Whether Tom or Andy was the most surprised at the happening would be hard to say. The former had not meant to hit so hard and he certainly did not intend to knock the squint-eyed youth down. The latter's fall was due, as much as anything, to his senseless, rushing tactics and to the fact that he slipped on the green grass. The bully was up in a moment, however, but he knew better than to try conclusions with Tom again. Instead he stood out of reach and spluttered:

"You just wait, Tom Swift! You just wait!"

"Well, I'm waiting," responded the other calmly.

"I'll get even with you," went on Andy. "You think you're smart because you got ahead of me, but I'll get square!"

"Look here!" burst out the young inventor determinedly, taking a step toward his antagonist, at which Andy quickly retreated, "I don't want any more of that talk from you, Andy Foger. That's twice you've made threats against me today. You put that log across the road, and if you try anything like it for your second attempt I'll make you wish you hadn't. That applies to you, too, Sam," he added, glancing at the other lad.

"I---I ain't gone' to do nothin'," declared Sam.

"I told Andy not to put that tree---"

"Keep still, can't you!" shouted the bully. "Come on. We'll get even with him, that's all," he muttered as he went back into the bushes where the auto was. Andy cranked up and he and his crony getting into the car were about to start off.

"Hold on!" cried Tom. "You'll take that log from across the road or I'll have you arrested for obstructing traffic, and that's a serious offense."

"I'm goin' to take it away!" growled Andy. "Give a fellow a show can't you?"

He cast an ugly look at Tom, but the latter only smiled. It was no easy task for Sam and Andy to pull the log out of the way, as they could hardly lift it to slip the rope under. But they finally managed it, and, by the power of the car, hauled it to one side. Then they speed off.

"I 'clar t' gracious, dem young fellers am most as mean an' contrary as mah mule Boomerang am sometimes," observed Eradicate. "Only Boomerang ain't quite so mean as dat."

"I should hope not, Rad," observed Tom. "I'm ever so much obliged for your warning. I guess I'll be getting, home now. Come around next week; we have some work for you."

" 'Deed an' I will," replied the colored man. "I'll come around an' eradicate all de dirt on yo' place, Mistah Swift. Yais, sah, I's Eradicate by name, and dat's my perfession---eradicatin' dirt. Much obleeged, I'll call around. Giddap, Boomerang!"

The mule lazily flicked his ears, but did not stir, and Tom, knowing the process of arousing the animal would take some time, hurried up the hill to where he had left his motor-cycle. Eradicate was still engaged on the task of trying to arouse his steed to a sense of its duty when the young inventor fIashed by on his way home.

"So now you own a broken motor-boat," observed Mr. Swift when Tom had related the circumstances of the auction. "Well, now you have it, what are you going to do with it?"

"Fix it, first of all," replied his son. "It needs considerable tinkering up, but nothing but what I can do, if you'll help me."

"Of course I will. Do you think you can get any speed out of it?"

"Well, I'm not so anxious for speed. I wart a good, comfortable boat, and the Arrow will be that. I've named it, you see. I'm going back to Lanton this afternoon, take some tools along, and repair it so I can run the boat over to here. Then I'll get at it and fix it up. I've got a plan for you, dad."

"What is it?" asked the inventor, his rather tired face lighting up with interest.

"I'm going to take you on a vacation trip."

"A vacation trip?"

"Yes, you need a rest. You've been working, too hard over that gyroscope invention."

"Yes, Tom, I think I have," admitted Mr. Swift. "But I am very much interested in it, and l think I can get it to work. If I do it will make a great difference in the control of aeroplanes. It will make them more stable able to fly in almost any wind. But I certainly have puzzled my brains over some features of it. However, I don't quite see what you mean."

"You need a rest, dad," said Mr. Swift's son kindly. "I want you to forget all about patents, invention, machinery and even the gyroscope for a week or two. When I get my motor-boat in shape I'm going to take you and Ned Newton up the lake for a cruise. We can camp out, or, if we had to, we could sleep in the boat. I'm going to put a canopy on it and arrange some bunks. It will do you good and perhaps new ideas for your gyroscope may come to you after a rest."

"Perhaps they will, Tom. I am certainly tired enough to need a vacation. It's very kind of you to think of me in connection with your boat. But if you're going to get it this afternoon you'd better start if you expect to get back by night. I think Mrs. Baggert has dinner ready."

After the meal Tom selected a number of tools from his, own particular machine shop and carried them down to the dock on the lake, where his two small boats were tied.

