Leaving the Tarantula to drift at her sweet will, all haste was made by the youthful adventurers in regaining the side of the Sea King. When they reascended to the deck of that craft, after making fast the Vagrant, they found a newcomer among the crew to greet them,—namely, MacDuffy, the engineer, who announced that he had made temporary repairs.

“But they willna be lastin’ lang, I’m thinkin’,” he said ruefully, “I dinna ken if they will carry us a hundred miles.”

“And it’s a good three hundred or more back to that river mouth,” cried Ned in dismay.

“Aye, lad, it wull be all of that,” agreed the Scotchman.

A sudden idea struck Jack.

“Is there any one on board who understands wireless besides Ned Bangs?” he asked abruptly.

Sam Serviss, a youngish-looking seaman,—he was third officer of the Sea King,—stepped forward.

“I can read Morse and Continental,” he said simply, “and I’ve taken lessons from Ned Bangs here. I guess at a pinch I could operate a wireless all right.”

“Good. That puts my plan on a feasible basis,” exclaimed Jack.

“What may the plan be?” asked Captain Andrews interestedly.

“Just this: The Sea King will proceed to Lone Island, navigated by Mr. Serviss here. On the island, as you know, is a wireless plant. The generator is not a very powerful one, but you can harness the island apparatus to the generators of the Sea King, and obtain as much current as you want,—two kilowatts if necessary. I have a plan to increase the power of the Vagrant’s outfit, so that we can keep in touch with you.”

Captain Andrews and MacDuffy nodded. Jack went on, while they all listened with deep attention.

“The Sea King carries a gasolene launch. On arrival at Lone Island you can try to get into communication with us. In the meantime the launch can be despatched to Galveston for the supplies and tools needful to mend that shaft properly. This being done, Mr. Serviss will watch the wireless for further instructions, or, in case of need, proceed to our rescue.”

“Then you mean to go back to Yucatan the noo?” inquired MacDuffy.

“Of course,” rejoined Jack, quick as a flash, and in a tone that showed he had indeed arrived at a definite conclusion in the matter. “It’s my duty and Tom’s to rescue our relatives, and that as soon as possible.”

“And you’ll no be countin’ on taking me?” asked MacDuffy, rather piteously.

Jack shook his head.

“The capacity of the Vagrant is limited, Mr. MacDuffy,” he said, “and we may have to adopt another means of transportation before we get through—I mean the aero-auto.”

“Good. The very thing,” was Ned’s enthusiastic comment.

“I guess Captain Andrews, Tom, Ned, Jupe and myself will be a big enough force to take along,” went on Jack; “of course, we’ll carry the gas-guns and a supply of ordinary firearms and ammunition.”

The boy’s plans were so clear and well-defined that there was no opposition. By this time the sky was streaked with gray and rose color in the east, and a wan light overspread the sea. It showed them the faint and distant outlines of the Tarantula, drifting seaward in the clutch of some strong ocean current. Evidently, then, they had nothing to fear from that source.

The work of hoisting the aero-auto from its well on the Sea King, and transferring the odd land-and-air traveler to the Vagrant was set about at once. Blocks and tackles were reeved on the derrick boom of the after mast of the Sea King, and with wondrously little effort, the vehicle the Boy Inventors had evolved was transferred to the flush after deck of the Vagrant, where it was lashed in place, the ropes that bound it being affixed to ringbolts on the deck.

The Flying Road Racer must be described in some detail here, as it is destined to figure largely in after events of the Boy Inventors’ lives. The auto part of the wonderful machine, then, was a cigar-shaped affair of aluminum, with four wheels of the “disc” type. It was fitted much like an ordinary auto, with padded seats in front and in the tonneau, equipped with shock absorbers, and was twelve feet in length.

In the front of the car the engine, a hundred horse-power, eight-cylinder, four-cycle machine, was installed. The controls led to the steering wheel, just as is the case in ordinary cars. The crank shaft, however, projected through the front of the car, and was provided with a slotted terminal, by means of which an eight-foot aerial propeller, carried in sections in the car itself, might be affixed at will.

