The machinery could be replaced, the central storage places could be refilled, and the many doors closed again. But the central room containing the air plant was no small matter. Channing took a sad look at the lush growth of Martian saw grass and sighed. It was growing nicely now, they had nurtured it into lusty growth from mere sprouts in trays and it was as valuable--precisely--as the lives of the three thousand-odd that lived, loved, and pursued happiness on Venus Equilateral. It was a youthful plant, a replacement brought in a tearing hurry from Mars to replace the former plant that was heaved into the incinerator by a well-meaning but ignorant man who thought that an air plant must be huge, moving levers, whirling gears, bubbling retorts, and a sprig of parsley. Channing closed his eyes and shuddered in mock horror. "Chop out the center," he said. The "center" meant the topmost fronds of the long blades; their roots were embedded in the trays that filled the cylindrical floor. Some of the blades would die--Martian saw grass is tender in spite of the wicked spines that line the edge--but this was an emergency with a capital E. Cleaning the centermost channel out of the station was no small job. The men who put up Venus Equilateral had no idea that someone would be using the station for a sighting tube some day. The many additions to the station through the years made the layout as regular and as well-planned as the Mammoth Cave in Kentucky. So for hour upon hour, men swarmed in the central, weightless channel and wielded acetylene torches, cutting steel. Not in all cases, but there were many. In three miles of storage rooms, a lot of doors and bulkheads can be thrown up without crowding the size of the individual rooms. Channing spoke into the microphone at the North end of Venus Equilateral, and said: "Walt? We've got a sight. Can you see?" "Yop," said Walt. "And say, what happens to me after that bum guess?" "That was quite a stretch, Walt. That 'hour, God willing,' worked itself into four hours, God help us." "O.K., so I was optimistic. I thought that those doors were all on the center line." "They are supposed to be, but they aren't huge and a little misalignment can do a lot of light-stopping. Can we juggle mirrors now?" "Sure as shooting. Is Freddy out in the flitter?" "He says he is guessing that he is at the right distance now. I'm set at a right angle now"--Don began to fumble through a volume of Vega's "Logarithms and Trigonometrical Functions"--"eighty-nine degrees, forty-five minutes, and forty seconds. Can you set your mirror that close?" "Nope," answered Walt without a qualm. "Not a chance. I can hit it about ten seconds plus or minus, though." "Make it plus nothing, minus twenty," said Don. "I was playing by ear, this time on account of my slipstick is busted."