin- plane of the paper, r=the thickness of the shell, and 

 let p denote the density of the shell. 



The volume of the elementary soli 1 at .17 is r* sin 

 (so<>. Art. 130). The attraction of the whole shell acts B 



the attraction of the element at M resolved alonu; PC is 



.-hall eliminate ^ from this expression by means of the 

 equation 



therefore sin 6 . = 



</// er 



c - r cos = 



lore the attraction of J/ on P along PC 



