"How do you change direction?"

"If you push the stick sideways, the car turns in the same direction. When you are on your new course you return the stick to vertical."

"Does that both bank and handle the rudder? Say, I didn't see a rudder nor any other control surfaces. Why should it turn?"

"There aren't any control surfaces. The car is gyro stabilized. We rotate the car around the rigid reference frame of the gyros and let the screw push away in our new direction."

Perry nodded slowly. "That seems all right, except that she must side slip like the very devil on a turn."

"That's right, Perry, but ordinarily it doesn't matter. If you need to prevent it, you can turn past your new course and hold it there until the side slip is killed."

Perry's face cleared. "Yes, I suppose so, but I would hate to try to fly a tight military formation in her."

"You couldn't. This is a family model, for quiet people like me. It isn't very fast and it's as nearly foolproof and automatic as they can make it. They claim that if you can use a knife and fork you can fly a 'Cloud House'."

"What speed does she make?"

"I cruise her at about five hundred kilometers. I could make five hundred and fifty but there's a nasty vibration at that speed. I may need a new propellor."

Perry whistled. "If that is a moderate speed for a family car, what's the record these days?"

"About three thousand. That is with rockets of course. But I don't like a rocket ship. They make me nervous and they are devilish to handle. Give me my old-fashioned electric runabout. I'm in no hurry."

"Which reminds me. I gather this baby must be electric drive, but how?"

"The rotor and the prop are driven by induction motors. The power comes from storage batteries. The gyros each have their own induction windings. They run all the time."

"Storage batteries—I should think they would be too heavy."

"These aren't heavy for the power they store. They call 'em chlorophyll batteries because the principle involved is supposed to be similar to the photosynthesis of plants. But don't ask me why. I'm a dancer, not a physicist. However there are some new models on the market that make their own electricity from coal."

"Directly?"

"I don't know. It doesn't burn if that's what you mean."

Perry slapped his thigh. "Edison was working on that when he died."

"Too bad he didn't perfect it. We've had it only about ten years. See here, Perry, want to try the controls?"

"Yes indeed. Wait a minute though. How do I change altitude when I'm in 'plane' combination. "

"You can get as much as ten degrees dive or climb by changing this setting. It rotates the car about the horizontal gyro axis. You can use that when hovering with the rotor to keep from drifting in the wind, provided the wind isn't more than seventy-five kilometers."

"In that case you could maneuver by rotor if you wanted to, couldn't you."

"Yes, but it's slow of course. Do you know what all your instruments mean?"

"You keep an eye on the instruments. I'll fly by ear for a while." Perry took the car up a couple of thousand feet and cautiously put her through her paces. Presently when he had the feel of the controls he undertook to see what it would do. He soared and dropped, flew straight away and slewed her into sudden turns. He discovered that he could jamb her about one hundred and eighty degrees and stop her dead with the propeller. After this stunt Diana touched his arm:

"Perry, if you knock off the propeller, we'll have to go home on the rotor." He looked crestfallen.

"Oh, I'm sorry. I thought anything she could do, she could handle."

"That is very nearly true. But my prop may be out of balance, you know. In any case the screw itself is a gyro and you were processing it on a rigid frame."

He set the controls at neutral and turned to her. "Diana, if you are a dancer and no physicist, how do you know so much about mechanics?"

She looked surprised. "Any schoolgirl knows that much."

"I can see education has improved." He returned to the controls and tried new stunts; stalling, changing combinations, maneuvering on the rotor. The flight brought them back near the canyon—'Diana's canyon' as Perry regarded it—and the waterfall caught Perry's eye. He lowered away cautiously and eased the craft slowly over toward the veil of water until they hovered halfway down and a hundred feet from the falls. They both sat in silent contemplation for several minutes until a shift in the wind forced Perry to return to the controls. He rose out of the canyon and settled down in level flight. Then he spoke. His voice was low and fervent. "Boy, but that fall is something!" He turned to Diana. "It's nearly as beautiful as you are, Dian'." She looked up and met his eyes for a moment, then dropped her lids, without replying. They were flying west. Presently Diana spoke.

"Where are we going, Perry?"

"I hadn't thought about it. Where would you suggest?"

"Would you like to see San Francisco?"

"Fine!"

"Then let me set the course."

"I can do it. I know this country." He located the South Fork of the American River and followed it by eye until it joined the Sacramento River. Presently Diana got up and went to the rear of the car. When they were approaching Sacramento she announced lunch. "Can't do," answered Perry. "I'm coming into traffic." She peered over his shoulder.

"I'll set the robot to circle Sacramento and pick up the San Francisco beam. You mustn't fly in traffic until you have qualified in the rules. Now come to lunch."

Hot soup. Stuffed eggs and celery. Oatmeal cookies and grapes. Cold milk. When it was inside Perry felt no desire to move. He lay on his stomach with his head over the edge of the lazy bench and watched the ground slip by the deck port. Diana regarded him lazily. Presently the ground changed to water.

"Coming into San Francisco!" he cried, jumped to his feet and seated himself in the bow.

"Don't touch the controls, Perry," Diana cautioned. "They are on full automatic." Perry didn't answer for they were slicing across the bay bridge.

"Dian', is that the same bridge?"

"I believe so."

Perry looked proud. "They had engineers in my day, too."

"Indeed they did."

"Why, there is the Ferry Building. Don't tell me that has stood all these years."

"No, that is a replica. It's a museum of California history."

"There's Nob Hill! And the Fairmont Hotel."

"You're right, but I don't see how you recognized it. It's only been there ten years."

"I can see how it's not the same building. But it's in the right place." The car changed course and commenced leisurely to circle the city in a clockwise direction. Several other aircraft were in the same circle at the same speed.

"The streets are decked over, aren't they? What's that moving under the glass decks?"

"Those are the streets, with people traveling on them."

"But how? I don't see any automobiles or other vehicles, yet they are going pretty fast."

"The streets move in strips. The strip nearest the buildings goes five kilometers an hour, then next ten and so on to the middle. Those have seats on them and travel forty kilometers."

"How about the end of the line?"

"The end of the line? Oh, they travel in loops. If you stay on one you come back to where you started. The cross traffic is on a lower level, naturally. Shall we land, Perry?"

His brow furrowed. "What do you think? I probably don't know how to behave. Besides I can't go into a city like this, can I?" He indicated his bare condition.

"No real reason why you shouldn't, except to avoid being conspicuous. But the public kit you bought yesterday is by you in the locker under the bench you are sitting on." Diana dug it out, and gave it to him. Perry donned it. It consisted of a kilt of bright blue silk hung on a broad leather belt with pockets and hooks in it. A strap over one shoulder helped to support the belt. Slashes in the kilt were lined with bright silver stuff which glittered as he moved. The belt and strap were black with chromium fittings which matched his sandals. Diana surveyed him.