whizzing over the ground, eventually to rise in the air, but for the
fact that a rope, attached to the craft, and to some stationary object,
holds it back.

Now if this rope is hooked to a spring balance, which in turn is made
fast to the stationary object, the "thrust" of the propellers will be
registered in pounds on the scale of the balance. Anywhere from five
hundred to nine hundred pounds of thrust will take a monoplane or
biplane up. But Tom wanted more than this.

Once more the motor coughed and spluttered, and the big blades whirled
about so fast that they seemed like solid pieces of wood. Tom stood on
the ground near the levers which controlled the speed, and Ned watched
the scale.

"How much?" yelled the young inventor.

"Eight hundred."

Tom turned on a little more gasolene.

"How much?" he cried again.

"Ten hundred. That'll do!"

"No, I'm going to try for more."

Again he advanced the spark and gasolene levers, and the comparatively
frail craft vibrated so that it seemed as if she would fly apart.

"Now?" yelled Tom.

"Eleven hundred and fifty!" cried Ned.

"Good! That'll do it. She'll give more after she's been running a
while. We'll go up."

Ned scrambled to his seat, and Tom followed. He had an arrangement so
that he could slip loose the retaining rope from his perch whenever he
was ready.

Waiting until the motor had run another minute, the young inventor
pulled the rope that released them. Over the smooth starting ground
that formed a part of the Swift homestead darted the aeroplane. Faster
and faster she moved, Ned gripping the sides of his seat.

"Here we go!" cried Tom, and the next instant they shot up into the air.

Ned Newton had ridden many times with his chum Tom, and the sensation
of gliding through the upper regions was not new to him. But this time
there was something different. The propellers seemed to take hold of
the air with a firmer grip. There was more power, and certainly the
speed was terrific.

"We're going fast!" yelled Ned into Tom's ear.

"That's right," agreed the young inventor. "She'll beat anything but my
Sky Racer, and she'd do that if she was the same size." Tom referred to
a very small aeroplane he had made some time before. It was like some
big bird, and very swift.

Up and onward went the remodeled airship, faster and faster, until,
when several miles had been covered, Ned realized that the young
inventor had achieved another triumph.

"It's