Jarvis paused and shuddered. "The brute half poisoned Leroy," he continued. "We dragged ourselves back to the auxiliary, called you, and did what we could to treat ourselves. Leroy took a long dose of the cognac that we had with us; we didn't dare try anything of Tweel's because his metabolism is so different from ours that what cured him might kill us. But the cognac seemed to work, and so, after I'd done one other thing I wanted to do, we came back here--and that's all." "All, is it?" queried Harrison. "So you've solved all the mysteries of Mars, eh?" "Not by a damned sight!" retorted Jarvis. "Plenty of unanswered questions are left." "_Ja!_" snapped Putz. "Der evaporation--dot iss shtopped how?" "In the canals? I wondered about that, too; in those thousands of miles, and against this low air-pressure, you'd think they'd lose a lot. But the answer's simple; they float a skin of oil on the water." Putz nodded, but Harrison cut in. "Here's a puzzler. With only coal and oil--just combustion or electric power--where'd they get the energy to build a planet-wide canal system, thousands and thousands of miles of 'em? Think of the job we had cutting the Panama Canal to sea level, and then answer that!" "Easy!" grinned Jarvis. "Martian gravity and Martian air--that's the answer. Figure it out: First, the dirt they dug only weighed a third its earth-weight. Second, a steam engine here expands against ten pounds per square inch less air pressure than on earth. Third, they could build the engine three times as large here with no greater internal weight. And fourth, the whole planet's nearly level. Right, Putz?" The engineer nodded. "_Ja!_ Der shteam--engine--it iss _sieben-und zwanzig_--twenty-seven times so effective here." "Well, there _does_ go the last mystery then," mused Harrison. "Yeah?" queried Jarvis sardonically. "You answer these, then. What was the nature of that vast empty city? Why do the Martians _need_ canals, since we never saw them eat or drink? Did they really visit the earth before the dawn of history, and, if not atomic energy, what powered their ship? Since Tweel's race seems to need little or no water, are they merely operating the canals for some higher creature that does? _Are_ there other intelligences on Mars? If not, what was the demon-faced imp we saw with the book? There are a few mysteries for you!" "I know one or two more!" growled Harrison, glaring suddenly at little Leroy. "You and your visions! 'Yvonne!' eh? Your wife's name is Marie, isn't it?" The little biologist turned crimson. "_Oui_," he admitted unhappily. He turned pleading eyes on the captain. "Please," he said. "In Paris _tout le monde_--everybody he think differently of those things--no?" He twisted uncomfortably. "Please, you will not tell Marie, _n'est-ce pas_?" Harrison chuckled. "None of my business," he said. "One more question, Jarvis. What was the one other thing you did before returning here?"