“Don’t the Canadian custom officers help?” asked Ned.

“Well, they haven’t been of any aid to us so far,” was the answer.  “No doubt they are trying, but it’s hard to get an airship at night when you’re on the ground, and can’t even see it.”

“How did they come to use airships?” asked Tom.

“Well, it was because we were too sharp after them when they tried to run things across the line afoot, or by wagons,” replied the agent.  “You must know that in every principal city, at or near the border line, there is a custom house.  Goods brought from Canada to the United States must pass through there and pay a duty.”

“Of course if lawless people try to evade the duty they don’t go near the custom house.  But there are inspectors stationed at the principal roads leading from the Dominion into Uncle Sam’s territory, and they are always on the lookout.  They patrol the line, sometimes through a dense wilderness, and again over a desolate plain, always on the watch.  If they see persons crossing the line they stop them and examine what they have.  If there is nothing dutiable they are allowed to pass.  If they have goods on which there is a tax, they either have to pay or surrender the goods.”

“But don’t the smugglers slip over in spite of all the precautions?” asked Ned.  “Say at some lonely ravine, or stretch of woods?”

“I suppose they do, occasionally,” replied Mr. Whitford.  “Yet the fact that they never can tell when one of the inspectors or deputies is coming along, acts as a stop.  Yon see the border line is divided up into stretches of different lengths.  A certain man, or men, are held responsible for each division.  They must see that no smugglers pass.  That makes them on the alert.”

“Why, take it out west, I have a friend who told me that he often travels hundreds of miles on horseback, with pack ponies carrying his camping outfit, patroling the border on the lookout for smugglers.”

“In fact Uncle Sam has made it so hard for the ordinary smuggler to do business on foot or by wagon, that these fellows have taken to airships.  And it is practically impossible for an inspector patroling the border to be on the lookout for the craft of the air.  Even if they saw them, what could they do?  It would be out of the question to stop them.  That’s why we need some one with a proper machine who can chase after them, who can sail through the air, and give them a fight in the clouds if they have to.”

“Our custom houses on the ground, and our inspectors on horse back, traveling along the border, can’t meet the issue.  We’re depending on you, Tom Swift, and I hope you don’t disappoint us.”

“Well,” spoke Tom, when Mr. Whitford had finished.  “I’ll do my best for you.  It won’t take very long to complete my searchlight, and then I’ll give it a trial.  My airship is ready for service, and once I find we’re all right I’ll start for the border.”