“It will be safe enough to light up now, I guess,” announced Captain Andrews, when the anchorage had been accomplished. Jack had told him previously that they would need deck lights to work by when it was possible to use them without danger of detection.

When the incandescents on the after deck were switched on the boys at once fell to work on their “Flying Road Racer,” as Jack and Tom had christened the craft. There was much to be done, and they worked quickly. The tank was supplied with crystals and water, and the gauge before long showed a pressure which the lads knew was sufficient to inflate the bag when occasion arose.

This done. Jack determined to make a test of the engines. First, seeing that the neutral clutch was in working order, he pressed a button which set the self-starting apparatus,—run by electricity from a storage battery of great power and lightness,—into action. With a buzz and a whirr the machinery started, and bit by bit the lad speeded the motor up to its maximum number of revolutions per minute,—namely, two thousand. While the crank shafts whirled round he carefully examined the lubricating appliances. They worked as well as everything else, and fully satisfied with his test, the young inventor shut down the engine, with the announcement that so far as the machinery was concerned everything was in readiness for an immediate flight, or ground cruise.

While this had been going on, Jupe had been placing a stock of provisions on board, and Captain Andrews had assembled his navigating instruments and chronometers, which he had brought with him from the Sea King. By midnight Jack declared that it was time for the aero-auto’s passengers to get aboard.

A thrill of excitement ran through the whole party at these words; but Tom seemed suddenly to recollect something and stepped to Jack’s side, talking in a low voice.

The young leader nodded his assent to Tom’s proposal, whatever it was, and Tom vanished below, summoning Jupe to help him. When he returned, he had his arms full of mechanical apparatus, and the same was true of Jupe, who grunted under his burdens. All this impedimenta was placed in the tonneau, in lockers under the seats.

It now only remained to bolt on the aerial propeller, adjust the side-planes and fix the rudder. This was speedily done.

At twelve-thirty o’clock the party cast off the lashings which had bound the Flying Road Racer to the Vagrant’s deck. Jack climbed into the driver’s seat, taking his place at the aerial steering wheel. Tom sat beside him.

Captain Andrews, Ned Bangs and Jupe, whose eyes were almost popping out of his head, seated themselves in the broad, roomy tonneau.

The lights had already been switched off on I board the Vagrant and everything made snug. The silver casket, the gas-guns, the ammunition, and the other accessories from the Professor’s cabin which had not yet been opened, were, of course, on board the Flying Road Racer.

Jack bent forward and snapped a button switch. A hooded light above the various gauges and instruments on the dashboard shone out, shedding a soft but bright light on the appliances, but not striking up into the young leader’s eyes.

“All ready?” queried the lad, giving a backward glance.

“Ready as we ever will be, old top,” quoth the slangy Mr. Bangs.

“Let her go,” said Tom in a tense voice.

Jack’s pulses throbbed, and his heart beat a bit quicker than was comfortable as he turned the valve that admitted gas to the bag above them.

With a swishing sound, not unlike escaping steam, the folds of the great gas container began to fill out. It gradually assumed shape, swelling till it reached what appeared to be vast proportions. When Jack shut off the gas the huge, cigar-shaped balloon above them looked like an immense dark cloud, superimposed over their heads.

The bag took just fifteen minutes to inflate. During this time not a word was spoken on board the Flying Road Racer. The tension was far too great for speech.

As Jack shut off the gas a tremor ran all through the novel craft. She tugged and swayed at the single rope, reeved through a ringbolt, that still bound her to the deck. The suspension wires thrummed musically under the pressure.

“Let go!” yelled Jack suddenly.

Tom, who had been holding the end of the rope, dropped it. Instantly the Flying Road Racer gave a bound upward.

“Bust my toplights!” bellowed Captain Andrews in excitement at the novel sensation.

Jupe’s lips might have been seen to move. He appeared to be praying. Ned Bangs’ hands were clenched tightly. He was very pale.

“Look out for the tree tops!” cried Tom suddenly.

The wonderful craft, with her precious freight, swayed drunkenly toward the crests of a group of giant ceiba trees. For one instant disaster, at the very outset of their voyage, appeared inevitable.

But suddenly there was a whirring sound, like the drone of a monstrous night beetle. The engine was driving the propeller round at top speed.

Jack twisted the steering wheel over, and the Flying Road Racer, rising at the rate of a hundred feet a minute, shot clear of the menacing tree tops.

Up and up into the night she rose, while her occupants, forgetting their first alarm in their enthusiasm, gave a mighty cheer, careless, for the minute, of who might hear it.

The voyage of the Flying Road Racer had begun under a fortunate star indeed.

Directly the tree tops were cleared Jack set the planes at a rising angle, and the upward course of the Flying Road Racer was more rapid. She seemed fairly to shoot up into the ether.

“How do you like it?” asked Tom, turning his head-to speak to those in the tonneau.

“Ah’d like it better, Marse Tom, ef I didn’t feel I done lef’ mah insides behin’ me,” faltered Jupe.

“You’ll soon get over that feeling,” declared Tom confidently. “Just hark at that engine! She’s running as true as a human heart.”

“She is that,” agreed Jack, enthusiastically, “Tom, old boy, we’ve got the greatest land-and-air-craft ever put together.”

“And to think that you two lads, hardly more than schoolboys, invented her,” struck in Captain Andrews admiringly.

“I guess my father had a whole lot to do with it,” rejoined Jack modestly; “we could never have mastered a lot of knotty points without his aid.”

“Well, that doesn’t detract from what you’ve accomplished one bit,” declared Ned with enthusiasm. “This is the mode of traveling of the future all right.”

“We hope to make it so some day,” was Tom’s reply.

The night was almost windless, save for a slight puff now and then. But this didn’t bother the Flying Road Racer once she was under control, and Jack had managed to climb upward on an almost straight course.

Now he peered over the edge of the aluminum body. Beneath him he could see the gleam of the river in the starlight.

“We’ll follow the stream,” he decided. “It is bound to bring us to Herrera’s plantation.”

“Keep at a good height, though,” admonished Captain Andrews. “We know that those fellows have high-powered rifles.”

“We are now twenty-five hundred feet above the earth,” said Jack, glancing at the barograph. “We’ll go higher.”

He pulled a lever, setting the rising planes at a more acute angle. Up the aerial staircase they climbed, till the barograph’s indicator pointed to the figures five thousand.

Then Jack turned the prow of the craft in a westerly direction, while Tom, through night glasses, watched the earth so far below them, following the course of the river through the binoculars.

At forty miles an hour the Flying Road Racer swept through the air on her momentous errand.