“If we stay here much longer,” replied Sue, “the passengers will start thinking of us.”

She spoke more truthfully than she had guessed.

CHAPTER 12

Dr. Lawson's silence, the Chief Engineer decided, had gone on long enough. It was high time to resume communication.

“Everything all right, Doctor?” he asked in his friendliest voice.

There was a short, angry bark, but the anger was directed at the Universe, not at him.

“It won't work,” Lawson answered bitterly. “The heat image is too confused. There are dozens of hot spots, not just the one I was expecting.”

“Stop your ski. I'll come over and have a look.”

Duster Two slid to a halt; Duster One eased up beside it until the two vehicles were almost touching. Moving with surprising ease despite the encumbrance of his space suit, Lawrence swung himself from one to the other and stood, gripping the supports of the overhead canopy, behind Lawson. He peered over the astronomer's shoulder at the image on the infrared converter.

“I see what you mean; it's a mess. But why was it uniform when you took your photos?”

“It must be a sunrise effect. The Sea's warming up, and for some reason it's not heating at the same rate everywhere.”

“Perhaps we can still make sense out of the pattern. I notice that there are some fairly clear areas—there must be an explanation for them. If we understood what's happening, it might help.”

Tom Lawson stirred himself with a great effort. The brittle shell of his self-confidence had been shattered by this unexpected setback, and he was very tired. He had had little sleep in the last two days, he had been hurried from satellite to spaceship to Moon to dust-ski, and after all that, his science had failed him.

“There could be a dozen explanations,” he said dully. “This dust looks uniform, but there may be patches with different conductivities. And it must be deeper in some places than in others; that would alter the heat flow.”

Lawrence was still staring at the pattern on the screen, trying to relate it to the visual scene around him.

“Just a minute,” he said. “I think you've got something.” He called to the pilot. “How deep is the dust around here?”

“Nobody knows; the Sea's never been sounded properly. But it's very shallow in these parts—we're near the northern edge. Sometimes we take out a fan blade on a reef.”

“As shallow as that? Well, there's your answer. If there's rock only a few centimeters below us, anything could happen to the heat pattern. Ten to one you'll find the picture getting simpler again when we're clear of these shoals. This is only a local effect, caused by irregularities just underneath us.”

“Perhaps you're right,” said Tom, reviving slightly. “If Selene has sunk, she must be in an area where the dust's fairly deep. You're sure it's shallow here?”

“Let's find out; there's a twenty-meter probe on my ski.”

A single section of the telescoping rod was enough to prove the point. When Lawrence drove it into the dust, it penetrated less than two meters before hitting an obstruction.

“How many spare fans have we got?” he asked thoughtfully.

“Four—two complete sets,” answered the pilot. “But when we hit a rock, the cotter pin shears through and the fans aren't damaged. Anyway, they're made of rubber; usually they just bend back. I've only lost three in the last year. Selene took out one the other day, and Pat Harris had to go outside and replace it. Gave the passengers some excitement.”

“Right—let's start moving again. Head for the gorge; I've a theory that it continues out underneath the Sea, so the dust will be much deeper there. If it is, your picture should start getting simpler, almost at once.”

Without much hope, Tom watched the patterns of light and shade flow across the screen. The skis were moving quite slowly now, giving him time to analyze the picture. They had traveled about two kilometers when he saw that Lawrence had been perfectly right.

The mottlings and dapplings had begun to disappear; the confused jumble of warmth and coolness was merging into uniformity. The screen was becoming a flat gray as the temperature variations smoothed themselves out. Beyond question, the dust was swiftly deepening beneath them.

The knowledge that his equipment was effective once more should have gratified Tom, but it had almost the opposite result. He could think only of the hidden depths above which he was floating, supported on the most treacherous and unstable of mediums. Beneath him now there might be gulfs reaching far down into the Moon's mysterious heart; at any moment they might swallow the dust-ski, as already they had swallowed Selene.