He left the house, and in a few moments returned with a squad of soldiers, who took the assailants in charge.  Fritz explained to the officer how the two men had been captured, and the German officer complimented the boys highly for their prompt action.

After the two prisoners had been led away, Hal bethought himself of the remark Fritz had made concerning his biplane.

“Do you mean to say your aeroplane is ready for use?” he asked.

“Yes; I am going to make a short flight this afternoon.  Would you care to watch me?”

“Would we!” exclaimed Hal.  “You can just bet we would!”

“All right, then; come on.”

The two lads followed Fritz to his workshop.  Inside the boys approached the large aircraft, which rested lightly on its wheels at the end of the speedway.  The huge planes which served as wings stretched out on either side like two great box kites, while underneath the aviator’s seat the gearing could be plainly seen.

The aviator looked at the machine with great pride, and spoke of the improvements he had made in the propellers and in the system of power transmission.  He explained to the boys that, by this direct system, he had gained twenty per cent more velocity; and, now that the war had begun, he hoped to be able to prove this to the army experts.

The boys helped Fritz push the machine out into the open, and watched intently while he tested the steering gear and tried the ignition.  After some further tinkering, Fritz finally took his seat, pulled a lever, and, after skimming the ground for a few rods, the machine rose gracefully into the air.

“By George!” said Hal to Chester, as the craft rose from the ground.  “That looks easy.  I believe I could do it myself.”

“It looks easy,” Chester admitted.  “But how do you suppose a fellow would feel sailing along up there?”

“I guess it would scare me a little at first, but, just the same, I should like to try it.”

After circling around for several minutes, Fritz brought the machine back to its starting point and, lightly as a bird it dropped to the ground.

“Would you like to take a short flight?” he asked the boys.

Chester backed away.

“Not for me,” he declared.  “I would lose my head sure, if I got up there.”

Hal laughed.

“You don’t want to pay any attention to him when he talks like that,” he told Fritz.  “I never saw anything yet he was afraid to do.”

“After what I saw in the house to-day, I can well believe that,” replied the young German.  “Would you like to go up?” to Hal.  “You know the machine will only carry two.”

“Why, yes,” answered Hal; “I would like it.”

“Climb in, then,” ordered Fritz.

Not without some misgiving Hal obeyed.

Once more the huge machine skimmed gracefully over the ground, and again went sailing into space.