Explains the phenomenon of Brownian motion, which serves as a mathematical model for random processes. Topics addressed include kinetic theory, Einstein's theory, particle displacement, and others. Points out that observations of the random course of a particle suspended in fluid led to the first accurate measurement of atomic mass. (DH)

One application of modeling is studying the ways in which molecules fit together to form chemical compounds. Describes the forces acting between molecules and how three-dimensional graphical modeling is employed in developing rational principles for drug design. (JN)