Fact sheet.First published: Astounding, April 1938.
Download full text from Chomikuj.pl (badly formatted HTML; I'd to edit it in a text editor on PC discarding entire HTML header & footer, & saving it as TXT file, before it would read correctly in Moon+ Reader on my tablet).
Nominated for Retro Hugo Awards 1939 in short story category.
Among the stories from Astounding/Analog issues edited by John Campbell.
Related: Stories of Lester del Rey.