346 Rotation of a Solid Body round a Fixed Point. 



the ellipsoid of gyration be described through the point B', it 

 will be perpendicular to the line R'B". The general construc- 

 tion for permanent axes is, therefore, the following : Let the 

 ellipsoid of gyration be described, and confocal ellipsoids : any 

 line which pierces one of these ellipsoids at right angles is a per- 

 manent axis of rotation for the point of intersection. 



