He was determined to be thorough in all he did, and this consumed more or less time, so that when he finally pronounced the monoplane in perfect condition the afternoon was half gone.

Still, they must go up and put in an hour or two searching.  Andy was too wild with impatience to hear of anything else, and Frank saw no reason for not complying.

“But we must be sure to get down again before night comes,” he remarked, after they had made a successful rise and were speeding above the top of the thick forest.  “If we should be caught out at night I rather guess it would be a serious piece of business.”  And Andy agreed with him.

For quite a time they soared aloft, Andy using the binoculars almost constantly, watching the country below and occasionally sweeping the distance.

Frank was thrilled to hear his chum suddenly give utterance to a cry, but it was more of amazement than delight that gave birth to this ejaculation.

“What is it now, Andy; more insurrectos?” he demanded, ready to manipulate the planes and strike for higher regions.

“No, no, not this time,” came the quick reply; “but Frank, as sure as you live, there’s that plagued old biplane just rising up yonder a mile away.  And somehow I seem to feel that it spells trouble for us.”

CHAPTER XVI.

THE AIR CHASE.

One hasty glance told Frank that there could be no mistake.  Only too well did he know the construction of that same biplane that had in the near past competed with them for honors in the race for Old Thunder Top’s crown.

“You’re right, Andy,” he said, earnestly; “and it seems to me they’re heading for us right now.  What do you make them out to be?  Can you see who is handling the wheel?  Is it Puss Carberry?”

“Yes, I’m dead sure of that; but Frank, there’s somebody else with him!”

“Sandy?” asked his chum.

“No, it can’t be.  There, I had a good look at him, and Frank, he’s got a beard!  It’s a man!” answered Andy, in tense tones.

Frank’s first action was to move a lever that would change their course and place the biplane directly behind them.  His next was to throw on more speed, so that the faithful little motor started to humming with the old-time rapidity that reminded Andy of the occasion when they put it to its best efforts in order to rush ahead of their rival of the air.

“Then we must guess from that Puss and Sandy have fallen into the hands of the rebels, since there are no government troops up here, the senor said,” he observed, presently.  “Are they gaining on us now, Andy?”

“I don’t think so,” replied the one who held the glass, “though Puss seems to be getting a whole lot of speed out of his Gnome engine right now.  Reckon he must have overhauled it, or else found some way to put her up another notch.”

“How strange to think that our old rivalry is being renewed away down here in this country, thousands of miles from home,” remarked Frank, after a while.