Now it was a butterfly with broken wings, for Andy had slashed the canvas of the planes in a score of places.

“The scoundrel!” growled Tom.  “I’ll make him suffer for this!  He’s all but ruined my aeroplane.”

Tom walked around his pet machine.  As he came in front, and saw the propeller, he gave another exclamation.  The fine wooden blades of several layers, gracefully curved, which had cost him so much in time and labor to build up, and then fashion to the right shape, had been hacked, and cut with an axe.  The propeller was useless!

“More of Andy’s work,” murmured Tom.  “This is about the worst yet!”

There came over him a feeling of great despondency, which was succeeded by a justifiable rage.  He wanted to take after the bully, and give him a merciless beating.  Then a calmer mood came over Tom.

“After all, what’s the use?” he reasoned.  “Whipping Andy wouldn’t mend the butterfly.  She’s in bad shape, but I can repair her, when I get time.  Luckily, he didn’t meddle with the engine.  That’s all right.”  A hasty examination had shown this.  “I guess I won’t do anything now,” went on Tom.  “I’ll have my hands full getting Mr. Fenwick’s airship to run.  After that I can come back here and fix up my own.  It’s a good thing I don’t have to depend on her for making the trip to Philadelphia.  Poor butterfly! you sure are in a bad way,” and Tom felt almost as if he was talking to some living creature, so wrapped up was he in his trim little monoplane.

After another disheartening look at his air craft, the young inventor started to leave the shop.  He looked at a door, the fastening of which Andy had broken to gain admittance.

“I should have had the burglar alarm working, and this would never have happened,” reasoned Tom.  All the buildings were arranged so that if any one entered them after a certain hour, an alarm would ring in the house.  But of late, the alarm had not been set, as Tom and his father were not working on any special inventions that needed guarding.  It was due to this oversight that Andy was able to get in undetected.

“But it won’t happen again,” declared Tom, and he at once began connecting the burglar-apparatus.  He went into the house, and told his father and the engineer what had occurred.  They were both indignant, and the engineer declared that he would sleep with one eye open all night, ready to respond to the first alarm.

“Oh, there’s no danger of Andy coming back right away,” said Tom.  “He’s too frightened.  I wouldn’t be surprised if he disappeared for a time.  He’ll be thinking that I’m after him.”

This proved true, as Andy had left town next morning, and to all inquiries his mother said he had gone to visit relatives.  She was not aware of her son’s meanness, and Tom did not tell her.

Mr. Damon arrived from his home in Waterfield that day, and, with many “blessings,” wanted to know if Tom was ready for the trial of the electrical airship.