ut of the crater there came no sound of heavy objects striking, though Sarka felt there should have, for the cubes were almost as heavy as a man.
Then his hair almost stood on end under his helmet, for under that first aircar, where he had first seen it, the initial cube was again gleaming into life!
The thing had dissolved while being hurled over the rim, and reformed in its proper place, its station as silent sentinel under the aircar!
These cubes then, were indeed sentinels—sentinels impossible to injure. Though no force had been used against Sarka and Jaska, Sarka had the feeling that they were powerless, and that here on the edge of a crater of the Moon awful forces were being mustered against them. Mustered slowly, sluggishly, yet surely, as though the mentality which mustered them knew them helpless, and that there was no need to hurry!
As for Jaska, she merely clung to Sarka and waited—trusting him no matter what might transpire.
On a blind chance, Sarka brought out his ray director again, turned its muzzle toward that invisibly-blue column, pressed with his fingers, moving the director back and forth.
Instantly the blue column seemed to break short off, while the broken upper portion started racing outward toward the Earth. Sarka watched it, and noted that the yellowish glow on the Earth, even as he watched, was fading out—disappearing!
"If the ray will smash the blue column, Jaska," he said, "it will also destroy its source! Come! We will go look for it!"