shop for, Frank?"

His cousin was looking very grave.

"Well, you forget that we've been working overtime this winter on several little inventions that, if we ever complete them, will make a stir in the world of aviation."

"Jupiter, I had let that slip away from me, for a fact, Frank!" exclaimed the other, looking rather startled.

"Of course, it sounds pretty big for us to even imagine that any party could take enough interest in what the Bird boys are doing to come up here, intending to break into the shop, and learn our secrets; but what else can we think, tell me that, Andy?"

"But they wouldn't find out much, even if they had six hours to poke around our shop in, would they, Frank?"

"I guess you're right, because we've made it a rule to be cautious enough to hide our work and cover our tracks as we go along. But let's get busy now, and put the plane into shape, so we can slip along home. And as we work we can keep on talking as much as we want to," Frank went on to say.

The farmer and Felix still loitered around, determined to see the wonderful contrivance make a start, and expecting the greatest treat of their lives, when that event occurred.

Such experienced workers as the two Bird boys had now become would find little or no trouble about carrying out the work they had on hand. Every steel wire guy was kept as taut as a fiddle string; and by the time they were done handling the aeroplane it would be in apple-pie shape for work.

"Did they smash much in the shop, Frank?" Andy asked after they had been working some little time, and making fair progress.

"Why, no, it didn't seem to me that they took the time to do great damage; and that's why I fancy they were scared off, somehow or other. They went in a hurry, or else they would never have forgotten those things. And when I looked around I made up my mind that they were just mad because they didn't find our machine at home, and so tried to let us know that fact."

"Perhaps it was a second detachment of the same crowd that came out here?" suggested Andy, speculatively.

"Tell me, what would they be doing with electric torches, and black masks? Now, you can see that these have been pretty well used; they're not new ones just cut out by pattern at home with mother's scissors. These have been made by an experienced operator, and were bought either for a mask ball or some other purpose."

"Well, perhaps we'll never know the truth about it," grumbled Andy, who never liked anything to puzzle him and would lie awake half the night trying to find the answer to a conundrum that had been offered to him by a boy friend.

"Oh! yes, I've got a hunch that we will," chirped his cousin, with a sublime confidence that quite won Andy's heart; if he could not see any good reason for hope himself, the fact that his chum pinned his faith on it was enough to bolster up his own courage.

Meanwhile they were both as busy as bees, and the work was approaching completion.

"What are you looking up every little while that way for?" Frank asked, after noticing that Andy cocked his eye upward several times, and appeared to be scanning the heavens in an expectant manner; "the day is all right, so far as wind goes, and we ought to get along home without a bit of trouble."

"Oh! I wasn't bothering my head about that part of it," the other replied, with a scornful smile. "We've been out in all sorts of weather; and now that we have a chance to try this new invention of the Wrights', that makes it next to impossible to tilt an aeroplane over no matter how you move around when up in the air, we can feel safer than ever. Even a fool would be kept from meeting with an accident when protected by that wonderful balancing bar that responds to the slightest movement of the human body."

"Then it was something else you had on your mind, was it, Andy?"

"Well, I was wondering just what took Percy and Sandy out at daybreak this morning, that's all," replied the other.

"What's that? Did you see them pass over in their biplane this morning?" demanded the other.

"Felix woke me up at dawn to tell me there was a queer chugging overhead, that sort of scared him. I jumped up, because of course I knew what that must mean. And sure enough I was just in time to see a biplane pass over at a good height, and head up the lake. I lost it back of the barn, because a flock of crows came flying along, stretching out for a mile or two; and among the lot I couldn't make out just what was biplane and which was crow. It was pretty high up, too, I thought."

"But you made sure it was Percy's biplane?" asked Frank, interested somewhat, for somehow the other rival flier was always doing such bold stunts that he could not help feeling as though it might pay to keep track of what he was doing, lest their interests clash unexpectedly, in midair perhaps.

"I ought to know the way it glides, and the whole general look; and I'd be willing to take my affidavy that was the Canvas-back, as he calls his biplane."

"And he was in it, of course, with Sandy too?" Frank went on.

"I could just make out that there were two aboard," said Andy, "but somehow it seemed to me that Percy had altered his whole way of piloting his airship, or else he was drunk, and hardly knew what he was doing."

Frank whistled to indicate his surprise and consternation:

"When it gets as rough as that you can take it from me that Percy's mother will hear something simply awful about him before long. He's bound to go from bad to worse; and everybody knows what the end of such an aviator is going to be."

"But what under the sun could he be off at daylight this morning for?" Andy went on to remark, as though that thing had been bothering him ever since the moment he lost track of the biplane among the teetering, cawing crows.

Frank shrugged his shoulders as he replied:

"Did you ever know any reason for half the things Percy does? He just acts from a sudden impulse. Remember all that happened when he followed us down there to Columbia in South America, and tried to give us all the trouble he could make up. And there have been lots of other times too, we can look back at, all of which prove what I am saying that he is often like a ship without a rudder. Now, perhaps, he's got the crazy notion in his head that we might prosecute him either for what he tried to do up here to our hydroplane, or on account of breaking into our hangar, and doing a certain amount of damage, if the vandal was Percy Carberry."

"That sounds a little reasonable, anyhow, Frank. Queer that I never seem to get hold of these things, and they just float along as easy as anything to you. But it looks as if we had her all primed up now as steady as a church. How about it, Frank?"

For answer the other touched several taut wire guys with a peculiar little movement of finger and thumb, and each one responded with a musical note that was the sweetest possible sound in the responsive ear of the young aviators.

"All done, and let's be off," he said, presently, after the last test had been applied.

Accordingly they shook hands with Farmer Quackenboss, his good wife, and Felix, in the palm of which latter Andy made sure to leave a greenback that made the boy grin broadly.

Three minutes later Frank sang out the word, and both the farmer and Felix ran along with the machine for a dozen paces or so, when it left them behind, taking on speed, and finally rushing over the ground at a tremendous pace.

Uptilting the planes caused it to leave the ground and start to curve gracefully upward, as the whizzing propeller did its noisy duty.

They could hear the farmer and his hired hand shouting themselves hoarse with delight at having actually witnessed the start of a modern aeroplane; but naturally the sound grew fainter and fainter in their ears as they left the field and the squatty farmhouse far behind.

Having arisen to the height of several hundred feet, Frank headed toward Bloomsbury. Like a true