fixing up his aeroplane."

"Look!" suddenly exclaimed Ned. "There's that agent now! He's going to the depot to get a train, I guess," and he pointed to the government man, who had so lately interviewed Tom. "I'm going to speak to him!" impulsively declared Ned.

"I wouldn't," objected Tom, but his chum had already hastened on ahead, and soon was seen talking excitedly to Mr. Whitford. Tom sauntered up in time to hear the close of the conversation.

"I'm much obliged to you for your information," said the custom officer, "but I'm afraid, just as you say your chum felt about it, that there's nothing in it. This Foger chap may have been bad in the past, but I hardly think he's in with the smugglers. What I'm looking for is not a lad who has one airship, but someone who is making a lot of them, and supplying the men who are running goods over the border. That's the sort of game I'm after, and if this Andy Foger only has one aeroplane I hardly think he can be very dangerous."

"Well, perhaps not," admitted Ned. "But I thought I'd tell you."

"And I'm glad you did. If you hear anything more. I'll be glad to have you let me know. Here's my card," and thanking the boys for their interest Mr. Whitford passed on.

Tom and Ned gave the noiseless airship a test the next day. The craft, which was the stanch Falcon, remodeled, was run out of the shed, Koku the giant helping, while Mr. Swift stood looking on, an interested spectator of what his son was about to do. Eradicate, the old colored man, who was driving his mule Boomerang, hitched to a wagon in which he was carting away some refuse that had been raked up in the garden, halted his outfit nearby.

"I say, Massa Tom!" he called, as the young inventor passed near him, in making a tour of the ship.

"Well, Rad, what is it?"

"Doan't yo'-all want fo' ma an' Boomerang t' gib yo'-all a tow? Mebby dat new-fangled contraption yo'-all has done put on yo' ship won't wuk, an' mebby I'd better stick around t' pull yo'-all home."

"No, Rad, I guess it will work all right. If it doesn't, and we get stuck out a mile or two, I'll send you a wireless message."

"Doan't do dat!" begged the colored man. "I neber could read dem wireless letters anyhow. Jest gib a shout, an' me an' Boomerang will come a-runnin'."

"All right, Rad, I will. Now, Ned, is everything in shape?"

"I think so, Tom."

"Koku, just put a little more wind in those tires. But don't pump as hard as you did the other day," Tom cautioned.

"What happened then?" asked Ned.

"Oh, Koku forgot that he had so much muscle, and he kept on pumping air into the bicycle wheel tires until he burst one. Go easy this time, Koku."

"I will, Mr. Tom," and the giant took the air pump.

"Is he going along?" asked Ned, as he looked to see that all the guy wires and stays were tight.

"I guess so," replied Tom. "He makes good ballast. I wish Mr. Damon was here. If everything goes right we may take a run over, and surprise him."

In a little while the noiseless airship was ready for the start. Tom, Ned and Koku climbed in, and took their positions.

"Good luck!" Mr. Swift called after them. Tom waved his hand to his father, and the next moment his craft shot into the air. Up and up it went, the great propeller blades beating the air, but, save for a soft whirr, such as would be made by the wings of a bird, there was absolutely no sound.

"Hurrah!" cried Tom. "She works! I've got a noiseless airship at last!"

"Say, don't yell at a fellow so," begged Ned, for Tom had been close to his chum when he made his exulting remark.

"Yell! I wasn't yelling," replied Tom. "Oh, I see what happened. I'm so used to speaking loud on the other airships, that make such a racket, that I didn't realize how quiet it was aboard the new Falcon. No wonder I nearly made you deaf, Ned. I'll be careful after this," and Tom lowered his voice to ordinary tones. In fact it was as quiet aboard his new craft, as if he and Ned had been walking in some grass-grown country lane.

"She certainly is a success," agreed Ned. "You could creep up on some other airship now, and those aboard would never know you were coming."

"I've been planning this for a long time," went on our hero, as he shifted the steering gear, and sent the craft around in a long, sweeping curve. "Now for Waterford and Mr. Damon."

They were soon above the town where the odd man lived, and Tom, picking out Mr. Damon's house, situated as it was in the midst of extensive grounds, headed for it.

"There he is, walking through the garden," exclaimed Ned, pointing to their friend down below. "He hasn't heard us, as he would have done if we had come in any other machine."

"That's so!" exclaimed Tom. "I'm going to give him a sensation. I'll fly right over his head, and he won't know it until he sees us. I'll come up from behind."

A moment later he put this little trick into execution. Along swept the airship, until, with a rush, it passed right over Mr. Damon's head. He never heard it, and was not aware of what was happening until he saw the shadow it cast. Then, jumping aside, as if he thought something was about to fall on him, he cried:

"Bless my mosquito netting! What in the world--"

Then he saw Tom and Ned in the airship, which came gently to earth a few yards further on.

"Well of all things!" cried Mr. Damon. "What are you up to now, Tom Swift?"

"It's my noiseless airship," explained our hero. "She doesn't make a sound. Get aboard, and have a ride."

Mr. Damon looked toward the house.

"I guess my wife won't see me," he said with a chuckle. "She's more than ever opposed to airships, Tom, since we went on that trip taking moving pictures. But I'll take a chance." And in he sprang, when the two lads started up again. They made quite a flight, and Tom found that his new motor exceeded his expectations. True, it needed some adjustments, but these could easily be made.

"Well, what are you going to do with it, now that you have it?" asked Mr. Damon, as Tom once more brought the machine around to the odd man's house, and stopped it. "What's it for?"

"Oh, I think I'll find a use for it," replied the young inventor. "Will you come back to Shopton with us?"

"No, I must stay here. I have some letters to write. But I'll run over in a few days, and see you. Then I'll go on another trip, if you've got one planned."

"I may have," answered Tom with a laugh. "Good-bye."

He and Ned made a quick flight home, and Tom at once started on making some changes in the motor. He was engaged at this work the next day, when he noticed a shadow pass across an open window. He looked up to see Ned.

"Hello, Tom!" cried his chum. "Have you heard the news?"

"No, what news? Has Andy Foger fallen out of his airship?"

"No, but there are a whole lot of Custom House detectives in town, looking for clews to the smugglers."

"Still at it, eh? Shopton can't seem to keep out of the limelight. Has anything new turned up?"

"Yes. I just met Mr. Whitford. He's back on the case and he has several men with him. They received word that some smuggled goods came to Shopton, and were shipped out of here again."

"How, by airship?"

"No, by horse and wagon. A lot of cases of valuable silks imported from England to Canada, where the duty is light, were slipped over the border somehow, in airships, it is thought. Then they came here by freight, labeled as calico, and when they reached this town they were taken away in a wagon."

"But how did they get here?"

"On the railroad, of course, but the freight people had no reason to suspect them."

"And where were they taken from the freight station?"

"That's what the customs authorities want to find out. They think there's some secret place here, where the goods are stored and reshipped. That's why so many detectives are here. They are after the smugglers hot-footed."