A PARTICULAR METHOD IN CENTROIDS 231 



99— i'^cibc 



••• 99' =■!«• 



But gg' in the limit is twice the distance O,^' of the required 

 Center of Mass from the center of the ellipse, 



.*. this distance is §a. (19) 



This result gives the position of the pole of an ellipsoid of 

 magnetisahle matter, in a uniform -field in the direction of the a 

 axis of the ellipsoidS^^ 



(') See Maxwell's Treatise on Electricity, Vol. II, Section 437. 



