The bricklayer does negligent work on the walls of the flue he is putting in, and one night, years afterward, a spark creeps through the crevice and reaches a wooden beam that lies there, and soon the house is in flames and perhaps precious lives perish.

The bricklayer was unfaithful.

The foundryworker, in casting the great iron supports for a bridge, is unwatchful for an instant, and a bubble of air makes a flaw.

It is buried away in the heart of the beam and escapes detection.

One day, years later, there is a terrible disaster.