atic equilibrium attachments and the balancing
weights were looked at again and again.

As for the engine, had it been a delicate watch, Tom could not have
scrutinized each valve, wheel, cam and spur gear more carefully. Then
the gasoline tank was filled, the magneto was looked after, the oil
reservoirs were cleaned out and freshly filled, and finally the lad
remarked:

"Well, I guess I'm ready. Come along, Mr. Damon."

"Am I going with you in the test?"

"Surely. I've been counting on you. If you're to be with me in the
race, you want to get a sample of what we can do. Take your place. Mr.
Jackson, are you ready to time us?"

"All ready, Tom."

"And, dad, do you feel well enough to check back Mr. Jackson's results?
I don't want any errors."

"Oh, yes, Tom. I can do it."

"Very well, then. Now this is my plan. I'm going to mount upward on an
easy slant, and put her through a few stunts first, to warm up, and see
that everything is all right. Then, when I give the signal, by dropping
this small white ball, that means I'm ready for you to start to time
me. Then I'll begin to try for the record. I'll go about the course in
a big ellipse, and--well, we'll see what happens."

While Mr. Damon was in his seat the young inventor started the
propeller, and noted the thrust developed. It was satisfactory, as
measured on the scale, and then Tom took his place.

"Let her go!" he cried to Mr. Jackson and Eradicate, after he had
listened to the song of the motor for a moment. The Humming-Bird flew
across the course, and a moment later mounted into the air.

Tom quickly took her up to about two thousand feet, and there, finding
the conditions to his liking, he began a few evolutions designed to
severely test the craft's stability, and to learn whether the engine
was working properly.

"How about it?" asked Mr. Damon anxiously.

"All right!" shouted Tom in his ear, for the motor was making a great
racket. "I guess we'll make the trial next time we come around. Get
ready to drop the signal ball."

Tom slowly brought the aeroplane around in a graceful curve. He sighted
down, and saw the first tall white pole that marked the beginning of
the course.

"Drop!" he called to Mr. Damon.

The white rubber ball went to the earth like a shot. Mr. Jackson and
Mr. Swift saw it, and started their timing-watches. Tom opened the
throttle and advanced the spark. The great test was on!

The Humming-Bird trembled and throbbed with