When Tom returned with the articles Jack had asked for, he found his cousin busily engaged in taking the cork out of one of the life jackets. This was easily done, as it was in granulated form. Having emptied the jacket, the boy heated some of the liquid rubber over Jupe’s fire till it was about the consistency of cream. This done, he proceeded to coat the canvas of the empty life jacket with the compound. Before he did this, however, he sewed a patch on over the hole he had made to drain the cork, leaving a bit of rubber tube, also found in the supply locker of the Flying Road Racer, sticking out. Tom, after a few minutes, began to realize dimly what the ingenious lad was doing; but he didn’t get the full understanding of Jack’s idea till the latter, having allowed the rubber coating to dry, walked toward the Flying Road Racer with it. “I see what you’ve made now. Jack,” he cried. “It’s an airproof canvas bag, and you’re——” “Going to fill it with gas and see if it will rise,” said Jack. As he spoke he placed the end of the rubber tube he had left protruding from the canvas life jacket, over a small stop-cock on the gas tank of the Flying Road Racer. When he turned the valve a hissing sound followed and the rubber-coated life jacket began to fill, just as any air-tight envelope would have done. When it was half full a laughable thing occurred, giving abundant evidence of the bag’s buoyancy. Jack, who was holding it, was suddenly lifted off his feet as the bag began to rise, tearing the end of the rubber tube off the valve as it did so. Just as he was lifted into the air, for he actually couldn’t make up his mind to let go of his invention, Tom seized his feet and dragged him to the sand again. A rope was secured and the bag lashed to a bush after the end of the tube had been tied. “By cracky!” cried Tom, “that’s the invention of the century. How on earth did you come to think of it?” “I suppose old Mother Necessity had something to do with it,” said Jack; “but the fact that those life jackets lay right close to us helped a lot. I reasoned it out that they would float on the water, and therefore, if they could be emptied and made air-tight, they would rise when filled with gas equally well.” “And you’re going to hitch the aerials on to that one and send them up?” “I’m not sure that one of them will be enough to raise such a weight of copper wire. I guess we’ll make another one.” “And I’ll help you,” cried Tom enthusiastically. Half an hour later when Mr. Jesson and his brother-in-law returned from exploring the island, which they had found to be a desolate spot some five miles off shore, they found two busy lads. The wires had been strung on “spreaders” cut from the brush. Then one of the ends was connected to each of the buoyant “balloons” that were to carry the antenna aloft.