of warm water and some minerals to get it started?

And Phillip felt as if he was being reduced to nothing, because, even though the men didn't say anything, it was implicit in their relationship with him that he would know what to do. But he didn't, and the men knew it, but they couldn't say it in words. He was just as helpless before the face of this discovery as anyone else.

"You don't suppose it was angels that did it?" said Ralph, with a slight hint of sarcasm in his voice.

They were having breakfast. The clock showed only half an hour before they had to start work again.

"What do you think?" Phillip threw it back at him.

"Many a true word spoken in jest!" said Paul.

"There's nothing in the Bible to suggest that angels go about building polygons," said Phillip, dryly. "I'm sure they have other, more important things to do."

"Like what?"

"I'd rather not get into a religious discussion."

"How about running a few more tests on the metal?" suggested John, neatly changing the subject.

Almost relieved, Phillip took him up on it immediately.

"What do you suggest?"

"Let's work on the supposition that these creatures, whatever they are, have taken into account that one day we humans would get here, and actually discover their handiwork. What would they think we humans would do?"

"If I was an intelligent creature with that sort of knowledge I'd anticipate human thinking."

"Construct some sort of entrance which only humans could find and open?"

"Exactly!" said John. "So what do we have which is essentially human?"

"I've tried the diamond drill, and several acids, but they're all natural to the universe. They're all mineral, or metal, or chemical." said Phillip. "Human life is more than machines and metals? How about life? There's no life on the moon, so we could try some sort of living thing test..." his voice trailed off as he failed to think of anything remotely suitable. It was an area he had never studied. He was an engineer, not a biologist.