Above the main body of the car was a light, but strong, framework supporting a balloon bag,—also cigar-shaped, and of the finest oiled silk,—of a capacity of about fifty thousand cubic feet of gas, and with a theoretical lifting power of forty-five hundred pounds. The method of inflating this bag at will, and thus converting the auto into a practicable dirigible, was the most startling innovation about the invention.

The body of the car, as has been said, was cylindrical, with sharp ends, like a mammoth perfecto cigar. This cylinder was divided in half, longitudinally, by a floor of aluminum alloy. The entire lower chamber thus formed was a big generating tank for a gas having a lifting capacity exceeding hydrogen vapor by a ratio of three to one. This gas was generated from brownish crystals formed of a compound of hydrogen-saturated alum and another chemical akin to radium, which the boys, for the present, kept a close secret.

Two pounds of these crystals, when forty gallons of water were added to them, formed close to sixty thousand cubic feet of the powerful inflation gas. One hundred pounds of the crystals were carried in a special compartment of the aero-auto, and constituted an ample supply for all emergencies. To inflate the bag, then, all that had to be done was to unbolt a metal hand-hole in the floor of the front section of the car. Through this the crystals were dumped into the tank beneath and the water added. The opening of the generator was then closed and clamped down tight, hermetically sealing the tank. The gas, under compression, was explosive, and was utilized to run the motor as well as for inflation purposes.

Immediately in front of the operator of the car was a gauge showing at all times the pressure in the tank, and when the gas bag was in operation the amount of gas in that also was indicated. When sufficient gas was generated, the operator turned a valve and the gas from the tank instantly began rushing into the bag carried on the framework above him. The bag was so folded that it inflated without necessitating much attention. Three broad bands of rubberized fabric of great strength encircled the gas bag proper.

To these were attached wires of a tensile strength exceeding anything hitherto known. The other ends of the wires, of course, were fastened to the body of the aero-auto, so that when the bag was sufficiently buoyant the entire car and its occupants were borne aloft. By means of an exhaust pump connected with the motor, the volume of gas could be reduced at will, causing the entire aero-auto to sink at the pleasure of those directing the machine.

“Astern” of this wonderful invention was a rudder of vulcanized silk and vanadium steel framework, which, when the invention was in use as a land vehicle, was folded. When it was desired to take the air the release of a simple clutch caused the rudder to assume its proper position. At the same time, two long planes could be attached to the sides of the car, to be used in ascending or descending. The machine had two steering and governing devices. One wheel was used for the auto control, and another “tiller” was put in use when it was soaring through the air. The control of the aerial rudder, planes and engine, all centered in this second wheel, thus putting the craft, at all times, under one man—or boy—management. In conclusion, it may be mentioned that the craft was equipped with speedometer, barometer, barograph and patent self-starting devices, doing away with the old-fashioned “cranking” of the engine. The wheels were fitted with semi-solid tires of great size and strength, and the shock-absorbers before mentioned obviated any danger of a severe jar or jounce on landing. The machine had been given several trials at High Towers and had been found to work perfectly.

It is not necessary here to give a description of the loading of the aero-auto, the leave takings, and the final instructions and messages that passed between the Vagrant and the Sea King. Suffice it to say, that at eight o’clock that morning all preparations on both sides were completed and that at eight-ten precisely the two vessels parted company. The Sea King steamed northward slowly, bound for Lone Island, and the Vagrant headed for the mouth of the river on which the plantations of the rascally Mexican were situated. At that time the Tarantula had drifted out of the adventurers’ ken altogether, over the eastern horizon.

Leaving Captain Andrews and Jupe in charge of the Vagrant, the lads, thoroughly exhausted now that the strain and care of the long night were over, sought their bunks and were soon wrapped in slumber. In their dreams they flew high above the plateaus and rugged ranges of the mysterious land for which they were bound, questing the unknown in search of the lost ones.