Before the next sunup they were ready. Clothed in garments of linten fiber, they looked like savages from fifty thousand years before. Yet their present condition could have belonged to no primitive era. They were united by a tough line of twisted strands, and their equipment was lashed to their backs. To human eyes they would have been as invisible as spirits. Were they to demonstrate, even unintentionally, android superiority in yet another field? Maybe, maybe not. From the outlet of the crevice in the rock, they flung themselves into the atmosphere above the gray desert. Their great advantage at this stage was that, at the Martian dawn fringe, there were many updrafts, for the air, chilled fearfully at night, was already warming. At once they were sucked upward, as if by a vertical wind. Still, the first phase of their climb took many hours. They kept watching for upward-moving motes to guide them. Short, rocketlike bursts of heavy neutrons from their Midas Touch cylinders provided the reaction or kick to get them into the swiftest vertical currents. Mars dropped far below, a dun plain marked here and there by the straight, artificial valleys or "canals." The relative vastness of a world to beings of pinpoint dimensions was nullified by the distance of altitude, until it looked no more extensive than it would have to the eyes that used to be theirs. Mars developed a visible curvature and a rim of haze, fired to redness by the rising sun. The sky above darkened from hard, deep blue toward the blackness of space, and the stars sharpened. The sun blazed whitely, and the frosty wings of its corona began to show. The thinning atmosphere seemed to develop a definite surface far beneath the three voyagers. They had spoken little in their ascent; but now the free movement of sound was smothered by the increasing vacuum, and there were only gestures and lip movements to convey meanings. But there was not much that really needed to be said. The plan remained simple: get into trains of upward-jetting molecules, marked by small blurs or warpings of light. Absorb some of that upward surge into yourselves. How often had this same thing happened, without conscious design? Molecules move fast in a high vacuum. Molecular velocity was heat, wasn't it? But here it could not burn. For heat is chained to matter, and here there was just not enough matter to be hot. Ed thought that they must be getting close to the Martian velocity of escape now. Only three-point-two miles per second. They might have attained it more simply by making greater use of their Midas Touch cylinders. There was scarcely any reactive thrust more efficient than that of neutrons hurled at almost the speed of light. But there was a pride in accomplishing it in a more difficult way. Besides, the energy supply for the weapons must be conserved.