the interior a sheet of shining material, which might have been glass but for the fact that it was folded half a dozen times. Placing it on the table, this sheet opened to its full capacity as soon as the weight of his fingers was removed.

"Flexible and elastic, you see, Uncle," said Joe. "And yet not extensible. See—it does not stretch. Transparent, of course—one of its least advantages—but yet one of great value in the construction of an airship."

"What! You don't mean to tell me you build the ship of that? How? What part does it form? I—look here, Joe, you're romancing."

Joe smiled; his deep-sunk eyes took on the clever expression, to which his uncle had become familiar. He placed two long objects on the table, and stood leaning the tips of his strong fingers upon them. He might have been a lecturer, and his uncle a student about to absorb his wisdom. As for the objects he had placed on the table, one was a long piece of the same transparent material, an eighth of an inch thick, perhaps, two inches wide before it was bent, and now bent all the way down its length into a right angle. In fact, composed of iron it would be known simply as "angle iron". The other object was a tube, perhaps half an inch in diameter, two feet in length, and of thinner material. Both were transparent, and exceedingly light in weight, as Andrew assured himself instantly.

"Go on," he said huskily. "What is the stuff? Not talc—that I can tell easily. Not celluloid either—you'd never be such a fool as to build a ship of such a highly inflammable material. That stuff's lighter, also. What is it?"

But Joe was not yet to be persuaded into an answer. He spread the thin transparent sheet out, caught the four corners, and taking a jug of water, poured some of the contents into the centre of the sheet. Not a drop penetrated it. Joe demonstrated the fact quietly and without show of haste. Then he stepped to the window and cast the water out. A moment later he was striking a match.

"Stop! Stop! How do I know that it isn't like celluloid?" cried Andrew in some alarm. "Supposing it fires. Supposing there's an explosion."

Joe smiled. "It won't," he said curtly. "Look there."

The flame was licking round one of the corners of this thin sheet of material. It blackened the surface above, while that below, immersed in the flame, gradually changed colour. It became a dull red, then got redder and redder till it was glowing. Slowly it changed its form, the corner curled up into a globule. The latter separated itself from the sheet and tumbled on to the glass-topped table, where it broke into a number of smaller drops.

"Glass! No—too light by far. Not celluloid. Not talc. Then what is it?" demanded Andrew impatiently, taking the various articles and examining them. "Why, this angle piece is strong—as strong as aluminium!" he cried.

"Stronger—stronger and tougher," asserted Joe. "You can bend it; it's flexible. You can bend it double, and still it comes back to its original formation. Aluminium would crack at once; even steel would. Now, try the tube. See, it kinks when you bend it, though it requires some strength to do that. Now, set it on its end on the floor; we'll put a book on the top end. Sit on the book, Uncle."

Andrew did so—gingerly it must be confessed—for this transparent tube with its small diameter and its walls less than an eighth of an inch in thickness looked as if it would at once succumb to his avoirdupois. But it did not. He sat boldly upon the book now. He balanced himself upon the frail support and jerked his feet from the ground.

"Jingo!" he cried. "What in thunder is the stuff? It's strong, strong as possible. Surprisingly powerful stuff. It bends if you use sufficient force, yet doesn't break. It's tough; you've shown me that, for a knife edge bites into it with difficulty. Then it softens and melts at a fairly high temperature, proving that it can be easily treated and moulded. Well?"

"I call it celludine," said Joe, not without some trace of pride in his tuneful voice." I dropped upon the stuff quite by accident, for at the 'Varsity' I was fond of working in a laboratory. Asbestos enters into its composition, that I can tell you. It is easily manufactured, the materials of which it is composed are inexpensive. It can be rolled into plates and bars and drawn into tubes. Better than all, perhaps, when bars and tubes and angle pieces are being built into a framework rivet holes can be punched with the simplest pneumatic tool, while the joins and the rivets can be instantly and securely welded together with an electric heating iron. Thus every joint becomes a solid piece."

Andrew wiped his forehead—this was something—he even chuckled.

"Reitberg'd have fits," he laughed. "He'd be beginning to get anxious about that money if he heard what you were saying. But get along. This stuffs fine. I can see that, and I'm quite a child in such matters."

"Then it is hardly necessary for me to explain that I build my framework of this celludine. That frame is wonderfully strong, stronger a great deal than if composed of aluminium, and constructed far more rapidly and at less cost. It has another advantage Zeppelins have broken up before now, simply because certain portions of their frames have fractured under great strain. With this material the flexibility is such that the frame gives before a strain, grudgingly it is true, but gives without receiving damage, and instantly returns to its former shape once the strain is removed. Now let us proceed. I cover the frame with the same material. It is waterproof and gas-proof. Note that, Uncle. I fashion partitions of the same material. Thus my balloonettes are formed. There is no need for the twenty and more balloonettes. All that weight is removed. There are merely the partitions and the outer covering, and since celludine is the lightest material of any that I have yet discovered, you can follow that here I have a material with which I can make a ship at once lighter than a Zeppelin, though of equal size, while it is stronger and more flexible. Add the important fact that the whole thing is transparent."

"Eh? Why? Where does the advantage come?"

It was natural, perhaps, that Andrew should not follow his reasoning so quickly.

"Imagine the ship to be inflated and in the air," said Joe. "Well, gas is transparent. So's the framework of the ship. She is invisible almost, except for engines and gear of a similar description."

This time his uncle mopped his forehead busily. He was glad that he had taken up that challenge. He was beginning to hope that some day it might be his turn to gloat over Mr. Reitberg. He could even conjure up the huge airship which Joe Gresson would build. Facts were in his case far easier of digestion than any amount of theorizing, and here his nephew was providing him with facts. As a practical man Andrew could decide that this celludine was essentially suitable for the building of a vessel to sail the air. Now he could realize better than ever that success was possible. But a few hours ago he had been content to take Joe's mere word for it. His own common sense now supported that belief. He drew in a series of deep breaths, while he handled the samples before him. Unconsciously it seemed his hand sought his handkerchief and he mopped his fevered brow. Then he drew a cheque book from an inner pocket, seated himself at a desk, and took up a pen.

"Pay Joseph Gresson ten thousand pounds," he wrote, and attached his signature.

"There," he said, with a beaming smile, smacking his nephew heartily on the back, "get to at the work, Joe. Call for more when you want it. Don't stint yourself; spend freely if necessary, for there's no time to