"They work very much like the ship-drive, which was developed from them. A battery in the handle energizes them so they use the heat they contain to make a lethal punch without a kick-back. They'll get pretty cold after a dozen or so shots." He sat down and Holmes went on almost angrily, "The garrison had to get food here. It didn't come in ships. They had to purify the air. They've nothing to do it with! How did they manage?" Keller smiled faintly. He pointed to a control on the wall. "If that worked, we could ask. It is supposed to be communication with base. It is turned on. Nothing happens." "Do you know what I'm thinking?" demanded Holmes. "I'm thinking of a matter-transmitter! It's been pointed out before that we'll never reach the stars in spaceships limited to one light-speed. What good would be voyages that lasted ten, twenty, or fifty years each way? But if there could be matter-transmitters--" Keller said gently, "Transmitters, no. Transposers, yes." It was a familiar enough distinction. To break down an object into electric charges and reconstitute it at some distant place would be a self-defeating operation. It could have no actual value. To transmit a hundred and fifty pounds of electric energy--the weight of a man converted into current--would require the mightiest of bus-bars for a conductor, and months of time if it was not to burn out from overload. The actual transmission of mass as electric energy would be absurd. But if an object could simply be transposed from one place to another; if it could be translated from place to place; if it could undergo substitution of surroundings.... That would be a different matter! Transposition would be instantaneous. Translation would require no time. Substitution of position--a man who was here this instant would be there the next--would have no temporal aspect. Such a development would make anything possible. A ship might undertake a voyage to last a century. If a matter-transposer were a part of it, it could be supplied with fuel and air and foodstuffs on its voyage. Its crew could be relieved and exchanged whenever it was desired. And when it made a planet-fall a hundred years and more from home, why, home would still be just around the transposer. With matter-transposition an interstellar civilization could arise and thrive, even though limited to the speed of light for its ships. But a culture spread over hundreds of light-years would be unthinkable without something permitting instant communication between its parts. "All right!" said Holmes doggedly. "Call them transposers! This fortress had to be supplied. We've found no sign that ships were used to supply it. It needed to have its air renewed and refreshed. We've found no sign of anything but emergency stores of air in case some unknown air-supply system failed. What's the matter with looking for a matter-transposer?"