Along with the novel itself, many editions (and most recent editions) of the book also include "Whirligig World", an essay by Clement on creating the planet Mesklin that was first published in the June 1953 Astounding.
Bersama dengan novel itu sendiri, beberapa edisi (dan edisi-edisi paling terbaru) dari buku tersebut juga meliputi "Whirligig World", sebuah esay karya Clement tentang pembuatan planet Mesklin yang mula-mula terbit dalam Astounding edisi Juni 1953.