«The White Invaders» by Ray Cummings

The White Invaders is a science fiction novella by American author Ray Cummings first published in Astounding Stories in December 1931.
Out of their unknown fourth dimensional realm materializes a horde of White Invaders with power invincible.
When a young boy tells Don that he's seen a ghost, Don only laughs. There's no such thing as ghosts, and the little boy probably saw a reflection. But to prove the boy wrong, Don and his friend go to the hill where the boy says that the ghost floated towards him and through a rock.
Don, however, brings his shotgun just in case - after all, it could've been a wild animal of some kind. And when they discover that it wasn't a ghost at all, but something altogether weirder, they must defend themselves from the onslaught of these White Invaders - or face annihilation of everyone they've ever known!
Ray Cummings (1887-1957) was an American author of science fiction, rated one of the "founding fathers of the science fiction pulp genre".
Having worked for Thomas Alva Edison, Ray Cummings was inspired by science’s possibilities and began to write science fiction.
His most highly regarded work was the novel The Girl in the Golden Atom published in 1922. His career resulted in some 750 novels and short stories, using also the pen names Ray King, Gabrielle Cummings, and Gabriel Wilson.