Rusting

Activity keeps the mind from rusting.

In the shadow of sleek new expressways and gleaming high-rise buildings sit wooden shacks with rusting corrugated iron roofs and festering open sewers.

The "Scorpion," a Soviet-built submarine that tracked U.S. vessels across the Pacific Ocean during the Cold War is slowly rusting in Long Beach harbor.

An example will best make the matter clear, and throw light, perhaps, on many cases of apparently mysterious rustings.