Mr. Chadwick, breathless from his scramble across the dunes, met the boys in the shelter of the shed. They now saw that what he held in his hand was a despatch of some sort. He soon explained that it was a wireless message, relayed from the yacht Valkyrie,—via Sciuticut,—stating that his friend Professor Bismarck Von Dinkelspeil, on board the Valkyrie, was bound for South America on a scientific search of some sort, and intended to pay him a call at High Towers regarding the practicability of devising some sort of a novel boat. Details were not given.

“I hastened over here as soon as I got the despatch,” he said, “as I knew that you boys were transforming the Road Racer into some novel form. The Professor may be here to-morrow, and if you wish me to I’ll present you to him and you may be able to meet his demands. I’m too busy at present on that new steel reducing furnace to spare any time.”

“He gives no details?” asked Jack.

“No, as you see, it’s just a hurried despatch dated from his yacht. He is a celebrated man and has been all over the world on various scientific quests, in the interests of zo?logy mainly. But you boys look excited. What’s the matter?”

Jack speedily placed his parent in possession of the situation confronting them.

“The yacht is in need of aid, you think?” he asked when Jack completed a hurried and breathless recital.

“Without doubt. Hark! There’s another gun,” cried the boy. “I wish we could go to their help.”

“If we had a boat——” began Jack’s father. But the boy cut him short. Without further delay he plunged into an explanation of the Wondership. Mr. Chadwick looked amazed for an instant, but then his face resumed its customary air of studious calm.

“You think your device will work?” he asked, regarding Jack keenly.

“I’m sure of it. In fact, we have buoyancy to spare. On paper——”

“Paper and practice are different things, my boy.”

“I know, sir, but——”

“You see, there are human lives at stake out there. It’s worth risking,” broke in Tom, unable to keep silence any longer. “Can’t we go?”

Mr. Chadwick considered an instant.

“Let me take a look at your ‘Wondership,’ as you call it,” he said.

With what rapidity Jack exhibited the craft and showed off her good points may be imagined. While they were thus engaged there came the sound of another gun. Then Mr. Chadwick spoke.

“Is everything ready?”

“Down to the last nut on the ultimate bolt,” declared Jack.

“Plenty of gas?”

“A reservoir full and more gas-making stuff in the reserve chamber.”

“Very well, then. I’m ready when you are.”

And without any more words Mr. Chadwick climbed into the machine, using in his ascent a small ladder set against the gleaming metallic sides. The boys exchanged glances. But they didn’t make any comment. It was not a time for words. While they waited even, events might be transpiring aboard the strange yacht of an unknown, possibly tragic, nature.

“Open the doors, Tom,” ordered Jack, in a voice that sounded like anybody else’s rather than his own.

Tom hastened to obey. The big panels in front of the shed rolled back. The opening thus revealed framed a wild sea-scape of rising waves, overcast sky and, in the center, the yacht, her reversed ensign making a bright splotch of color against the leaden background. But as yet the wind was merely puffy, and not blowing with dangerous strength.

Having opened the doors, Tom hastened back. He climbed in by Jack’s side.

“Are we all ready?” he asked, with a gulp. In his excitement his heart was bounding with sufficient velocity to be uncomfortably evident. But he managed, by an effort, to keep calm, or rather to appear so.

“As ready as we’ll ever be, I guess. Be ready to lower those hydroplanes when I give the word.”

Tom nodded. The hydroplanes worked on toggle-joints and could be lowered and locked when required. This was a part of his duty that the boys had already rehearsed. Jack’s hand sought a lever. A hissing sound followed. The gas was beginning to rush into the big gas-bag. Its folds began to puff out and writhe as if some living thing was within it.

“I’ll start when it is half full,” announced Jack in a sober voice.

“How’s the pressure?” inquired Tom, whose face was pale.

“Fine; a trifle over five hundred pounds. We’ll fill quickly on that.”

In the rear seat, which might be likened to the tonneau of an auto, sat Mr. Chadwick. Not a trace of emotion was visible on his strong features. Through his spectacles he eyed the boys’ preparations with interest. It was by no means his first trip in the Flying Road Racer, as he still called it, and he knew that the boys thoroughly understood her management. Therefore he did not embarrass them with questions or suggestions.

