"Slow her down, Ned!" cried Tom, for the Arrow was shooting so swiftly through the water that the young inventor found it impossible to pull up the balloonist. Ned hurried back to the motor, and, when the boat's way had been checked, it was an easy matter to pull the dripping and almost exhausted man into the craft.

"Are you much hurt?" asked Mr. Swift anxiously, for Tom was too much out of breath with his exertion to ask any questions. For that matter the man was in almost as bad a plight. He was breathing heavily, as one who had run a long race.

"I---I guess I'm all right," he panted. "Only burned a little on my hands. That---that was a close call!"

The boat swung around and headed for shore, on which was quite a throng of persons. Some of them had cheered when they saw the plucky rescue.

"I'm afraid we can't save your balloon," gasped Tom as he looked at the place where the canvas was still floating and burning.

"No matter. It wasn't worth much. That's the last time I'll ever go up in a hot-air balloon," said the man with more energy than he had before exhibited. "I'm done with 'em. I've had my lesson. Hereafter an aeroplane or a gas balloon for me. I only did this to oblige the fair committee. I'll not do it again."

The man spoke in short, crisp sentences, as though he was in too much of a hurry to waste his words.

"Let it sink," he went on. "It's no good. Glad to see the last of it."

Almost as he spoke, with a final hiss and a cloud of steam that mingled with the black smoke, the remains of the big bag sunk beneath the surface of the lake.

"We must get you ashore at once and to a doctor," said Mr. Swift. "You must be badly burned."

"Not much. Only my hands, where some burning pieces of canvas fell on' em. If I had a little oil to put on I'd be all right."

"I can fix you up better than that," put in Tom. "I have some Vaseline."

"Good! Just the thing. Pass it over," and the man, though he spoke shortly, seemed grateful for the offer. "My name's Sharp," he went on, "John Sharp, of no place in particular, for I travel all over. I'm a professional balloonist. Ha! That's the stuff!"

This last was in reference to a bottle of Vaseline, which Tom produced. Mr. Sharp spread some over the backs of his hands and went on:

"That's better. Much obliged. I can't begin to thank you for what you did for me---saved my life. I thought it was all up with me---would have been but for you. Mustn't mind my manner---it's a way I have---have to talk quick when you're balloonin'---no time-- -but I'm grateful all the same. Who might you people be?"

Tom told him their names and Mr. Swift asked the aeronaut if he was sure he didn't need the services of a physician.

"No doctor for me," answered the balloonist. "I've been in lots of tight places, but this was the worst squeeze. If you'll put me ashore, I guess I can manage now."

"But you're all wet," objected Tom. "Where will you go? You need some other clothes," for the man wore a suit of tights and spangles.

"Oh, I'm used to this," went on the performer. "I frequently have to fall in the water. I always carry a little money with me so as to get back to the place where I started from. By the way, where am I?"

"Opposite Daleton," answered Tom. "Where did you go up from?"

"Pratonia. Big fair there. I was one of the features."

"Then you're about fifteen miles away," commented Mr. Swift. "You can hardly get back before night. Must you go there?"

"Left my clothes there. Also a valuable gas balloon. No more hot-air ones for me. Guess I'd better go back," and the aeronaut continued to speak in his quick, jerky sentences.

"We'd be very glad to have you come with us, Mr. Sharp," went on the inventor. "We are not far from Shopton, and if you would like to remain over night I'm sure we would make you comfortable. You can proceed to Pratonia in the morning."

"Thanks. Might not be a bad idea," said Mr. Sharp. "I'm obliged to you. I've got to go there to collect my money, though I suppose they won't give it all to me."

"Why not?" demanded Ned.

"Didn't drop from my parachute. Couldn't. Fire was one reason--- couldn't reach the parachute, and if I could have, guess it wouldn't have been safe. Parachute probably was burned too. But I'm done with hot-air balloons though I guess I said that before."

