is a dim-untiiiuity in patting from 

 H of r greater >f the external surfar 



those of r less than tin* radius rnal surface, 



>; but it 

 ,ly -0 when r* .ts in the 



-a 



o we coi KkrcompotfJ 



i*ogrntt>u3 shells ejvrcfsc* no attraction a 

 aU.i trrior of it* internal turface* 



Let us now find the vnlui- of - - : s belonging to the 



mass of the cylin ' it we liave, bj Art. 239, 



-ration, calling r, the radiua of the internal 



-~> 

 -i- 4ir I prdr 



J 



H necessary, because i = when r r, , since it 



it so tor all ill- j-.ii !, of .0 surface of which 



r = r, , i 



For oxtcnml points we ought to have 



(7 

 -3r"f 



Make r r t , then, by reason of the preceding equal 



pi 



C--4ir| prdr. 



