"An elongated uniform body, e.g., a dressed lath of pine, has three primary centers - the center of gravity, the center of oscillation, and the center of velocity. The center of gravity is the center of the body; the center of oscillation is two-thirds from the end as the point of suspension; the center of velocity is at two-thirds of one-third from the end; i.e., at two-ninths from the end as the point of suspension.
"This elongated body suspended at the end, or at one-third from the end, the oscillations are the same. The one-third above the point of suspension so balances the two-thirds below that the oscillations are performed in the same time for both suspensions. When it is suspended at two-thirds of the one-third. i.e., one-ninth of the whole length above the center of oscillation, one-ninth above balances two-ninths below; the oscillating part is thus, as it were, one-ninth shorter than at the center of oscillation, and gives rise to the center of velocity." [Scientific Basis and Build of Music, page 92-93]
[Mechanical] That point in the axis of a vibrating body in which, if the whole matter were concentrated, the body would continue to vibrate in the same time. It lies in the same axis as the center of gravity, but is necessarily situated farther from the point of suspension. (Horner, J. G. ; Dictionary of Terms Used in Mechanical Engineering; The Technical Press, Ltd., London, England, 1960)