"Aren't you going back on your motor-cycle" asked his father. "No, Dad, I'm going to row over to Lanton, and, if I can get the Arrow fixed, 'I'll tow my rowboat back."

"Very well, then you won't be in any danger from Andy Foger. I must speak to his father about him."

"No, dad, don't," exclaimed the young inventor quickly. "I can fight my own battles with Andy. I don't fancy he will bother me again right away."

Tom found it more of a task than he had anticipated to get the motor in shape to run the Arrow back under her own power. The magneto was out of order and the batteries needed renewing, while the spark coil had short-circuited and took considerable time to adjust. But by using some new dry cells, which Mr. Hastings gave him, and cutting out the magneto, or small dynamo which produces the spark that exploded the gasoline in the cylinders, Tom soon had a fine, "fat" hot spark from the auxiliary ignition system. Then, adjusting the timer and throttle on the engine and seeing that the gasoline tank was filled, the lad started up his motor. Mr. Hastings helped him, but after a few turns of the flywheel there were no explosions. Finally, after the carburetor (which is the device where gasoline is mixed with air to produce an explosive mixture) had been adjusted, the motor started off as if it had intended to do so all the while and was only taking its time about it.

"The machine doesn't run as smooth as it ought to," commented Mr. Hastings. "No, it needs a thorough overhauling," agreed the owner of the Arrow. "I'll get at it tomorrow," and with that he swung out into the lake, towing his rowboat after him.

"A motor-boat of my own!" exulted Tom as he twirled the steering wheel and noted how readily the craft answered her helm. "This is great!"

He steered down the lake and then, turning around, went up it a mile or more before heading for his own dock, as he wanted to see how the engine behaved.

"With some changes and adjustments I can make this a speedy boat," thought Tom. "I'll get right at it. I shouldn't wonder if I could make a good showing against Mr. Hastings' new Carlopa, though his boat's got four cylinders and mine has but two."

The lad was proceeding leisurely along the lakeshore, near his home, with the motor throttled down to test it at low speed, when he heard some one shout. Looking toward the bank, Tom saw a man waving his hands.

"I wonder what he wants?" thought our hero as he put the wheel over to send his craft to shore. He heard a moment later, for the man on the bank cried:

"I say, my young friend, do you know anything about automobiles? Of course you do or you wouldn't be running a motor-boat. Bless my very existence, but I'm in trouble! My machine has stopped on a lonely road and I can't seem to get it started. I happened to hear your boat and I came here to hail you. Bless my coat-pockets but I am in trouble! Can you help me? Bless my soul and gizzard!"

"Mr. Damon" exclaimed Tom, shutting off the power, for he was now near shore. "Of course I'll help you, Mr. Damon," for the young inventor had recognized the eccentric man of whom he had purchased the motor-cycle and who had helped him in rounding up the thieves.

"Why, bless my shoe-laces, if it isn't Tom Swift!" exclaimed Mr. Damon, who seemed very fond of calling down blessings upon himself or upon articles of his dress or person.

"Yes '. I'm here," admitted Tom with a laugh.

"And in a motor-boat, too! Bless my pocketbook, but did that run away with some one who sold it to you cheap?"

"No, not exactly," and the lad explained how he had come into possession of it. By this time he was ashore and had tied the Arrow to an overhanging tree. Then Tom proceeded to where Mr. Damon had left his stalled automobile. The eccentric man was wealthy and his physician had instructed him to ride about in the car for his health. Tom soon located the trouble. The carburetor had become clogged, and it was soon in working order again.

"Well, now that you have a boat ', I don't suppose you will be riding about the country so much," commented Mr. Damon as he got into his car. "Bless my spark-plug! But if you ever get over to Waterfield, where I live, come and see me. It's handy to get to by water."

"I'll come some day," promised the lad.

"Bless my hat band, but I hope so," went on the eccentric individual as he prepared to start his car.

Tom completed the remainder of the trip to his house without incident and his father came down to the dock to see the motor- boat. He agreed with his son that it was a bargain and that it could easily be put in fine shape.

The youth spent all the next day and part of the following working on the craft. He overhauled the ignition system, which was the jump-spark style, cleaned the magneto and adjusted the gasoline and compression taps so that they fitted better. Then he readjusted the rudder lines, tightening them on the steering wheel, and looked over the piping from the gasoline tank.

The tank was in the forward compartment, and, upon inspecting this, the lad concluded to change the plan by which the big galvanized iron box was held in place. He took out the old wooden braces and set them closer together, putting in a few new ones.

