So minutes passed, until at least ten had crept by since their coming.  Frank had everything tuned up, and knew of not the least chance where he could improve the conditions of planes or motor, for all seemed to be as nearly perfect as they could be made.

Both boys cast frequent glances aloft, and as a rule toward that particular quarter where they presently expected to see something moving.  They were keyed up to a pretty lively pitch of excitement, though Frank did not show it half as much as his younger cousin, who was always affected this way.

Then suddenly Andy called out: 

“There she rises, Frank!  Oh! look at them boring up, will you, in that corkscrew spiral way!  Tell me that Casper Blue doesn’t know his business; Perc will never get as much out of his biplane as that old and experienced aviator means to.  Are we going to follow suit, Frank?”

“Get aboard!” came the prompt answer; and it was almost laughable to see how nimbly Andy obeyed this order.

Frank lost no time in starting, and they went away with a rush, passing over the abandoned field that was now given up pretty much to thistles and burdocks, with a sprinkling of iron-weeds.

It was rather rough sledding, to be sure, and as the bicycle wheels pounded over the turf the boys had to hold on to keep their seats.

But when sufficient momentum had been acquired, Frank elevated the fore plane, and immediately there was the greatest relief felt; for they began to rise in the air, and all that terrible bumping stopped for good.  The change was wonderful, and it felt as though they were gliding on velvet.

“We’re off!” exclaimed Andy, exultantly.

Frank said nothing.  He did not possess quite the same sanguine nature that his cousin had.  Andy seldom allowed thoughts of possible disaster to annoy him, but on the other hand Frank was always trying to head off trouble.

He realized that with this launching of their new hydro-aeroplane they would be entering upon an extra hazardous game, the outcome of which no one could foresee.  The two men whom they expected to follow must be desperate fellows, who would resort to almost any hazard rather than allow themselves to be caught.

And it was not an amateur aviator like Percy Carberry who was opposed to them now, but one who had had long experience in the art of harnessing a flying machine to do his bidding.

Once they left the ground behind them, Frank started to spiral upward much in the same way the others had done.  One thing he was glad of, and this was the presence of Andy alongside.  Casper Blue might be a daring air pilot, but with his companion a perfect greenhorn in all that pertained to the art, he would be more or less handicapped.  A sudden incautious movement on the part of the novice might prove the undoing of the precious pair.

Once they had risen to a certain height, and the aeroplane was turned so as to follow the other air craft, which was speeding away, headed directly into the north.  Of course, those aboard must know that they were being chased.  They could not have failed to see the hydroplane, (as it is generally called, though the true word to cover it would be hydro-aeroplane) even before it left the field, once they started to ascend.