Roy rewarded their helper with a substantial bill, and they were all warm in their thanks.

“‘Twasn’t nuthin’,” declared the man, “an’ now I guess I’ll go to ther house and have my hired man fill in this road.  Things is come to a fine pass when such things kin happen.”

As the rescued party sped on toward the aviation field they fully agreed with the rustic’s opinion.  Had it not been for sheer luck they would have suffered extremely serious consequences as the result of a rascal’s device.  But as it was Kelly’s plot against them appeared to have failed.

CHAPTER XX.

AN ATTACK IN THE AIR.

“B-o-o-m!”

The sound of a gun crashed out as the auto sped through the gates of the aviation field and rapidly skimmed across to where the aeroplanes had been parked.

“Just in time!” cried Peggy; “that’s the five-minute warning gun.”

By this time the grandstand was well filled and a band was playing lively airs.  At the starting line three of the Kelly aeroplanes were gathered ready for the signal for the start of the altitude flight.  The instant the car came to a standstill Jimsy was out and in a jiffy had the new spark plug adjusted.  There was no time to test it, but he felt pretty confident that it would work all right.

“All ready!” shouted the official in charge of the starting arrangements.

“Ready!” rejoined Jimsy heartily, as he adjusted his leather helmet and Jake and Roy started the engine.

Kelly, whose back had been turned while he talked to some of his troup, faced round at the sound of the boy’s voice.

“What, you here!” he choked out, his face purple.

“Yes; do you know any reason why I shouldn’t be?” asked Jimsy, with meaning emphasis.

Under the lad’s direct gaze Kelly’s eyes fell.  He couldn’t face the lad, but turned away.

“There, if that isn’t proof of his guilt I’d like to know what is,” declared Jimsy to Roy.

“But the rascal covered up his tracks so cleverly that we can’t prove anything on him,” muttered Roy disgustedly.

At the same instant the starting bomb boomed out.  The crowd yelled, and the drummer of the band pounded his instrument furiously.  Above the uproar sounded the sharp, crackerlike report of the motors.  As more power was applied they roared like batteries of Gatling guns.

Into the air shot one of them, a black biplane.  It was followed by the others, two monoplanes and a triplane.  Jimsy ascended last, but as this was not a race, but a cloud-climbing contest, he was in no hurry.  He was anxious to see what the other air craft could do.

Up they climbed, ascending the aerial stairway, while the crowd below stared up, at the risk of stiff necks in the immediate future.

Jimsy chose spiraling as his method of rising.  But the others went upward in curious zigzags.  This was because their machines were not equipped with the stability device, and they could not attempt the same tactics.  Before long Jimsy was high above the others.  From below he appeared a mere dot in the blue.  But still he flew on.