Close to Critical by Hal Clement Page A

that its glow would not be seen from the cliff. He found the trail with little trouble, though Fagin was sensibly keeping to the valleys as much as possible, and finally caught up with the Teacher. Fagin heard his report, and approved. "It's probably the best you could have done," he said. "I'll be surprised if we get through the night without having company, though."
    "So will I," admitted Nick.
    In spite of this pessimism, the hours passed without any sign of pursuit. Nick's higher speed allowed him to keep up with the robot, even though he had to detour puddles which the machine took in its stride. The raindrops grew clear, and correspondingly dangerous; puddles and lakes larger, deeper, and harder to avoid as the bottom of Tenebra's atmosphere gradually underwent its nightly change in phase.
    "Even with your staying on dry land and leaving such an open trail, they must be having trouble following by now," remarked Fagin during one of the brief spells when they were together. "A lot of the places where you went must be well under water by now, and they can't be boiling them off with torches at this hour; the water's too clear to let them get away with it. I'm starting to feel a little happier about the whole situation."
    "I'm not," said Nick.
    "Why not?"
    "The pools are getting very big, and some of the valleys ahead are long and deep. I remember the night before last there were some pretty big rivers emptying into the sea. If we meet one of those, and I don't see how we can help it, we're stuck."
    "On the contrary, that seems to me the best thing that could happen. Swift can't follow through a river."
    "Neither can I."
    "Not under your own power. I can carry you, and it's pretty safe; we haven't met any creatures in sixteen years capable of living, or at least being active, in clear water - though I must admit I've always been expecting it."
    "There were some in the ocean."
    "That isn't water, for the most part, except late at night. Anyway, I think we needn't worry about ocean life. You've made me happier than I've been for some time; let's look for one of these rivers." "All right. I hope you're right." Nick was accustomed enough to being knocked out by oxygen-free water, but somehow didn't like the idea of being carted around like a sack in that state; If Fagin thought it was all right, though . . .
    It looked for a while as though he needn't have worried. With the common perversity of the inanimate, once a river was wanted, none could be found. They kept on their original course, knowing the futility of zigzagging over unknown ground, and got closer and closer to the sea; but they actually reached it, not too many hours before day, without finding a river.
    They had reached the "shore" far south of the region where the others awaited them; Nick had selected their course so that there would be no question of which way to turn when they reached the coast. He had mapped enough to know what measuring uncertainties could mean.
    Without hesitation, therefore, he directed Fagin to follow the "shore" to the left. They were, of course, far inland from the hill which Nick had planned to use to trap Swift, but that was the least of their troubles at the moment. The chief annoyance was the lack of a river; a second one, which made itself apparent an hour or so after they reached the sea, was the appearance behind them of a distinct glow of light. There was no question what it was; the sun just didn't get that distinct, or even that bright.
    "They're gaining on us. I wonder how long my fires delayed them?" muttered Nick when the glow caught his eye. Fagin had not seen it yet, apparently, and Nick saw nothing to be gamed in calling his attention to it. He just looked that much more intensely for a river ahead.
    The robot finally spotted the light as well, and understood its meaning as clearly as had Nick. "If they get too close before we find a river, you'd better go on ahead at your best speed; you can probably outrun them."
    "What