It

platform. It

of lightning. But this was . . . .
The air opened out before him, raggedly framing a bright-lit three-dimensional picture. He was staring down across a foaming river to the rim of a towering green and yellow forest. The crash of the river filled the building. Something bulky and black at the far left . . .  but the scene was gone—
The interior of the laboratory building lay quiet and unchanged before them again. Dowland said hoarsely, “How did you know what was going to happen?”
“I was in a position to spend several hours observing it,” Trelawney said, “from the other side. You see now, I think, that we can put your mountaineer’s kit to some very practical use here.”
Dowland glanced across the building. “The walls . . .”
“Metasteel,” Trelawney said, “and thank God for that. The building’s sound; the stresses haven’t affected it. We’ll have some anchor points. A clamp piton against that wall, six feet above the console walk and in line with it, another one against the doorframe here, and we can rope across.”
Dowland saw it, unsnapped his harness, fed the end of the magnerope through the eye of a piton, and twisted it tight. “Are we going together?” he asked.
Trelawney shook his head. “You’re going, Dowland. Sorry about that, but this is no time for sporting gestures. The rope doesn’t eliminate the danger. But if you find your feet suddenly dangling over the air of a very old time, you’ll still stay here—I hope. If you don’t make it across, I’ll follow. We get i