参考文献: [1]Newton, I., The Principia:Mathematical Principles of Natural Philosophy (Trans.I. B. Cohen andA.Whitman). Berkeley, CA: University of California Press, 1999. [2]Jackson, J.D., Classical Electrodynamics, 3rd ed., NewYork: Wiley, p.177, 1998. [3]季灏 中国工程科学 10(2006)60-65