ar, the motor took up the increase, and
whirled the big propellers with mighty force.

Then, in a last endeavor to prevent the collision, Mr. Vardon sent the
craft down at a sharp slant, intending to dive under the other.

But this move was anticipated by Larson, who was steering the Larabee.

He, too, sent his craft down, but just when a collision seemed about to
take place, it was prevented by Mr. Vardon, who was a more skillful
pilot.

The propellers of the Abaris worked independently, on a sort of
differential gear, like the rear wheels of an automobile. This enabled
her to turn very short and quickly, by revolving one propeller in one
direction, and one in the opposite, as is done with the twin screws of
a steamer.

And this move alone prevented what might have been a tragedy. But it
was also the cause of a disaster to Dick's aircraft.

With a rush and a roar the Larabee passed over the Abaris as she was so
suddenly turned, and then something snapped in the machinery of the big
airship. She lost speed, and began to go down slightly.

"Did they hit us?" cried Dick, in alarm.

"No, but we've broken the sprocket chain on the port propeller,"
answered Mr. Vardon.

"We'll have to be content with half speed until we can make repairs.
Come now, everybody to work. Those crazy folks may come back at
us--that is begging your pardon for calling your uncle crazy, Dick."

"You can't offend me that way. He MUST be crazy to act the way he did.
I can't understand it. Of course Larson was steering, but my uncle
must have given him orders to do as he did, and try to wreck us."

"I shall report whoever the army man was that did not make an attempt
to stop their attack on us," declared Lieutenant McBride, bitterly. "I
don't know who was assigned to the Larabee, but he certainly ought to
be court-martialed."

"Perhaps no army representative was aboard at all," suggested Paul.

"There were three persons on the airship," said Larry. "I saw them."

"And the race would not be counted unless an army representative was
aboard," declared Lieutenant McBride. "So they would not proceed
without one. No, he must have been there, and have entered into their
plot to try and wreck us. I can't understand it!"

"They've evidently given it up, whatever their game was," called Innis.
"See, there they go!"

He pointed to the other airship, which was now some distance away,
going on at good speed, straight for San Francisco.