FIRST EDITION, paperback. Collection of stories by these masters of science fiction. Introduction by Pohl, and these STORIES: Critical Mass (1962); A Gentle Dying (1961); Nightmare with Zeppelins (1958); Best Friend (1941); The World of Myrion Flowers (1961); Trouble in Time (1940); The Engineer (1956); Mars-Tube (1941); The Quaker Cannon (1961).
Used availability for Frederik Pohl's The Wonder Effect
September 1974 : UK Paperback
September 1962 : USA Mass Market Paperback