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)

Describes an Apple computer program (listing available from author) which simulates Fraunhofer and Fresnel diffraction using vector addition techniques (vector chaining) and allows user to experiment with different shaped multiple apertures. Graphics output include vector resultants, phase difference, diffraction patterns, and the Cornu spiral…