The boys were much interested in the somewhat odd performer, and, on his part, he seemed to take quite a notion to Tom, who told him of several things that he had invented. "Well," remarked Mr. Swift after a while, during which the boat had been moving slowly down the lake, "if we are not to go ashore for a doctor for you, Mr. Sharp, suppose we put on more speed and get to my home? I'm anxious about a robbery that occurred there," and he related some facts in the case.

"Speed her up!" exclaimed Mr. Sharp. "Wish I could help you catch the scoundrels, but afraid I can't---hands too sore," and he looked at his burns. Then he told how he had made the ascension from the Pratonia fair grounds and how, when he was high in the air, he had discovered that the balloon was on fire. He described his sensations and told how he thought his time had surely come. Sparks from the hot air used to inflate it probably caused the blaze, he said.

"I've made a number of trips," he concluded, "hot air and gas bags, but this was the worst ever. It got on my nerves for a few minutes," he added coolly.

"I should think it would," agreed Tom as he speeded up the motor and sent the Arrow on her homeward way.

The boys and Mr. Swift were much interested in the experiences of the balloonist and asked him many questions, which he answered modestly. Several hours passed and late that afternoon the party approached Shopton.

"Here we are!" exclaimed Mr. Swift, relief in his tones. "Now to see of what I have been robbed and to get the police after the scoundrels!"

When the boat was nearing the dock Mr. Sharp, who had been silent for some time, suddenly turned to Tom and asked:

"Ever invent an airship?"

"No," replied the lad, somewhat surprised. "I never did."

"I have," went on the balloonist. "That is, I've invented part of it. I'm stuck over some details. Maybe you and I'll finish it some day. How about it?"

"Maybe," assented Tom, who was occupied just then in making a good landing. "I am interested in airships, but I never thought I could build one."

"Easiest thing in the world," went on Mr. Sharp, as if it was an everyday matter. "You and I will get busy as soon as we clear up this robbery." He talked as though he had been a friend of the family for some time, for he had a genial, taking manner.

A little later Mr. Swift was excitedly questioning Garret Jackson concerning the robbery and making an examination of the electrical shop to discover what was missing.

"They've taken some parts of my gyroscope!" he exclaimed, "and some valuable tools and papers, as well as some unfinished work that will be difficult to replace."

"Much of a loss?" asked Mr. Sharp with a business-like air.

"Well, not so large as regards money," answered the inventor, "but they took things I can never replace, and I will miss them very much if I cannot get them back."

"Then we'll get them back!" snapped the balloonist, as if that was all there was to it.

The police were called up on the telephone and the facts given to them, as well as a description of the stolen things. They promised to do what they could, but, in the light of past experiences, Tom and his father did not think this would be much. There was little more that could be done that evening. Ned Newton went to his home, and, after Mr. Swift had insisted in calling in his physician to look after Mr. Sharp's burns the balloonist was given a room next to Tom's. Then the Swift household settled down.

"Well," remarked Tom to his father, as he got ready for bed, "this sure has been an exciting day."

"And my loss is a serious one," added the inventor somewhat sadly.

"Don't worry, dad," begged his son. "I'll do my best to recover those things for you."

Several days passed, but there was no clew to the thieves. That they were the same ones who had stolen the turbine model there was little doubt, but they seemed to have covered their tracks well. The police were at a loss, and, though Tom and Mr. Sharp cruised about the lake, they could get no trace of the men. The balloonist had sent to Pratonia for his clothing and other baggage and was now installed in the Swift home, where he was invited to stay a week or two.

One night when he was looking over some papers he had taken from his trunk the balloonist came over to where Tom was making a drawing of a new machine he was planning and said:

"Like to see my idea for an airship? Different from some. It's a dirigible balloon with an aeroplane front and rear to steer and balance it in big winds. It would be a winner, only for one thing. Maybe you can help me."

"Maybe I can," agreed Tom, who was at once interested.

"We ought to be able to do something. Look at our names---Swift and Sharp---quick and penetrating---a good firm to build airships," and he laughed genially. "Shall we do it?"

"I'm willing," agreed Tom, and the balloonist spread his plans out on the table, he and the young inventor soon being deep in a discussion of them.