"It's the birds we had to study, the birds in the air," he said. "When I was about your age I was an engineer, and I used to study birds, because they gave us the best pattern for an air-ship; it's nature's own pattern, and you can't beat nature. There's the breast bone, for instance, provided with a sort of keel to serve as a point of attachment for the muscles that set the wings in motion. There's the small head, with a pointed beak, like a ship's bow. Then you've got the light expanding wings that press like a fan on the elastic air waves. Those are nature's aeroplanes, Mr. Herrick, and that's the model we've had to follow. Then there's the tail, tapering off--that's nature's rudder." "We get everything except the feathers," ventured Linton. "Feathers are not essential," was the answer. "There are wings of other sorts. The bat has no feathers. It is fitted with a sort of umbrella frame from top to toe, so to say, that can be expended when required for flying. But for an air-ship we get the best model in the frigate-bird or the albatross--that's what we've aimed at in our newest aeroplanes." "And the best motive power?" queried Linton. "The air itself, compressed as we've got it here," said Mr. Jardine, with decision. "Air can do everything. Nearly a century ago, 'Puffing Billy,' the primitive locomotive, proved that the adhesion of the wheels to the rails was sufficient to give drawing power. Everybody had doubted it. Then everybody doubted whether anything heavier than air could be sustained and move in air. That's why they wasted money and lives in ballooning. The fallacy was disproved. We are disproving it at this very moment. Then came another problem--what was the right sort of motor? They tried everything. There were endless difficulties as regards the steam engine. The internal combustion motor was a remarkable source of power. They used it largely in submarines. It gave the necessary electrical energy when the vessel was propelled under the sea. But petrol was not the last word in locomotion. The first and last power, when you know how to harness it, is the air itself. That's what we've come to after many false starts and failures. You see, you get extreme lightness combined with great power. The bursting pressure and the reduced pressure are all calculated to a nicety per lb. to the square inch. You can have power that will serve for a toy-ship--say three-quarters of a minute, for a flight of 200 yards; or you can build upon the same basis for any size, weight, or distance that can be required." "Isn't it wonderful!" exclaimed his daughter with enthusiasm; and Linton nodded. "Wonderful, indeed, yet here it is!" Her father went on stolidly: "It was proved many years ago that a flying machine weighing nearly 8,000 lbs., carrying its own engine, fuel, and passengers, can lift itself into the air. An aeroplane will always lift a great deal more than a balloon of the same weight."