Free A Fall of Moondust by Arthur C. Clarke Page A

experimenter; this was something unusual in an age when most so-called
     astronomers were really mathematicians who never went near an observatory.
    He was now so tired that only sheer cussedness kept him going. If the scanner had
     not worked first time, he would have postponed testing it until he had some sleep.
     But by the good luck that is occasionally the reward of skill, it
did
work; only a few minor adjustments were needed before the image of the Sea of Thirst
     began to build up upon the viewing screen.
    It appeared line by line, like an old-fashioned TV picture, as the infra-red detector
     scanned back and forth across the face of the Moon. The light patches indicated relatively
     warm areas, the dark ones, regions of cold. Almost all the Sea of Thirst was dark,
     except for a brilliant band where the rising sun had already touched it with fire.
     But in that darkness, as Tom looked closely, he could see some very faint tracks,
     glimmering as feebly as the paths of snails through some moonlit garden back on Earth.
    Beyond doubt, there was the heat-trail of
Selene
; and there also, much fainter, were the zigzags of the dust-skis that even now were
     searching for her. All the trails converged towards the Mountains of Inaccessibility
     and there vanished beyond his field of view.
    He was much too tired to examine them closely, and in any event it no longer mattered,
     for this merely confirmed what was already known. His only satisfaction, which was
     of some importance to him, lay in the proof that another piece of Lawson-built equipment
     had obeyed his will. For the record, he photographed the screen—then staggered to
     bed to catch up with his arrears of sleep.
    Three hours later he awoke from a restless slumber. Despite his extra hour in bed,
     he was still tired, but something was worrying him and would not let him sleep. As
     the faint whisper of moving dust had disturbed Pat Harris in the sunken
Selene
, so also, fifty thousand kilometres away, Tom Lawson was recalled from sleep by a
     trifling variation from the normal. The mind has many watchdogs; sometimes they bark
     unnecessarily, but a wise man never ignores their warning.
    Still bleary-eyed, Tom Lawson left the cluttered little cell that was his private
     cabin aboard Lagrange, hooked himself on to the nearest moving belt, and drifted along
     the gravityless corridors until he had reached the Observatory. He exchanged a surly
     good-morning (though it was now late in the satellite’s arbitrary afternoon) with
     those of his colleagues who did not see him in time to take avoiding action. Then,
     thankful to be alone, he settled down among the instruments that were the only things
     he loved.
    He ripped the photograph out of the one-shot camera where it had been lying all night,
     and looked at it for the first time. It was then that he saw the stubby trail emerging
     from the Mountains of Inaccessibility, and ending a very short distance away in the
     Sea of Thirst.
    He must have seen it last night when he looked at the screen—but he had not noticed
     it. For a scientist, that was a serious, almost an unforgivable lapse and Tom Lawson
     felt very angry with himself. He had let his preconceived ideas affect his powers
     of observation.
    What did it mean? He examined the area closely with a magnifier. The trail ended in
     a small, diffuse dot, which he judged to be about two hundred metres across. It was
     very odd—almost as if
Selene
had emerged from the mountains, and then taken off like a spaceship.
    Tom’s first theory was that she had blown to pieces, and that this smudge of heat
     was the aftermath of the explosion. But in that case, there would have been plenty
     of wreckage, most of it light enough to float on the dust. The skis could hardly have
     missed it when they passed through this area—as the thin, distinctive track of one
     showed it had indeed done.
    There had to be some other explanation, yet the alternative seemed absurd. It