Osgood set Noodles to run a peculiar tube in a circle around the bank at a distance of several yards. This was the part that Noodles couldn't quite grasp, but he was sure by now that the old inventor knew his business. When he had run clear around the bank and attached both ends of the tube to Osgood's apparatus they backed toward the bank, and Osgood threw a switch. The dew in the air began to collect on an invisible barrier which, as a consequence, became visible: a great cylinder around the bank whose walls drew together overhead. Osgood nodded happily. "The surface tension will build as the water collects," he said. "Now - spread the second tube!"
Noodles repeated the process with a second tube, which formed a ring about an inch inside the first one. They attached its ends; they again flipped a switch; and a second invisible wall formed inside the first. Osgood waited. "Less moisture in here," he grumbled, "but if we wait...."
Over the next few minutes the two invisible walls collected more and more of the moisture in the air: they became oddly shimmering domes, one inside the other, which completely enclosed the bank. Osgood and Noodles set about pulling the inner tube closer to the bank. They did this in several stages, narrowing the inner dome, until the two walls were perhaps four feet apart. "Don't go in there!" Osgood cautioned. "We have a near perfect vacuum."
Noodles was happy to agree. He'd seen a bat fly into the space between the walls and when it had plummeted to the ground it could not, honestly, still be called a bat. "How long will it last?" he whispered.
Osgood laughed. "No need to be quiet!" he shouted. "The sound waves can't pass through the barrier!"
Then he turned serious. "We have about half an hour, I'd say. The water vapor is already being drawn into the vacuum.