SUPPORT FOR FARADAY VIEW OF CIRCULATION IN A FINE-POWDER CHLADNI HEAP

Faraday, like Chladni, saw fine powder collect in a circular heap at a n antinode of a vibrating plate. In each vibration cycle, the heap exp eriences a free-flight interval during which pressure gradients in the heap's interior drive powder centerward, as Faraday proposed. When he ap-floor collision terminates flight, pressure gradients reverse direc tion; but passage of a compaction front has locked particles against f urther movement. Before a next flight interval, an increase in porosit y will reverse the compaction that accompanied heap-floor collision.