Zintal, the Martian physicist, turned from his Martian companions and crossed the room toward a large, ornate machine. From his pocket Zintal took a couple of shiny Martian coins and dropped them in the slot and pressed a number of buttons in sequence. He waited. The machine clicked faintly and made a noise similar to a Compur shutter set to one second. Then a small door became illuminated below the keyboard. Zintal opened the door in a semi-absent-minded way and reached in for his purchase. His