Ever and anon, as they traveled they looked back up at the Earth which was their home. It still was visible, though plainly smaller with distance, and for a time Sarka's heart misgave him; but he only clasped tighter the hand of Jaska and moved on. They were just at the base of the first hill, which had now become a mountain of gloomy, forbidding aspect, when the first sound they had heard on the moon came to them. A sound that was a commingling of the laughter of Dalis, the barking of jackals of the olden times, the humming of a million Beryls revolving at top speed, and a strident buzzing such as neither had ever heard. Had they been discovered? Was the sound a warning? They could not know; but as they stared at the crest of the hill, two long, snaky, waving things appeared above the crest, undulating, waving to and fro, as though questing for something. They crouched low in the white ashes at the base of the mountain, and waited, scarcely breathing. CHAPTER XIII _The Lunar Cubes_ For a long time Sarka and Jaska remained still, like sentinels, listening to the strange discord which seemed to emanate from behind the hill at whose base they crouched. "Look!" said Sarka at last. "There against the sky, beyond and between those two waving tentacles! Note that column of light, scarcely lighter than the light which surrounds it everywhere? It looks like a massive column just lighter than everything around it, yet so little lighter that you have to watch closely to see it at all?" Jaska stared for all of a minute, before she thought back her answer. "I see it," she said. "Note now whether it goes, as it reaches outward into Space!" Jaska followed the mighty height of the thing, outward and outward, and then gasped. "Sarka," she said, "its end touches the Earth in the very heart of that strange glow we spoke about!" "Exactly! And people of Earth know nothing about it, because it is invisible to them! It is only from Outside that the glow it makes against the Earth is visible! If we can divert its direction, or render it useless in any way, the Moon will no longer be thrust away by its force!" A pause of indecision, then Sarka thought again: "Let us go, Jaska! Keep behind me, right on my heels!" Slowly, fighting against something that seemed determined to pull, or hurl, them outward from the surface of the Moon with each forward movement they made, they essayed the side of the hill, pausing at the end of what seemed like hours in a sort of hollow just large enough to mask their bodies and stared over its edge into one of the craters of the Moon. Out of the depths of that crater came the discordant sounds, which now were almost deafening, and out of that crater too came the almost invisibly bluish column whose outer tip touched the Earth. * * * * *