1. H. Hertz,The Principles of Mechanics(Dover, New York, 1956).
2. W. Yourgrau and S. Mandelstam,Variational Principles in Dynamics and Quantum Theory(Saunders, New York, 1969).
3. C. C. Gillespie,Scientific Biography(Scribners, New York, 1972), Vol. I, p. 348.
4. An extension of the Gauss-Hertz principle
5. C. A. Truesdell,The Kinematics of Vorticity(Indiana University, Bloomington, Ind., 1954), p. 93.