1. R. P. Feynman, R. B. Leighton, and M. Sands, The Feynman Lectures on Physics (Addison Wesley, Reading, MA, 1966), Vol. 1, chapt. 46.
2. M. von Smoluchowski, Phys. Z. XIII, 1069 (1912).
3. S. Leibler, Nature 370, 412 (1994)
4. J. Maddox, ibid. 365, 203 (1993)
5. J. Maddox, ibid. 369, 181 (1994)