He listened. Everywhere that humans live, there are insects and birds and other tiny creatures which are essential parts of the ecological system to which the human race is adjusted. They have to be carried to and established upon every new world that mankind hopes to occupy. But there was no sound of such living creatures here.
It was probable that the bellowing roar of the Med Ship's emergency rockets was the only real noise the city had heard since its people went away.
The stillness bothered Murgatroyd. He said, "Chee!" in a subdued tone and stayed close to Calhoun. Calhoun shook his head. Then he said abruptly:
"Come along, Murgatroyd!"
He went back to the building housing the grid controls. He didn't look at the spaceport log this time. He went to the instruments recording the second function of a landing-grid. In addition to lifting up and letting down ships of space, a landing-grid drew down power from the ions of the upper atmosphere and broadcast it. It provided all the energy that humans on a world could need. It was solar power, in a way, absorbed and stored by a layer of ions miles high, which then could be drawn on and distributed by the grid. During his descent Calhoun had noted that broadcast power was still available. Now he looked at what the instruments said.
The needle on the dial showing power-drain moved slowly back and forth. It was a rhythmic movement, going from maximum to minimum power-use, and then back again. Approximately six million kilowatts was being taken out of the broadcast every two seconds for half of one second. Then the drain cut off for a second and a half, and went on again for half a second.
Frowning, Calhoun raised his eyes to a very fine color photograph on the wall above the power dials. It was a picture of the human-occupied part of Maya, taken four thousand miles out in space. It had been enlarged to four feet by six, and Maya City could be seen as an irregular group of squares and triangles measuring a little more than half an inch by three-quarters. The detail was perfect. It was possible to see perfectly straight, infinitely thin lines moving out from the city. They were multiple-lane highways, mathematically straight from one city to another, and then mathematically straight—though at a new angle—until the next. Calhoun stared thoughtfully at them.
"The people left the city in a hurry," he told Murgatroyd, "and there was little confusion, if any. So they knew in advance that they might have to go. They were ready for it. If they took anything, they had it ready packed in their cars. But they hadn't been sure they'd have to go because they were going about their businesses as usual. All the shops were open and people were eating in restaurants, and so on."
Murgatroyd said, "Chee!" as if in full agreement.
"Now," demanded Calhoun, "where did they go? The question's really where could they go! There were about eight hundred thousand people in this city. There'd be cars for everyone, of course, and two hundred thousand cars would take everybody. But that's a lot of ground-cars! Put 'em two hundred feet apart on a highway, and that's twenty-six cars to the mile on each lane. Run them at a hundred miles an hour on a twelve-lane road—using all lanes one way—and that's twenty-six hundred cars per lane per hour, and that's thirty-one thousand ... two highways make sixty-two ... three highways.... With two highways they could empty the city in under three hours, and with three highways close to two. Since there's no sign of panic, that's what they must have done. Must have worked it out in advance, too. Maybe they'd done it before it happened ... whatever it was that happened."