The Hawk was about a hundred feet above the surface of the earth. A long rope depended from the car, and twenty or thirty feet of it dragged along the ground as the car moved.
"Vat's der rope for, Matt?" inquired Carl.
"If that was an ordinary balloon," replied Matt, "we'd call the rope a guide-rope. Usually the guide-rope helps to save gas and ballast. When you want a balloon to go up, you know, you throw out sand; when you want it to come down, you let out gas. That trailing rope acts as ballast. When the gas expands, and the ship wants to rise, part of the rope that trails is lifted from the ground and throws more weight on the car; and when the gas contracts, and the car shows a tendency to descend, more of the rope falls on the ground and takes just that much weight off the car."
"Dot's as clear as mud!"
"I can't understand why they've got a drag on the air-ship," muttered Matt. "I supposed the propeller and the steering-blades were enough to send such a craft wherever it was wanted to go."
As the Hawk came nearer, Matt's trained eyes and ears convinced him that the driver of the air-ship was a poor motorist. Evidently he did not understand the engine he was handling. The air-ship zigzagged erratically on its course, and the long bag ducked upward and downward in a most hair-raising manner. On top of that, Matt could hear one of the cylinders misfiring.
The Hawk's drag-rope was trailing along the roadway. First it was on one side of the road, and then on the other, following the irregular swaying and plunging of the car.
"Come on, Carl!" called Matt, turning and running for the automobile. "If that rope strikes our car it may damage it. We've got to fend it off."
"Dose air-ship fellers vas mighdy careless!" answered Carl, hurrying after his chum. "Dot rope mighdt knock town fences, und preak vinders, und do plendy more tamages."
"There isn't power enough at the other end of it to do much damage," Matt answered, posting himself at the rear of the automobile and watching the advancing rope with sharp eyes.