Here, there must have been blue sky, thin, frosty wind. The small, Mars-sized planet had been far from the sun. Yet perhaps the greenhouse effect of a high percentage of carbon dioxide in its atmosphere and the radioactive heat of its interior had helped warm it. At least it had been warm enough to evolve life of the highest order, eons ago. Poof had gone the blue sky and this whole world, all in a moment, the scattered pieces forming the asteroids. Accident? More likely it was a huge, interplanetary missile from competing Mars. The Martians had died, too--as surely, though less spectacularly. Radioactive poison, perhaps... Here, there had been an instant of unimaginable concussion, and of swift-passing flame. The drying out was soon ended. Then, what was left had been preserved in a vacuum through sixty millions of years. Frank Nelsen had glimpsed ancient Mars, preserved on the Moon. Now he glimpsed its opponent culture, about which more was generally known. "It's real," Ramos grunted. "Hoppers find surface-fragments like this, quite often." Nelsen hardly cared about the archeological aspects just then. Excitement and hope that became certainty, enlivened his dulled brain. "An energy source," he grated joyfully. "The Big Answer to Everything, out here! And it's always self-contained in their buildings..." They pushed the collapsed and blackened thing with the slender bones, aside. They crept into the flat, horizontal spaces of the dwelling--much more like chinks than the rooms that humans would inhabit. They shoved away soft, multi-colored fabrics spun from glass-wool, a metal case with graduated dials and a lens, baubles of gold and glinting mineral. In a recess in the masonry, ribboned with glazed copper strips that led to clear globes and curious household appliances, they found what they wanted. Six little oblong boxes bunched together. Their outsides were blue ceramic. Frank Nelsen and Miguel Ramos began to work gingerly, though the gloves of their old Archer Threes were insulated. Here, sixty million years of stopped time had made no difference to these nuclear batteries, that, because of the universal character of physical laws, almost had to be similar in principle to their own. They had almost known that it would make no difference. There had been no drain of power through the automatic safety switches. "DC current, huh?" Ramos said, breathing hard of the rotten air in his helmet. "Yeah--gotta be," Frank answered quickly. "Same as from a thermocouple. Voltage about two hundred. Lots of current, though. Hope these old ionics'll take it." "We can tap off lower, if we have to... Here--I'll fix you, first... Grab this end..." They had a sweating two hours of rewiring to get done.