“That’s enough,” announced Jack presently, when the bag was almost full, “that will lift us and I’ll fill out the wrinkles while we are in the air.”

“You’re going up first, then?”

“Of course. That will give you a chance to get over your ‘rattles’ before we drop.”

“Rot!” vociferated Tom indignantly. “I’m not rattled a bit.”

But his shaking hands and shining eyes belied his words. If not “rattled,” Tom was considerably excited. Jack, on the other hand, although his pulses were throbbing uncomfortably fast and a large lump appeared to have clambered into his throat and stuck there, was outwardly as cool as ice.

“Ready, Dad! I’m going to start! Hold tight!”

“All right, my boy. Go ahead as soon as you’re ready.”

Jack pressed a button on the steering pillar. The self-starting mechanism, operated by the same storage batteries that ran the lights and the ventilating fans, whirred loudly in response. An instant later he applied the gas. A volley of explosions followed. The shed was filled with an odd, sickly odor.

Again Jack’s hands flew, and with a jolt the Wondership leaped forward, rumbling over the wooden floor.

Straight out toward the sand dunes she rolled, her engine pulsing like a throbbing human heart. The light but strong framework vibrated under the strain. The great propeller of magnesium-vanadium metal became a mere shadowy blur.

Outside the shed a sort of runway had been built leading down to high water mark. As the odd craft rushed toward the waves Tom was conscious of a queer feeling, centering at the pit of his stomach.

“Guess I must be scared,” he snorted indignantly to himself, and then broke off with a sudden exclamation.

“What’s that?”

“What’s what?” came from Jack, who was busy adjusting levers and buttons.

“Why, that.”

As he spoke, both boys became aware of an odd sort of muffled sound, coming seemingly from under the seat on which they were stationed.

“Something’s wrong with the machinery,” cried Tom, as the odd sound came again.

“Can’t be. She’s working like a clock,” rejoined Jack. “Hold tight,—we’re going up.”

As Jack spoke, he applied a full stream of gas to the limp bag, and the Wondership shot upward with the swiftness of a rocket. A gust of wind struck them and sang weirdly through the rigging and supports. But the craft never wavered on her course. As she shot upward, though, from the yacht, heard above the hum and buzz of the machinery, came the sound of another gun.

“They’re wishing us luck!” cried Jack.

“We’ll need all we can get,” came a voice. “By the bounding brown buffaloes of Brunswick, this is the limit!”

“Hullo! What’s the matter with you, Tom?” cried Jack looking around in astonishment, as he manipulated the craft with a skill born of long practice.

“I didn’t speak, Jack. It was that same mysterious voice. This craft is haunted, I believe.”

“Nonsense. We must be imagining things,” declared Jack; “but I’m almost sure I heard a voice.”

“So am I. How is she working, Jack?” asked Tom, dismissing the subject. He thought that his overwrought nerves were at work.

“Finely. I’m heading straight for the yacht. I mean to circle her and then,” he paused an instant and added, “drop!”

Jack now pushed the craft ahead at full speed. Faster and faster she went. Far below them lay the sullenly heaving ocean. Beyond, but very close now, was the yacht.

“All right, Tom. Get ready now.”

Tom jumped to his work. In a few seconds the novel aluminum hydroplanes were adjusted and fixed in place. The yacht was right below them now, but the figures on her deck were dwarfed to pigmies. Jack set the suction pump to work, reducing the gas supply in the bag.

Slowly at first, and then faster, the great air craft began to fall toward the gray sea. The propeller ceased revolving. In almost total silence, except for the boys’ quick breathing, the descent continued. Suddenly a wild cry split the air. It appeared to come from the Wondership itself.

“Let me out! Put me ashore! By the buck-jumping broncos of Butte, I wasn’t born for a watery grave!”

“Gracious!” cried Jack, in a startled tone, as a head of red hair poked itself out from under the seat, “we’ve got an aerial stowaway aboard!”