Upward shot the Falcon. With every revolution of her big propellers she came nearer and nearer to the fleeing craft of the supposed smugglers who were using every endeavor to escape.
"Do you think you can catch them, Tom?" asked Mr. Whitford as he stood at the side of our hero in the pilot house, and looked upward and forward to where, bathed in the light of the great search-lantern, the rival craft was beating the air.
"I'm sure we can—unless something happens."
"Bless my overshoes! What can happen?" asked Mr. Damon, who, after finding that everything in the motor room was running smoothly, had come forward. Ned was attending to the searchlight. "What can happen, Tom?"
"Almost anything, from a broken shaft to a short-circuited motor. Only, I hope nothing does occur to prevent us from catching them."
"You don't mean to say that you're actually going to try to catch them, do you, Tom?" asked the custom officer, "I thought if we could trail them to the place where they have been delivering the goods, before they shipped them to Shopton we'd be doing well. But I never thought of catching them in mid-air."
"I'm going to try it," declared the young inventor. "I've got a grappling anchor on board," he went on, "attached to a meter and windlass. If I can catch that anchor in any part of their ship I can bring them to a stop, just as a fisherman lands a trout. Only I've got to get close enough to make a cast, and I want to be above them when I do it."
"Don't you think you can catch them, Tom?" asked Mr. Damon.
"Well, I'm pretty sure I can, and yet they seem to have a faster biplane than I gave them credit for. I guess I'll have to increase our speed a little," and he shifted a lever which made the Falcon shoot along at nearly doubled speed.
Still the other airship kept ahead, not far, but sufficiently so to prevent the grappling anchor from being tossed at her rail.
"I wonder if they are the smugglers?" questioned Mr. Damon. "It might be possible, Tom, that we're chasing the wrong craft."
"Possible, but not probable," put in Mr. Whitford. "After the clew we got, and what the Indians told us, and then to have a biplane come sailing over our heads at night, it's pretty sure to be the one we want. But, Tom, can't you close up on 'em?"
"I'm going to try. The machinery is warmed up now, and I'll send it to the limit."
Once more he adjusted the wheels and levers, and at his touch the Falcon seemed to gain new strength. She fairly soared through the air.
Eagerly those in the pilot house watched the craft they were pursuing. She could be seen, in the glare of the big searchlight, like some bird of gloom and evil omen, fluttering along ahead of them.
"They certainly have a fine motor!" cried Tom. "I was sure I could have caught up to them before this."
"How do you account for it?" asked Mr. Damon.
"Well, they're flying a good deal lighter than we are. They probably have no load to speak of, while we carry a heavy one, to say nothing of Koku."
"Diamonds aren't very heavy," put in Mr. Whitford grimly. "I think they are smuggling diamonds to-night. How I wish we could catch them, or trace them to where they have their headquarters."
"Bless my stars! They've gone!" suddenly exclaimed Mr. Damon. "They've disappeared, Tom, I can't see them."
It was indeed true. Those in the pilot house peering ahead through the darkness, could not get a glimpse of the airship they were pursuing. The beam of the searchlight showed nothing but a black void.
All at once the beam shifted downward, and then it picked up the white-winged craft.
"They went down!" cried Tom. "They tried to drop out of sight."
"Can't you get them?" asked Mr. Whitford.
"Oh, yes, we can play that game too. I'll do a little volplaning myself," and the young inventor shut off the power and coasted earthward, while Ned, who had picked up the forward craft, kept the searchlight playing on her.
And now began a wonderful chase. The smugglers' craft, for such she proved later to be, did her best to dodge the Falcon. Those managing the mechanism of the fleeing airship must have been experts, to hold out as they did against Tom Swift, but they had this advantage, that their craft was much lighter, and more powerfully engined as regards her weight. Then, too, there were not so many on board, and Tom, having a combined balloon and aeroplane, had to carry much machinery.
It was like the flight of two big birds in the air. Now the smugglers' craft would be mounting upward, with the Falcon after her. Again she would shoot toward the earth, and Tom would follow, with a great downward swoop.
Ned kept the great lantern going, and, though occasionally the craft they were after slipped out of the focus of the beams, the young bank clerk would pick her up again.
To the right and left dodged the forward airship, vainly endeavoring to shake off Tom Swift, but he would not give up. He followed move for move, swoop for swoop.
"She's turning around!" suddenly cried Mr. Damon. "She's given up the flight, Tom, and is going back!"
"That's so!" agreed Mr. Whitford. "They're headed for Canada, Tom. We've got to catch 'em before they get over the Dominion line!"
"I'll do it!" cried Tom, between his clenched teeth.
He swung his airship around in a big circle, and took after the fleeing craft. The wind was against the smugglers now, and they could not make such good speed, while to Tom the wind mattered not, so powerful were the propellers of the Falcon.
"I think we're gaining on them," murmured Mr. Damon.
Suddenly, from the engine room, came a cry from Ned.
"Tom! Tom!" he shouted, "Something is wrong with the gas machine! She registers over five hundred pounds pressure, and that's too much. It's going up, and I haven't touched it!"
"Mr. Damon, take the wheel!" exclaimed the young inventor. "I've got to see what's wrong. Hold her right on their trail."
Tom sprang to the motor room, and one glance at the gas generating machine showed him that they were in dire peril. In some manner the pressure was going up enormously, and if it went up much more the big tank would blow to pieces.
"What is it?" cried Ned, from his position near the light.
"I don't know! Something wrong."
"Are you going to give up the chase?"
"I am not. Stick to the light. Koku, tell Mr. Damon to hold her on the course I set. I'll try to get this pressure down!" And Tom Swift began to work feverishly, while his ship rushed on through the night in danger, every moment, of being blown to atoms. Yet the young inventor would not give up, and descend to earth.
