“The Brain Stealers of Mars,” a 1936 short story by John W. Campbell

Thanks to some kind soul at Scribd, you can read "The Brain Stealers of Mars,” a short story written by legendary American science fiction editor John W. Campbell (1910-1971). Originally published in the December 1936 issue of Thrilling Wonder Stories magazine, the story revolves around two scientists who have been outlawed from Earth for working to develop atomic energy. They travel to a vegetated Mars, where they encounter centaur-like Martian shape-changers who repeatedly duplicate the scientists, even their memories. The opening lines:

ROD BLAKE looked up with a deep chuckle. The sky of Mars was almost black, despite the small, brilliant sun, and the brighter stars and planets that shone visibly, Earth most brilliant of all, scarcely sixty million miles away.

"They'll have a fine time chasing us, back there, Ted." He nodded toward the brilliant planet.

Ted Penton smiled beatifically.

"They're probably investigating all our known haunts. It's their own fault if they can't find us -- outlawing research on atomic power." ...

According to The Mechanics of Wonder: The Creation of the Idea of Science Fiction (1999), by scholar Gary Westfahl:

Campbell’s stories from 1935 to 1937 demonstrate, in fact, that he was failing to become a major author even before he became the editor of Astounding Stories -- the factor usually cited to explain his decline. Eventually, Campbell was reduced to writing terrible imitations of Stanley G. Weinbaum like “The Brain Stealers of Mars” for Thrilling Wonder Stories.

Considering how long I waited to read Campbell’s story, major disappointment. Too confusing. Trying to keep all the duplicate scientists straight hurt my brain!

[via Tinkoo Valia of Variety SF]