hi 1:1 A( i:. ! T 



'(Ja)l- ' (2.) 



m 



rabn v " 



I the centre of gravity of the surface formed 

 by rcvolviug the cunre r a (I + cos 0) round the initial 

 ll-r. 



-2a*(l+COS0), 



tV \MV/ 



therefore '* 



-. 



Ti. N 



-l 



cos 4 - sin -dO 



f w 6 



vrly I cos 4 - 8in 5 ^r 



J % * ' 



~ _ \^ < / 



2 ii.i 



Any Surface. 



be a si -ivcn surfac< 



one of its boundaries, and suppose its thickness indefii 



