The tapering white obelisk thrust upward from the earth like a giant needle. The Briggses entered the base of it, went up the elevator, and caught glimpses of stairway landings as the cage rose slowly. When they stepped out on the platform near the top, they walked to the pair of port openings on one side and looked out. In the time it had taken them to get to the top of Washington Monument, a light fog, borne on the slight evening breeze, had enveloped the tall shaft at its midsection; they could see nothing of the ground below. They were isolated from Earth, connected to it only by the elevator well. "Isn't this eerie?" Mrs. Briggs asked Timmy. He looked around casually and yawned. "On an Elroom program," he said, "you would be able to see all the way down. I don't think this is so hot." He yawned again. "I'm thirsty." "We'll be going down in a minute, Timmy." "I've got the route figured better than Itineraries for the next stop," George said. "If we could leave in twenty minutes--" * * * * * Aragonite crystals on the cavern's ceiling twinkled brightly in reflection of glowing electric lights. The fragile beauty of the boxwork formation took Mrs. Briggs's breath away. "It's just like lace," she whispered to George, pointing to the frosty tracery glistening in the honeycombed walls. "Tom Bingham discovered this cave," the guide intoned before the tourists seated in the giant chamber, his voice echoing from the walls. "He heard a whistling sound and found it came from a small opening. That's why they call this Wind Cave. The wind goes in and out." "Why does it do that?" someone asked. "Difference in atmospheric pressure," the guide said. "Another interesting thing about this cave: It's always forty-seven degrees. Doesn't make any difference whether it's summer or winter. Always the same in here." "I don't hear any wind," Timmy said to his mother and father. "Why isn't the wind whistling?" "When the barometer falls, the wind blows out," his father explained. "When the barometer rises, the wind blows in." "Why isn't the wind whistling now?" Timmy insisted. "The barometer must be standing still, son." "This isn't any good. On an Elroom program the wind would be whistling." "Hush," Mrs. Briggs said. "I'm thirsty," Timmy said. "We'll be leaving in a few minutes." "You'll get plenty of wind when I rev up the _Caddie_ on our next hop," George said. * * * * * "Think of that," George said. "It's a whole mile down to the river." Timmy leaned forward to take a deep look over the precipice at Yaki point. "Boy!" he said. "This is pretty good. Almost makes me dizzy." Below, the Colorado River was bright quicksilver, threading its way circuitously through the canyon. The striated walls rose majestically from the floor to towering temples. The boy turned from the rock to look at the tufts of clouds floating by in the deep blue sky. "I'm thirsty," he said.