"It's not easy to follow the outline here," he said. "Wait till the ship's finished. But you can see this much. She's long and pointed at either end, and looks like a flattened cigar. That's how she differs from the Zeppelins. She's built very flat, and extends on either side till the top and bottom half come together in what may be called a lateral keel." "Why? Where's the reason?" "To protect her against gusts of wind and gales. A Zeppelin can't escape. Every breath plays on her big lateral bulk. In my ship the wind strikes a thin keel on whichever side it comes, is divided there, and passes over and under the ship, sliding as it were upwards and downwards away from the gradually-sloping surfaces which lead from those keels. In fact, the ship is almost as flat as a tortoise, and as wide comparatively, though she's very much longer." "And--and this flattening of the ship makes her laugh at gales?" asked Andrew, staring at the plans before him. "Certainly--her shape, and other fittings. Now, let's return to the Zeppelin. It's a huge framework of aluminium, built very light and covered with a material of neutral tint." "Which holds the necessary gas." "No, Uncle. Which merely covers the aluminium skeleton. Inside the frame there are twenty or more balloonettes, inflated with gas. Thus if one bursts, or two, or more even, the ship still floats." "Canny that! Smart!" declared Andrew. "Well, yours? It's a similar framework, I suppose? The same balloonettes? Where does the difference come?" Joe bent again to his bag and produced a parcel, which he rapidly opened. He drew from 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.