"Lots. I think we're in for a good time." an exciting one, anyhow, if what he says is true. But what in the world is an air glider, Tom?"

"It's the last word in aeroplanes. You don't need a motor to make it go."

"Don't need a motor?"

"No, the wind does it all. It's a sort of aeroplane, but the motion comes from the wind, acting on different planes, and this is accomplished by shifting weights. In it you can stand still in a fierce gale, if you like."

"How, by tying her fast on the ground?"

"No, hovering in the air. It's all done by getting the proper balance. The harder the wind blows the better the air glider works, and that's why I think it will be just the thing for Siberia. I'm going to get right at work on it, and you'll help me; won't you?"

"I sure will. Say, is platinum worth much?"

"Worth much? I should say it was! It's got gold beat now, and the available supply is very small, and it's getting more scarce. Russia has several mines, and the metal is of good quality. I've used some Russian platinum, but the kind Mr. Petrofsky gave me to-day was better than the best I ever had. If we can only find that lost mine we'll be millionaires all right."

In brief, the air glider was like an aeroplane save that it had no motor. It was raised by a strong wind blowing against transverse planes, and once aloft was held there by the force of the air currents, just like a box kite is kept up. To make it progress either with or against the wind, there were horizontal and vertical rudders, and sliding weights, by which the equilibrium could be shifted so as to raise or lower it. While it could not exactly move directly against the wind it could progress in a direction contrary to which the gale was blowing, somewhat as a sailing ship "tacks."

And, as has been explained, the harder the wind blew the better the air glider worked. In fact unless there was a strong gale it would not go up.

"But it will be just what is needed out there in that part of Siberia," declared the exile, "for there the wind is never quiet. Often it blows a regular hurricane."

"That's what we want!" cried Tom. He had made several models of the air glider, changing them as he found out his errors, and at last he had hit on the right shape and size.

Midway of the big glider, on which work was now well started, there was to be an enclosed car for the carrying of passengers, their food and supplies. Tom figured on carrying five or six.

"We're certainly going up!" yelled Ned, as he sat beside Tom in the cabin of the air glider.

"That's right!" agreed the young inventor rather proudly, as he grasped two levers, one of which steered the craft, the other being used to shift the weights. "We're going up. I was pretty sure of that. The next thing is to see if it will remain stationary in the air, and answer the rudder."

"Bless my top knot!" cried Mr. Damon. "You don't mean to tell me you can stand still in a gale of wind, Tom Swift."

"That's exactly what I do mean. You can't do it in an aeroplane, for that depends on motion to keep itself up in the air. But the glider is different. That's one of its specialties, remaining still, and that's why it will be valuable if we ever get to Siberia. We can hover over a certain spot in a gale of wind, and search about below with telescopes for a sign of the lost platinum mine.

"How high are you going up?" demanded Ned, for the air glider was still mounting upward on a slant. If you ever scaled a flat piece of tin, or a stone, you'll remember how it seems to slide up a hill of air, when it was thrown at the right angle. It was just this way with the air glider--it was mounting upward on a slant.

"I'm going up a couple of hundred feet at least," answered Tom, "and higher if the gale-strata is there. I want to give it a good test while I'm at it."

Ned looked down through a heavy plate of glass in the floor of the cabin, and could see Mr. Petrofsky and Eradicate looking up at them.

"Bless my handkerchief!" cried Mr. Damon, when his attention had been called to this. "It's just like an airship."

"Except that we haven't a bit of machinery on board," said Tom. "These weights do everything," and he shifted them forward on the sliding rods, with the effect that the air glider dipped down with a startling lurch.

"We're falling!" cried Ned.

"Not a bit of it," answered Tom. "I only showed you how it worked. By sliding the weights back we go up."

He demonstrated this at once, sending his craft sliding up another hill of air, until it reached an elevation of four hundred feet, as evidenced by the barograph.

"I guess this is high enough," remarked Tom after a bit. "Now to see if she'll stand still."

Slowly he moved the weights along, by means of the compound levers, until the air glider was on an "even keel" so to speak. It was still moving forward, with the wind now, for Tom had warped his wing tips.

"The thing to do," said the young inventor, "is to get it exactly parallel with the wind-strata, so that the gale will blow through the two sets of planes, just as the wind blows through a box kite. Only we have no string to hold us from moving. We have to depend on the equalization of friction on the surfaces of the wings. I wonder if I can do it."

It was a delicate operation, and Tom had not had much experience in that sort of thing, for his other airships and aeroplanes worked on an entirely different principle. But he moved the weights along, inch by inch, and flexed the tips, planes and rudders until finally Ned, who was looking down through the floor window, cried out

"We're stationary!"

"Good!" exclaimed Tom. "Then it's a success."

"And we can go to Siberia?" added Mr. Damon.

"Sure," assented the young inventor. "And if we have luck we'll rescue Mr. Petrofsky's brother, and get a lot of platinum that will be more valuable than gold."

It would not be true to say that the air glider was absolutely stationary. There was a slight forward motion, due to the fact that it was not yet perfected, and also because Tom was not expert enough in handling it.

The friction on the plane surfaces was not equalized, and the gale forced the craft along slightly. But, compared to the terrific power of the wind, the air glider was practically at a standstill, and this was remarkable when one considers the force of the hurricane that was blowing above below and through it.

For actually that was what the hurricane was doing. It was as if an immense box kite was suspended in the air, without a string to hold it from moving, and as though a cabin was placed amidships to hold human beings.

"This sure is great!" cried Ned. "Have you got her in control, Tom?"

"I think so. I'll try and see how she works."

By shifting the weights, changing the balance, and warping the wings, the young inventor sent the craft higher up, made it dip down almost to the earth, and then swoop upward like some great bird. Then he turned it completely about and though he developed no great speed in this test made it progress quarteringly against the wind.

"It's almost perfect," declared Tom. "A few touches and she'll be all right."