where Xo is a constant vector and AX,-t — XitX{t, t = 1, 2, . . . , k. If in particular all eigenvalues {Atl, . . . , A,t} are mutually different, then M is said to be of i-type. A Jfc-type submanifold is said to be null if one of the A;t, t — 1, 2, . . . , k, is null. It is easy to see that if M is compact, then Xo in (1.1) is exactly the centre of mass in E . A submanifold M of a hypersphere ...