In writing fantastic science tales, two themes have attracted me more than others, and have seemed to offer the amplest possibilities and the deepest stimulus to imagination: the inter- planetary and the inter-dimensional themes. Among those of my stories that can be classed, more or less accurately, as science fiction, the majority have dealt either with worlds remote in space, or worlds hidden from human perception by their different vibratory rate or atomic composition.

I am glad that my tale of life on Venus, "World of Horror," (An alternate title for "The Immeasurable Horror," originally published in Weird Tales, Sept. 1931, and in OTHER DIMENSIONS (Arkham House, 1970).) found favour with many readers of Tales of Wonder. I hope to return presently to this type of story, which, though exploited by so many authors, is still rich in unsounded potentialities. Indeed, there are no limits to their development except those of the writer's imagination. Here, however, lies the difficulty, since it is impossible for one to conceive forms and conditions of life, matter and energy that are wholly diverse from all terrestrial states and forms.

And yet, when one considers the fantastic variations of life on this one tiny planet, there seems little reason to presuppose that life on other worlds will necessarily repeat, or even resemble, the types known to us. In future ages, when space-transit has become a reality, our wildest fictions may seem feeble and commonplace beside the fantasies of Nature itself that explorers will discover on alien globes.

Among my several inter-dimensional stories, I think "City of Singing Flame" is the best. I owe its inspiration to several camping sojourns amid time high Sierras, at a spot within easy walking distance of the Crater Ridge described by Angarth and Hastane. The Ridge is a wild eerie place, differing wholly in its geology and general aspect from the surrounding region, exactly as pictured in the story. It impressed my imagination profoundly, suggesting almost at first sight the contiguity of some unknown, invisible world to which it might afford the mundane approach and entrance. And, since I have never explored the whole of its area, I am not altogether sure that the worn, broken column-ends found by the story's narrators do not really exist somewhere among the curiously shaped and charactered stones that lie in such strange abundance there!

All fantasy apart, however, it seems to me that the theory of interlocking worlds in one that might be offered and defended. We know nothing of the ranges of vibration, the forms of matter and energy, that may lie beyond the testing of our most delicate instruments. Spheres and beings whose atomic structure removes them from all detection may float through or beside the Earth, no less oblivious of our existence than we of theirs. Transit between planes of space, though filled with obvious material difficulties, is at least more readily comprehensible than time-travelling.