A Fall of Moondust

by Arthur C. Clarke

Lawrence picked up a tall vertical cylinder, the lower third of which was filled with an amorphous grey substance. He tilted it—and the stuff began to flow. It moved more quickly than syrup, more slowly than water, and it took a few seconds for its surface to become horizontal again after it had been disturbed. No one could ever have guessed, by looking at it, that it was not a fluid. “This cylinder is sealed,” explained Lawrence, “with a vacuum inside, so the dust is showing its normal behaviour. In air, it’s quite different; it’s much stickier, and behaves rather like very fine sand or talcum powder. I’d better warn you—it’s impossible to make a synthetic sample that has the properties of the real thing; it takes a few billion years of desiccation to produce the genuine article. If you want to do some experimenting, we’ll ship you as much dust as you like; heaven knows, we can spare it.