Benjamin Widom, who since 1983 has been the Goldwin Smith Professor of Chemistry in the Cornell University Department of Chemistry and Chemical Biology, has been named one of the two recipients of the 1998 Boltzmann medal.

The medal is awarded by the Commission on Statistical Physics of the International Union of Pure and Applied Physics. The award will be presented at the 20th International Conference on Statistical Physics to be held in Paris next month.

The other winner of this year's award is Elliott H. Lieb, professor of mathematics and physics at Princeton University.

The citation on Widom's award reads: "For his illuminating studies of the statistical mechanics of fluids and fluid mixtures and their interfacial properties, especially his clear and general formulation of scaling hypotheses for the equation of state and surface tensions of fluids near critical points."

Widom explains that a liquid and a vapor to which it evaporates, or from which it condenses, are said to be two different "phases" of the substance. When the evaporation and condensation occur at equal rates, the phases are in equilibrium. At high enough temperatures and pressures (for water, a temperature of 705 degrees Fahrenheit, or a pressure 218 times that of the earth's atmosphere) the two previously distinct phases become identical. This is called the "critical point" of the phase equilibrium.

Near the critical point the fluids have special properties: Their compressibility is exceptionally great (or infinite at the critical point itself) and the tension of the interface between them -- the surface tension -- is exceptionally low (vanishing at the critical point).

Widom's award was mostly for his contributions to the understanding and quantitative characterization of such critical phenomena in various contexts in which they occur in nature.

Widom was born in Newark, N.J., received his bachelor's degree at Columbia University in 1949 and earned his Ph.D. at Cornell in 1953. He became an instructor of chemistry at Cornell in 1954, was appointed assistant professor in 1955 and a full professor in 1963. He was chair of the chemistry department between 1978 and 1981. He was elected a member of the National Academy of Sciences in 1974 and a fellow of the American Academy of Arts and Sciences in 1979.

The award is named for Ludwig (Eduard) Boltzmann (1844-1906), a Viennese physicist who was a pivotal figure in the modern science of statistical mechanics.