, and, had he moved, the big taper pin, which
held the plunger to the axle, would have struck his temple and
probably would have killed him, for the pin, which held the plunger
rigid, projected several inches from the smooth side of the rod.

"Koku, what is the matter? Why are you there?" cried Tom, for he
could see nothing wrong with the machinery now. The airship was
sailing on as before.

"Bolt break," explained the giant briefly, for he had learned some
engineering terms since he had been with Tom. "Bolt that hold pump
fast to floor crack off. Pump him begin to jump up. Make bad noise.
Koku hold him down, but pretty hard work. Better put in new bolt,
Mr. Tom."

They could see the strain that was put upon the giant in his
swelling veins and the muscles of his hands and arms, for they stood
out knotted, and in bunches. With all his great strength it was all
Koku could do to hold the pump from tearing completely loose.

"Quick, Ned!" cried Tom. "Shut off all the power! Stop the pump!
I've got to bolt it fast. Start the gas machine, Mr. Damon. You know
how to do it. It works independent of the motor. You can let go in a
minute, Koku!"

It took but a few seconds to do all this. Ned stopped the main
motor, which had the effect of causing the propellers to cease
revolving. Then the airship would have gone down but for the fact
that she was now a balloon, Mr. Damon having started the generating
machine which sent the powerful lifting gas into the big bag over
head.

"Now you can let go, Koku," said Tom, for with the stooping of the
motor the air pump ceased plunging, and there was no danger of it
tearing loose.

"Bless my court plaster!" cried Mr. Damon. "What happened, Tom?"

As the giant arose from his kneeling position the cause of the
accident could easily be seen. Two of the big belts that held down
one end of the pump bed-plate to the floor of the airship, had
cracked off, probably through some defect, or because of the long
and constant vibration on them.

This caused a great strain on the two forward bolts, and the pump
started to tear itself loose. Had it done so there would have been
a serious accident, for there would have been a tangle in the
machinery that might never have been repairable. But Koku, who, it
seems, had been watching the pump, saw the accident as soon as it
occurred. He knew that the pump must be held down, and kept rigid,
and he took the only way open to him to accomplish this.

H