finally gave up. I'd tackle the problem again tomorrow. Maybe something on the asteroid, some magnetic rock or something, threw it off. I washed my hands in the laboratory sink and then, while I wiped them on a towel, glanced at Red, who was lying on his bunk reading. For the first time I noticed how skinny he was getting. Lack of exercise, I presumed. We were going to have to do something to build up our muscles again. I supposed I had lost weight just as much as he had. It would be tough to weigh ourselves here, since we had only the balance in the laboratory. Spring scales wouldn't work on the asteroid—we wouldn't have weighed enough to register, even though our mass was probably about the same as an average man's on earth.

Red put the book aside, closed his eyes and smiled. My eyes fell on the book for some reason. Then suddenly I saw a page flip over. I didn't realize at first that this couldn't happen.

There wasn't any draft in the place, I was sure of that. A draft would mean a leak in the laboratory and alarms would tell us when that happened. There was no motion, nothing to cause a page in the book to turn.

Another page turned and I was sure I wasn't dreaming. I pulled myself over to the door, opened it a trifle.

"Red!" I called softly.

"Dollie!" He was dreaming. Dollie was one of the dozen or so girls he was always talking about in his sleep.

I pulled myself to his side and punched him gently. Red woke up. "You're a hell of a guy," he said.

"Yes," I said. "You were dreaming about Dollie. But I saw something happen here and I wanted you to see it too." I pointed at the book. The pages were still now. Suddenly one of them flipped over.

"Somebody, or something is reading your book," I said.

We didn't figure it out then and I wasn't even sure that I'd made the right diagnosis, but things went on every day afterwards that left me convinced there was something else living on this hunk of rock besides Red and me. It didn't have mass, apparently, because we tried our best to touch it.

Once when it got to fooling around with the laboratory balance, Red and I encircled the balance with our arms and then squeezed together without feeling a thing.

It wasn't energy, because we tried every instrument to detect electricity, heat, light, and radio. But it was alive, because it moved. It read books and monkeyed with the lab scales.

And at last I decided that maybe it had something to do with the apparent discrepancy in the asteroid's change in mass. After that I had a great deal to work on.

Red began behaving queerly too. He swore that he was getting too small for his clothing. His shoes, he said, were almost a size too large. I was too busy to check, so I put it down as a loss in weight.

We'd spent a year on the asteroid when we were due to pass Mars. So our first anniversary was spent in checking our movements with a telescope, a camera and a chronometer. We discovered our mass—or that of Asteroid 57GM—had depreciated another 25 per cent. It now had only half the mass it was supposed to have. This was too much of an error for even a grade school student.

"I'll bet some astronomers back on earth will get redder than my hair when we get home," Red said.

I shook my head. "It hasn't anything to do with their observations," I said. "It's what is happening now to you and me. We're losing mass someway."

There was only one way to check it and that was to weigh ourselves. So I rigged up a rude sort of a balance by weighing out chunks of rock until we had a mass equal to what we should weigh, placing them on a teeter-totter arrangement I rigged up in the lab.

"It'll be close enough to learn if we've lost half our mass," I said.

Red showed a weight loss equal to about 20 pounds on earth. I had gained a little weight. These figures were only relative, and dependent on whether or not the rocks we'd used on the balance had lost mass also. But something