“Well, all we can do now is wait,” the young inventor muttered, wiping his arm across his forehead.

Tom passed the night in a fitful sleep, half expecting to be wakened at any moment by the stand-by crew on watch.  No alarm occurred, however.

Dawn broke, and Chow delighted all hands with a hearty breakfast of bacon, eggs, and corn fritters.  More hours of waiting dragged by.

“What time do you think the attack will occur?” Bud asked.

Tom shrugged.  “The ‘twenty-four-hour’ business may have been approximate.  But I’d say from two o’clock on is the danger period.”

The young inventor checked frequently with Washington and the other crews stationed around the country.  Suddenly the radiotelephone operator gave a yell.

“Your father is on the line, skipper!”

The scientist was calling from the receiver-computer headquarters at Enterprises.  “Exman has reported a quake pulse will be sent in seven minutes—­at 21.36 G.M.T.”

“I’m ready, Dad,” Tom said, then asked for various technical details before hanging up.

He passed the word to the crew and glanced at his watch.  A hasty, last-moment inspection was carried out, every man checking certain details of the setup.

Soon the pulsemakers began ticking inside the dual-control spheres as they picked up the frequency signal by radio.  Tom studied the gauge dials.

Tension mounted rapidly among the waiting group.  The same thought was throbbing through every mind: 

Was the nation on the brink of a terrible disaster?  Or would Tom Swift’s invention safeguard the threatened area?

As the deadline approached, Tom pushed a button.  The mighty hydraulic drivers throbbed into action, sending out their pulse waves across the continent!

CHAPTER XVIII

EARTHQUAKE ISLAND

Now came the hardest part of all for Tom and his companions—­waiting to learn if the shock deflectors had succeeded in blotting out the enemy quake wave.

No one spoke.  As the silence deepened inside the cave, the suspense became almost unbearable.  Minutes passed.

“When will we know, skipper?” a crewman ventured at last.

“Soon, I hope,” Tom replied tersely.

But the waiting seemed endless.  Bud’s eyes met Tom’s.  The flier grinned and held up crossed fingers, just as Tom had done to Mike Burrows the previous evening.  Tom managed a feeble grin in response.

Suddenly the telephone shrilled, shattering the silence of the cave.  Tom snatched it from the radioman’s hands.

“Tom Swift here!...  Yes?...  Thank heavens!  I guess we can all be grateful, Dr. Miles!”

“Providence protected us, I’m sure, Tom,” the seismologist replied at the other end of the line.  “But in this instance it worked through Tom Swift’s Quakelizors!  The Bona Fide plant and the surrounding area never even felt the tremor—­your quake deflectors worked perfectly!”