Peter Debye won the Nobel Prize of 1936 for his research on the electrical properties of matter, as found in the polarity of molecules. His work has importance in modern physics, by indicating the fundamental status of charge in nature. This paper is the first to show a detailed derivation of Debye’s formula for finding molecular weight from the patterns of light scattered by solutions of molecules. The paper was given to Sigma Xi of Orange County in July, 2001