Was one of his colleagues watching, even at this moment, from his vantage point high above the Moon?) But this was no picture painted on a screen by flying electrons; this was the real thing, the strange, amorphous stuff that had swallowed twenty-two men and women without trace. And across which he, Tom Lawson, was about to venture on this insubstantial craft.
He had little time to brood. The ski vibrated beneath him as the fans started to spin; then, following Duster One, it glided slowly out onto the naked surface of the Moon.
The low rays of the rising sun smote them as soon as they emerged from the long shadow of the Port buildings. Even with the protection of the automatic filters, it was dangerous to look toward the blue-white fury in the eastern sky. No, Tom corrected himself, this is the Moon, not Earth; here the sun rises in the west. So we're heading northeast, into the Sinus Roris, along the track Selene followed and never retraced.
Now that the low domes of the Port were shrinking visibly toward the horizon, he felt something of the exhilaration and excitement of all forms of speed. The sensation lasted only for a few minutes, until no more landmarks could be seen and they were caught in the illusion of being poised at the very center of an infinite plain. Despite the turmoil of the spinning fans, and the slow, silent fall of the dust parabolas behind them, they seemed to be motionless. Tom knew that they were traveling at a speed that would take them clear across the Sea in a couple of hours, yet he had to wrestle with the fear that they were lost light-years from any hope of salvation. It was at this moment that he began, a little late in the game, to feel a grudging respect for the men he was working with.
This was a good place to start checking his equipment. He switched on the detector, and set it scanning back and forth over the emptiness they had just crossed. With calm satisfaction, he noted the two blinding trails of light stretching behind them across the darkness of the Sea. This test, of course, was childishly easy; Selene's fading thermal ghost would be a million times harder to spot against the waxing heat of dawn. But it was encouraging. If he had failed here, there would have been no point in continuing any further.
"How's it working?" said the Chief Engineer, who must have been watching from the other ski.
"Up to specification," replied Tom cautiously. "It seems to be behaving normally." He aimed the detector at the shrinking crescent of Earth; that was a slightly more difficult target, but not a really hard one, for it needed little sensitivity to pick up the gentle warmth of the mother world when it was projected against the cold night of space.
Yes, there it was - Earth in the far infrared, a strange and at first glance baffling sight. For it was no longer a clean-cut, geometrically perfect crescent, but a ragged mushroom with its stem lying along the equator.
It took Tom a few seconds to interpret the picture. Both Poles had been chopped off. That was understandable, for they were too cold to be detected at this setting of the sensitivity. But why that bulge across the unilluminated night side of the planet? Then he realized that he was seeing the warm glow of the tropical oceans, radiating back into the darkness the heat that they had stored during the day. In the infrared, the equatorial night was more brilliant than the polar day.
It was a reminder of the fact, which no scientist should ever forget, that human senses perceived only a tiny, distorted picture of the Universe. Tom Lawson had never heard of Plato's analogy of the chained prisoners in the cave, watching shadows cast upon a wall and trying to deduce from them the realities of the external world. But here was a demonstration that Plato would have appreciated: Which Earth was "real"? The perfect crescent visible to the eye, the tattered mushroom glowing in the far infrared - or neither?
The office was small, even for Port Roris - which was purely a transit station between Earthside and Farside, and a jump. ing-off point for tourists to the Sea of Thirst. (Not that any looked like jumping off in that direction for some time.) The Port had had a brief moment of glory thirty years before, as