He proposed the theory that an important feature might be that extra evaporation happens near the edge of the drop, because recondensation of evaporated material would happen less on the outside than in the middle. And in fact, Rob Deegan's experiments showed that Todd's basic idea was right. Deegan made a dispersion of particles that were big enough to see in a microscope but small enough that they wouldn't fall to the bottom, so the movement of particles to the edge over time could be directly observed. The growth of the ring essentially followed the power law that Dupont had predicted. Among the physical phenomena they have studied are water drops, sand piles and mixed nuts.
Compaction affects the preparation of building sites for construction, and roadbeds for paving.
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