Astounding Stories of Super-Science, August 1930

Then, in a trice, it was gone, and a feeling of uneasiness, more compelling than he had ever known before, coursed through the soul of Sarka. Where had the cube gone? What was it? What was its purpose? He tore his eyes away from the spot where he had last seen it, and stared away to the shadow beneath the second nearest aircar, where he had glimpsed another of the cubes. The cube there, too, was fading out. "Sarka! Sarka! Look!" came to his brain the thoughts of Jaska. Sarka turned and stared at her, and a feeling of fear for which he could not account at all took fast hold of him. The eyes of Jaska, wide and staring as they had been when he commanded her to look away from the cube under the aircar, were staring at that flat, table-like rock, off to his right. There, almost in the center of the rock, a gleaming something was taking shape! Just a dull spot, in the center of the yellow glow; then the beginning of the outline of a cube. Then, all at once, the cube itself, gleaming and baleful! Sarka gasped in terror. He had seen the cube vanish, its glow disappear, and now here it was, almost close enough to touch, on a rock beside him, gleaming and baleful as before! That it was the same cube he had seen under the first aircar, he somehow knew without being told. That it was a sentient thing he also knew, for now there was no mistaking the fact that, but for the presence in the little hollow of Jaska and Sarka, the cube would not have moved.