Adam listened. How strange, low, sad the moan! His keen ears, attuned to all varieties of desert sound, seemed to fill and expand. The moan swelled to a low roar, lulling now, then rising. Like no sound he had ever heard before, it had strange affinity with the abyss of shadows. Suddenly the air around Adam began a steady movement northward. Its density increased, or else the movement, or pressure behind, made it appear so. And it grew swift, until it rustled the brush. Down in the valley the roar swelled like the movement of a mighty storm through a forest. When the gale reached the gateway below Adam it gave a hollow bellow.
The last of the warm, still air was pressed beyond Adam, apparently leaving a vacuum, for there did not appear to be air enough to breathe. The roar of wind sounded
