Robin was now wearing a rabbit-fur outfit of coat, pants, and hat during the winter periods, equipped with bone buttons he'd carved from the Moonhound skeletons. He was, if anything, beginning to gain weight, but he was also aware of the paleness of his skin. He wondered whether staying in this sunless world a sufficient number of years would not make him as palely transparent as the Moonhounds.

But all this time Robin had not forgotten his ultimate mission—to reach the surface and signal for help. He had worked out the problem in his own mind. He had to make some sort of space suit, something that would permit him to venture out on the nearly airless surface long enough to set up a signal that astronomers might see.

He knew he had the materials for part of this suit in the metal salvaged from the rocket nose. He could polish a section sufficiently to make a heliograph with which he could flash a code message to any high-powered telescope that might be pointed his way. But he had also to fashion the metal into an airtight space helmet, and that he did not know how to do. The suit itself he could probably fashion from cloth and tanned skins, sew and seal it tight enough with animal fats and bone glue to be airtight for a short period, but he needed the helmet. He had the glass for it too, the little peepholes for the camera outlets and a large circular plate that had been set in the very base of the cargo nose and evidently intended for a wide-vision camera shot of the Earth. This plate would be his face plate.

Robin was aware of the hissing noise that he had first noticed on his arrival, but he had never investigated it. It was far off, somewhere along the wall of the cavern. One work period, when he found himself ahead of schedule, he set out to find the source of the noise.

Following the wall, with Cheeky running ahead chattering, the hiss gradually grew in volume. Robin made his way over a sharp cleft, skirted a large bubble-cave in the wall, and after about two miles of walking, came upon the source.

Issuing from a break in the outer cavern wall was a stream of blue flame. For several hundred feet around it no vegetation grew, the ground being covered with thin gray ash. Robin looked at the loudly hissing lance of blue fire.

It probably was a breakthrough from some adjoining bubble, one filled with a gas of some inflammable sort. Somehow in the course of the breakthrough, this leakage had been set aflame. And there it was now, a burning gas jet, sharp and hot.

At that moment, Robin knew he had the answer to his metalworking problem. He'd tried to melt the metal of the rocket over his fires but he had been totally unsuccessful. But this jet, this hot blue flame, this surely would do the trick!

For him the space helmet was now a certainty. It might take time, but now it could be done. That and more was possible, for he had enough metal to make a few necessities like a decent frying pan and a pot to use for boiling and perhaps a water container for a really long exploration trip.

That was the end of Robin's first "Stone Age" period and the beginning of his "Iron Age."