e young inventor was holding his own with his two chief rivals, and
was feeling rather proud of his car, when there came from it a report
like a pistol shot.

"Blow out!" yelled Tom desperately, steering to one of the several
repair stations on the inner side of the track. "Be ready with the
extra wheel, Mr. Sharp!"

"Right you are!" cried the balloonist. The car was scarcely stopped
when he had leaped out, and had the lifting jack under the left rear
wheel, where the tire had gone to the bad. He and Tom labored like
Trojans to take off the wheel, and put on the other. They lost five
minutes, and when they got under way again the red and the green cars
were three quarters of a lap ahead.

"You've got to catch them!" declared Sharp firmly.

But the red and the green car drivers saw their advantage, and were
determined to hold it. Tom could not catch them without going his
limit, and he did not want to do this just yet. However, he had his
opportunity when about two hundred miles had been covered. Both the red
and the green cars had tire troubles, but the red one was delayed
scarcely two minutes as there was a corps of mechanics on hand to take
off the defective wheel and put on another. Still Tom regained his lost
ground, and once more the race between those three cars was even.

In the rear of Tom's car Mr. Sharp was mending the blown-out tire,
though there was still one spare wheel on reserve. Tom, in front,
peered eagerly at the track. Nearly side by side raced the red and the
green cars, the latter somewhat to the rear.

It was at the three hundred and fiftieth mile that Tom had another
blow-out. This time it took a little longer to change the wheel, and
the red and green cars gained a full lap on him. The track was now so
dusty that it was difficult to see the contesting cars. Many had
dropped out, and more were on the verge of giving up.

With the odds against him, Tom started in to regain the lost ground.
Narrowly he watched his electric power. Slowly he saw it dropping.
Would he have enough left to finish out the race? He feared not. The
hours were passing. Still there was a hundred miles yet to go twenty
circuits of the track. Some of the spectators were getting weary and
leaving. The band played spasmodically.

Suddenly Tom saw the red car shoot to one side of the track, toward a
charging station; The green car followed.

"That's our cue!" cried the young inventor "We need a little more
'juice' and