When RAY CUMMINGS took leave of this planet early in 1957, the world of modern science-fiction lost one of its genuine founding fathers. For the imagination of this talented writer supplied a great many of the most basic themes upon which the present superstructure of science-fiction is based. Following the lead of Jules Verne and H. G. Wells, Cummings successfully bridged the gap between the early dawning of science-fiction in the last decades of the Nineteenth Century and the full flowering of the field in these middle decades of the Twentieth. Born in 1887, Cummings acquired insight into the vast possibilities of future science by a personal association with Thomas Alva Edison. During the 1920's and 1930's, he thrilled millions of readers with his vivid tales of space and time. The infinite and the infinitesimal were all parts of his canvas, and past, present, and future, the interplanetary and the extra-dimensional, all made their initial impact on the reading public through his many stories and novels. * * * * * Previously published in an ACE edition is his novel, _The Man Who Mastered Time_ (D-173). * * * * *