An example of an extended metaphor used n popular science writing:
"If the material forming the planets was formerly in the form of separate particles, say, 0.0001 cm in diameter, there must have been some 1045 particles moving along the elliptical orbits of all various sizes and elongations. it is clear that, in such heavy traffic, numerous collisions must have taken place between the individual particles, and that, as the result of such collisions, the motion of the entire swarm must have become to a certain extent organised. In fact, it is not difficult to understand that such collisions served either to pulverise the 'traffic violators' or to force them to 'detour' into less crowded 'traffic lanes'. What are the laws that would govern such 'organised' or at least partially organised 'traffic'? … the nonintersecting traffic-rules pattern for individual groups of particles moving at the same mean distance from the sun and possessing therefore the same period of rotation.
…
By careful analysis of the situation Weizsäcker was able to show …an arrangement [that] would assure 'safe traffic' within each individual ring, but , since these rings rotated with different periods, there must have been 'traffic accidents' where one ring touched another.""
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
