"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."