“That’s the way to talk!” cried Ned.  “Never say die!  Don’t give up the ship, and all that.  But, Tom, what you need now is a little fun.  You’ve been poking away at this too long.  Come on out on the lake, and have a ride in the motor boat.  It will do you good.  It will do me good.  I’m a bit rusty myself—­been working hard lately.  Come on—­let’s go out on the lake.”

“I believe I will!” exclaimed Tom, after thinking it over for a moment.  “I need a little fresh air.  Sitting in that telephone booth, trying to get an image on a plate, and not succeeding, has gotten on my nerves.  I want to write out an order for Koku to take to town, though.  I want to get some fresh selenium, and then I’m going to make new plates.”

Tom made some memoranda, and then, giving Koku the order for the chemist, the young inventor closed up his shop, and went with Ned down to Lake Carlopa, where the motor boat was moored.

This was not the same boat Tom had first purchased, some years ago, but a comparatively new and powerful craft.

“It sure is one grand little day for a ride,” remarked Ned, as he got in the craft, while Tom looked over the engine.

“Yes, I’m glad you came over, and routed me out,” said the young inventor.  “When I get going on a thing I don’t know enough to stop.  Oh, I forgot something!”

“What?” asked Ned.

“I forgot to leave word about Mr. Railing’s airship.  It’s all fixed and ready for him, but I put on a new control, and I wanted to explain to him about it.  He might not know how to work it.  I left word with father, though, that if he came for it he must not try it until he had seen me.  I guess it will be all right.  I don’t want to go back to the house now.”

“No, it’s too far,” agreed Ned.

“I have it!” exclaimed Tom.  “I’ll telephone to dad from here, not to let Halling go up until I come back.  He may not come for his machine; but, if he does, it’s best to be on the safe side Ned.”

“Oh, sure.”

Accordingly, Tom ’phoned from his boat-house, and Mr. Swift promised to see the bird-man if he called.  Then Ned and Tom gave themselves up to the delights of a trip on the water.

The Kilo, which name Tom had selected for his new craft, was a powerful boat, and comfortable.  It swept on down the lake, and many other persons, in their pleasure craft, turned to look at Tom’s fine one.

“Lots of folks out to-day,” observed Ned, as they went around a point of the shore.

“Yes, quite a number,” agreed Tom, leaning forward to adjust the motor.  “I wonder what’s got into her?” he said, in some annoyance, as he made various adjustments.  “One of the cylinders is missing.”

“Maybe it needs a new spark plug,” suggested Ned.

“Maybe.  Guess I’ll stop and put one in.”

Tom slowed down the motor, and headed his boat over toward shore, intending to tie up there for a while.