instead of the ravings of a maniac."

"I suggest," he said stiffly, "that you reserve judgement until that time comes, sir."

And that was all he knew about the danger, real or imaginary, that had driven two men into insanity. He would have six months in which to find the answer. Six months minus— He looked at the chronometer and saw that twenty minutes had passed since he left the cruiser. Somehow, it seemed much longer ...

He moved to light a cigarette and his metal soles scraped the floor with the same startling loudness he had noticed before. The bubble was as silent as a tomb.

It was not much larger than a tomb; a sphere eighteen feet in diameter, made of thin sheet steel and criss-crossed outside with narrow reinforcing girders to keep the internal air pressure from rupturing it. The floor under him was six feet up from the sphere's bottom and the space beneath held the air regenerator and waste converter units, the storage batteries and the food cabinets. The compartment in which he sat contained chair, table, a narrow cot, banks of dials, a remote-control panel for operating the instruments mounted outside the hull, a microfilm projector, and a pair of exerciser springs attached to one wall. That was all.

There was no means of communication since a hyperspace communicator would have affected the delicate instruments with its radiations but there was a small microfilm library to go with the projector so that he should be able to pass away the time pleasantly enough.

But it was not the fear of boredom that was behind the apprehension he could already feel touching at his mind. It had not been boredom that had turned Horne into a suicide and Silverman into—

Something cracked sharply behind him, like a gunshot in the stillness, and he leaped to his feet, whirling to face it.

It was only a metal reel of data tape that had dropped out of the spectrum analyzer into the storage tray.

His heart was thumping fast and his attempt to laugh at his nervousness sounded hollow and mirthless. Something inside or outside the bubble had driven two men insane with its threat and now that he was irrevocably exiled in the bubble, himself, he could no longer dismiss their fear as products of their imagination. Both of them had been rational, intelligent men, as carefully selected by the Observation Bureau as he had been.

He set in to search the bubble, overlooking nothing. When he crawled down into the lower compartment he hesitated then opened the longest blade of his knife before searching among the dark recesses down there. He found nothing, not even a speck of dust.

Back in his chair again he began to doubt his first conviction. Perhaps there really had been some kind of an invisible force or entity outside the bubble. Both Horne and Silverman had said that "it" had tried to get in to kill them.

They had been very definite about that part.

There were six windows around the bubble's walls, set there to enable the attendant to see all the outside-mounted instruments and dials. He went to them to look out, one by one, and from all of them he saw the same vast emptiness that surrounded him. The galaxy—his galaxy—was so far away that its stars were like dust. In the other directions the empty gulf was so wide that galaxies and clusters of galaxies were tiny, feeble specks of light shining across it.

All around him was a void so huge that galaxies were only specks in it....

Who could know what forces or dangers might be waiting out there?

A light blinked, reminding him it was time to attend to his duties. The job required an hour and he was nervous and not yet hungry when he had finished. He went to the exerciser springs on the wall and performed a work-out that left him tired and sweating but which, at least, gave him a small appetite.

The day passed, and the next. He made another search of the bubble's interior with the same results as before. He felt almost sure, then, that there was nothing