“I had to wait a while before the thing was cool enough to approach with comfort. When I did, I found that the nose compartment this time was not empty. There was an affair rather like a fishing-box inside, with the compartments of one side full of junk and those on the other empty. I finally took a chance on reaching in for it, once it was cool enough to touch.
“When I got it out in the sunlight, I found that the full compartments were covered with little glassy lids, which were latched shut; and there was a: tricky connection between the two sides which made it necessary to put something in an empty compartment and close its lid before you could open the corresponding one on the other side. There were only half a dozen spaces, so I fished out some junk of my own — a wad of paper from my notebook, a chunk of granite, a cigarette, some lichen from the rocks around, and so on — and cleaned out the full compartments. One of the things was a lump of platinum and related metals that must have weighed two pounds.
“Right then I settled down to some serious thinking. In the first place, the torpedo came from off this planet. The only space ship I’d ever heard of was the projectile in Jules Verne’s story, but people of this planet don’t send flying torpedoes with no visible means of propulsion carrying nuggets of what I knew even then was a valuable metal; and if they do, they don’t call attention to the practice by broadcasting weird languages loudly enough to be heard a mile away.
“Granting that the torpedo came from outer space, its behavior seemed to indicate only one thing — its senders wanted to trade. At any rate, that was the theory I decided to act on. I put all the junk except the platinum nugget back where it came from, and put the box back in the nose of the torpedo. I don’t yet know if they could see me or not — I rather doubt it, for a number of reasons — but the door closed almost at once and the thing took off — straight up, out of sight. I was sorry I hadn’t had much of value to stuff in my side of the box. I had thought of sending them a rifle cartridge to indicate we had a mechanical industry, but remembered the temperature at which the thing had arrived and decided against it.
“It took two or three hours for the torpedo to make its round trip. I had set up my tent and rounded up some firewood and water by the time it came back, and I found out my guess was right. This time they had put another platinum nugget in one compartment, leaving the others empty; and I was able to remember what I had put in the corresponding space on the previous visit.
“That about tells the story.” Mr. Wing grinned at his son. “I’ve been swapping cigarettes for platinum and indium nuggets for about thirty years now — and you can see why I wanted you to study some astronomy!” Don whistled gently.
“I guess I do, at that. But you haven’t explained this,” he indicated the metal cube on which his father was sitting.
“That came down a little later, grappled to a torpedo, and the original one took off immediately afterwards. I have always supposed they use it to find this spot again. We’ve sort of fallen into a schedule over the years. I’m never here in the winter any more, and they seem to realize that; but from two to three days after I snap this switch off and on a few times, like this,” he demonstrated, “the exchequer gets a shot in the arm.”
Don frowned thoughtfully, and was silent for a time.
“I still don’t see why you keep it a secret,” he said at last. “If the affair is really interplanetary, it’s tremendously important.”