CLUSTERING AND COLLAPSE IN GRANULAR MATERIAL. Collections of grains (salt, sand, sugar, seeds, steel balls, etc.) represent a sort of 4th state of matter. Granular materials share some properties with solids (they bear loads), liquids (they pour), and ideal gases (they constitute collections of non-cohesive particles), but they also have peculiar properties of their own. For one thing temperature is not important. Freezing or baking grains doesn't make them flow any better. The thermal energy of a grain is a trillion times less than the energy it takes to lift one grain on top of another. In an effort to explore the differences and similarities between granular materials and other types of matter, scientists often tumble and shake grains in various containers. In one experiment at Georgetown University (Jeffrey Olafsen, 202- 687-6004, olafsen@physics.georgetown.edu) a layer of thousands of tiny steel balls on a tray is vertically shaken. This agitated system can be "cooled" by decreasing the amplitude of the shaking. Below a certain "granular temperature" the balls start to cluster together. In a still cooler state, many of the balls collapse (one might say crystallize) into a condensate which remains at rest even as other balls continue to move about. Besides wanting to apply knowledge about granular materials in a variety of industrial settings (foodstuffs, paint mixing, pharmaceuticals, agriculture), researchers hope to find more relations among the many things in the universe that clump and condense (atoms, bacteria, galaxies). Olafsen will report these findings next week at the 1998 Meeting of the APS Division of Fluid Dynamics in Philadelphia. (See also Olafsen and Urbach, Physical Review Letters, 16 Nov 1998 and Pouliquen et al., Physical Review Letters, 10 Nov 1997; see figure at Physics News Graphics.)