1. A. Einstein (1905), Collected Papers of Albert Einstein, Vol.2, Anna Beck and Peter Havas, eds. (Princeton University Press, Princeton, 1989).
2. M. Kaku, Introduction to Superstrings (Springer, New York, 1988).
3. See, for example, H. Ohanian, Modern Physics (Prentice-Hall, New York, 1987). C. Rangacharyulu, Elements of Modern Physics, in preparation.
4. O. Klein and Y. Nishina, Z. Phys. 52 (1929) 853; English translation in O. Klein Memorial Lectures (World Scientific, Singapore, 1994), Vol. 2, p. 113.