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3. Oleg D. Jefimenko, Electrostatic Motors. Electret Scientific Company, Star City (1973).
4. W.K.H. Panofsky, and M. Phillips, Classical Electricity and Magnetism. Addison-Wesley Publishing Co., Inc., Reading, MA, p. 106 (1955).
5. H. H. Woodson, and J. R. Melcher. Electromechanical Dynamics. Part I: Discrete Systems. John Wiley & Sons, Inc., New York, pp. 60–88 (1968).