His exclamation was called out by a sudden change in the method of advance adopted by those in the leading aeroplane. Instead of keeping along in a direct line the biplane had uptilted and was now shooting downward in what seemed a terribly perilous way; just as though the pair of precious scoundrels had taken a notion to end the pursuit by seeking a plunge into the water.
But both boys knew differently, and that this was only a volplane, adopted by experienced and rash aviators as a means of reaching the lower air currents more rapidly than by slow spirals; or else undertaken when having engine trouble that threatens destruction.
Frank was ready to follow suit. It would not be the first time by long odds that the Bird boys had accomplished this speedy method of descending from high altitudes. There was always an exhilaration about the clever trick that appealed irresistibly to their natures; though Frank would never have attempted it unless reasonably sure that the conditions were favorable for success.
"Hold fast, Andy!" he remarked, quietly.
The hum of the motor suddenly ceased, and with its cessation the hydroplane was turned head-on toward the surface of the lake, four thousand feet below.
Down they went, plunging toward what seemed to be instant destruction; but a steady hand was at the wheel, and the pilot knew just what was necessary to do at the proper instant in order to bring this rapid descent to a stop, and right the airship on a level keel.
But there was no time just then to note what the rival aeroplane might be doing. Whether the experienced airman in charge managed to stop that downward plunge before reaching the surface of the lake; or failing went to his death, was a matter that did not concern them now, since they had their own affairs to look after.
To tell the truth, Andy's heart seemed to be in his throat as they made the drop. As yet they had never tried out the new hydroplane in a trick of this sort; and hence really did not know just how it might act; though Frank must have been pretty confident, else he would never have attempted it.
Given the choice the Bird boys would easily have decided to descend from their lofty height by means of the much safer if slower "spirals," each circle seeing the aeroplane lower than before. But since the reckless man in the other air craft led the way, Frank had chosen to follow. He believed that he could accomplish any feat that was possible to Casper Blue, especially now that the old air navigator had a handicap in the way of a crippled arm.
The water seemed rushing up to meet them; so it looked to Andy, whose anxious gaze was fastened upon the lower depths, as they dipped down in that terrific swoop. But then, he had seen the same thing when over the land, so that in itself this did not daunt him.