"The tank will not vibrate so when I'm going at full speed," he explained to his father.

"Is that where the strange man was tampering with the lock the day of the auction?" asked Mr. Swift.

"Yes, but I don't see what he could want in this compartment, do you dad?"

The inventor got into the boat and looked carefully into the rather dark space where the tank fitted. He went over every inch of it, and, pointing to one of the thick wooden blocks that supported the tank, asked:

"Did you bore that hole in there, Tom?"

No, it was there before I touched the braces. But it isn't a hole, or rather, someone bored it and stopped it up again. It doesn't weaken the brace any."

No, I suppose not. I was just wondering weather that was one of the new blocks or an old one."

"Oh, an old one. I'm going to paint them, too, so in case the water leaks in or the gasoline leaks out the wood won't be affected. A gasoline tank should vibrate as little as possible, if you don't want it to leak. I guess I'll paint the whole interior of this compartment white, then I can see away into the far corners of it."

"I think that's a good idea," commented Mr. Swift.

It was four days after his purchase of the boat before Tom was ready to make a long trip in it. Up to that time he had gone on short spins not far from the dock, in order to test the engine adjustment. The lad found it was working very well, but he decided with a new kind of spark plugs for the two cylinders that he could get more speed out of it. Finally the forward compartment was painted and a general overhauling given the hull and Tom was ready to put, his boat to a good test.

"Come on, Ned," he said to his chum early one evening after Mr. Swift had said he was too tired to go out on a trial run. "We'll see what the Arrow will do now."

>From the time Tom started up the motor it was evident that the boat was going through the water at a rapid rate. For a mile or more the two lads speeded along, enjoying it hugely. Then Ned exclaimed:

"Something's coming behind us."

Tom turned his head and looked. Then he called out:

"It's Mr. Hastings in his new Carlopa. I wonder if he wants a race?"

"Guess he'd have it all his own way," suggested Ned.

"Oh, I don't know. I can get a little more speed out of my boat."

Tom waited until the former owner of the Arrow was up to him.

"Want a race?" asked Mr. Hastings good-naturedly.

"Sure!" agreed Tom, and he shoved the timer ahead to produce quicker explosions.

The Arrow seemed to leap forward and for a moment was ahead of the Carlopa, but with a motion of his hand to the spark lever Mr. Hastings also increased his speed. For a moment the two boats were on even terms and then the larger and newer one forged ahead. Tom had expected it', but he was a little disappointed.

"That's doing first rate," complimented Mr. Hastings as he passed them. "Better than I was ever able to make her do even when she was new, Tom."

This made the present owner of the Arrow feel somewhat consoled. He and Ned ran on for a few miles, the Carlopa in the meanwhile disappearing from view around a bend. Then Tom and his chum turned around and made for the Swift dock.

"She certainly is a dandy!" declared Ned. "I wish I had one like it."

"Oh, I intend that you shall have plenty of rides in this." went on his friend. "When you get your vacation, you and dad and I are going on a tour," and he explained his plan, which, it is needless to say, met with Ned's hearty approval.

Just before going to bed, some hours later, Tom decided to go down to the dock to make sure he had shut off the gasoline cock leading from the tank of his boat to the motor. It was a calm, early summer night, with a new moon giving a little light, and the lad went down to the lake in his slippers. As he neared the boathouse he heard a noise.

"Water rat," he murmured, or maybe muskrats. I must set some traps."

As Tom entered the boathouse he started back in alarm, for a bright light flashed up, almost in his eyes.

"Who's here?" he cried, and at that moment someone sprang out of his motor-boat, scrambled into a rowing craft which the youth could dimly make out in front of the dock and began to pull away quickly.

"Hold on there!" cried the young inventor. "Who are you? What do you want? Come back here!"

The person in the 'coat returned no answer. With his heart doing beats over-time Tom lighted a lantern and made a hasty examination of the Arrow. It did not appear to have been harmed, but a glance showed that the door of the gasoline compartment had been unlocked and was open. Tom jumped down into his craft.

"Some one has been at that compartment again!" he murmured. "I wonder if it was the same man who acted so suspiciously at the auction? What can his object be, anyhow?

The next moment he uttered an exclamation of startled surprise and picked up something from the bottom of the boat. It was a bunch of keys, with a tag attached, bearing the owner's name.

"Andy Foger!" murmured Tom. "So this is, how he was trying to get even! Maybe he started to put a hole in the tank or in my boat."